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We describe RAPID: a Real-time Automated Plankton Identification Dashboard, deployed on the Plankton Imager, a high-speed line-scan camera that is connected to a ship water supply and captures images of particles in a flow-through system. This end-to-end pipeline for zooplankton data uses Edge AI equipped with a classification (ResNet) model that separates the images into three broad classes: Copepods, Non-Copepods zooplankton and Detritus. The results are transmitted and visualised on a terrestrial system in near real time. Over a 7-days survey, the Plankton Imager successfully imaged and saved 128 million particles of the mesozooplankton size range, 17 million of which were successfully processed in real-time via Edge AI. Data loss occurred along the real-time pipeline, mostly due to the processing limitation of the Edge AI system. Nevertheless, we found similar variability in the counts of the three classes in the output of the dashboard (after data loss) with that of the post-survey processing of the entire dataset. This concept offers a rapid and cost-effective method for the monitoring of trends and events at fine temporal and spatial scales, thus making the most of the continuous data collection in real time and allowing for adaptive sampling to be deployed. Given the rapid pace of improvement in AI tools, it is anticipated that it will soon be possible to deploy expanded classifiers on more performant computer processors. The use of imaging and AI tools is still in its infancy, with industrial and scientific applications of the concept presented therein being open-ended. Early results suggest that technological advances in this field have the potential to revolutionise how we monitor our seas. [ABSTRACT FROM AUTHOR]

We describe RAPID: a Real-time Automated Plankton Identification Dashboard, deployed on the Plankton Imager, a high-speed line-scan camera that is connected to a ship water supply and captures images of particles in a flow-through system. This end-to-end pipeline for zooplankton data uses Edge AI equipped with a classification (ResNet) model that separates the images into three broad classes: Copepods, Non-Copepods zooplankton and Detritus. The results are transmitted and visualised on a terrestrial system in near real time. Over a 7-days survey, the Plankton Imager successfully imaged and saved 128 million particles of the mesozooplankton size range, 17 million of which were successfully processed in real-time via Edge AI. Data loss occurred along the real-time pipeline, mostly due to the processing limitation of the Edge AI system. Nevertheless, we found similar variability in the counts of the three classes in the output of the dashboard (after data loss) with that of the post-survey processing of the entire dataset. This concept offers a rapid and cost-effective method for the monitoring of trends and events at fine temporal and spatial scales, thus making the most of the continuous data collection in real time and allowing for adaptive sampling to be deployed. Given the rapid pace of improvement in AI tools, it is anticipated that it will soon be possible to deploy expanded classifiers on more performant computer processors. The use of imaging and AI tools is still in its infancy, with industrial and scientific applications of the concept presented therein being open-ended. Early results suggest that technological advances in this field have the potential to revolutionise how we monitor our seas.

Yeasts are prevalent in the open ocean, yet we have limited understanding of their ecophysiological adaptations, including their response to nitrogen availability, which can have a major role in determining the ecological potential of other planktonic microbes. In this study, we characterized the nitrogen uptake capabilities and growth responses of marine-occurring yeasts. Yeast isolates from the North Atlantic Ocean were screened for growth on diverse nitrogen substrates, and across a concentration gradient of three environmentally relevant nitrogen substrates: nitrate, ammonium, and urea. Three strains grew with enriched nitrate while two did not, demonstrating that nitrate utilization is present but not universal in marine yeasts, consistent with existing knowledge of nonmarine yeast strains. Naganishia diffluens MBA_F0213 modified the key functional trait of cell size in response to nitrogen concentration, suggesting yeast cell morphology changes along chemical gradients in the marine environment. Meta-analysis of the reference DNA barcode in public databases revealed that the genus Naganishia has a global ocean distribution, strengthening the environmental applicability of the culture-based observations. This study provides novel quantitative understanding of the ecophysiological and morphological responses of marine-derived yeasts to variable nitrogen availability in vitro , providing insight into the functional ecology of yeasts within pelagic open ocean environments. [ABSTRACT FROM AUTHOR]

