Copepod Assemblages Research Articles

Unraveling Functional Diversity Patterns in Hyporheic Zones: A Trait-Based Approach Applied to Copepods from the Rio Gamberale Creek

Despite the recognized ecological significance of hyporheic zones, biological investigations into their ecology, especially concerning functional diversity, remain limited. This is particularly true for copepod assemblages, abundant in the transitional zone between groundwater and surface waters, requiring more thorough exploration. To bridge this knowledge gap, our study extensively monitored a hyporheic zone within a mountain creek and examined nine functional traits across twelve copepod species found in this environment. Through the application of RLQ and fourth-corner analysis, as well as functional diversity indices including functional richness, evenness, divergence, and dispersion, we aimed to establish links between functional traits and environmental factors. Our findings revealed relationships between environmental features—specifically electrical conductivity, pH, and ammonium concentration—and the trait composition of copepod assemblages, which were influenced by species abundances. Considering the intimate connection between functional traits and ecosystem services, assessing functional diversity within hyporheic zones offers valuable insights into its functionality in terms of services rendered. This study emphasizes the importance of understanding and managing functional diversity in hyporheic zone dynamics to ensure the health and stability of ecotones and, by extension, riverine and groundwater ecosystems.

Bioconcentration and lethal effects of gas-condensate and crude oil on nearshore copepod assemblages

The progressive establishment of gas platforms and increasing petroleum accidents pose a threat to zooplankton communities and thus to pelagic ecosystems. This study is the first to compare the impacts of gas-condensate and crude oil on copepod assemblages. We conducted microcosm experiments simulating slick scenarios at five different concentrations of gas-condensate and crude oil to determine and compare their lethal effects and the bioconcentration of low molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs) in eastern Mediterranean coastal copepod assemblages. We found that gas-condensate had a two-times higher toxic effect than crude oil, significantly reducing copepod survival with increased exposure levels. The LMW-PAHs bioconcentration factor was 1–2 orders of magnitude higher in copepods exposed to gas-condensate than in those exposed to crude oil. The median lethal concentration (LC50) was significantly lower in calanoids vs. cyclopoid copepods, suggesting that calanoids are more susceptible to gas-condensate and crude oil pollution, with potential trophic implications.

Lipid transfers within the lower food web of western Arctic seas

Polar marine ecosystems are undergoing major transformations due to climate change. Alterations of the physical and chemical growth conditions for plankton are likely to propagate through the food web, potentially having major consequences for the animals that Inuit harvest for subsistence. These alterations can impact the nutritional qualities of plankton through physiological responses or indirectly via changes in the taxonomic composition of assemblages. This study focuses on lipids, which provide a vital source of energy in cold waters, and on essential fatty acids (EFA), such as omega-3 and omega-6 FA, which are necessary for the function, growth, and reproduction of organisms. To better understand how EFA propagate and accumulate in the lower food web, we compared the fatty acid composition of phytoplankton and copepods across a large portion of the western Arctic. The bulk lipid profiles of copepod assemblages were determined largely by their taxonomic composition, but specific fatty acid groups (e.g., omega-6 and saturated fatty acids) exhibited strong correlations with water properties (e.g., pH, salinity). A comparative analysis of specific fatty acids suggests that the animals accumulate eicosapentaenoic acid (EPA) but metabolize its precursors, although these processes were not measured directly. The proportions of EPA, docosahexaenoic acid, and specific omega-7 FA (e.g., 16:1ω7) were much higher in copepods than in phytoplankton, and a fatty acid diatom marker accounted for over 45% of the fatty acid pool in copepods. The positive relationship between proportions of this marker in copepods and phytoplankton implies that the fatty acid content of copepods is influenced primarily by recent feeding. These results underscore the importance of long-lived subsurface chlorophyll maxima for trophic transfers of EFA in the strongly stratified waters of the Pacific-influenced sector of the Arctic Ocean and question the paradigm that copepods rely principally on brief surface blooms to rapidly store lipids for the following winter.

