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The ocean represents the largest biome on earth; however, we have only begun to understand the diversity and function of the marine microbial inhabitants and their interactions with macroalgal species. Macroalgae play an integral role in overall ocean biome health and serve both as major primary producers and foundation species in the ecosystem. Previous studies have been limited, focusing on the microbiome of a single algal species or its interaction with selected microbes. This project aimed to understand overall biodiversity of microbial communities associated with five common macroalgal species and to determine the drivers of these communities at ‘Ewa Beach, O‘ahu, HI. Representative species of Chlorophyta (green), Ochrophyta (brown), and Rhodophyta (red) algae, each species having various levels of calcification, thallus complexity, and status as native or invasive species, were collected from an intertidal bench in May 2019. A portion of the V3-V4 variable region of the small-subunit rRNA gene was amplified for high-throughput sequencing using universal bacterial primers to elucidate the core and variable algal microbiome. Significant differences in bacterial community composition were only partially explained by host species, whether the host was native or invasive, and thallus complexity. Macroalgal phylum explained the most variation in associated microbial communities at ‘Ewa Beach. This study advances our understanding of microbial-macroalgal interactions and their connectivity by producing insight into factors that influence the community structure of macroalga-associated microbiota. IMPORTANCE Generally, most eukaryotic organisms form relationships with microbes that are important in mediating host organismal health. Macroalgae are a diverse group of photosynthetic eukaryotic organisms that serve as primary producers and foundational species in many ecosystems. However, little is known about their microbial counterparts across a wide range of macroalgal morphologies, phylogenies, and calcification levels. Thus, to further understand the factors involved in bacterial community composition associated with macroalgal species at one point in time, representative samples were collected across phyla. Here, we show that both host macroalga phyla and morphology influenced the associated microbial community. Additionally, we show that the invasive species Avrainvillea lacerata does not have a unique microbial community on this intertidal bench, further supporting the idea that host phylum strongly influences microbial community composition.

Stable isotope tracer addition can enhance the isotopic differences of primary producers for a wider food-web resolution than the use of natural abundance stable isotopes (NASIs) alone, particularly in ecosystems where primary producers have similar NASI values. To investigate the food sources and the trophic status of benthic infauna in an intertidal area near a Halophila minor seagrass bed within inner Tai Tam Bay, Hong Kong, China, a 15N addition experiment was conducted, and the results were compared with those from NASI data. Only benthic microalgae (BMA) were labeled by applying 15N-enriched NH4Cl to the sediment daily for the first 7 days during a 21-day study. In contrast to the NASI results, Bayesian mixing models based on the isotope tracer experiment suggested a larger dietary contribution of BMA for nematode Daptonema sp. and copepods, whereas a higher reliance on phytoplankton and seagrass detritus was noted for polychaete Neanthes sp. However, both NASI and isotope tracer addition demonstrated that seagrass detritus was a major food source for nematode Spilophorella sp. The present isotope tracer experiment also revealed a contrasting result of the relatively lower contribution of meiofauna in the diets of carnivores/omnivores as compared to the results of NASIs. This finding suggested that the isotope values in these consumers may have not reached an equilibrium with the added isotope in the study period. Thus, there is a need for applying NASI coupled with isotope tracer addition in the investigation of ecosystems in which primary producers have similar isotope values, especially in ecosystems with lower tissue turnover rates, in order for a more accurate determination of dietary contribution and trophic status of consumers in the food-web study.

The indirect effects of top predators on the biomass of lower trophic levels have been extensively documented, especially in aquatic ecosystems and are commonly characterized as “trophic cascades.” There have also been studies showing that predator diversity can play an important role in mediating these trophic cascades. In addition, some studies have demonstrated that the diversity of consumers can impact the stability of their resources. However, the effects of predator diversity on the stability of lower trophic levels (cascading effects of predator diversity) have not yet been studied. We conducted a field pond mesocosm experiment and accompanying laboratory microcosm experiment in which we grew phytoplankton with zooplankton herbivores, manipulating the presence and co-habitation of two heteropteran predators while controlling for total expected predation. We hypothesized that if the predators partitioned their herbivore prey, for example by size, then co-presence of the predators would lead to 1) increased average values and 2) decreased temporal variability of phytoplankton biomass. We present evidence that the predators partitioned their herbivore prey, and found that this simultaneous suppression of different herbivore groups reduced the variability of edible (smaller) phytoplankton biomass, without affecting mean phytoplankton biomass. We also found that phytoplankton more resistant to herbivory were not affected by our manipulations, indicating that the zooplankton herbivores played an important role in mediating this cascading diversity-stability effect. Our results demonstrate that predator diversity can indirectly stabilize primary producer biomass via a “diversity-stability cascade” in the manner of a trophic cascade, seemingly dependent on predator complementarity and the vulnerability of taxa to consumption, and independent of a more traditional trophic cascade in which average biomass is enhanced. Predator diversity, especially in terms of functional traits relating to differential prey use such as body size, may be important for regulating ecosystem stability, and may provide a way to improve the reliability of algal crop yields via biological control.

In this multi-proxy palaeo study, the response of primary producers and consumers to anthropogenic disturbances in a large shallow lake was investigated. Overall, eutrophication and water-level changes (partly inferred by bisaccate pollen grains) are well-reflected in changes in sedimentation rates of pigments, diatom and cladoceran species composition and other proxies (e.g. Rhabdocoela oocytes). In particular, the stepwise decrease in relative abundance of Pediastrum simplex compared to P. boryanum/P. duplex proved to be a good indicator for eutrophication intensity. Furthermore, reductions in the body size (i.e. coenobia diameter) of Pediastrum simplex were clearly related to phases of low visibility that were caused by lake damming in the 1950 s and by accelerating eutrophication in the 1990 s. During the latter period, strong algal growth led to turbid conditions, which are indicated by the co-occurrence of the diatoms Fragilaria crotonensis, Aulacoseira ambigua and A. granulata, the green algae Staurastrum sp. as well as the cladoceran Anthalona cf. milleri. This study highlights that subfossil remains, which are often found in, for instance, standard cladoceran analysis (green algae such as Pediastrum spp. and Staurastrum spp. or bisaccate pollen grains), can add valuable information to the reconstruction of past environmental conditions and biotic response. Such better and more holistic understanding of freshwater ecosystems is crucial to meet future challenges in a rapidly changing world.

As the rate of global change increases, the structure and functioning of marine ecosystems, including the food webs that underpin them, will radically alter. Forecasting the consequences of these changes requires a sound understanding of the fundamental components of marine food webs: their community composition, baseline biomass and productivity. Epifauna, a term restricted here to small invertebrates (both mobile and sessile) that inhabit living and non-living surfaces within marine ecosystems, are a ubiquitous and pivotal component of marine food webs, supporting the flow of energy through marine ecosystems and providing a critical trophic link between benthic primary producers and higher-order consumers. Yet, despite their importance, epifauna are rarely studied compared to the more visible and gregarious components of marine ecosystems. They are also typically neglected in management strategies for the protection of marine habitats. In addition, the plethora of alternative terms used within this research field (macrobenthos, cryptofauna, epibiont, mesograzer) can be a barrier to understanding and assimilating existing research knowledge. This review provides an assessment of epifaunal communities studied within tropical, subtropical and temperate marine ecosystems globally. We first review alternative terms used to describe marine epifaunal communities, with the aim of offering a consensus-based definition of epifauna as an aid for unifying different research areas. We then review the primary literature on epifauna, including the scarce information on tropical marine habitats. We outline how a detailed understanding of epifaunal communities within individual habitats is needed to predict how benthic food webs will alter under global change. While epifauna can persist under degraded habitat conditions, changes to taxonomic composition can fundamentally affect secondary productivity, and impact higher-order consumers through changes in prey size-spectra and foraging habitats. Finally, we issue a “call-to-arms” for increased focus on the study of epifauna, given their potential to underpin critical aspects of marine ecosystem functioning. We highlight the potential for eDNA sampling, other new technologies, and monitoring by citizen scientists to facilitate the use of epifaunal community metrics, including incorporation into marine ecosystem planning.