The composition of ecological communities varies not only between different locations but also in time. Understanding the fundamental processes that drive species toward rarity or abundance is crucial to assessing ecosystem resilience and adaptation to changing environmental conditions. In plankton communities in particular, large temporal fluctuations in species abundances have been associated with chaotic dynamics. On the other hand, microbial diversity is overwhelmingly sustained by a "rare biosphere" of species with very low abundances. We consider here the possibility that interactions within a species-rich community can relate both phenomena. We use a Lotka--Volterra model with weak immigration and strong, disordered, and mostly competitive interactions between hundreds of species to bridge single-species temporal fluctuations and abundance distribution patterns. We highlight a generic chaotic regime where a few species at a time achieve dominance but are continuously overturned by the invasion of formerly rare species. We derive a focal-species model that captures the intermittent boom-and-bust dynamics that every species undergoes. Although species cannot be treated as effectively uncorrelated in their abundances, the community's effect on a focal species can nonetheless be described by a time-correlated noise characterized by a few effective parameters that can be estimated from time series. The model predicts a nonunitary exponent of the power-law abundance decay, which varies weakly with ecological parameters, consistent with observation in marine protist communities. The chaotic turnover regime is thus poised to capture relevant ecological features of species-rich microbial communities. [ABSTRACT FROM AUTHOR]

Zooplankton plays a pivotal role in lentic water bodies, linking planktonic primary producers to higher trophic levels and being a cornerstone of the planktonic food web of ponds and lakes. Because of its ease of culture, large size, rich ecology, abundance in northern temperate lakes where limnology is rooted, and the ability to work with clones, Daphnia has, in the last centuries grown to become a key model system in ecology, evolution, and ecotoxicology. Consequently, a vast majority of freshwater zooplankton ecology focuses on the role of Daphnia. While generating essential insights, this has also deviated attention from the broad ecological impact of other zooplankton. Here, we emphasize how other zooplankton taxa have an important impact in nature - often in qualitatively different ways than Daphnia. We illustrate this point by focusing on two key zooplankton functions (herbivory and stoichiometry) and suggest research to capitalize on the success story of mechanistic ecological, eco-evolutionary, and genomic Daphnia work to develop a richer set of model organisms. We currently have the tools to do so and integrating mechanistic insights in multispecies settings would foster a better understanding of the rich diversity and ecology of freshwater zooplankton. [ABSTRACT FROM AUTHOR]

Estimates of the prevalence of dead zooplankton are increasingly necessary in marine ecological studies. We aimed to identify the relative proportions of live/dead individuals of three of the historically most abundant taxa of zooplankton in Magdalena Bay, Mexico: copepods, decapods, and diplostracans. Abundance data and environmental variability were recorded monthly at neap tides during 2015–2018. Samples were stained with neutral red to distinguish living from dead individuals. Copepods were the most abundant group and showed a significant annual variability in their abundance during the study period. Influenced by a preceding warm spell and the El Niño event of 2015–2016, the lowest abundances and the highest recorded standing mortalities of all three taxa were reported in 2015; standing mortality during El Niño was double that otherwise observed. A significant correlation was found between some of the environmental variables analyzed (salinity, temperature) and increased standing mortalities in copepods and decapods. We found differences between the percentages of live/dead organisms between the years analyzed and also between the taxonomic groups involved (copepods 17%, decapods 21%), which underlines the importance of including mortality analyses in ecological studies of zooplankton. [ABSTRACT FROM AUTHOR]

The small sizes of most marine plankton necessitate that plankton sampling occur on fine spatial scales, yet our questions often span large spatial areas. Underwater imaging can provide a solution to this sampling conundrum but collects large quantities of data that require an automated approach to image analysis. Machine learning for plankton classification, and high-performance computing (HPC) infrastructure, are critical to rapid image processing; however, these assets, especially HPC infrastructure, are only available post-cruise leading to an ‘after-the-fact’ view of plankton community structure. To be responsive to the often-ephemeral nature of oceanographic features and species assemblages in highly dynamic current systems, real-time data are key for adaptive oceanographic sampling. Here we used the new In-situ Ichthyoplankton Imaging System-3 (ISIIS-3) in the Northern California Current (NCC) in conjunction with an edge server to classify imaged plankton in real-time into 170 classes. This capability together with data visualization in a heavy.ai dashboard makes adaptive real-time decision-making and sampling at sea possible. Dual ISIIS-Deep-focus Particle Imager (DPI) cameras sample 180 L s-1, leading to >10 GB of video per min. Imaged organisms are in the size range of 250 µm to 15 cm and include abundant crustaceans, fragile taxa (e.g., hydromedusae, salps), faster swimmers (e.g., krill), and rarer taxa (e.g., larval fishes). A deep learning pipeline deployed on the edge server used multithreaded CPU-based segmentation and GPU-based classification to process the imagery. AVI videos contain 50 sec of data and can contain between 23,000 - 225,000 particle and plankton segments. Processing one AVI through segmentation and classification takes on average 3.75 mins, depending on biological productivity. A heavyDB database monitors for newly processed data and is linked to a heavy.ai dashboard for interactive data visualization. We describe several examples where imaging, AI, and data visualization enable adaptive sampling that can have a transformative effect on oceanography. We envision AI-enabled adaptive sampling to have a high impact on our ability to resolve biological responses to important oceanographic features in the NCC, such as oxygen minimum zones, or harmful algal bloom thin layers, which affect the health of the ecosystem, fisheries, and local communities.

