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Aquaculture is important for food security and livelihoods, especially in the developing tropics. Many nutrients supplied by feed degrade water quality, waste resources and lead to nutrient loss. Halophytes have the potential to recover these nutrients from aquaculture effluents. Most studies have focused on temperate species, but there is a need for extractive species suitable for integration in tropical saline aquaculture. Sea purslane Sesuvium portulacastrum is a promising candidate providing biomass for human consumption with potential pharmaceutical applications, but to date, nutrient uptake has not been studied in this species. This study investigated the nutrient removal from milkfish wastewater by systems planted with S. portulacastrum in hydroponics versus planted in sand. Most nutrients were removed from the wastewater within 48 h. Phosphorus and nitrogen were most efficiently removed in treatments with plants and sand and on average lower in the hydroponic incubations. However, in hydroponic systems, plants assimilated 50.2% of the added labelled N with no significant difference in recovery after 48 h when 15NH4 or 15NO3 was added. The recovery of wastewater N into plant biomass was several-fold higher in hydroponics than in sand substrate. Integration of S. portulacastrum into aquaculture turns aquaculture effluents into a valuable resource. [ABSTRACT FROM AUTHOR]

Algal blooms are increasing worldwide, driven by elevated nutrient inputs. However, it is still unknown how tropical benthic algae will respond to heatwaves, which are expected to be more frequent under global warming. In the present study, a multifactorial experiment was carried out to investigate the potential synergistic effects of increased ammonium inputs (25 μM, control at 2.5 μM) and a heatwave (31°C, control at 25°C) on the growth and physiology (e.g., ammonium uptake, nutrient assimilation, photosynthetic performance, and pigment concentrations) of two bloom‐forming algal species, Cladophoropsis sp. and Laurencia sp. Both algae positively responded to elevated ammonium concentrations with higher growth and chlorophyll a and lutein concentrations. Increased temperature was generally a less important driver, interacting with elevated ammonium by decreasing the algaes' %N content and N:P ratios. Interestingly, this stress response was not captured by the photosynthetic yield (Fv/Fm) nor by the carbon assimilation (%C), which increased for both algae at higher temperatures. The negative effects of higher temperature were, however, buffered by nutrient inputs, showing an antagonistic response in the combined treatment for the concentration of VAZ (violaxanthin, antheraxanthin, zeaxanthin) and thalli growth. Ammonium uptake was initially higher for Cladophoropsis sp. and increased for Laurencia sp. over experimental time, showing an acclimation capacity even in a short time interval. This experiment shows that both algae benefited from increased ammonium pulses and were able to overcome the otherwise detrimental stress of increasingly emerging temperature anomalies, which provide them a strong competitive advantage and might support their further expansions in tropical marine systems. [ABSTRACT FROM AUTHOR]

In the last three decades, quantitative approaches that rely on organism traits instead of taxonomy have advanced different fields of ecological research through establishing the mechanistic links between environmental drivers, functional traits, and ecosystem functions. A research subfield where trait-based approaches have been frequently used but poorly synthesized is the ecology of seagrasses; marine angiosperms that colonized the ocean 100M YA and today make up productive yet threatened coastal ecosystems globally. Here, we compiled a comprehensive trait-based response-effect framework (TBF) which builds on previous concepts and ideas, including the use of traits for the study of community assembly processes, from dispersal and response to abiotic and biotic factors, to ecosystem function and service provision. We then apply this framework to the global seagrass literature, using a systematic review to identify the strengths, gaps, and opportunities of the field. Seagrass trait research has mostly focused on the effect of environmental drivers on traits, i.e., “environmental filtering” (72%), whereas links between traits and functions are less common (26.9%). Despite the richness of trait-based data available, concepts related to TBFs are rare in the seagrass literature (15% of studies), including the relative importance of neutral and niche assembly processes, or the influence of trait dominance or complementarity in ecosystem function provision. These knowledge gaps indicate ample potential for further research, highlighting the need to understand the links between the unique traits of seagrasses and the ecosystem services they provide. [ABSTRACT FROM AUTHOR]

The lack of top‐down control on Tripneustes gratilla, a sea urchin commonly known to graze on seagrass, and the bottom‐up control of its feeding preference, led to the overgrazing of seagrass meadows of the species Thalassodendron ciliatum in Changuu Island (Zanzibar Archipelago). The impact of overgrazing on seagrasses was assessed by mapping the presence of grazed versus non‐grazed seagrass patches in the study site, while the top‐down control on T. gratilla was assessed by measuring the abundance of its fish predators. The feeding preference and distribution of T. gratilla were characterized by calculating the electivity indexes for each seagrass species and measuring sea urchin density, respectively. Approximately half of the patches of T. ciliatum were overgrazed, while predatory fishes of T. gratilla were absent from the site. The Vanderploeg and Scavia's Relativized Electivity Index indicated that T. gratilla had a feeding preference for T. ciliatum, which was also supported by higher urchin densities within T. ciliatum dominated patches. Bottom‐up control of grazing activity was observed by quantifying and analyzing morphological, nutritional, and the chemical defense traits of the seagrass in relation to feeding preference and urchin density. Feeding was positively correlated to the seagrass tissue C:P ratio (ρ = 0.9), whereas urchin density showed no correlations. The bottom‐up control of the feeding preference and agglomeration of T. gratilla in T. ciliatum meadows, together with the lack of evidence of substantial top‐down control and the long recovery time of T. ciliatum led to the overgrazing of this species at this site. Overgrazing, therefore, was shown to be the result of multiple factors ranging from the traits of the seagrass and feeding preference of T. gratilla, to the abundance of predators in this area. [ABSTRACT FROM AUTHOR]