The frequency of heatwave events in Europe is increasing as a result of climate change. This can have implications for the water quality and ecological functioning of aquatic systems. We deployed three spectroradiometer WISPstations at three sites in Europe (Italy, Estonia, and Lithuania/Russia) to measure chlorophyll-a at high frequency. A heatwave in July 2019 occurred with record daily maximum temperatures over 40 ◦C in parts of Europe. The effects of the resulting storm that ended the heatwave were more discernable than the heatwave itself. Following the storm, chlorophyll-a concentrations increased markedly in two of the lakes and remained high for the duration of the summer while at one site concentrations increased linearly. Heatwaves and subsequent storms appeared to play an important role in structuring the phenology of the primary producers, with wider implications for lake functioning. Chlorophyll-a peaked in early September, after which a wind event dissipated concentrations until calmer conditions returned. Synoptic coordinated high frequency monitoring needs to be advanced in Europe as part of water management policy and to improve knowledge on the implications of climate change. Lakes, as dynamic ecosystems with fast moving species-succession, provide a prism to observe the scale of future change. This research is part of the H2020 EOMORES (GA n. 730066) and ESA CCI LAKES project (GA n. 40000125030/18/I-NB). We would like to thank the “Cooperativa dei Pescatori del Trasimeno” for the support in the WISPstation installation and maintenance, ARPA Umbria for useful discussions, and the Province of Perugia for the availability to use the platform in Polvese Island. Research in Estonia was also financed by Estonian Research Council grants PSG10 and PUT1598. Centre for Limnology is thanked for the opportunity to use the pier for WISPstation instal- lation and Ilmar Ansko and Martin Ligi for the instrument maintenance. We kindly acknowledge the Lithuanian Hydrometeorological Service under the Ministry of Environment for the provided meteorological data. We would like to thank the Curonian Spit National Park and Administration of Neringa municipality for the permission to install the WISPstation in Pervalka (the Curonian Lagoon, Lithuania) and Vilius Zeigis and Jonas Gintauskas for the instrument installation and maintenance. We thank Daniela Stroppiana for help with the analysis of the water spectral signatures. We thank the editor and three reviewers for their time in providing comments and suggestions that improved this manuscript. This research is part of the H2020 EOMORES (GA n. 730066) and ESA CCI LAKES project (GA n. 40000125030/18/I-NB). We would like to thank the “Cooperativa dei Pescatori del Trasimeno” for the support in the WISPstation installation and maintenance, ARPA Umbria for useful discussions, and the Province of Perugia for the availability to use the platform in Polvese Island. Research in Estonia was also financed by Estonian Research Council grants PSG10 and PUT1598. Centre for Limnology is thanked for the opportunity to use the pier for WISPstation instal- lation and Ilmar Ansko and Martin Ligi for the instrument maintenance. We kindly acknowledge the Lithuanian Hydrometeorological Service under the Ministry of Environment for the provided meteorological data. We would like to thank the Curonian Spit National Park and Administration of Neringa municipality for the permission to install the WISPstation in Pervalka (the Curonian Lagoon, Lithuania) and Vilius Zeigis and Jonas Gintauskas for the instrument installation and maintenance. We thank Daniela Stroppiana for help with the analysis of the water spectral signatures. We thank the editor and three reviewers for their time in providing comments and suggestions that improved this manuscript.

Seaweeds are important primary producers and bioremediation materials, but its litter produced during growth and harvest is one of the restrictions to the sustainable development of seaweed cultivation. In this study, we conducted field investigation and indoor experiments to analyze the bioaccumulation and release of metals in Gracilaria lemaneiformis during the growth and decaying. The investigation revealed the 3.5 × 105 t (wet weight) G. lemaneiformis from a 1500 ha cultivation area bioaccumulated 1925–2353 kg Zn, 233.5–251 kg Cu, 70.5–80.5 kg Pb and 25.5–47 kg Cd, indicating that G. lemaneiformis is a good metals remover. The growth and decaying period of G. lemaneiformis releases, absorbs or adsorbs metals. It has the function of a “heavy metal pool”, simultaneously accumulate and release metals. G. lemaneiformis has a strong influence on heavy metals cycling in the seaweed cultivation ecosystem and provides a very good sample for biogeochemistry study for the globally seaweed sustainable development.

Ecosystem engineers have large impacts on the communities in which they live, and these impacts may feed back to populations of engineers themselves. In this study, we assessed the effect of ecosystem engineering on density-dependent feedbacks for midges in Lake Mývatn, Iceland. The midge larvae reside in the sediment and build silk tubes that provide a substrate for algal growth, thereby elevating benthic primary production. Benthic algae are in turn the primary food source for the midge larvae, setting the stage for the effects of engineering to feed back to the midges themselves. Using a field mesocosm experiment manipulating larval midge densities, we found a generally positive but nonlinear relationship between density and benthic production. Furthermore, adult emergence increased with the primary production per midge larva. By combining these two relationships in a simple model, we found that the positive effect of midges on benthic production weakened negative density dependence at low to intermediate larval densities. However, this benefit disappeared at high densities when midge consumption of primary producers exceeded their positive effects on primary production through ecosystem engineering. Our results illustrate how ecosystem engineering can alter density-dependent feedbacks for engineer populations.

Objectives Existing information on Arctic marine food web structure is fragmented. Integrating data across research programs is an important strategy for building a baseline understanding of food web structure and function in many Arctic regions. Naturally-occurring stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) measured directly in the tissues of organisms are a commonly-employed method for estimating food web structure. The objective of the current dataset was to synthesize disparate δ15N, and secondarily δ13C, data in the Canadian Beaufort continental shelf region relevant to trophic and ecological studies at the local and pan-Arctic scales. Data description The dataset presented here contains nitrogen and carbon stable isotope ratios (δ15N, δ13C) measured in marine organisms from the Canadian Beaufort continental shelf region between 1983 and 2013, gathered from 27 published and unpublished sources with associated sampling metadata. A total of 1077 entries were collected, summarizing 8859 individual organisms/samples representing 333 taxa across the Arctic food web, from top marine mammal predators to primary producers.

17 pages, 6 figures, 1 table.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY), Variations in stable carbon and nitrogen isotope compositions in incremental tissues of pelagic sharks can be used to infer aspects of their spatial and trophic ecology across life-histories. Interpretations from bulk tissue isotopic compositions are complicated, however, because multiple processes influence these values, including variations in primary producer isotope ratios and consumer diets and physiological processing of metabolites. Here we challenge inferences about shark tropho-spatial ecology drawn from bulk tissue isotope data using data for amino acids. Stable isotope compositions of individual amino acids can partition the isotopic variance in bulk tissue into components associated with primary production on the one hand, and diet and physiology on the other. The carbon framework of essential amino acids (EAAs) can be synthesised de novo only by plants, fungi and bacteria and must be acquired by consumers through the diet. Consequently, the carbon isotopic composition of EAAs in consumers reflects that of primary producers in the location of feeding, whereas that of non-essential amino acids (non-EAAs) is additionally influenced by trophic fractionation and isotope dynamics of metabolic processing. We determined isotope chronologies from vertebrae of individual blue sharks and porbeagles from the North Atlantic. We measured carbon and nitrogen isotope compositions in bulk collagen and carbon isotope compositions of amino acids. Despite variability among individuals, common ontogenetic patterns in bulk isotope compositions were seen in both species. However, while life-history movement inferences from bulk analyses for blue sharks were supported by carbon isotope data from essential amino acids, inferences for porbeagles were not, implying that the observed trends in bulk protein isotope compositions in porbeagles have a trophic or physiological explanation, or are suprious effects. We explored variations in carbon isotope compositions of non-essential amino acids, searching for systematic variations that might imply ontogenetic changes in physiological processing, but patterns were highly variable and did not explain variance in bulk protein δ13C values. Isotopic effects associated with metabolite processing may overwhelm spatial influences that are weak or inconsistently developed in bulk tissue isotope values, but interpreting mechanisms underpinning isotopic variation in patterns in non-essential amino acids remains challenging, The internship of SM at the Woods Hole Oceanographic Institution was funded by the School of Ocean and Earth Science at University of Southampton. Stable isotope analyses were paid by CT and ST research budgets and SM Ph.D. and placement funding