Abstract Colony formation is a common feature among nonmotile marine phytoplankton. Several theories exist around the potential benefits of larger colonies. Here, we test the hypothesis that predation is one of the drivers behind colony formation and chain length plasticity. We exposed cultures of Thalassiosira rotula, Chaetoceros curvisetus, and Chaetoceros affinis to copepodamides, a chemical alarm cue released by copepods and perceived as an indicator of predation threat by their prey. This was coupled with a grazing experiment, which compared copepod grazing rates on different chain lengths. Our results show that T. rotula and C. curvisetus decreased their chain lengths by 79% and 49%, respectively, in response to copepodamides. Single cells and short chains were grazed at lower rates compared with long chains, and the copepodamide‐driven size shift led to 30% and 12% lower grazing in T. rotula and C. curvisetus, respectively. In contrast, C. affinis showed a slight increased chain length in response to copepodamides although nonsignificant. We found that 2 of 3 studied species reduce their chain length in response to the presence of copepod grazers. Altered size structure has implications for the route of carbon in the marine food webs and carbon export to deeper strata.

Freshwater phytoplankton and zooplankton are complex and diverse communities which greatly contribute to the functioning of freshwater ecosystems, constituting a path of nutrient cycling. The relationships of these communities are often driven by species' functional traits, such as defensive features and grazing adaptations. The aim of the present work was to study if the functional traits of phytoplankton (primary producers) promote specific traits of zooplankton (consumers). We calculated community weighted mean (CWM) of a trait of phytoplankton and zooplankton communities and constructed decision trees to study the relationships between the functional traits of both communities. We found that specific functional traits of zooplankton were most significantly promoted by size and shape of algal particles, followed by potential toxicity and spines possession, which had limited, however still important effects. Armor possession and motility of algae were found not to be promoting any functional traits of zooplankton. Easy-to-handle algal particles promoted greater variability of zooplankton's functional traits, while large, hard to manage algal particles (often characteristic for cyanobacteria) promoted zooplankton taxa bearing more specialized functional traits. Our study shows that phytoplankton functional traits can be considered as a biotic filter, leading to the selection of advantageous functional traits among zooplankton community. [ABSTRACT FROM AUTHOR]

Phytoplankton induce defensive traits in response to chemical alarm signals from grazing zooplankton. However, these signals are potentially vulnerable to changes in pH and it is not yet known how predator recognition may be affected by ocean acidification. We exposed four species of diatoms and one toxic dinoflagellate to future pCO2 levels, projected by the turn of the century, in factorial combinations with predatory cues from copepods (copepodamides). We measured the change in growth, chain length, silica content, and toxin content. Effects of increased pCO2 were highly species specific. The induction of defensive traits was accompanied by a significant reduction in growth rate in three out of five species. The reduction averaged 39% and we interpret this as an allocation cost associated with defensive traits. Copepodamides induced significant chain length reduction in three of the four diatom species. Under elevated pCO2Skeletonema marinoi reduced silica content by 30% and in Alexandrium minutum the toxin content was reduced by 30%. Using copepodamides to induce defensive traits in the absence of direct grazing provides a straightforward methodology to assess costs of defense in microplankton. We conclude that copepodamide signalling system is likely robust to ocean acidification. Moreover, the variable responses of different taxa to ocean acidification suggest that there will be winners and losers in a high pCO2 world, and that ocean acidification may have structuring effects on phytoplankton communities.