Understanding species-specific trait responses under future global change scenarios is of importance for conservation efforts and to make informed decisions within management projects. The combined and single effects of seawater acidification and warmer average temperature were investigated by means of the trait responses of Cymodocea serrulata , a tropical seagrass, under experimental conditions. After a 35 d exposure period, biochemical, morphological, and photo-physiological trait responses were measured. Overall, biochemical traits mildly responded under the individual exposure to high temperature and increasing p CO2 values. The response of C. serrulata was limited to a decrease in %C and an increase in the sucrose content in the rhizome under the high temperature treatment, 32 °C. This suggests that this temperature was lower than the maximum tolerance limit for this species. Increasing p CO2 levels increased %C in the rhizome, and also showed a significant increase in leaf δ13C values. The effects of all treatments were sublethal; however, small changes in their traits could affect the ecosystem services they provide. In particular, changes in tissue carbon concentrations may affect carbon storage capacity, one key ecosystem service. The simultaneous study of different types of trait responses contributes to establish a holistic framework of seagrass ecosystem health under climate change. [ABSTRACT FROM AUTHOR]

Seagrass meadows provide valuable ecosystem services but are fragile and threatened ecosystems all over the world. This review highlights the current advances in seagrass research from Viet Nam. One goal is to support decision makers in developing science-based conservation strategies. In recent years, several techniques were applied to estimate the size of seagrass meadows. Independent from the method used, there is an alarming decline in the seagrass area in almost all parts of Viet Nam. Since 1990, a decline of 46.5% or 13,549 ha was found. Only in a few protected and difficult-to-reach areas was an increase observed. Conditions at those sites could be investigated in more detail to make suggestions for conservation and recovery of seagrass meadows. Due to their lifestyle and morphology, seagrasses take up compounds from their environment easily. Phytoremediation processes of Thalassia hemprichii and Enhalus acoroides are described exemplarily. High accumulation of heavy metals dependent on their concentration in the environment in different organs can be observed. On the one hand, seagrasses play a role in phytoremediation processes in polluted areas; on the other hand, they might suffer at high concentrations, and pollution will contribute to their overall decline. Compared with the neighboring countries, the total Corg stock from seagrass beds in Viet Nam was much lower than in the Philippines and Indonesia but higher than that of Malaysia and Myanmar. Due to an exceptionally long latitudinal coastline of 3,260 km covering cool to warm water environments, the seagrass species composition in Viet Nam shows a high diversity and a high plasticity within species boundaries. This leads to challenges in taxonomic issues, especially with the Halophila genus, which can be better deduced from genetic diversity/population structures of members of Hydrocharitaceae. Finally, the current seagrass conservation and management efforts in Viet Nam are presented and discussed. Only decisions based on the interdisciplinary cooperation of scientists from all disciplines mentioned will finally lead to conserve this valuable ecosystem for mankind and biodiversity. [ABSTRACT FROM AUTHOR]

Tropical seagrass meadows are formed by an array of seagrass species that share the same space. Species sharing the same plot are competing for resources, namely light and inorganic nutrients, which results in the capacity of some species to preempt space from others. However, the drivers behind seagrass species competition are not completely understood. In this work, we studied the competitive interactions among tropical seagrass species of Unguja Island (Zanzibar, Tanzania) using a trait-based approach. We quantified the abundance of eight seagrass species under different trophic states, and selected nine traits related to light and inorganic nutrient preemption to characterize the functional strategy of the species (leaf maximum length and width, leaves per shoot, leaf mass area, vertical rhizome length, shoots per meter of ramet, rhizome diameter, roots per meter of ramet, and root maximum length). From the seagrass abundance we calculated the probability of space preemption between pairs of seagrass species and for each individual seagrass species under the different trophic states. Species had different probabilities of space preemption, with the climax species Thalassodendron ciliatum, Enhalus acoroides, Thalassia hemprichii , and the opportunistic Cymodocea serrulata having the highest probability of preemption, while the pioneer and opportunistic species Halophila ovalis, Syringodium isoetifolium, Halodule uninervis , and Cymodocea rotundata had the lowest. Traits determining the functional strategy showed that there was a size gradient across species. For two co-occurring seagrass species, probability of preemption was the highest for the larger species, it increased as the size difference between species increased and was unaffected by the trophic state. Competitive interactions among seagrass species were asymmetrical, i.e., negative effects were not reciprocal, and the driver behind space preemption was determined by plant size. Seagrass space preemption is a consequence of resource competition, and the probability of a species to exert preemption can be calculated using a trait-based approach. [ABSTRACT FROM AUTHOR]