Ocean primary production is the basis of the marine food web, sustaining life in the ocean via photosynthesis, and removing carbon dioxide from the atmosphere. Recently, a small but significant decrease in global marine primary production has been reported based on ocean color data, which was mostly ascribed to decreases in primary production in the northern Indian Ocean, particularly in the Bay of Bengal.Available reports on primary production from the Bay of Bengal (BoB) are limited, and due to their spatial and temporal variability difficult to interpret. Primary production in the BoB has historically been described to be driven by diatom and chlorophyte clades, while only more recent datasets also show an abundance of smaller cyanobacterial primary producers visually difficult to detect. The different character of the available datasets, i.e., direct counts, metagenomic and biogeochemical data, and satellite-based ocean color observations, make it difficult to derive a consistent pattern. However, making use of the most highly resolved dataset based on satellite imaging, a shift in community composition of primary producers is visible in the BoB over the last 2 decades. This shift is driven by a decrease in chlorophyte abundance and a coinciding increase in cyanobacterial abundance, despite stable concentrations of total chlorophyll. A similar but somewhat weaker trend is visible in the Arabian Sea, where satellite imaging points towards decreasing abundances of chlorophytes in the north and increasing abundances of cyanobacteria in the eastern parts. Statistical analysis indicated a correlation of this community change in the BoB to decreasing nitrate concentrations, which may provide an explanation for both the decrease in eukaryotic nitrate-dependent primary producers and the increase in small unicellular cyanobacteria related to Prochlorococcus, which have a comparably higher affinity to nitrate. Changes in community composition of primary producers and an overall decrease in system productivity would strongly impact oxygen concentrations of the BoB's low-oxygen intermediate waters. Assuming decreasing nitrate concentrations and concurrent decreasing biomass production, export, and respiration, oxygen concentrations within the oxygen minimum zone would not be expected to further decrease. This effect could be enhanced by stronger stratification as a result of future warming and thus possibly counteract oxygen decrease as a direct effect of stratification. Therefore, given a decrease in primary production, the BoB may not be at a tipping point for becoming anoxic, unless external nutrient inputs increase. Ocean primary production is the basis of the marine food web, sustaining life in the ocean via photosynthesis, and removing carbon dioxide from the atmosphere. Recently, a small but significant decrease in global marine primary production has been reported based on ocean color data, which was mostly ascribed to decreases in primary production in the northern Indian Ocean, particularly in the Bay of Bengal. Available reports on primary production from the Bay of Bengal (BoB) are limited, and due to their spatial and temporal variability difficult to interpret. Primary production in the BoB has historically been described to be driven by diatom and chlorophyte clades, while only more recent datasets also show an abundance of smaller cyanobacterial primary producers visually difficult to detect. The different character of the available datasets, i.e., direct counts, metagenomic and biogeochemical data, and satellite-based ocean color observations, make it difficult to derive a consistent pattern. However, making use of the most highly resolved dataset based on satellite imaging, a shift in community composition of primary producers is visible in the BoB over the last 2 decades. This shift is driven by a decrease in chlorophyte abundance and a coinciding increase in cyanobacterial abundance, despite stable concentrations of total chlorophyll. A similar but somewhat weaker trend is visible in the Arabian Sea, where satellite imaging points towards decreasing abundances of chlorophytes in the north and increasing abundances of cyanobacteria in the eastern parts. Statistical analysis indicated a correlation of this community change in the BoB to decreasing nitrate concentrations, which may provide an explanation for both the decrease in eukaryotic nitrate-dependent primary producers and the increase in small unicellular cyanobacteria related to Prochlorococcus, which have a comparably higher affinity to nitrate. Changes in community composition of primary producers and an overall decrease in system productivity would strongly impact oxygen concentrations of the BoB's low-oxygen intermediate waters. Assuming decreasing nitrate concentrations and concurrent decreasing biomass production, export, and respiration, oxygen concentrations within the oxygen minimum zone would not be expected to further decrease. This effect could be enhanced by stronger stratification as a result of future warming and thus possibly counteract oxygen decrease as a direct effect of stratification. Therefore, given a decrease in primary production, the BoB may not be at a tipping point for becoming anoxic, unless external nutrient inputs increase.

The SUP05 clade of gammaproteobacteria (Thioglobaceae) comprises both primary producers and primary consumers of organic carbon in the oceans. Host-associated autotrophs are a principal source of carbon and other nutrients for deep-sea eukaryotes at hydrothermal vents, and their free-living relatives are a primary source of organic matter in seawater at vents and in marine oxygen minimum zones. Similar to other abundant marine heterotrophs, such as SAR11 and Roseobacter, heterotrophic Thioglobaceae use the dilute pool of osmolytes produced by phytoplankton for growth, including methylated amines and sulfonates. Heterotrophic members are common throughout the ocean, and autotrophic members are abundant at hydrothermal vents and in anoxic waters; combined, they can account for more than 50% of the total bacterial community. Studies of both cultured and uncultured representatives from this diverse family are providing novel insights into the shifting biogeochemical roles of autotrophic and heterotrophic bacteria that cross oxic-anoxic boundary layers in the ocean. Expected final online publication date for the Annual Review of Marine Science, Volume 14 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Biological soil crusts (biocrusts) are communities of microbes that inhabit the surface of arid soils and provide essential services to dryland ecosystems. While resistant to extreme environmental conditions, biocrusts are susceptible to anthropogenic disturbances that can deprive ecosystems of these valuable services for decades. Until recently, culture-based efforts to produce inoculum for cyanobacterial biocrust restoration in the southwestern United States focused on producing and inoculating the most abundant primary producers and biocrust pioneers, Microcoleus vaginatus and members of the family Coleofasciculaceae (also called Microcoleus steenstrupii complex). The discovery that a unique microbial community characterized by diazotrophs, known as the cyanosphere, is intimately associated with M. vaginatus suggests a symbiotic division of labor in which nutrients are traded between phototrophs and heterotrophs. To probe the potential use of such cyanosphere members in the restoration of biocrusts, we performed coinoculations of soil substrates with cyanosphere constituents. This resulted in cyanobacterial growth that was more rapid than that seen for inoculations with the cyanobacterium alone. Additionally, we found that the mere addition of beneficial heterotrophs enhanced the formation of a cohesive biocrust without the need for additional phototrophic biomass within native soils that contain trace amounts of biocrust cyanobacteria. Our findings support the hitherto-unknown role of beneficial heterotrophic bacteria in the establishment and growth of biocrusts and allow us to make recommendations concerning biocrust restoration efforts based on the presence of remnant biocrust communities in disturbed areas. Future biocrust restoration efforts should consider cyanobacteria and their beneficial heterotrophic community as inoculants. IMPORTANCE The advancement of biocrust restoration methods for cyanobacterial biocrusts has been largely achieved through trial and error. Successes and failures could not always be traced back to particular factors. The investigation and application of foundational microbial interactions existing within biocrust communities constitute a crucial step toward informed and repeatable biocrust restoration methods.

The recycling of scarce nutrient resources in the sunlit open ocean is crucial to ecosystem function. Ammonium oxidation, the first stage of the nitrification process, directs ammonium derived from organic matter decomposition towards the regeneration nitrate, an important resource for photosynthetic primary producers. However, the technical challenge of making nitrification rate measurements in oligotrophic conditions combined with the remote nature of these marine systems means that data availability, and the understanding that provides, is limited. This study reports rate measurements of ammonium oxidation over a 13, 000 km transect within the photic zone of the Atlantic Ocean. These measurements, at relatively fine resolution (order 300 km), permit the examination of interactions with environmental conditions that may warrant explicit development and inclusion in model descriptions. At all locations we report measurable rates with significant variability between and within Atlantic provinces. This adds to evidence that nitrification is an important component of pelagic nitrogen cycling which modifies the inorganic nitrogen inventory of the sunlit ocean. Particular features of interest included a significant hemispheric difference in ammonium oxidation rate and elevated rates associated with mesoscale eddy features. Statistical analysis of potential links between ammonium oxidation rate and routinely measured ecosystem variables indicated significant correlative structure, explaining ~65 % of the data variability. Differences between sampling depths were of the same magnitude or greater than horizontally resolved differences along the transect length, identifying distinct biogeochemical niches between depth horizons. Principle component analysis demonstrated that the best overall match between ammonium oxidation rate and environmental variables involved a combination of chlorophyll-a concentration, the duration of the light phase and silicate concentration (which we argue to be a short-term tracer of physical instability). Results allude to an association between ammonium oxidation and potentially short-term product(s) of photosynthetic activity and subsequent degradation. Approximately 35 % of data variability was not explained, which may include descriptions of DOM pool dynamics.