Effects of a beaver dam on the benthic copepod assemblage of a Mediterranean river

As known “ecosystem engineers”, beavers influence river hydrology, geomorphology, biochemistry, and biological assemblages. However, there is a lack of research regarding the effects of beaver activities on freshwater meiofauna. In this study, we investigated the taxonomic and functional composition of the benthic copepod assemblage of a segment of the Tiber River (Italy) where a beaver dam, created about 7 weeks before our survey, had formed a semi-lentic habitat upstream and a lotic habitat downstream of the dam. We also analyzed the copepod assemblage before and after a flood event that destroyed the beaver dam, providing a unique opportunity to observe changes in a naturally reversing scenario. Our analyses revealed that, while the taxonomic composition and functional traits of the copepod assemblage remained largely unchanged across the recently formed semi-lentic and lotic habitats, substantial differences were evident between the dammed and undammed states. The dammed state showed lower copepod abundances, biomass, and functionality than the undammed one. These results highlight the role of beaver dams in changing the composition and functionality of meiofaunal assemblages offering insights into the dynamic interactions within aquatic ecosystems.

Variation in Copepod Morphological and Life History Traits along a Vertical Gradient of Freshwater Habitats

Understanding trait selection factors is vital for decoding the processes shaping species’ assemblages. However, trait-based studies in freshwater crustacean copepod assemblages are scarce, especially in groundwater environments. We explored how environmental filtering influences functional traits in copepod assemblages across four freshwater habitats (an alluvial aquifer, a hyporheic zone, a stream benthic zone and a lake littoral) along a depth gradient. Each habitat had distinct environmental templates based on light, temperature and dissolved oxygen. We analysed 4898 individuals from 43 copepod species and examined 12 morphological and life history traits. The results revealed significant differences in copepod traits among habitats, notably in ovigerous female biomass, egg biomass and ovigerous female percentages. Furthermore, despite some statistical uncertainty, notable differences were also observed in the number of juveniles, male-to-female abundance ratios and overall biomass. No significant differences were observed in juvenile biomass, egg characteristics, body size dimorphism or juvenile-to-adult ratios among habitats. The trait variations offer insights into copepod-mediated ecosystem services, particularly carbon recycling. To gain a deeper understanding of copepod adaptations to environmental features and anthropogenic changes, future research should consider additional functional traits, such as locomotion and feeding habits.

Marine copepod assemblages in the Arctic: The effect of frontal zones on biomass and productivity

The Barents Sea, as the largest Arctic shelf region with high productivity, supports vital commercial fisheries. The region's ecosystem is significantly impacted by both warm Atlantic Water (AW) and cold Arctic Water (ARW), resulting in frontal zones that delineate differing water masses. Zooplankton populations serve as the primary link between primary producers and higher trophic levels. To evaluate the potential influence of frontal zones on copepods, we conducted a summer survey focusing on sites where diverse water masses interacted. Our findings revealed that species richness, diversity, biomass, and daily production of common copepods were highest in the Polar Front, separating AW and ARW, as well as in the eastern frontal zones (Barents Sea Water and Novaya Zemlya Coastal Water). Herbivorous copepods, such as Calanus spp. and Pseudocalanus spp., dominated in terms of total copepod biomass and production, whereas the small omnivore Oithona similis prevailed by abundance. Multivariate analysis demonstrated a strong correspondence between frontal zones and copepod assemblages. The primary factors explaining spatial variations in copepod biomass and production included the geographic positions of sampling stations, depth, and chlorophyll a concentration. Our research underscores the significance of oceanographic fronts as zones of critical importance for overall pelagic productivity in Arctic regions.