Eutrophication is one of the main threats to seagrass meadows, but there is limited knowledge on the interactive effects of nutrients under a changing climate, particularly for tropical seagrass species. This study aimed to detect the onset of stress in the tropical seagrass, Halophila stipulacea , by investigating the effect of in situ nutrient addition during an unusually warm summer over a 6-month period. We measured a suite of different morphological and biochemical community metrics and individual plant traits from two different sites with contrasting levels of eutrophication history before and after in situ fertilization in the Gulf of Aqaba. Nutrient stress combined with summer temperatures that surpassed the threshold for optimal growth negatively affected seagrass plants from South Beach (SB), an oligotrophic marine protected area, while H. stipulacea populations from North Beach (NB), a eutrophic and anthropogenically impacted area, benefited from the additional nutrient input. Lower aboveground (AG) and belowground (BG) biomass, reduced Leaf Area Index (LAI), smaller internodal distances, high sexual reproductive effort and the increasing occurrence of apical shoots in seagrasses from SB sites indicated that the plants were under stress and not growing under optimal conditions. Moreover, AG and BG biomass and internodal distances decreased further with the addition of fertilizer in SB sites. Results presented here highlight the fact that H. stipulacea is one of the most tolerant and plastic seagrass species. Our study further demonstrates that the effects of fertilization differ significantly between meadows that are growing exposed to different levels of anthropogenic pressures. Thus, the meadow's "history" affects it resilience and response to further stress. Our results suggest that monitoring efforts on H. stipulacea populations in its native range should focus especially on carbohydrate reserves in leaves and rhizomes, LAI, internodal length and percentage of apical shoots as suitable warning indicators for nutrient stress in this seagrass species to minimize future impacts on these valuable ecosystems. [ABSTRACT FROM AUTHOR]

Posidonia oceanica is a key foundation species in the Mediterranean providing valuable ecosystem services. However, this species is particularly vulnerable towards high coastal nutrient inputs and the rising frequency of intense summer heat waves, but their combined effect in situ has received little attention so far. Here, we investigated the effects of in situ nutrient addition during an unusually warm summer over a 4-month period, comparing different morphological, physiological and biochemical population metrics of seagrass meadows growing in protected areas (Ischia) with meadows already exposed to significant anthropogenic pressure (Baia – Gulf of Pozzuoli). Our study highlights that the effects of warmer than usual summer temperatures on the population level of seagrass meadows can be exacerbated if the plants are already exposed to higher anthropogenic pressures. Morphological and population level indicators mainly changed over time, possibly impacted by season and the warmer temperatures, and displayed more pronounced reductions in seagrasses from impacted sites. The additional nutrient supply had even more deleterious effects, as shown by a decrease in approximately 67% in cover in fertilized plots at high impacted sites and 33% at low impacted sites. Moreover, while rhizome starch concentration showed a seasonal increase in plants from low impacted sites it displayed a trend of a 27% decrease in fertilized plots of the high impacted sites. Epiphyte biomass was approximately four-fold higher on leaves of plants growing in impacted sites and even doubled with the additional nutrient input. Predicting and anticipating stress in P. oceanica is of crucial importance for conservation and management efforts, given the limited colonizing and reproductive ability and extremely slow growth of this ecosystem engineer. Our results suggest that monitoring efforts should focus especially on leaf area index (LAI), carbohydrate concentrations in the rhizomes, and epiphyte cover on leaves as indicators of the onset of stress in Posidonia oceanica , which can be used by decision makers to take appropriate measures before damage to the ecosystem becomes irreversible, minimize future human interference and strengthen the resilience of these important ecosystems. [ABSTRACT FROM AUTHOR]

"Nutrient dynamics in seagrass ecosystems", in Seagrasses: Biology, Ecology and Conservation. Climate change, eutrophication, responses of seagrasses to single and combined stressors, seagrasses, spatial-temporal modeling Keywords: seagrasses; climate change; eutrophication; responses of seagrasses to single and combined stressors; spatial-temporal modeling EN seagrasses climate change eutrophication responses of seagrasses to single and combined stressors spatial-temporal modeling 1 3 3 05/02/22 20220428 NES 220428 Awareness of the ecological importance of seagrasses is growing due to recent attention to their role in carbon sequestration as a potential blue carbon sink (Fourqurean et al., [2]; Bedulli et al.), as well as their role in nutrient cycling (Romero et al., [9]), sediment stabilization (James et al., [4]), pathogen filtration (Lamb et al., [6]), and the formation of essential habitats for economically important marine species (Jackson et al., [3]; Jones et al.). [Extracted from the article]

Increasing temperature and CO2 concentration are among the most important factors affecting marine ecosystems under climate change. We investigated the morphological, biochemical, and physiological trait responses of seedlings of the tropical seagrass Enhalus acoroides under experimental conditions. Trait responses were greater under temperature effects than increasing CO2 concentration. Seedlings under rising temperatures showed enhanced leaf growth, lower leaf nutrient content, and stimulated down-regulating mechanisms in terms of photo-physiology. Increasing CO2 concentrations did not show any significant effects independently. There was a significant interaction for some of the trait responses considered, such as leaf number and carbon content in the roots, and trends of higher starch concentrations in the leaves and lower rETRmax under combined enriched CO2 and high temperature, even though none of these interactions were synergistic. Understanding the single and interactive trait responses of seagrass seedlings to increasing temperature and CO2 concentration is of importance to determine the relative responses of early life stages of seagrasses, which may differ from adult plants, in order to form a more holistic view of seagrass ecosystem health under climate change. [ABSTRACT FROM AUTHOR]

Farming of Eucheuma denticulatum is a major activity in Zanzibar affecting seagrass ecosystems primarily through shading and trampling. The aim of this study was to test the impacts of shading and trampling during seaweed farming on seagrass meadows composed by Halophila stipulacea and Thalassia hemprichii and their associated benthic macroalgae. Areas covered by these species were selected for the building of seaweed farms in three treatments: seaweed farm plots (with shading and trampling effects), trampling plots (with trampling effects only), and control plots (with no shading or trampling effects). Reduction of light within the plots was recorded over 9 weeks. Percentage cover of seagrasses and macroalgae and shoot density of seagrasses were measured over 12 weeks to assess the impact of shading and trampling by seaweed farming activities. Light was significantly reduced in the seaweed farm plots by 75 to 90% by the end of a seaweed growth cycle. H. stipulacea, despite its capacity for rapid growth, was significantly affected by the combination of shading and trampling under the seaweed farm treatment, while the climax seagrass species T. hemprichii was unaffected. Due to the decline in H. stipulacea, benthic macroalgae cover increased in the seaweed farm treatment, suggesting a change in seagrass community dynamics. In contrast, trampling had a negative effect on the benthic macroalgae as an isolated disturbance, which suggests that seagrasses are more resistant to trampling than macroalgae and would likely dominate the benthic macrophyte community under these conditions. [ABSTRACT FROM AUTHOR]