According to current estimates, the annual volume of crude oil entering the ocean due to both anthropogenic activities and naturally occurring seepages reaches approximately 8.3 million metric tons. Huge discharges from accidents have caused large-scale environmental disasters with extensive damage to the marine ecosystem. The natural clean-up of petroleum spills in marine environments is carried out primarily by naturally occurring obligate hydrocarbonoclastic bacteria (OHCB). The natural hosts of OHCB include a range of marine primary producers, unicellular photosynthetic eukaryotes and cyanobacteria, which have been documented as both, suppliers of hydrocarbon-like compounds that fuel the ‘cryptic’ hydrocarbon cycle and as a source of isolation of new OHCB. A very new body of evidence suggests that OHCB are not only the active early stage colonizers of plastics and hence the important component of the ocean’s ‘plastisphere’ but also encode an array of enzymes experimentally proven to act on petrochemical and bio-based polymers. eng

This paleolimnological study aims to investigate how natural processes and anthropogenic land-use changes have affected sedimentary phosphorus (P) forms and primary producers in a small, temperate lake (Lake Fuglsø, Denmark) throughout the Holocene. Our multi-proxy approach uses pollen, X-ray fluorescence scanning, carbon (C) and nitrogen contents and stable isotopes, sequential P extraction, 31P nuclear magnetic resonance spectroscopy, pigments, diatoms, and plant macrofossils from a 14C-dated sediment record. We found three periods of human impact: (1) low disturbance from domestic grazing during the early/mid Neolithic (~3600 to ~2600 BC), (2) higher disturbance because of animal husbandry and some grain cultivation during the Late Bronze and Pre-Roman Iron Age (~800 BC to AD ~100), and (3) strong disturbance caused by domestic grazing, intensified crop cultivation and, in particular, by retting of fiber plants during the Middle Ages and Renaissance (AD ~1000 to ~1700). Cultural eutrophication during the latter phase caused unprecedented changes in the lake, including altered species composition, high production, and strongly accelerated sediment accumulation rates. Generally, catchment deforestation was related to elevated proportions of metal (iron, aluminum, calcium)-bound P forms in the sediment, while high tree cover correlated with elevated proportions of P forms associated with organic material (“organic” P, humic-bound P, refractory organic P) and loosely bound P. During phases with forest in the catchment, silicon (Si) inputs to the lake were insufficient and diatom frustules were mostly absent in the sediments. In contrast, diatoms thrived in the lake when the landscape was open and erosional Si influx was high. This study is the first to show long-term (~eight millennia) and recurring Si limitation of diatoms, a finding that may explain the absence of diatoms in sediment records of other sites too. In summary, human land-use with preceding deforestation accelerated the transport of nutrients and elements from the terrestrial to the aquatic environment, leading to substantial and irreversible changes in Lake Fuglsø. Our study is a good example of the tight links between catchment processes and lake status, indicating that catchment dynamics should be considered in lake restoration projects, particularly for lowland lakes with high catchment : lake area ratios.

There is strong evidence of an increase in primary production (PP) in the Arctic Ocean (AO) over the last two decades. Further increases will depend on the interplay between decreasing light limitation for primary producers, as the sea ice extent and thickness decrease, and the availability of nutrients, which is controlled by, but not limited to, inputs from the Atlantic and the Pacific Oceans. While these inputs are the major nutrient sources to the AO, ocean vertical mixing is required to bring the nutrients into the photic zone. We analyze data collected in the Western Eurasian Basin (WEB) between 1980 and 2016 and characterize the nutrient climatology of the various water masses. We conclude that there were no significant trends in the concentrations of the two macronutrients that typically limit PP in the AO (nitrate and silicic acid, in the case of diatoms), except a decreasing trend for silicic acid in Polar Surface Water (PSW), which is consistent with the reported increase in PP in the AO. We suggest that the Whalers Bay polynya, located in the northwestern corner of Svalbard, may act as a mixing hotspot, creating patches of nutrient replenished PSW. These patches may then be advected to higher latitudes under the ice pack, later boosting PP upon release from light limitation or else, keeping a nutrient reservoir that may be used in a subsequent growth season. It is likely that this remaining nutrient reservoir will decrease as sea ice cover retreats and light limitation alleviates.

Disturbance impacts the spatial distribution of primary producers, which can have cascading effects on ecosystem function. The lower-intertidal zone on the rocky shores of the Pacific Northwest is one such place where wave energy creates a mosaic-like distribution between two assemblages: surfgrass (Phyllospadix scouleri) meadows and macroalgal forests dominated by kelp. We simulated wave disturbance by experimentally removing patches of surfgrass monocultures, resulting in a macroalgal assemblage with increased diversity, biomass, and net primary productivity in the following year. Although surfgrass had a higher C:N compared to macroalgal assemblages, macroalgal assemblages achieved a higher biomass, fixed carbon at a faster rate, and released more dissolved organic carbon (DOC) during photosynthesis. Thus, despite similar standing amounts of carbon, macroalgal assemblages have increased carbon turnover-from fixation to DOC release. Comparative photophysiology indicated that surfgrasses have a competitive advantage over other macrophytes at low light levels, allowing them to persist when disturbance is reduced. Unexpectedly, disturbance in this system increased the potential for carbon sequestration when surfgrass monocultures were replaced by diverse macroalgae.

Microbial eukaryotes (or protists) in marine ecosystems are a link between microbial primary producers and all higher trophic levels. The rate at which heterotrophic protistan grazers consume microbial prey and recycle organic matter is an important factor that influences marine microbial food webs and carbon cycling. At deep-sea hydrothermal vents, chemosynthetic bacteria and archaea form the base of a food web that functions in the absence of sunlight, but the role of protistan grazers in these highly productive ecosystems is largely unexplored. Here, we pair grazing experiments with a molecular survey to quantify protistan grazing and to characterize the composition of vent-associated protists in low-temperature venting fluids from Gorda Ridge in the North East (NE) Pacific Ocean. Results reveal protists exert higher predation pressure at vents compared to the surrounding deep seawater environment and may account for consuming 28-62% of the daily stock of prokaryotic biomass within the hydrothermal vent food web. The vent-associated protistan community was more species rich relative to the background deep sea, and patterns in the distribution and co-occurrence of vent microbes provide additional insights into potential predator-prey interactions. Ciliates, followed by dinoflagellates, Syndiniales, rhizaria, and stramenopiles dominated the vent protist community and included bacterivorous species, species known to host symbionts, and parasites. Our findings provide an estimate of protistan grazing pressure within hydrothermal vent food webs, highlighting the role that diverse deep-sea protistan communities have in carbon cycling.SignificanceHeterotrophic protists are ubiquitous in all aquatic ecosystems and represent an important ecological link because they transfer organic carbon from primary producers to higher trophic levels. Here, we quantify the predator-prey trophic interaction among protistan grazers and microbial prey at multiple sites of hydrothermal venting near the Gorda Ridge spreading center in the NE Pacific Ocean. Grazing pressure was higher at the site of active diffuse flow and was carried out by a highly diverse assemblage of protistan species; elevated grazing rates are attributed to higher concentrations of chemosynthetic microorganisms and biological diversity localized to hydrothermal vent environments.

The paper summarizes the two stages of the forest ecosystem formation: (i) the establishing phase of the primary producers, which takes place beneath the tree canopy, as a consequence of having produces large amounts of seeds; (ii) the phase of spontaneous immigration of consumers and decomposers towards these massifs, which brings about the formation of the biocenosis and the forest ecosystem. This second stage is documented by thorough researchers carried out in experimental plantations installed in steppe, forty years after.

Summary Most plants grow and develop by taking up nutrients from the soil while continuously under threat from foraging animals. Carnivorous plants have turned the tables by capturing and consuming nutrient-rich animal prey, enabling them to thrive in nutrient-poor soil. To better understand the evolution of botanical carnivory, we compared the draft genome of the Venus flytrap (Dionaea muscipula) with that of its aquatic sister, the waterwheel plant Aldrovanda vesiculosa, and the sundew Drosera spatulata. We identified an early whole-genome duplication in the family as source for carnivory-associated genes. Recruitment of genes to the trap from the root especially was a major mechanism in the evolution of carnivory, supported by family-specific duplications. Still, these genomes belong to the gene poorest land plants sequenced thus far, suggesting reduction of selective pressure on different processes, including non-carnivorous nutrient acquisition. Our results show how non-carnivorous plants evolved into the most skillful green hunters on the planet., Highlights • An early whole-genome duplication is the source of carnivory-associated genes • Trap-specific genes were recruited from the roots • Expansion of specific gene families enabled fine-tuning of hunting styles • Evolution of plant carnivory was paralleled by massive gene loss, Palfalvi et al. reconstruct the evolution of plant carnivory in the Droseraceae by comparative genome analysis. A common whole-genome duplication is the source for recruitment of genes to carnivory-related functions. Different hunting styles evolve by expansions of defined gene families. The analyzed genomes have massively lost genes.