Effects of tropical cyclone Amphan on the copepods of the Ganges estuary

ABSTRACT Tropical cyclones are increasingly affecting estuarine communities. The effects of category-5 tropical cyclone Amphan (landfall on 20 May 2020 near the Ganges estuary mouth) on the copepod community of the Ganges estuary were studied. Copepod assemblages were sampled before (February–December 2019), shortly after (31 May–12 June 2020) and post-(September–November 2020) Amphan periods. It was hypothesized that shortly after Amphan a relatively homogeneous community consisting of a few estuarine specialists would succeed but that would soon be replaced by a heterogeneous one; however, those specialists would continue their dominance. Shortly after Amphan species richness declined but the recovery process was completed within months, led by Paracalanus parvus, Bestiolina similis, Acartia spinicauda, Acartiella tortaniformis and Oithona brevicornis. Spatial homogeneity of the community that prevailed in pre- and shortly after Amphan was lost in post-Amphan. The unilateral dominance of B. similis observed in the pre-Amphan period was challenged by P. parvus, A. spinicauda, A. tortaniformis and O. brevicornis after Amphan. Shortly after Amphan A. spinicauda proliferated and co-dominated the estuary with A. tortaniformis but the latter replaced the former within a few months. The copepod community experienced rearrangements in species composition, abundance and dominance hierarchy; therefore, its regular monitoring is recommended.

The effects of the Patagonian shelf-break front on copepod abundance, biodiversity, and assemblages

Fronts play an important role in ecological processes, having multiple effects on the structure of plankton communities. The Argentine Sea is characterized by the presence of the large and very productive Patagonian shelf-break front (PSBF). This is a permanent front, with high thermohaline gradients defined between the relatively warmer and fresher shelf waters and those of the Malvinas Current. We studied the effects of the PSBF in the vertical and horizontal structure of the copepod community along two transects crossing the front. For all the variables studied, the outer shelf plus the front behaves as a unity, different of the offshore oceanic region. The highest copepod abundances were recorded on the outer shelf and shelf-break front, while the highest diversity was verified in the oceanic regime. Three copepod assemblages were identified associated to different regions: outer shelf and front (OS-PSBF), upper (UMW) and deeper (DMW) Malvinas waters, each one characterized by its own set of indicator species, having different reproductive and feeding strategies. Sac-spawners, ambush or cruise-feeders, and detritivore or omnivore species, occurred in DMW, while broadcasters, filter-feeders and mainly herbivores dominated at UMW and OS-PSBF. The PSBF acts as a leaky boundary between the oceanic regime (UMW and DMW) and the outer shelf-front regime (OS-PSBF), the first one characterized by higher copepod diversity and several functional groups, and the last one depicted by higher copepod abundance and only one functional group. In addition to its high primary production, the PSBF and surroundings are important to provide diversity of pelagic habitats that promote the existence of different assemblages, which are characterized by species having similar functional traits and that could play a similar role in the ecosystem.

Dataset of benthic copepods in the littoral zones of Lake Maggiore

Copepods (Crustacea: Copepoda) are widespread in aquatic ecosystems worldwide and represent an important component of the meiobenthic metazoan assemblages of lake littorals. Yet, little is currently known about the diversity of benthic copepods in lentic habitats. We gathered information on the benthic copepod assemblages of the littoral zone of Lake Maggiore as part of the Interreg Italy-Switzerland 2014-2020 Parchi Verbano Ticino project (ID: 481668), funded by the European Regional Development Fund (ERDF). Lake Maggiore is a large and deep temperate lake in north-western Italy human-managed from mid-March to mid-September. This contributes to substantial changes in water levels in relation to human activities such as hydropower, industrial and agricultural uses. We compiled a dataset listing 234 occurrences of benthic copepod species recorded from three littoral sampling sites situated in three protected areas, two of which are part of the Natura 2000 network in Italy and one is part of the Emerald Network in Switzerland. We collected the specimens during the summer-autumn period in 2019-2021. We identified the copepods at the species level and created a dataset with individual georeferenced occurrence records for each species, organized in a standardized Darwin Core Archive format. We made available, through the Global Biodiversity Information Facility (GBIF), a total of 13 distinct taxonomic entities and 234 unique georeferenced occurrence records related to the benthic copepod assemblages of the littoral zone of Lake Maggiore (Tabilio Di Camillo et al., 2023). The dataset has the potential to support the authorities in charge of managing Lake Maggiore’s water levels in addressing the ecological risk relevant to the littoral zone and in developing shared implementation strategies for sustainable water management.