During the last 150 years, the tropical seagrass species Halophila stipulacea has established itself in the southern and eastern parts of the Mediterranean Sea. More recently (2018), Halophila decipiens was observed for the first time in the eastern Mediterranean, and was described as the second non-native seagrass species in the Mediterranean Sea. We implemented a species distribution model (SDM) approach to (1) hindcast the habitat suitability of H. stipulacea over the last 100 years in the Mediterranean basin, and (2) to model the increase in the potential habitat suitability of H. stipulacea and H. decipiens during the current century under two very different climate scenarios, RCP 2.6 (lowest carbon emission scenario) and RCP 8.5 (highest carbon emission scenario). In addition, a principal component analysis (PCA) and k -means cluster based on temperature and salinity drivers were applied to visualize the distance and relatedness between the native and invasive H. stipulacea and H. decipiens populations. Results from this PCA suggest that the H. stipulacea populations of the Mediterranean and Red Sea are likely to be similar. In contrast, H. decipiens from the Mediterranean is more related to the Atlantic populations rather than to the Red Sea populations. The hindcast model suggests that the expansion of H. stipulacea was related to the increases in seawater temperatures in the Mediterranean over the last 100 years. The SDMs predict that more suitable habitat will become available for both tropical species during this century. The habitat suitability for H. stipulacea will keep expanding westward and northward as the Mediterranean continues to become saltier and warmer. In comparison, the SDMs built for H. decipiens forecast a restricted habitat suitability in the south-eastern Mediterranean Sea at the present environmental conditions and predicts a progressive expansion with a potential increase in habitat suitability along 85% of the Mediterranean coastline. The predicted rapid expansion of non-native seagrass species could alter the Mediterranean's seagrass community and may entail massive impacts on associated ecosystem functions and services, impacts that have severe socio-economic consequences. [ABSTRACT FROM AUTHOR]

Seagrass meadows are declining globally. The decrease of seagrass area is influenced by the simultaneous occurrence of many factors at the local and global scale, including nutrient enrichment and climate change. This study aims to find out how increasing temperature and nutrient enrichment affect the morphological, biochemical and physiological responses of three coexisting tropical species, Thalassia hemprichii , Cymodocea serrulata and Halophila stipulacea. To achieve these aims, a 1-month experiment under laboratory conditions combining two temperature (maximum ambient temperature and current average temperature) and two nutrient (high and low N and P concentrations) treatments was conducted. The results showed that the seagrasses were differentially affected by all treatments depending on their life-history strategies. Under higher temperature treatments, C. serrulata showed photo-acclimation strategies, while T. hemprichii showed decreased photo-physiological performance. In contrast, T. hemprichii was resistant to nutrient over-enrichment, showing enhanced nutrient content and physiological changes, but C. serrulata suffered BG nutrient loss. The limited response of H. stipulacea to nutrient enrichment or high temperature suggests that this seagrass is a tolerant species that may have a dormancy state with lower photosynthetic performance and smaller-size individuals. Interaction between both factors was limited and generally showed antagonistic effects only on morphological and biochemical traits, but not on physiological traits. These results highlight the different effects and strategies co-inhabiting seagrasses have in response to environmental changes, showing winners and losers of a climate change scenario that may eventually cause biodiversity loss. Trait responses to these stressors could potentially make the seagrasses weaker to cope with following events, due to BG biomass or nutrient loss. This is of importance as biodiversity loss in tropical seagrass ecosystems could change the overall effectiveness of ecosystem functions and services provided by the seagrass meadows. [ABSTRACT FROM AUTHOR]

Summary: Tropical marine seagrasses live in environments with low nutrient concentrations. However, as land development intensifies along tropical coastlines, the marine environment in which these organisms grow is becoming more nutrient‐rich.Nitrogen (N) uptake, assimilation, translocation and storage under a diversity of N sources in enriched conditions were investigated in two tropical seagrass species, Cymodocea serrulata and Thalassia hemprichii, from an oligotrophic marine environment.Both seagrasses were able to take up different inorganic and organic N sources through their above‐ and belowground tissues when enriched with high N concentrations. The uptake rates of T. hemprichii were generally higher than C. serrulata in leaves and rhizome, whereas root uptake was systematically higher in C. serrulata.Acropetal and basipetal translocation was observed in both species. Reduction and assimilation of N, measured in terms of their nitrate reductase and glutamine synthetase activity, were correlated with nitrate and ammonium uptake rates, respectively. Cymodocea serrulata showed a tendency to immediately use the available N, whereas T. hemprichii allocated more N in assimilation and storage investment. The responses of these seagrasses to N‐enrichment demonstrate their ability to adapt to over‐enrichment by varying N sources in the first step of the eutrophication process. [ABSTRACT FROM AUTHOR]