Zooplankton plays a Central role in the transfer of matter and energy from primary producers to high trophic organisms, and zooplankton serves as an essential component of sedimentary material that supplies organic matter to the bottom of marine basins. The paper presents new data on the distribution of a number of heavy metals (Cd, Co, Cr, Cu, Mo, Ni, Pb) and As in the Calanus zooplankton collected in July–August 2017 in the North-Eastern, Eastern and Central parts of the Barents Sea. It is shown that the spatial distribution of metals in zooplankton organisms is influenced by both biotic ecosystem factors associated with bioproductivity and hydrological and geochemical parameters of the habitat (North Polar Front). In the zooplankton of the Arctic water mass to the South-East of Franz Josef Land, there was an increased content of essential heavy metals Cu, Zn and Cr in comparison with the coastal and Atlantic water masses. Zooplankton from the Central part of the sea (Atlantic water mass), where phytoplankton production is reduced, is characterized by the lowest concentrations of most elements (Ni, Cu, Zn, As and Pb). The highest concentrations were found for both essential heavy metals (Zn and Cu) and toxic metalloid As, which may indicate non-selective bioaccumulation of trace elements by copepods.

Animals exert both direct and indirect controls over elemental cycles, linking primary producer‐based (green) and decomposer‐based (brown) food webs through top‐down trophic interactions and bottom‐up element regeneration. Where animals are aggregated at high biomass, they create hotspots of elemental cycling. The relative importance of animal control on elemental cycling depends on animal biomass, species functional traits (i.e. feeding mode and stoichiometry), and their overlap. We evaluated how animal community complexity affects the mechanisms regulating energy flow to the brown food web. We conducted a mesocosm experiment where we varied the biomass and overlap of animals with different life history and stoichiometric traits (stream fish and mussels) and measured how this influenced the quantity and fraction of labile carbon available to microbes. We used linear models and structural equation modelling to evaluate direct (excretion) and indirect (herbivory, nutrient availability, and nutrient stoichiometry) effects of animals on bioavailable dissolved organic carbon (BDOC) concentration. In experimental stream mesocosms, we found support for both direct (DOC excretion) and indirect (grazing) animal influences on BDOC concentration. Although we found that snail, fish, and mussel biomass increased nutrient concentrations, neither nutrient concentration nor stoichiometry had a significant effect on BDOC concentration. This has been due to the high background nutrient concentration context of our stream mesocosm water. Snails, probably due to their high biomass and small body size, exerted a significant positive direct control on BDOC concentration. Fish and mussels exerted a significant negative indirect control on BDOC via their effects (grazing and bioturbation) on algal biomass. Our results imply that primary consumers with different feeding strategies provide a key mechanism regulating the flow of DOC into the brown food web through direct (excretion) and indirect (grazing) controls on primary producers. This highlights that animals can provide important controls on the production of bioavailable organic energy supporting microbes in aquatic ecosystems, but the importance of these controls depends on the nutrient context and the distribution of primary producer and animal biomasses.

SUMMARY Pelleting is commonly used in the production of poultry feed as it can reduce waste, kill pathogenic bacteria, and improve productivity. However, high temperatures used during production can negatively impact some feed ingredients. Omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA)-rich ingredients are often added to poultry feed to increase the n-3 LC-PUFA concentration of meat and eggs, adding value due to the health benefits associated with n-3 LC-PUFA consumption. Fish oils have traditionally been used for this purpose, but the n-3 LC-PUFA they contain are susceptible to oxidation, which can result in rancidity in enriched poultry products. Alternatively, protists that are primary producers of n-3 LC-PUFA are used. When provided in an unextracted form, these organisms could potentially protect the n-3 LC-PUFA they contain from oxidation. Aurantiochytrium limacinum is a marine protist, rich in docosahexaenoic acid (DHA), an n-3 LC-PUFA associated with various health benefits. We supplemented layer feed with A. limacinum and investigated the effect of pelleting on the recovery of DHA from feed and the efficiency of DHA transfer from feed to eggs. Pelleting did not decrease the concentration of DHA in feed. Also, no differences were observed between the groups fed mash or pelleted feeds in terms of the level of DHA enrichment of eggs. These results indicate that DHA, in the form of an A. limacinum biomass, is resistant to pelleting conditions and can be used as an ingredient in pelleted poultry diets to increase the DHA concentration of poultry products.

Primary producers need strategies and tools to assist in monitoring water use with a view to improving physical and financial productivity. The purpose of this research is to integrate farmer financial accounting data with soil moisture and climate data to better account for water use on farm. Farm-accounting systems, if present, lack the sophistication to allow growers to analyze use, loss, and productivity of water. Water-accounting technologies, if present, do not readily link to business systems to provide the optimal real-time financial decision-making data, nor the necessary context for new technologies to support a broader integrated approach to water management. Findings of desk-based technology benchmarking suggest elements required include real-time sensory data integration that allows for strategic allocation to the full suite of direct and indirect water costs. Key actor interview and producer surveys highlight demand for a farm business integrated water productivity tool and findings from field data collected in a potato case study provide demonstration of how irrigation decision-making can be supported by the crucial link between producers’ business systems and sensing technology. Refereed/Peer-reviewed

The existing study was taken to represent the current information in order to develop a mass-balanced ecosystem model within the resettled maritime boundary area of the Bay of Bengal (BoB), Bangladesh from July 2016 to June 2017 through ECOPATH approach covering over 90 000 km2. A total of 19 functional groups were considered representing all trophic levels in the foodweb where estimated trophic interactions between the groups were varied from 1 (primary producers and detritus) to 3.45 (sharks). The ecotrophic efficiency (EE) of most of the consumers was greater than 0.80; symbolizing a largely exploited ecosystem and high energy transfer from lower to higher trophic levels. Moreover, the gross efficiency (0.001 8) and transfer efficiency (11.12%) of the whole system symbolizes the “Developing Systems” with somewhat maturity currently. Ecosystem’s overhead (64.6) and ascendancy (35.4) also designate the ecosystem’s stability. Thus, this study determines that the resettled maritime area of BoB reserves significant backup strength to face stress situations having capacity to rapid restoration to the original states.

The Western Antarctic Peninsula (WAP) is a hot spot of global warming, including decreased sea-ice cover during winter and increased sedimentation during summer due to glacial melt. Subsequently, an altered irradiance and temperature regime in the water column may affect the performance of primary producers and change competitive structures. The brown, subtidal macroalgae Desmarestia menziesii and D. anceps are ecosystem engineers and of extreme importance for the Antarctic coastal ecosystem. Individuals of both species were collected from the field during the austral summer and exposed in two experiments to different temperatures (2 and 7 °C) or different irradiances (high and low) in combination with co-culturing the two algal species together (two-factorial design). No temperature, irradiance or co-cultivation effects on growth rates of D. menziesii and D. anceps were detected, but effects were possibly masked by the very low growth rates. Both D. menziesii and D. anceps are season anticipators, showing highest growth in late winter/spring and a dormancy state during summer. Photosynthetic efficiency was usually higher at 2 °C and low irradiance conditions compared to 7 °C and high irradiance and no co-culturing effects were detected. Parameters derived from P–E curves (rETRmax, Ek and α) were higher in D. menziesii compared to D. anceps, reflecting zonation patterns in the field. Future multifactorial experiments, taking seasons and different life-stages into account, are particularly needed to elucidate year-round effects of global warming on macroalgal key species that form the energetic base of the Antarctic coastal food webs.

Sea ice is an important control on gas exchange and primary production in polar regions. We measured net oxygen production (NOP) and gross oxygen production (GOP) using near-continuous measurements of the O2∕Ar gas ratio and discrete measurements of the triple isotopic composition of O2, during the transition from ice-covered to ice-free conditions, in Whycocomagh Bay, an estuary in the Bras d'Or Lake system in Nova Scotia, Canada. The volumetric gross oxygen production was 5.4+2.8-1.6 mmol O2 m−3 d−1, similar at the beginning and end of the time series, and likely peaked at the end of the ice melt period. Net oxygen production displayed more temporal variability and the system was on average net autotrophic during ice melt and net heterotrophic following the ice melt. We performed the first field-based dual tracer release experiment in ice-covered water to quantify air–water gas exchange. The gas transfer velocity at >90 % ice cover was 6 % of the rate for nearly ice-free conditions. Published studies have shown a wide range of results for gas transfer velocity in the presence of ice, and this study indicates that gas transfer through ice is much slower than the rate of gas transfer through open water. The results also indicate that both primary producers and heterotrophs are active in Whycocomagh Bay during spring while it is covered in ice.