Assessing spatial and temporal changes in diversity of copepod crustaceans: a key step for biodiversity conservation in groundwater-fed springs

Despite the close attention springs have received from a hydrologic perspective and as biodiversity hotspots, the multiple dimensions of spring meiofaunal assemblage diversity are still poorly investigated. Knowledge of beta diversity patterns and drivers can inform and improve management decisions on biodiversity conservation. Here, we analyzed beta diversity of copepod assemblages in karst springs in Central Italy by focusing on: 1) relative contributions of turnover and nestedness components to taxonomic and phylogenetic beta diversity; 2) temporal variation of species richness and beta diversity within and between the target springs in conjunction with models of the influence of physical-chemical parameters on within-spring diversity changes; 3) expected risk of habitat loss due to variation in groundwater recharge under climate change. To this end, we gathered data from 168 samples collected in four karst springs from 2004 to 2016. Overall, we found 48 copepod species, 22 of which are obligate groundwater dwellers while the remaining 26 usually occur in surface freshwaters. All springs showed significant changes in taxonomic and phylogenetic beta diversity over time. Total beta diversity was high for both the taxonomic and phylogenetic dimensions, and turnover was the main component. Inter-site variability in dissolved oxygen explained a noticeable part of temporal variation in beta diversity, likely reflecting the role of microhabitat heterogeneity in shaping site-specific assemblages. However, most of the temporal variation in species richness and beta diversity remained unexplained, suggesting a major role of other factors, such as seasonal discharge variations. Modelling of recharge rates for all the four springs over 2001–2020 suggested a potential >40% recharge deficit under dry conditions. Moreover, Cellular Automata-based modelling of rainfall over the Gran Sasso-Sirente hydrogeologic unit (feeding three of the four springs) predicted an overall precipitation decrease in the 2081–2095 period. Such changes could produce severe effects on springs’ microhabitats and related communities. Our results indicate that partitioning beta diversity, monitoring its temporal changes and assessing its environmental drivers are critical to evidence-based conservation of springs. Particularly, the high species turnover we have observed suggests that conservation strategies should seek to preserve as many microhabitats as possible within and among karst springs.

Copepod assemblage structure in a tropical eutrophic estuarine system in the Southwestern Atlantic Ocean: Ecological indicators and functional groups

Changes in the structure of copepod assemblages and their functional groups because of variations in environmental and water quality parameters were examined in Guanabara Bay, which is a heavily eutrophic system. Monthly samples were collected over 2 years from 2012 to 2013. Most environmental and water quality parameters, and copepod assemblage diversity and evenness, varied between the annual dry and rainy periods. Opportunistic broadcast-spawning species were the most abundant in the system, most commonly those with mixed feeding strategies. Copepod abundance, taxonomic and functional assemblage indices, and primary functional groups of copepods were negatively affected by increased water quality parameters. These results showed that even in the Guanabara Bay area with great water circulation, pollution negatively affected copepod assemblages. This study also illustrated the importance of analyzing functional diversity and groups for the realistic diagnosis of functioning assemblages and ecosystems.

Seasonal Changes in Abundance, Biomass, and Species Diversity of Zooplankton in Areas Offshore the Crimea (Black and Azov Seas)

New data are presented the seasonal changes in abundance, biomass of copepods and fodder zooplankton in areas offshore the Crimea. These investigations are based on the materials of five expeditions of the RV “Prof. Vodyanitsky” in the northern part of the Black Sea and the southern part of the Sea of Azov in different seasons of 2016. It was shown: 1) Seasonal differences in the taxonomic structure of the Copepoda taxocene from the shelf and deep waters were revealed. The warm-water invasive species Acartia (Acanthacartia) tonsa and Oithona davisae were relative numerous in the copepod assemblages on the shelf in summer and autumn. In the deep waters, with a low abundance of warm-water invaders, cold-water native species were dominating, and the structure of the Copepoda taxocene was more stable than on the shelf in these seasons. 2) Zooplankton abundance in 2016 was higher compared to 2010 and the 1990s. The data on zooplankton, supported by information about an increase in the species richness and abundance of fish larvae in recent years, make it possible to talk about the transition of the Black Sea ecosystem to a new, relatively stable state.