The aim of this work was to explore the feasibility of using plant functional traits to identify differences in sediment organic carbon (OC) storage within seagrass meadows. At 19 sites within three seagrass meadows in the coastal waters of Zanzibar, Tanzania, species cover was estimated along with three community traits hypothesized to influence sediment OC storage (above and belowground biomass, seagrass tissue nitrogen content, and shoot density). Sediments within four biogeographic zones (fore reef, reef flat, tidal channel, and seagrass meadow) of the landscape were characterized, and sediment cores were collected within seagrass meadows to quantify OC storage in the top 25 cm and top meter of the sediment. We identified five distinct seagrass communities that had notable differences in the plant traits, which were all residing within a thin veneer (ranging from 19 to 78 cm thick) of poorly sorted, medium to coarsely grained carbonate sands on top of carbonate rock. One community (B), dominated by Thalassodendron ciliatum, contained high amounts of above (972±74 gDWm-2) and belowground (682±392 gDWm-2) biomass composed of low-elemental-quality tissues (leaf C:ND24.5; rhizome C :ND97). While another community (C), dominated by small-bodied ephemeral seagrass species, had significantly higher shoot density (4178 shootsm-2). However, these traits did not translate into differences in sediment OC storage and across all communities the percentage of OC within sediments was similar and low (ranging from 0.15% to 0.75 %), as was the estimated OC storage in the top 25 cm (14.1±2.2Mg Cha-1) and top meter (33.9±7.7Mg Cha-1) of sediment. These stock estimates are considerably lower than the global average (194.2±20.2Mg C ha-1) reported for other seagrass ecosystems and are on the lower end of the range of estimates reported for the tropical Indo-Pacific bioregion (1.9 to 293Mg Cha-1). The uniformly low OC storage across communities, despite large inputs of lowquality belowground tissues in community B, indicates that the geophysical conditions of the coarse, shallow sediments at our sites were not conducive to OC stabilization and outweighed any variation in the quantity or quality of seagrass litter inputs. These results add to a growing body of evidence showing that geophysical conditions of the sediment modulate the importance of plant traits in regards to retention of OC within blue carbon ecosystems and cautions against the use of plant traits as a proxy for sediment OC storage across all seagrass ecosystems. [ABSTRACT FROM AUTHOR]

The global trend of unprecedented losses in coral reefs is particularly striking in the Caribbean, where dense algal assemblages are commonly replacing corals. So far, hardly anything is known about the ecology of the dominant algal groups. The present study compiled records of Chlorophytes from nine studies in the shallow reefs of Curaçao in the years preceding the onset of coral reef decline (1908–1978) and compared them with records from three recent (2007–2009) expeditions conducted at the same and nearby study locations along the south-west coast of the island. A total of 107 species were encountered, including seven new records for Curaçao (Anadyomene saldanhae, Bryopsis hypnoides, Chaetomorpha minima, Derbesia fastigiata, Ulva flexuosa subsp. paradoxa, Ulvella scutata and Ulvella lens). Sampled material revealed a higher species number during the dry seasons than during the wet seasons, indicating a seasonal variation in algal growth. Most species grew on hard substratum or were epibiotic, and 13 species were found growing on more than one substratum. Comparisons with earlier studies suggest an extension in depth range for nine species. The present work provides a comprehensive overview of the distribution of Chlorophytes of the island and can serve as an important baseline for further research on coral reef ecosystem changes. [ABSTRACT FROM AUTHOR]

The aim of this work was to explore the feasibility of using seagrass functional traits to predict differences in sediment carbon storage. At 19 sites within highly diverse seagrass meadows of Zanzibar, Tanzania, species cover was estimated along with three community traits hypothesized to influence sediment carbon storage (amount of above and belowground biomass, seagrass tissue nitrogen content, and shoot density). We identified five distinct seagrass communities that had notable variations in key plant traits but these differences did not translate into differences is sediment organic carbon (OC) storage. Across all communities, sediment OC was very low (ranging from 0.15% to 0.75%) and there were no differences in OC storage among communities, which was considerably lower (33.97.7Mg Cha-1) than the global average (194.220.2Mg Cha-1) reported for other seagrass ecosystems. In spite of high seagrass diversity and clear zonation among plant communities, sediments in all communities were shallow (ranging from 19 to 78cm) and composed of medium-coarse grained carbonate sand on top of carbonate rock. We propose that geophysical conditions of the sediment were not conducive to OC stabilization, and outweighed any variation in the quantity or quality of plant litter inputs, ultimately leading to low OC storage within all seagrass communities. This highlights the complexity of OC cycling in seagrass ecosystems and cautions against the use of plant traits as a proxy for OC storage across all seagrass ecosystems. [ABSTRACT FROM AUTHOR]

Coastal eutrophication is a key driver of shifts in bacterial communities on coral reefs. With fringing and patch reefs at varying distances from the coast the Spermonde Archipelago in southern Sulawesi, Indonesia offers ideal conditions to study the effects of coastal eutrophication along a spatially defined gradient. The present study investigated bacterial community composition of three coral reef habitats: the water column, sediments, and mucus of the hard coral genus Fungia, along that cross-shelf environmental and water quality gradient. The main research questions were: (1) How do water quality and bacterial community composition change along a coastal shelf gradient? (2) Which water quality parameters influence bacterial community composition? (3) Is there a difference in bacterial community composition among the investigated habitats? For this purpose, a range of key water parameters were measured at eight stations in distances from 2 to 55 km from urban Makassar. This was supplemented by sampling of bacterial communities of important microbial habitats using 454 pyrosequencing. Findings revealed that the population center Makassar had a strong effect on the concentrations of Chlorophyll a, suspended particulate matter (SPM), and transparent exopolymer particles (TEP), which were all significantly elevated at the inshore compared the other seven sites. Shifts in the bacterial communities were specific to each sampled habitat. Two OTUs, belonging to the genera Escherichia/Shigella (Gammaproteobacteria) and Ralstonia (Betaproteobacteria), respectively, both dominated the bacterial community composition of the both size fractions of the water column and coral mucus. The sampled reef sediments were more diverse, and no single OTUs was dominant. There was no gradual shift in bacterial classes or OTUs within the sampled habitats. In addition, we observed very distinct communities between the investigated habitats. Our data show strong changes in the bacterial community composition at the inshore site for water column and sediment samples. Alarmingly, there was generally a high prevalence of potentially pathogenic bacteria across the entire gradient. [ABSTRACT FROM AUTHOR]