Planktonic foraminifera are one of the primary calcifiers in the modern ocean, contributing 23%–56% of total global pelagic carbonate production. However, a mechanistic understanding of how physiology and environmental conditions control their abundance and distribution is lacking, hindering the projection of the impact of future climate change. This understanding is important, not only for ecosystem dynamics, but also for marine carbon cycling because of foraminifera's key role in carbonate production. Here we present and apply a global trait‐based ecosystem model of non‐spinose planktonic foraminifera ('ForamEcoGEnIE') to assess their ecology and global distribution under future climate change. ForamEcoGEnIE considers the traits of calcium carbonate production, shell size, and foraging. It captures the main characteristic of biogeographical patterns of non‐spinose species – with maximum biomass concentrations found in mid‐ to high‐latitude waters and upwelling areas. The model also reproduces the magnitude of global carbonate production relatively well, although the foraminifera standing stock is systematically overestimated. In response to future scenarios of rising atmospheric CO2 (RCP6 and RCP8.5), on a regional scale, the modelled foraminifera biomass and export flux increases in the subpolar regions of the North Atlantic and the Southern Ocean while it decreases everywhere else. In the absence of adaptation, the biomass decline in the low‐latitude South Pacific suggests extirpation. The model projects a global average loss in non‐spinose foraminifera biomass between 8% (RCP6) and 11% (RCP8.5) by 2050 and between 14% and 18% by 2100 as a response to ocean warming and associated changes in primary production and ecological dynamics. Global calcium carbonate flux associated with non‐spinose foraminifera declines by 13%–18% by 2100. That decline can slow down the ocean carbonate pump and create short‐term positive feedback on rising atmospheric pCO2. [ABSTRACT FROM AUTHOR]

Plankton communities play an important role in marine food webs, in biogeochemical cycling, and in Earth's climate; yet observations are sparse, and predictions of how they might respond to climate change vary. Correlative species distribution models (SDM's) have been applied to predicting biogeography based on relationships to observed environmental variables. To investigate sources of uncertainty, we use a correlative SDM to predict the plankton biogeography of a 21st century marine ecosystem model (Darwin). Darwin output is sampled to mimic historical ocean observations, and the SDM is trained using generalized additive models. We find that predictive skill varies across test cases, and between functional groups, with errors that are more attributable to spatiotemporal sampling bias than sample size. End‐of‐century predictions are poor, limited by changes in target‐predictor relationships over time. Our findings illustrate the fundamental challenges faced by empirical models in using limited observational data to predict complex, dynamic systems. Plain Language Summary: Marine plankton communities play a central role within Earth's climate system, with important processes often divided among different "functional groups." Changes in the relative abundance of these groups can therefore impact on ecosystem function. However, the oceans are vast, and samples are sparse, so global distributions are not well known. Statistical species distribution models (SDM's) have been developed that predict global distributions based on their relationships with observed environmental variables. They appear to perform well at summarizing present day distributions, and are increasingly being used to predict ecosystem changes throughout the 21st century. But it is not guaranteed that such models remain valid over time. Rather than wait 100 years to find out, we applied a statistical SDM to a complex virtual ocean, and trained it using virtual observations that match real‐world ocean samples. This allows us to jump forward to the end‐of‐century to test the accuracy of our predictions. The SDM performed well at qualitatively predicting "present day" plankton distributions but yielded poor end‐of‐century predictions. Our case study emphasizes both the importance of environmental variable selection, and of changes in the underlying relationships between environmental variables and plankton distributions, in terms of model validity over time. Key Points: We use a correlative species distribution model to predict the global plankton biogeography of a trait‐based ecosystem modelPredictive skill varies across test cases, with functional group, and spatiotemporally, with poor end‐of‐century performanceKey sources of uncertainty are traced to sampling biases in observations, and the temporal variability in target‐predictor relationships [ABSTRACT FROM AUTHOR]