Copepod Assemblages in A Large Arctic Coastal Area: A Baseline Summer Study

To provide a baseline description of copepod assemblages in the Pechora Sea, an estuarine area with great economical and ecological importance, we conducted a survey during the summer season. A total of 24 copepod taxa were identified in the study, with Acartia longiremis, Calanus finmarchicus, Centropages hamatus, Copepoda nauplii, Eurytemora affinis, Oithona similis, Pseudocalanus spp., and Temora longicornis being the most numerous. The high diversity (Shannon index = 2.51 ± 0.06), density (18,720 ± 3376 individuals m−3) and biomass (89 ± 18 mg dry mass m−3) of copepods were revealed. Populations of common small copepod taxa were dominated by the young stages, indicating spawning, while older copepodites prevailed among medium- and large-sized species, showing that their reproduction occurred before our survey. Cluster analysis indicated three groups of stations that mainly differed in the abundance of particular species. There were clear associations between copepod assemblages and environmental variables. Statistical analyses showed significant correlations between copepod abundance and water temperature or sampling depth, while other factors had a lesser influence. Our results suggest a strong effect of local circulation and currents on the spatial pattern of the copepod assemblages in the study area. This study may be useful for future biomonitoring in the south-eastern Barents Sea.

Copepod Assemblages at the Base of Mangrove Food Webs during a Severe Drought

The effect of severe drought on the functional groups that sustain the base of the mangrove food webs in semi-arid areas is largely unknown. We therefore analyzed the intra-annual variation in the assemblages and functional groups of copepods in a shallow, low-inflow estuary of the Brazilian semi-arid coast when the most severe drought ever occurred. The lowest density was found in April (upstream region) and the highest in August (downstream region). Three main functional groups were identified, sorted by spawning strategy, and further subdivided according to feeding strategy, trophic regime, and diel vertical migration behavior. The community was significantly influenced by the extreme drought period, presenting a temporal homogenization in terms of composition, and an expressive and unexpected increase in density in the dry period, possibly due to phytoplankton blooms resistant to hypersalinity and the occurrence of copepod species adapted to stressful conditions. The few stress-tolerant species sustaining the food webs with seasonal variations were observed simplifying the trophic variability. The results indicate that hypersalinity can induce changes in the zooplankton community, increasing copepod mortality risk and, so, promoting alteration in the trophic estuarine dynamic.

Surface copepod assemblages in shallow coastal waters off northeastern Yucatan Peninsula influenced by the Yucatan upwelling

The seasonal variability of the Yucatan upwelling is known to exert a definite influence on environmental and biological conditions over the Yucatan Shelf. The present study is the first to analyze the variability of surface mesoplanktonic copepods in coastal waters off northeastern Yucatan Peninsula. Copepod samples and environmental parameters were obtained monthly in surface waters (∼1 m depth) at twelve sampling sites (<20 m depth). The sampling period included the upwelling season (April–September: Up) and representative months of non-upwelling (November–December: NUp). Differences in copepod assemblage attributes (abundance, species composition and diversity) and environmental parameters were analyzed among sampling sites, months, and seasons. Forty-two copepod species were recorded. Paracalanus quasimodo, a coastal euryhaline species, was widely dominant throughout the study period (relative abundance: 54%, frequency of occurrence: 94%). Univariate and multivariate statistical analyses indicated that copepod assemblages and environmental parameters remained spatially homogeneous but varied significantly over time. Two copepod assemblages were found concerning temporal changes in dominant species, its numerical and relative abundance, diversity and contrasting assemblage–environment​ relationships. The first assemblage occurred in the Up season, with a clear dominance of P. quasimodo (known as a coastal upwelling indicator species), high total copepod abundance, low diversity, and evenness, and positively influenced by high dissolved inorganic nutrients and chlorophyl-a concentrations. The second assemblage, present in the NUp season, also showed a dominance of P. quasimodo but with reduced relative abundance and increased of indicator species of oligotrophic waters, such as Clausocalanus furcatus and Farranula gracilis, low total copepod abundance, high diversity, and evenness, and positively influenced by salinity. The present results reinforce previous conclusions about the major influence that the Yucatan upwelling exerts on diverse marine biota off northeastern Yucatan Peninsula, improving the knowledge about the influence of local environmental parameters linked with upwelling variability to structuring the copepod assemblages.