Coral reefs worldwide are affected by increasing dissolved inorganic carbon (DIC) and organic carbon (DOC) concentrations due to ocean acidification (OA) and coastal eutrophication. These two stressors can occur simultaneously, particularly in near-shore reef environments with increasing anthropogenic pressure. However, experimental studies on how elevated DIC and DOC interact are scarce and fundamental to understanding potential synergistic effects and foreseeing future changes in coral reef function. Using an open mesocosm experiment, the present study investigated the impact of elevated DIC (pHNBS: 8.2 and 7.8; pCO2: 377 and 1076 μatm) and DOC (added as 833 μmol L-1 of glucose) on calcification and photosynthesis rates of two common calcifying green algae, Halimeda incrassata and Udotea flabellum, in a shallow reef environment. Our results revealed that under elevated DIC, algal photosynthesis decreased similarly for both species, but calcification was more affected in H. incrassata, which also showed carbonate dissolution rates. Elevated DOC reduced photosynthesis and calcification rates in H. incrassata, while in U. flabellum photosynthesis was unaffected and thalus calcification was severely impaired. The combined treatment showed an antagonistic effect of elevated DIC and DOC on the photosynthesis and calcification rates of H. incrassata, and an additive effect in U. flabellum. We conclude that the dominant sand dweller H. incrassata is more negatively affected by both DIC and DOC enrichments, but that their impact could be mitigated when they occur simultaneously. In contrast, U. flabellum can be less affected in coastal eutrophic waters by elevated DIC, but its contribution to reef carbonate sediment production could be further reduced. Accordingly, while the capacity of environmental eutrophication to exacerbate the impact of OA on algal-derived carbonate sand production seems to be species-specific, significant reductions can be expected under future OA scenarios, with important consequences for beach erosion and coastal sediment dynamics. [ABSTRACT FROM AUTHOR]

Changes in the coral reef complex can affect predator-prey relationships, resource availability and niche utilisation in the associated fish community, which may be reflected in decreased stability of the functional traits present in a community. This is because particular traits may be favoured by a changing environment, or by habitat degradation. Furthermore, other traits can be selected against because degradation can relax the association between fishes and benthic habitat. We characterised six important ecological traits for fish species occurring at seven sites across a disturbed coral reef archipelago in Indonesia, where reefs have been exposed to eutrophication and destructive fishing practices for decades. Functional diversity was assessed using two complementary indices (FRic and RaoQ) and correlated to important environmental factors (live coral cover and rugosity, representing local reef health, and distance from shore, representing a cross-shelf environmental gradient). Indices were examined for both a change in their mean, as well as temporal (short-term; hours) and spatial (cross-shelf) variability, to assess whether fish-habitat association became relaxed along with habitat degradation. Furthermore, variability in individual traits was examined to identify the traits that are most affected by habitat change. Increases in the general reef health indicators, live coral cover and rugosity (correlated with distance from the mainland), were associated with decreases in the variability of functional diversity and with community-level changes in the abundance of several traits (notably home range size, maximum length, microalgae, detritus and small invertebrate feeding and reproductive turnover). A decrease in coral cover increased variability of RaoQ while rugosity and distance both inversely affected variability of FRic; however, averages for these indices did not reveal patterns associated with the environment. These results suggest that increased degradation of coral reefs is associated with increased variability in fish community functional composition resulting from selective impacts on specific traits, thereby affecting the functional response of these communities to increasing perturbations. [ABSTRACT FROM AUTHOR]

The composition of coral reef benthic communities is strongly affected by variation in water quality and consumer abundance and composition. This is particularly evident in highly populated coastal regions where humans depend on coral reef resources and where terrestrial run-off can change the chemical composition of the water. We tested the effects of grazing pressure and ambient water conditions along an established eutrophication gradient on the recruitment and successional development of benthic communities of the Spermonde Archipelago, Indonesia, through caging experiments with settlement tiles. Within 1 month, benthic community composition of the closest reef to land, near the city of Makassar, was significantly different from other sites further offshore, driven primarily by differences in recruitment of invertebrates or turf algae. In contrast to other caging experiments, consumer exclusion had no effect after 3 months, suggesting that larger, mobile consumers had little effect on the benthic communities of these reefs at all sites. Despite conditions that usually favour macroalgal development, this group was rarely observed on recruitment tiles even after 4 months of consumer exclusion. Furthermore, tiles from both the caged and open treatments retained high proportions of open space indicating the possible role of small-sized or non-fish consumers that were not excluded from the experiment. These results indicate that, unlike many other studies, benthic consumers in the Spermonde Archipelago had little effect on the recruitment and early succession of the reef habitat and that unexamined biota such as mesograzers may be significant in degraded systems. [ABSTRACT FROM AUTHOR]