The Ross Sea is characterized by a series of subsystems with different characteristics making it an extremely productive area. To understand whether species composition and functional traits of the plankton community can be used as biological tracers, we have analyzed the composition of phytoplankton and microzooplankton, and their potential relationships, in two different polynyas of the Ross Sea during the austral summer 2017. Sampling activities were carried out near Terra Nova Bay, between Cape Washington and the northern shore of the Drygalski Ice Tongue, and in the South-Central Ross Sea. We investigated the phytoplankton and microzooplankton structure using the phytoplankton body size classes and the tintinnids lorica oral diameter as functional traits, speculating on the relationship between the two plankton communities and their use as biological indicators in a changing Southern Ocean. Our data showed significant differences in terms of plankton composition and related functional traits between the two areas, suggesting the existence of distinct ecological dynamics despite the similar total carbon content. In Terra Nova Bay, heterotrophic dinoflagellates were the most abundant microzooplankton, in association with a large phytoplankton biomass mainly represented by diatoms and nano- and micro-phytoplankton. Tintinnids with large lorica oral diameters were abundant in Central Ross Sea, where phytoplankton was dominated by Phaeocystis antarctica and by the micro size class. Among microzooplankton , Protoperidinium defectum, P. applanatum and P. incertum were the most abundant dinoflagellates species, while Codonellopsis gaussi, C. gaussi forma cylindroconica, Laackmanniella prolongata and Cymatocylis drygalskii were the most abundant tintinnids. The phytoplankton was dominated by diatoms Pseudo-nitzschia subcurvata , Fragilariopsis cylindrus , F. curta and by the haptophyte P. antarctica. Our data indicate that beyond physical and chemical features defining distinct sectors of the Ross Sea, both species composition and functional traits of phytoplankton and microzooplankton represent a valid monitoring tool, especially with the ongoing global warming and its effects on Antarctic food webs. [ABSTRACT FROM AUTHOR]

Colony formation is a common feature among nonmotile marine phytoplankton. Several theories exist around the potential benefits of larger colonies.Here, we test the hypothesis that predation is one of the drivers behind colony formation and chain length plasticity. We exposed cultures of Thalassiosira rotula, Chaetoceros curvisetus, and Chaetoceros affinis to copepodamides, a chemical alarm cue released by copepods and perceived as an indicator of predation threat by their prey. This was coupled with a grazing experiment, which compared copepod grazing rates on different chain lengths.Our results show that T. rotula and C. curvisetus decreased their chain lengths by 79% and 49%, respectively, in response to copepodamides. Single cells and short chains were grazed at lower rates compared with long chains, and the copepodamide‐driven size shift led to 30% and 12% lower grazing in T. rotula and C. curvisetus, respectively. In contrast, C. affinis showed a slight increased chain length in response to copepodamides although nonsignificant.We found that 2 of 3 studied species reduce their chain length in response to the presence of copepod grazers. Altered size structure has implications for the route of carbon in the marine food webs and carbon export to deeper strata. [ABSTRACT FROM AUTHOR]

The oceans’ uptake of anthropogenic carbon dioxide (CO2) decreases seawater pH and alters the inorganic carbon speciation – summarized in the term ocean acidification (OA). Already today, coastal regions experience episodic pH events during which surface layer pH drops below values projected for the surface ocean at the end of the century. Future OA is expected to further enhance the intensity of these coastal extreme pH events. To evaluate the influence of such episodic OA events in coastal regions, we deployed eight pelagic mesocosms for 53 days in Raunefjord, Norway, and enclosed 56–61 m3 of local seawater containing a natural plankton community under nutrient limited post-bloom conditions. Four mesocosms were enriched with CO2 to simulate extreme pCO2 levels of 1978 – 2069 μatm while the other four served as untreated controls. Here, we present results from multivariate analyses on OA-induced changes in the phyto-, micro-, and mesozooplankton community structure. Pronounced differences in the plankton community emerged early in the experiment, and were amplified by enhanced top-down control throughout the study period. The plankton groups responding most profoundly to high CO2 conditions were cyanobacteria (negative), chlorophyceae (negative), auto- and heterotrophic microzooplankton (negative), and a variety of mesozooplanktonic taxa, including copepoda (mixed), appendicularia (positive), hydrozoa (positive), fish larvae (positive), and gastropoda (negative). The restructuring of the community coincided with significant changes in the concentration and elemental stoichiometry of particulate organic matter. Results imply that extreme CO2 events can lead to a substantial reorganization of the planktonic food web, affecting multiple trophic levels from phytoplankton to primary and secondary consumers.