Through respiration and photosynthesis, seagrass meadows contribute greatly to carbon and oxygen fluxes in shallow coastal waters. There is increasing concern about how shallow-water primary producers will react to a near-future climate scenario with increased temperature variation. When modelling primary productivity under high temperature variability, Q10 values are commonly used to predict rate changes depending on biophysical factors. Q10 values are often assumed to be constant and around 2.0 (i.e. a doubling of the rate with a temperature increase of 10 °C). We aimed to establish how the gas exchange of seagrass (Zostera marina) tissues at various maturity stages would respond over a broad range of temperatures. Seagrass shoot maturity stage clearly affected respiration and apparent photosynthesis, and the Q10 results indicated a skewed balance between the two processes, with a higher photosynthetic Q10 during periods of elevated temperatures. When estimating whole-plant Q10 in a realistic maximal temperature range, we found that the overall response of a seagrass plant’s net O2 exchange balance can be as much as three to four times higher than under ambient temperatures. Our findings indicate that plant tissue age and temperature should be considered when assessing and modelling carbon and oxygen fluctuations in vegetated coastal areas.

Aquatic and terrestrial organisms are being exposed to a number of anthropogenically-induced environmental stresses as a consequence of climate change. In addition, climate change is altering various linkages that exist between ecosystems on land and in water. Here we compare and contrast how climate change is altering aquatic and terrestrial environments and address some of the ways that the organisms in these ecosystems, especially the primary producers, are being affected by climate change factors, including changes in temperature, moisture, atmospheric carbon dioxide and solar UV radiation. Whereas there are some responses to climate change in common between terrestrial and aquatic ecosystems (e.g., changes in species composition and shifting geographic ranges and distributions), there are also responses that fundamentally differ between these two (e.g., responses to UV radiation). Climate change is also disrupting land-water connections in ways that influence biogeochemical and hydrologic cycles, and biosphere-atmosphere interactions in ways that can modify how aquatic and terrestrial ecosystems are affected by climate change and can influence climate change. The effects of climate change on these ecosystems are having wide-ranging effects on ecosystem biodiversity, structure and function and the abilities of these systems to provide essential services.

Carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of zooplankton are potentially good indicators of energy and nutrient fluxes, and trophic interactions in lake food‐webs, yet, are poorly understood. Based on a synoptic survey of 233 boreal lakes, we evaluated the relationships of water chemistry, hydromorphological, and land cover variables (lake/catchment‐specific factors), and the spatial position of lakes in the landscape (representing potential regional factors) with the δ¹³C and δ¹⁵N of nine meso‐zooplankton taxa. The δ¹³C variation of most taxa was negatively related to water chemistry variables associated with allochthonous inputs (colour/dissolved organic carbon), and positively correlated with nutrient concentrations (together explaining 12–69% of variation). Most of the δ¹³C variation explained by significant hydromorphological and land cover variables (% peat area, drainage basin area:lake area, shoreline development index, and lake area, explaining 26–47% of variation) was shared by significant water chemistry variables. Together, this suggests that δ¹³C variation of zooplankton reflects different environmental influences on δ¹³C of lake primary producers. The δ¹⁵N variation of most taxa was significantly related to pH, total phosphorous concentration (water chemistry variables, explaining 8–64% of variation), and water retention time (hydromorphological variable, explaining 13–87% of variation). These relationships are probably reflective of the association of zooplankton δ¹⁵N with terrestrial organic matter flux, environmentally‐induced biogeochemical nitrogen transformations and phytoplankton ¹⁵N fractionation. Specific water chemistry, hydromorphological, and land cover predictors of δ¹³C and δ¹⁵N and the direction of their effects (i.e. positive or negative) were largely similar among taxa. However, their degree of importance varied among taxa particularly for δ¹³C, probably due to contrasting feeding selectivity and resulting differences in allochthony. This suggests that δ¹³C of different taxa may respond differently to changes in limnological gradients due to environmental perturbations affecting boreal regions. The lake/catchment‐specific factors were more important than regional factors (lithology, soil properties and atmospheric nitrogen deposition; which are represented by the spatial position of lakes) in explaining δ¹³C and δ¹⁵N variation of zooplankton. Hence, before inferring regional effects in stable isotope studies, the influence of lake/catchment‐specific factors needs to be explicitly quantified.

Seagrass meadows are declining at alarming rates globally due to both anthropogenic activities and natural threats. Seagrasses play key ecological roles in coastal ecosystems as primary producers and providers of habitat and environmental structure. Therefore, mapping seagrass beds is indispensable for the effective monitoring and management of coastal vegetated habitats. In contrast to direct sampling techniques and optical remote sensing, active hydroacoustic techniques are relatively inexpensive and efficient for the detection of seagrass. We used a single beam echosounder to detect the spatial and temporal distribution characteristics of the eelgrass Zostera marina L. in an important overwintering habitat for the whooper swan Cygnus cygnus (Swan-Lake lagoon), northern China. We also distinguished echograms of the macroalgae Chaetomorpha linum K. and outlined its threat to seagrass. We also propose a method for calculating the accuracy of interpolation analyses. Results showed that: (1) The distribution of seagrass in Swan Lake varies with seasons, with maximum distribution area in summer. The maximum distribution area of seagrass beds in Swan Lake was 199.09 ha–231.67 ha, accounting for 41.48%–48.26% of the area of Swan Lake; (2) C. linum is a growing threat for seagrass beds of Swan-lake, with distribution area as high as 129.28 ha in May 2018. The invasion and competition by C. linum against seagrass beds could be one of the reasons for the decline in seagrass beds in Swan-Lake; (3) Topo to Raster has the highest interpolation accuracy and is the most conservative among three interpolation methods. Topo to Raster was the most suitable interpolation method for the sonar detection of seagrass beds. The findings may facilitate the application of sonar technology in seagrass monitoring and provide data for the formulation of appropriate seagrass bed management and restoration strategies and policies.

In the present study, we aimed to test the protectiveness of the bioavailability-normalization procedure, with its associated hazardous concentrations for x% of the species (HCx), that is currently implemented to derive environmental threshold concentrations for nickel (Ni) in European environmental legislative frameworks. We exposed a natural plankton-dominated community to 3 constant Ni concentrations, that is, a control with no Ni added (background Ni of 1.2-4 µg/L) and the bioavailability-normalized HC5 and HC50 of 24 and 97 µg dissolved Ni/L, respectively, during a 56-d microcosm experiment under high dissolved organic carbon (DOC) conditions (DOC of 14 mg/L at test initiation). The effects of the bioavailability-normalized HC5 and HC50 values were evaluated at the levels of community structure (community composition and plankton group abundances), community functioning (measured as indirect physicochemical proxies for overnight respiration and carbon fluxes), and individual species abundances. The bioavailability-normalized HC50 treatment had clear effects (defined as effects occurring on at least 2 consecutive sampling days) on both the structure and functioning of the investigated aquatic community. Through its effect on community functioning (i.e., reduced pH and DOC), Ni also influenced its own bioavailability. Clear direct effects of Ni were observed for only 3 species (the Cyanobacteria Oscillatoria sp. 1 and the rotifers Asplanchna/Testidunela sp. and Trichocerca group similis). Most other effects occurring in the plankton community in the HC50 treatment were indirect and likely driven by the direct effect of Ni on the Cyanobacteria Oscillatoria sp. 1, which was the dominant phytoplankton species in the control microcosms. In contrast, the bioavailability-normalized HC5 did not induce clear effects on community structure and functioning endpoints: these were only affected on individual sampling days. Clear (direct) effects were observed for only 2 plankton species (the rotifer Trichocerca group similis and the Cyanobacteria Oscillatoria sp. 1), but their abundances recovered to control levels at the end of the study. In addition, a few species (1 phytoplankton and 3 zooplankton species) were affected in the HC5 treatment only on the last sampling day. It is uncertain whether these species would have shown clear effects over a longer exposure duration. Thus, our study shows that the bioavailability-normalized HC5 of Ni at high DOC induced clear effects on a few individual species. However, the overall conclusion is that the bioavailability-normalized HC5 of Ni as derived through the procedure that is currently implemented in European legislative frameworks protects against clear effects on community structure and function. Environ Toxicol Chem 2019;38:1923-1939. © 2019 SETAC.

Functional traits are ecologically relevant characteristics of species. They are relevant to community structuring in face of environmental drivers (response traits) and to ecosystem processes (effect traits). For planktonic microcrustaceans, the link between functional traits and their responses or effects is not always clear. Our objective was to review the literature on linking functional traits to environmental drivers and ecosystem processes for planktonic cladocerans and copepods. Response traits are discussed in four categories: morphological, life history, behavioral, or physiological. Temperature, predation, resources, and stressors are important drivers of morphological and life-history traits. Body size, a morphological trait, is probably the most important trait, because it responds to several environmental characteristics and is correlated with physiological traits and to zooplankton impact on ecosystems functions. In an ecosystem perspective, zooplankton is an important energy link between primary producers and secondary consumers. In trophic webs, it may control phytoplankton biomass and productivity, with consequences for whole lakes. Its influence on carbon, nitrogen, and phosphorus cycles is expected to increase with body size. Other traits may be important, but there is a lack of information. We point out the need of more functional trait research, especially with freshwater copepods and neglected tropical species. For a better understanding of natural systems, an integrative approach of multiple traits with multiple environmental drivers and ecosystem functions is necessary.