Increasing dissolved inorganic carbon (DIC) concentrations associated with ocean acidification can affect marine calcifiers, but local factors, such as high dissolved organic carbon (DOC) concentrations through sewage and algal blooms, may interact with this global factor. For calcifying green algae of the genus Halimeda, a key tropical carbonate producer that often occurs in coral reefs, no studies on these interactions have been reported. These data are however urgently needed to understand future carbonate production. Thus, we investigated the independent and combined effects of DIC (pCO2 402 μatm/ pHtot 8.0 and 996 μatm/ pHtot 7.7) and DOC (added as glucose in 0 and 294 μmol L-1) on growth, calcification and photosynthesis of H. macroloba and H. opuntia from the Great Barrier Reef in an incubation experiment over 16 days. High DIC concentrations significantly reduced dark calcification of H. opuntia by 130 % and led to net dissolution, but did not affect H. macroloba. High DOC concentrations significantly reduced daily oxygen production of H. opuntia and H. macroloba by 78 % and 43 %, respectively, and significantly reduced dark calcification of H. opuntia by 70%. Combined high DIC and DOC did not show any interactive effects for both algae, but revealed additive effects for H. opuntia where the combination of both factors reduced dark calcification by 162 % compared to controls. Such species-specific differences in treatment responses indicate H. opuntia is more susceptible to a combination of high DIC and DOC than H. macroloba. From an ecological perspective, results further suggest a reduction of primary production for Halimeda-dominated benthic reef communities under high DOC concentrations and additional decreases of carbonate accretion under elevated DIC concentrations, where H. opuntia dominates the benthic community. This may reduce biogenic carbonate sedimentation rates and hence the buffering capacity against further ocean acidification. [ABSTRACT FROM AUTHOR]

A recent review of crown-of-thorns starfish ( Acanthaster planci; COTS) in Indonesia has suggested that their impacts have gone under-reported. In 2012-2013, we surveyed COTS at permanent transects within 12 sites of the Spermonde Archipelago, Indonesia, a coastal region close to two rivers and the heavily urbanised city of Makassar. Evidence of COTS was apparent at 8 of 12 sites surveyed with highest densities (37 starfish per 250 m at Barrang Lompo) comparable to those reported in the Indonesian historical literature. At Barrang Lompo and Bonetambung, the COTS outbreak resulted in the loss of half the live coral. Terrestrial effluents have reduced water quality in the Spermonde Archipelago, which further supports recent work linking water quality and COTS outbreaks, thus providing a warning of future outbreaks to Indonesian coastal managers given the country's increased urbanisation. [ABSTRACT FROM AUTHOR]

Localized impacts, such as eutrophication and overfishing, have been identified as major threats to reefs worldwide, resulting in changes in coral reef community composition, from coral-dominance to algal-dominance. Herbivory by fishes is frequently cited as a key process structuring benthic community response to stressors. Here, we experimentally tested the capacity of herbivorous fishes to remove macroalgae along an onshore-offshore spatial gradient in the Spermonde Archipelago, Indonesia; a coral reef system exposed to long-term anthropogenic disturbances. Bioassays of Sargassum and Padina spp. were collected from the reef flat and transplanted onto the reef slope at five islands varying in distance (1-55 km) from the coastline and city of Makassar, South Sulawesi. Supplementary underwater video deployment and fish surveys were used to identify species-specific differences in herbivore communities and rates of algal removal. Over a 24 h period, Padina was almost completely removed from the two outermost islands, but removal declined toward shore. With the exception of the site closest to Makassar, more than 50% of all transplanted macroalgae were removed. Species diversity of algal-consuming fishes and total bites increased toward off-shore, with only one species, Siganus virgatus (Siganidae), feeding at all sites. These changes in herbivore communities underline the capacity for functional resilience under varying levels of reef degradation. Our results exemplify the complexities of ecological functioning along environmental gradients. [ABSTRACT FROM AUTHOR]

Ocean acidification studies in the past decade have greatly improved our knowledge of how calcifying organisms respond to increased surface ocean CO levels. It has become evident that, for many organisms, nutrient availability is an important factor that influences their physiological responses and competitive interactions with other species. Therefore, we tested how simulated ocean acidification and eutrophication (nitrate and phosphate enrichment) interact to affect the physiology and ecology of a calcifying chlorophyte macroalga ( Halimeda opuntia (L.) J.V. Lamouroux) and its common noncalcifying epiphyte ( Dictyota sp.) in a 4-week fully crossed multifactorial experiment. Inorganic nutrient enrichment (+NP) had a strong influence on all responses measured with the exception of net calcification. Elevated CO alone significantly decreased electron transport rates of the photosynthetic apparatus and resulted in phosphorus limitation in both species, but had no effect on oxygen production or respiration. The combination of CO and +NP significantly increased electron transport rates in both species. While +NP alone stimulated H. opuntia growth rates, Dictyota growth was significantly stimulated by nutrient enrichment only at elevated CO, which led to the highest biomass ratios of Dictyota to Halimeda. Our results suggest that inorganic nutrient enrichment alone stimulates several aspects of H. opuntia physiology, but nutrient enrichment at a CO concentration predicted for the end of the century benefits Dictyota sp. and hinders its calcifying basibiont H. opuntia. [ABSTRACT FROM AUTHOR]