Invasion of the western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico by the Indo-Pacific lionfish, Pterois volitans/miles (Scopaenidae), has caused well-documented critical changes to coral reef ecosystems throughout the region. Most efforts to quantify these changes have focused on the charismatic adult stage; much less is known about the pelagic larval stage. While dispersal by the larval stage has likely been the main contributor to the rapid population expansion throughout the region, there are very few documented cases of larvae being collected anywhere in the invaded region where adult lionfish are abundant. We compared ichthyoplankton collected using identical sampling gear from the Straits of Florida in 2007–2008 (pre-lionfish population expansion to the Florida Keys) to those collected in 2014–2015 (during the ongoing expansion), providing the opportunity to test for a temporal change in the ichthyoplankton. Despite a substantially greater sampling effort in 2007–2008 [total of 938,126 m3 of water sampled compared to approximately 144,013 m3 (~ 15%) sampled in 2014–2015], we collected no lionfish larvae in 2007–2008, whereas in 2014–2015, 76 larvae were collected. The overall mean density in 2014–2015 of 0.4–0.7 lionfish larvae 1000 m−3 is comparable to a number of common reef fish families and is likely beginning to have an ecological impact on plankton constituents. As the invasion continues, additional studies of the ecological role of lionfish larvae in the plankton are warranted. [ABSTRACT FROM AUTHOR]

Microbial associations that result in phytoplankton mortality are important for carbon transport in the ocean. This includes parasitism, which in microbial food webs is dominated by the marine alveolate group, Syndiniales. Parasites are expected to contribute to carbon recycling via host lysis; however, knowledge on host dynamics and correlation to carbon export remain unclear and limit the inclusion of parasitism in biogeochemical models. We analyzed a 4-year 18S rRNA gene metabarcoding dataset (2016-19), performing network analysis for 12 discrete depths (1-1000 m) to determine Syndiniales-host associations in the seasonally oligotrophic Sargasso Sea. Analogous water column and sediment trap data were included to define environmental drivers of Syndiniales and their correlation with particulate carbon flux (150 m). Syndiniales accounted for 48-74% of network edges, most often associated with Dinophyceae and Arthropoda (mainly copepods) at the surface and Rhizaria (Polycystinea, Acantharea, and RAD-B) in the aphotic zone. Syndiniales were the only eukaryote group to be significantly (and negatively) correlated with particulate carbon flux, indicating their contribution to flux attenuation via remineralization. Examination of Syndiniales amplicons revealed a range of depth patterns, including specific ecological niches and vertical connection among a subset (19%) of the community, the latter implying sinking of parasites (infected hosts or spores) on particles. Our findings elevate the critical role of Syndiniales in marine microbial systems and reveal their potential use as biomarkers for carbon export., Competing Interests: The authors declare no competing interests., (© The Author(s) 2024. Published by Oxford University Press on behalf of the International Society for Microbial Ecology.)

The study is the first attempt to (i) model spring food webs in three SW Mediterranean ecosystems which are under different anthropogenic pressures and (ii) to project the consequence of this stress on their function. Linear inverse models were built using the Monte Carlo method coupled with Markov Chains to characterize the food-web status of the Lagoon, the Channel (inshore waters under high eutrophication and chemical contamination) and the Bay of Bizerte (offshore waters under less anthropogenic pressure). Ecological network analysis was used for the description of structural and functional properties of each food web and for inter-ecosystem comparisons. Our results showed that more carbon was produced by phytoplankton in the inshore waters (966–1234 mg C m −2 d −1 ) compared to the Bay (727 mg C m −2 d −1 ). The total ecosystem carbon inputs into the three food webs was supported by high primary production, which was mainly due to >10 µm algae. However, the three carbon pathways were characterized by low detritivory and a high herbivory which was mainly assigned to protozooplankton. This latter was efficient in channelling biogenic carbon. In the Lagoon and the Channel, foods webs acted almost as a multivorous structure with a tendency towards herbivorous one, whereas in the Bay the herbivorous pathway was more dominant. Ecological indices revealed that the Lagoon and the Channel food webs/systems had high total system throughput and thus were more active than the Bay. The Bay food web, which had a high relative ascendency value, was more organized and specialized. This inter–ecosystem difference could be due to the varying levels of anthropogenic impact among sites. Indeed, the low value of Finn’s cycling index indicated that the three systems are disturbed, but the Lagoon and the Channel, with low average path lengths, appeared to be more stressed, as both sites have undergone higher chemical pollution and nutrient loading. This study shows that ecosystem models combined with ecological indices provide a powerful approach to detect change in environmental status and anthropogenic impacts. [ABSTRACT FROM AUTHOR]