One of the most common anthropogenic impacts on river ecosystems is the effluent discharge from wastewater treatment plants. The effects of this contamination on stream biota may be intensified in Mediterranean climate regions, which comprise a drought period that leads to flow reduction, and ultimately to stagnant pools. To assess individual and combined effects of flow stagnation and sewage contamination, biofilm and gastropod grazers were used in a 5-week experiment with artificial channels to test two flow velocity treatments (stagnant flow/basal flow) and two levels of organic contamination using artificial sewage (no sewage input/sewage input). Stressors’ effects were determined on biofilm total biomass and chlorophyll (Chl) content, on oxygen consumption and growth rate of the grazers (Theodoxus fluviatilis), and on the interaction grazer-biofilm given by grazer’s feeding activity (i.e., biofilm consumption rate). The single effect of sewage induced an increase in biofilm biomass and Chl-a content, simultaneously increasing both grazers’ oxygen consumption and their feeding activity. Diatoms showed a higher sensitivity to flow stagnation, resulting in a lower content of Chl-c. Combined stressors interacted antagonistically for biofilm total biomass, Chl-b contents, and grazers’s feeding rate. The effect of sewage increasing biofilm biomass and grazing activity was reduced by the presence of flow stagnation (antagonist factor). Our findings suggest that sewage contamination has a direct effect on the functional response of primary producers and an indirect effect on primary consumers, and this effect is influenced by water flow stagnation.

Most coastal waters are at risk from microplastics, which vary in concentration and size. Rotifers, as important primary consumers linking primary producers and higher trophic consumers, usually coexist with the harmful alga Phaeocystis and microplastics in coastal waters; this coexistence may interfere with rotifer life-history traits and ingestion of Phaeocystis. To evaluate the effects of microplastics on rotifers, we designed a series of experiments concerning rotifer Brachionus plicatilis life-history traits and rotifer-Phaeocystis (predator-prey) population dynamics under different concentrations and sizes of microplastics. The results showed that small-sized microplastics (0.07 μm) at high levels (≥5 μg mL-1) decreased rotifer survival and reproduction, prolonged the time to maturation, and reduced the body size at maturation, whereas large-sized microplastics (0.7 and 7 μm) had no effect on rotifer life-history traits. For rotifer-Phaeocystis population levels, small-sized microplastics (0.07 μm) significantly delayed the elimination of Phaeocystis by rotifers; this is the first study to test the effects of microplastics on predator-prey dynamics. The results of rotifer-Phaeocystis population dynamics are consistent with the changes in the life-history traits of rotifers and further confirm the negative effects of small-sized microplastics (0.07 μm) on rotifers. These findings help to reveal the effect of pollutants on predator-prey population dynamics.

During the past few decades, the Yangtze River basin has undergone massive anthropogenic change. In order to evaluate the impacts of human interventions on sediment n-alkanes of lakes across this region, the aliphatic hydrocarbon fractions of 19 surface sediment samples collected from lakes along the middle reaches of the Yangtze River (MYR) were analyzed using gas chromatography–mass spectrometry. The n-alkanes extracted from the sediments contained a homologous series from C15 to C34, with a notable predominance of odd carbon compounds except for sediments from the more intensively industrialized Lake Daye, in which > C21 n-alkanes showed no odd/even predominance, and carbon preference index (CPI) approached unity. Abundance values of middle-chain (C21, C23, and C25) and long-chain (C27, C29, C31, and C33) n-alkanes in Lake Daye were approximately 4 to 3 times greater than the average for other lakes, reaching 272.4 and 486.3 μg/g TOC, respectively, in the study. Short-chain n-alkanes (C15, C17, and C19) in the sediments varied in abundance from 10.0 to 76.2 μg/g TOC across the study and showed a moderate correlation with total phosphorus (TP) concentrations in the overlying water. The results indicated anthropogenic eutrophication enhanced the accumulation of short-chain n-alkanes in sediments because the primary producers in which they are synthesized are highly susceptible to nutrient forcing. Middle-chain n-alkane abundances were less affected by eutrophication and generally enriched in macrophyte lakes, while long-chain n-alkanes tend to be low in sediments from more eutrophic water. In the case of Lake Daye, direct discharges of petroleum products from heavy industry have introduced quantities of petroleum n-alkanes (> C21), far exceeding the amounts of biogenic input, and the sediment > C21 n-alkanes detected in this study showed typical characteristics of petroleum source. In other lakes, inputs of petroleum products from surface runoff of vehicle/traffic emissions associated with urbanization and economic growth contributed comparatively few n-alkanes to sediments, resulting in declines in CPI for > C21 n-alkanes, most obviously in Lakes Huanggai, Donghu, and Futou. Calculated CPI values suggest that a major proportion of the n-alkanes present in these lakes are derived from biogenic input. The results of this study provided evidences that n-alkane profiles of lake sediments respond sensitively to human-induced eutrophication and different sources of petroleum pollution.

Oblique zooplankton tows were carried out in the Gerlache Strait from 17 to 22 January 2015 as part of the first Colombian oceanographic expedition to the Antarctic continent, to document the composition and structure of the epipelagic copepod assemblage, taking into account variations at a small spatial scale. The epipelagic environment of the Gerlache Strait was divided into two oceanographic regions during sampling: a stratified northern region and a homogeneous southern region. The epipelagic copepod assemblage comprised 17 species belonging to four orders and 13 families. Adult copepods as well as developmental stages ranging from copepodite II (C2) to copepodite V (C5) from eight different species were recorded in the study area. The dominant species by number was Oithona similis, followed by O. frigida, Ctenocalanus citer, Drescheriella glacialis, and Calanoides acutus. There were significant differences between the epipelagic copepod assemblages present in the northern and southern regions of the Gerlache Strait (Anosim, p = 0.01), with a dissimilarity percentage of 52%. Moreover, Aetideus armatus is reported for the first time in the western sector of the Antarctic Peninsula. The oceanographic conditions and the geomorphological characteristics of the study area modulated the surface circulation pattern, as well as the structure and composition of the primary producers during the study period, determining the spatial variation of the abundance and composition of the epipelagic copepod assemblage in the Gerlache Strait during the 2015 Austral summer.

Bivalves represent one of the most important components of freshwater zoobenthos, and their shells provide a substrate for many organisms to create epibiotic communities of predominantly facultative nature. Thus far, information regarding colonization of Unio tumidus by microorganism assemblages has been almost absent. Moreover, data on the functioning of trophic networks created by epibionts are also unavailable. Therefore, the present study aimed to examine the assemblage of epibiotic microorganisms inhabiting live and dead bivalves with regard to the physicochemical properties of the habitat and determine whether stable isotope levels in primary producers and consumers colonizing bivalve shells exhibit significant seasonal variability. The substrate characteristic and physicochemical properties of water – primarily biogenic compounds and total organic carbon clearly modified the taxonomic composition of microorganisms and the function of the trophic network. This was reflected by the increased diversity of microorganisms (phycoflora, ciliates and rotifers) on live bivalves and the increase in their abundance on dead bivalves. The level of stable isotopes exhibited clear seasonal variability in individual components of the epibiotic trophic network, whereas food preferences of the potential consumers (protozoans and rotifers) depended significantly on the availability and abundance of food.

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants, have been extensively applied and eventually leached into the surrounding environment. Marine microalgae are not only the dominant primary producers of marine ecosystem, but also food source for aquaculture. PBDEs have been found to remarkably inhibit growth, photosynthesis and metabolism of marine microalgae. However, whether they also affect swimming behavior of marine motile microalgae remains unknown. We chose BDE-47, BDE-99 and BDE-153 as model PBDEs, and the unicellular marine green flagellate, Platymonas subcordiformis, as test organism to figure out this issue. After two-hour exposure, motile cells proportion (MOT), swimming velocity (VCL, VAP and VSL), and swimming pattern (LIN and STR) of P. subcordiformis were measured via computer assisted cell movement tracking. Results suggest that the three PBDEs not only reduced motile cells proportion and swimming velocity, but also altered swimming pattern. BDE-47 was more toxic than BDE-99, followed by BDE-153, indicating their toxicity decreased as bromination degree increases. Swimming ability of P. subcordiformis was even completely arrested when BDE-47 and BDE-99 at 32 μg/L. The impairment of swimming ability by PBDEs might thereby hinder growth and survival of marine microalgae, and subsequently threaten marine ecosystem and aquaculture industry. More importantly, this study implies that marine microalgae swimming behavior test is more efficiency and sensitive than traditional marine microalgal bioassays, like growth and photosynthesis tests. We suggest that although future work is needed, swimming behavior analysis of P. subcordiformis with MOT, VCL and VAP as endpoints can be developed as a low-cost, convenient, fast, reliable and sensitive method for seawater quality assessment.