Atmospheric carbon dioxide emissions cause a decrease in the pH and aragonite saturation state of surface ocean water. As a result, calcifying organisms are expected to suffer under future ocean conditions, but their physiological responses may depend on their nutrient status. Because many coral reefs experience high inorganic nutrient loads or seasonal changes in nutrient availability, reef organisms in localized areas will have to cope with elevated carbon dioxide and changes in inorganic nutrients. Halimeda opuntia is a dominant calcifying primary producer on coral reefs that contributes to coral reef accretion. Therefore, we investigated the carbon and nutrient balance of H. opuntia exposed to elevated carbon dioxide and inorganic nutrients. We measured tissue nitrogen, phosphorus and carbon content as well as the activity of enzymes involved in inorganic carbon uptake and nitrogen assimilation (external carbonic anhydrase and nitrate reductase, respectively). Inorganic carbon content was lower in algae exposed to high CO, but calcification rates were not significantly affected by CO or inorganic nutrients. Organic carbon was positively correlated to external carbonic anhydrase activity, while inorganic carbon showed the opposite correlation. Carbon dioxide had a significant effect on tissue nitrogen and organic carbon content, while inorganic nutrients affected tissue phosphorus and N:P ratios. Nitrate reductase activity was highest in algae grown under elevated CO and inorganic nutrient conditions and lowest when phosphate was limiting. In general, we found that enzymatic responses were strongly influenced by nutrient availability, indicating its important role in dictating the local responses of the calcifying primary producer H. opuntia to ocean acidification. [ABSTRACT FROM AUTHOR]

Understanding whether nutrient availability and grazing by consumers can control macroalgal growth is important to mitigate blooms. To assess the effect of long-term nitrogen loading on macroalgae, we ran a field experiment in which we measured growth of green and red macroalgae in estuaries where loads and eutrophication status differed. The relative abundances of consumers differed among estuaries with more grazers in non-eutrophied estuaries, an important interaction of bottom-up and top-down controls. In the estuary with the lowest nitrogen load, grazers controlled green macroalgal growth, but in higher nitrogen-loaded estuaries, where grazing was lower, growth of green macroalgae overwhelmed potential grazer control. The red macroalga was not controlled by grazers, even in the estuary where grazing pressure was highest. In the low-loaded estuary, invertebrate predators exerted top-down control over grazers, but predation effects did not cascade to macroalgae. Bottom-up mechanisms dominated control of macroalgae through an interaction of direct stimulation of growth and indirect alteration of consumer abundances, and thus, long-term nutrient regimes are likely determining potential for bloom formation in Waquoit Bay. [ABSTRACT FROM AUTHOR]

Over the past three decades, Caribbean coral reefs have drastically changed in structure and organization due to anthropogenically driven environmental changes. The prognostic trend indicates a shift from coral- to more algal-dominated reefs coupled with a loss in biodiversity and destabilization of reef structure. This study focuses on the composition of the most common algal growth form, the turf, and investigates turf succession within a fringing Caribbean coral reef. In a field study starting October 2007, we followed succession of turf algal assemblages grown on artificial substrata for periods of 15 up to 333 days at different water depths (5, 15 and 25 m). Species composition and abundance,biodiversity, total cover, and biomass were investigated and compared in uni- and multivariate analyses. Despite the pronounced change in coral reef structure over the past years, we found little difference from primary succession patterns described 30 years earlier. Succession patterns revealed a high diversity, mainly driven by the filamentous brown algal order Ectocarpales, the crustose green alga Pringsheimiella scutata at early stage, and diverse filamentous Cyanobacteria at later stages. Overall, the study provides insight into the early successional stages of coral reef vegetation by identifying the key species and discussing possible factors determining reef development in relation to environmental change. [ABSTRACT FROM AUTHOR]

Receiving coastal waters and estuaries are among the most nutrient-enriched environments on earth, and one of the symptoms of the resulting eutrophication is the proliferation of opportunistic, fast-growing marine seaweeds. Here, we used a widespread macroalga often involved in blooms, Ulva spp., to investigate how supply of nitrogen (N) and phosphorus (P), the two main potential growth-limiting nutrients, influence macroalgal growth in temperate and tropical coastal waters ranging from low- to high-nutrient supplies. We carried out N and P enrichment field experiments on Ulva spp. in seven coastal systems, with one of these systems represented by three different subestuaries, for a total of nine sites. We showed that rate of growth of Ulva spp. was directly correlated to annual dissolved inorganic nitrogen (DIN) concentrations, where growth increased with increasing DIN concentration. Internal N pools of macroalgal fronds were also linked to increased DIN supply, and algal growth rates were tightly coupled to these internal N pools. The increases in DIN appeared to be related to greater inputs of wastewater to these coastal waters as indicated by high δ15N signatures of the algae as DIN increased. N and P enrichment experiments showed that rate of macroalgal growth was controlled by supply of DIN where ambient DIN concentrations were low, and by P where DIN concentrations were higher, regardless of latitude or geographic setting. These results suggest that understanding the basis for macroalgal blooms, and management of these harmful phenomena, will require information as to nutrient sources, and actions to reduce supply of N and P in coastal waters concerned. [ABSTRACT FROM AUTHOR]

The article discusses a study on macroalgal browsing in juvenile humphead parrotfish Bolbometopon muricatum in the Spermonde Archipelago, Indonesia. Topics include a description of the characteristics of the parrot fish which is inhabiting coral reefs, their contribution to bioerosion processes in the Australian Great Barrier Reef, and an observation of their juvenile colouration at Kapoposang Reef on October 2, 2013.

Deals with a study which assessed the effects of differences in land-derived nitrogen loads on shrimp abundance, shrimp species composition, growth rate and reproduction in estuaries of Waquoit Bay, Massachusetts. Species of shrimp identified in the study; Growth and reproductive effort of shrimp species; Methodology and results.