As an introduction to the following Themed Section on the significance of planktonic organisms to the functioning of marine ecosystems and global biogeochemical cycles we discuss the ramifications size imparts on the biology of plankton. We provide examples of how the characteristics of these microscopic organisms shape plankton population dynamics, distributions, and ecosystem functions. Key features of the marine environment place constraints on the ecology and evolution of plankton. Understanding these constraints is critical in developing a mechanistic understanding and predictive capacity of how planktonic ecosystems function, render their capacities in terms of biogeochemical cycling and trophic transfer, and how planktonic communities might respond to changing climate conditions. [ABSTRACT FROM AUTHOR]

Our best evidence is that life arose in the marine environment, and over many millennia of evolutionary proliferation, punctuated by occasional massive extinctions, marine protists have developed remarkably elegant and sometimes complex relationships with prokaryotic and eukaryotic symbionts. Current evidence of the range of marine protist taxa possessing symbionts, including their diversity and physiological functional relationships, is reviewed within an ecological context. Some perspectives are presented on potential opportunities for new avenues of research in unraveling the remarkable adaptive value of two or more genetically diverse marine unicellular organisms living in a close structural and physiological relationship. [ABSTRACT FROM AUTHOR]

We present the spatial distribution and abundance of the holoplanktonic family Iospilidae (Annelida, Polychaeta), along part of the eastern Brazilian coast, and its relation to environmental variables in the region. Samples were obtained from two collections made in 1998 and 2000 between 13°-25°S, and 28°- 42°W, on the Brazilian coast, between the Bay of Todos os Santos (BA) to Cape São Tomé (RJ). 216 stations were selected, covering the continental shelf, slope and oceanic regions, where plankton samples were collected for water and nutrient analysis. We analyzed environmental variables: temperature, salinity, dissolved oxygen, pH, ammonia, nitrite, nitrate, phosphate, silicate and chlorophyll-a. 363 individuals were collected, identifying two species, viz., Phalacrophorus uniformis and Phalacrophorus pictus, the first being the most abundant, with 354 individuals, while only nine specimens of P. pictus were found. Both species are mainly distributed in the oceanic region stations. The distribution of P. uniformis was related to the concentration of phosphate and nitrate. Significant differences between samples and between sectors of the continental shelf and oceanic region were found. [ABSTRACT FROM AUTHOR]

Swarming behaviour of copepods was studied at a coral reef in Lungdong Bay, northeastern Taiwan. Copepod distribution was documented by underwater photography and samples were obtained by SCUBA diving, deploying plankton nets, and suction devices. Copepod assemblages found at Lungdong Bay comprised four copepod orders (Calanoida, Cyclopoida, Harpacticoida and Poecilostomatoida). A new representative ofDioithonasp swarmed predominantly in summer (April to September 2008). The average density of the swarms was positively affected by temperature. Both the position and the average density were negatively affected by typhoons. Abundances were highest at the reef bottom, followed by the sea bottom outside the reef, in March and April 2008. In May, the highest densities were found at the water surface outside the reef. Adult females dominated the stage composition only at the reef surface during April, whereas early copepodids were most abundant at all other sampling dates and sites. [ABSTRACT FROM AUTHOR]

This article presents a study which taxonomically examined several caligid copepods (Copepoda: Caligidae), commonly known as sea lice, that were found in a collection of zooplankton from a coastal system of the southern Gulf of Mexico. Species that were identified include Caligus rufimaculatus, Caligus undulatus and Metacaligus rufus. The first species was previously reported and redescribed from specimens collected in the system. The second species is known only from plankton surveys and the third species has not been redescribed since its original description.

The article presents a study that analyzed the seasonal variability of the distribution and abundance of the copepod Acartia species in a coastal lagoon on the northern coast of the Yucatan Peninsula in Mexico during dry, rainy and northerlies seasons. It revealed two areas of the lagoon based on salinities and zooplankton biomass. It showed acartia lilljeborgii and A. tonsa as the most abundant species, representing together up to 95.5 percent of the overall abundance of the genus. A. tonsa's occurrence in the rainy, nortes, and dry seasons were 52.3, 30.6, and 17.1 percent, respectively.