Estuarine food webs can be supported by local benthic or pelagic primary producers and by the import of organic matter. Until now, studies precisely quantifying the main energy sources in estuarine food webs have been limited for diverse species. The main pathway by which primary nutrients and energy are transported is not explicit and impedes conservation and restoration of estuarine ecosystems in Marine Protected Areas (MPAs). In this study, carbon and nitrogen stable isotopes were measured, to assess the primary food sources for consumers in the subtidal zone of the Yellow River Estuary. More than half of the detected consumers showed a balanced diet, with no significant feeding preferences. The remaining consumers mainly relied on microphytobenthos (MPB) and Cordgrass (Spartina). MPB contributions ranged from 31% to 38% for fishes and from 24% to 33% for invertebrates, while the contribution of Spartina ranged from 30% to 43% for fishes and from 24% to 38% for invertebrates, respectively. MPB was regarded as the primary autochthonous food source, while Spartina was regarded as the primary allochthonous source. Consumers showed a low reliance on food sources originating from the Yellow River, with diets conforming more to a marine based pattern. This study provides the first detailed investigation of the contribution of food sources in the subtidal zone of the Yellow River Estuary. The results of this study enhance our understanding of energy pathways in estuarine ecosystems, in addition to providing data to inform the conservation and restoration of coastal ecosystems.

Diazotrophs have received recent appreciation as a major source of bioavailable nitrogen in the global oceans. They mostly flourish in warm, stratified, calm and nutrient depleted conditions in the ocean. Such conditions prevail during spring and autumn seasons in the Arabian Sea. Some previous experimental studies conducted during spring have suggested the highest rates of N2 fixation among other oceans in the eastern Arabian Sea, but there are no such records during autumn. In addition, modelling studies have suggested high rates of annual N2 fixation in the Arabian Sea. In this study, we conducted isotope labeling incubation experiments in the eastern Arabian Sea in autumn 2010 to estimate N2 fixation rates and primary production. Unlike previous studies conducted in this region, we did not witness any diazotrophic bloom, but our N2 fixation rates (1300–2500 μmol N m−2 d−1) were still comparable to the rates reported in previous studies conducted in spring, and among the highest rates observed in the global oceans. Our data suggest an important role of excess phosphate to sustain N2 fixation during autumn. Most intriguingly our study shows that N2 fixation supplies a surplus amount of bioavailable nitrogen required for primary producers during autumn in this region.

An ecosystem model of the Minho estuary (NW coast of Iberian Peninsula) was implemented in AQUATOX 3.1 (US-EPA) to check whether the effects of temperature rise, dry years, rainy years and river flow decrease acting isolated (single stressor) or combined (multiple stressor) would induce the same type of response on macroinvertebrate biomass variation and to identify the type of stressor interactions. The model was parameterised with site-specific and species-specific data and accounts for a food web with primary producers, benthic invertebrates, fish and detritus, with 12 biotic groups, 4 groups of detritus and 12 forcing functions. Results showed that macroinvertebrate biomass responded differently to single stressor and multiple stressor scenarios and interactions among the tested stressors were antagonistic. During medium term simulations (∼6 years), the biomass of macroinvertebrate communities from the Minho estuary was maintained or slightly increased in single scenarios of temperature rise but the occurrence of antagonistic interactions between temperature rise, river flow decrease, dry years and rainy years counteracted the increasing tendency in multiple stressor scenarios. Overall, the present results highlight the strong dependence of the system’s biomass and production on hydrodynamics and contribute to increase knowledge on the mechanistic processes behind this. Thus, we recommend an ecosystem-based management of the Minho River basin supported by models such as the present one.

The food webs of a coastal lagoon ecosystem in the southeastern Gulf of California were investigated through the use of stomach contents analyses and carbon (δ13C) and nitrogen (δ15N) stable isotopes of fish and macroinvertebrates. Food sources and species representative of primary producers and primary-to-tertiary consumers were examined. Macroinvertebrates (47.5%) and fish (45%) assemblages represented over 90% of the total biomass. The most representative groups were fish (45%), crustaceans (24%), mollusks (16%), and echinoderms (8.5%). Based on the results from stomach content analysis, stable isotope analysis, and mixing models using Bayesian statistics, the estuarine food web was reconstructed from food chain bases to tertiary consumers, including the most representative species in the ecosystem. Four food webs were identified according to the primary producers, and five trophic levels were identified. However, in the higher trophic levels, these food webs are indistinguishable due to the high degree of omnivory and the complexity of the system which allows the predation in different environments.

The marginal semi-enclosed Bohai Sea is an important ecosystem for many commercial as well as ecologically important species. At the same time, the Bohai Sea increasingly facing various anthropogenic disturbances which have been reported to affect the functioning of this ecosystem in many ways. Using Ecopath and Ecosim modeling suite (ver 6.5), this study examined the temporal changes in the ecological status of the Bohai Sea ecosystem. The present model comprises a total of 23 functional groups based on a year-round trawl survey conducted in 2016. The results of the present study showed that the mean trophic level of the commercial species as well as the overall fisheries species declined during the last few decades. The fundamental source of biomass flows within the Bohai Sea food web generated from the lower trophic levels. Primary producers (phytoplankton) and detritus contributed about 52.77% and 47.23%, respectively of the total energy flows originated from the base of the food web in 2016. Estimation of the ecological parameters during the decadal-scale suggests that the Bohai Sea ecosystem is at an immature stage. The niche overlap indices showed intermediate overlaps between prey species rather than predator species overlapping. The mixed trophic impacts indicated that the lower trophic levels had positive influences on most of the groups in the higher trophic levels, indicating the strong bottom-up ecosystem dynamics. Increased biomass of jellyfish and cephalopod had moderate adverse effects on other groups. This comparative analysis provides an important platform by increasing our understanding of the several food web properties that can be integrated within a future management plan of the Bohai Sea fisheries resources.

The structure and function of food web of Hooghly-Matla estuarine system (HMES) including Sundarban mangroves is studied to assess the health of the system. HMES, provides shelter and make a home to many economically important shell and fin fishes. This estuary is exposed to various threats such as increasing salinity, deterioration of soil fertility and productivity, pollution and loss of biodiversity. Ecological network analysis (ENA) is applied for the HMES to model the trophic flows in 22 ecological compartments using Ecopath (a software for network analysis), integrating ecological data for the 2013–2015. ENA is performed, including a set of indices, keystoneness and trophic spectrum analysis to describe the contribution of the 22 groups to the HMES functioning. Results show that 22 compartments of the HMES including primary producers (trophic level TL 1) to the top consumers (elasmobranch, TL 3.5), the ecotrophic efficiency ranges from 0.016 to 0.989. Small demersal fishes, prawns, shrimps and crabs are the most exploited groups of this ecosystem. Herbivory and detritivory ratio is 1:1 indicating relative absence of top predators and low maturation level. Maturity of the system, organization, relative order and disorder within the system, diversity of flow of material among compartments and overhead of the system has been assessed. Biomass over Total system throughput ratio (TB/TST), Total primary production over total respiration ratio (TPP/TR), Total primary production over biomass (TPP/TB) and system omnivory index (SOI) indicate the moderate maturity level of the system. The HMES trophic network has a moderate recycling level (FCI = 12.99%), a high total system throughput (TST = 22976.03 tonnes km−2 yr−1) and a low ascendency (A = 25799 tonnes km−2 yr−1), but a relatively low connectance (CI = 0.27), high internal relative ascendency (A = 29.6%) and a high omnivory index (OI = 0.203), indicating that this estuary is immature but relatively organized and complex, with strong production. HMES has some unique features in comparison to similar functioning geographically close estuaries or estuaries with similar environmental characteristics. System robustness and exergy are also estimated to assess ecosystem health and compared with other tropical systems. From a holistic point of view, present study conveys fundamental information and categorizes the status of the system.