The San Francisco Estuary (SFE) is a large, highly dynamic and ecologically important estuary on the west coast of the USA. We collected zooplankton and hydrographic data over a 3-year period (1997–1999) at six stations spanning the lower SFE to investigate long-term changes through comparison with a 1980–1981 survey of the area, El Niño-Southern Oscillation (ENSO) effects and the prevalence of non-indigenous species. Spatio-temporal patterns in the zooplankton were primarily regulated by seasonal and inter-annual fluctuations in marine and riverine forcings. Non-metric multidimensional scaling accounted for 82.7% of the variation in zooplankton composition. The strongest correlates of the three axes were salinity (r2 = 0.692), distance to marine influence and temperature (r2 = 0.492 and 0.309, respectively) and a lagged multivariate ENSO index (r2 = 0.299). Five zooplankton communities were identified, which showed predictable spatio-temporal progressions through the lower estuary. Inter-annual differences between El Niño and La Niña periods were substantial and appeared to be related to variable strengths of riverine and oceanic forcing. Between 1980–1981 and 1997–1999, a dramatic change occurred in the zooplankton of the lower SFE, such that dominance has shifted from native calanoid copepods to non-indigenous (Asian) cyclopoids. These changes in the zooplankton are expected to have significant but as yet unknown impacts on higher tropic levels and food web dynamics in the lower SFE. [ABSTRACT FROM PUBLISHER]

Chain formation is common among phytoplankton organisms but the underlying reasons and consequences are poorly understood. Here we show that chain formation is strongly impaired by waterborne cues from copepod grazers in the dinoflagellate Alexandrium tamarense. Chains of Alexandrium cells exposed to copepod cues responded by splitting into single cells or shorter chains. Motion analysis revealed significantly lower swimming velocities for single cells compared with chains, with two- to fivefold higher simulated predator encounter rates for two- and four-cell chains, respectively. In addition, the few remaining two-cell chains in grazed treatments were swimming at approximately half the speed of two-cell chains in treatments without grazers, which reduced encounter rates with grazers to values similar to that of single cells. Chain length plasticity and swimming behavior constitute unique mechanisms to reduce encounters with grazers. We argue that dinoflagellates can regulate the balance between motility and predator avoidance by adjusting chain length. The high predator encounter rate for motile chains may have contributed to the low prevalence of chain formation in motile phytoplankton compared with in nonmotile phytoplankton where chain formation is more common. [ABSTRACT FROM AUTHOR]

Abstract: The main purpose of this paper is to investigate a discrete time non-autonomous difference system of plankton allelopathy with delays. By employing continuous theorem proposed by Gains and Mawhin and some new techniques, a set of verifiable sufficient criteria are established for the existence of at least one strictly positive (componentwise) periodic solution, and as an application, we also examine some special case, showing that these conditions are similar to those of continuous differential system. It is also shown that the time delays are harmless for the existence of positive periodic solutions of system. [Copyright &y& Elsevier]

Microcystins (MCs) are toxic heptapeptides that are produced by filamentous cyanobacteria Planktothrix rubescens and Planktothrix agardhii via nonribosomal peptide synthesis. MCs share a common structure cyclo (-D-Alanine1-L-X2- D-erythro-ß-iso-aspartic acid3-L-Z4-Adda5-D-Glutamate6- N-methyl-dehydroalanine7) where X2 and Z2 are variable L-amino acids in positions 2, 4 of the molecule. Part of the mcyB gene (1,451 bp) that is involved in the activation of the X2 amino acid during MC synthesis was sequenced in 49 strains containing different proportions of arginine, homotyrosine, and leucine in position 2 of the MC molecule. Twenty-five genotypes were found that consisted of eight genotype groups (A-H, comprising 2-11 strains) and 17 unique genotypes. P. rubescens and P. agardhii partly consisted of the same mcyB genotypes. The occurrence of numerous putative recombination events that affected all of the genotypes can explain the conflict between taxonomy and mcyB genotype distribution. Genotypes B (homotyrosine and leucine in X2) and C (arginine in X2) showed higher nonsynonymous/synonymous (dN/dS) substitution ratios implying a relaxation of selective constraints. In contrast, other genotypes (arginine, leucine, homotyrosine) showed lowest dN/dS ratios implying purifying selection. Restriction fragment length polymorphism (RFLP) revealed the unambiguous identification of mcyB genotypes, which are indicative of variable X2 amino acids in eight populations of P. rubescens in the Alps (Austria, Germany, and Switzerland). The populations were found to differ significantly in the proportion of specific genotypes and the number of genotypes that occurred over several years. It is concluded that spatial isolation might favour the genetic divergence of microcystin synthesis in Planktothrix spp. [ABSTRACT FROM AUTHOR]