Effects of human-induced water level fluctuations on copepod assemblages of the littoral zone of Lake Maggiore

Human-induced water level fluctuations (WLFs) are among the major pressures threatening lake ecosystems. Their effect on meiobenthic species of the littoral zone has been poorly investigated. In this study, we aimed at assessing the effects of human-induced WLFs on the composition and functionality of the benthic copepod assemblages of the littoral zone of Lake Maggiore, Italy and Switzerland. From 1942 to present, the water level of Lake Maggiore has been regulated through the Miorina Dam. We monitored copepod assemblages during different water levels defined within the period of regulation by the dam, using taxonomy- and trait-based metrics. We observed variation in the overall abundance and biomass of copepods, as well as in the number of individuals belonging to some trait classes such as ovigerous females, opportunists, omnivores and deposit feeders. None of the investigated trait class was completely lost. The results of our study suggest that ecosystem services supplied by the littoral zone of Lake Maggiore are likely altered by human-induced WLFs. Our findings provide a first picture of WLF impacts on benthic copepod assemblages, which can be useful for future research expanding on other functional traits.

Community structure of zooplankton during the southwest-northeast monsoon transition period in the southeastern East China Sea

Abstract The assessment of zooplankton spatial structure is critical to quantifying plankton production and biochemical cycling. Here, we show the effect of monsoon-driven hydrographic changes on the spatial patterns of zooplankton at regional scales. Based on a field survey conducted during the monsoon transition, we assess the community structure and ash-free dry weight above 100 m depth in the Kuroshio edge area, southeastern East China Sea. The zooplankton community was dominated by copepods, with calanoids as the most abundant taxon followed by poecilostomatoids. Copepod assemblages comprised 81 species belonging to 41 families, and 23 genera, with Undinula vulgaris as the most abundant species. The richness of zooplankton taxa showed a mounting trend from the coast to offshore, which was opposite to the spatial variation of total zooplankton biomass. Our results suggest a leading influence of the Kuroshio Current during the southwest-northeast monsoon transition period in the southeastern East China Sea.

Functional diversity of copepod assemblages along a basin-scale latitudinal gradient in the North Pacific Ocean

The northern Pacific Ocean is one of the most sensitive areas globally to climate change. Copepods typically account for between 60% and 90% of mesozooplankton in the open ocean. Because copepods are a key link in marine food webs, their response to environmental changes is an important topic in marine biodiversity and ecosystem functioning relationships. The relationship between copepod assemblages and the marine environment in the northern Pacific Ocean from a traits-based perspective has been largely unknown until now. In this study, we used the functional traits and geographic distribution of 177 copepod species along a latitudinal gradient, ranging from 4°S to 46°N in the northern Pacific Ocean, to evaluate the latitudinal variation of functional diversity and assembly rules of copepod assemblages. Based on a cluster analysis of four key functional traits, seven functional groups were identified. Redundancy analysis revealed environmental preferences for different functional groups. Large carnivores showed a stronger preference for higher temperatures than small carnivores, Omnivores and herbivores showed a stronger preference for higher chlorophyll a concentrations. The distribution of detritivores was nearly independent of temperature and chlorophyll a concentration. Most functional diversity indices showed non-linear decreasing trends along the latitudinal gradient. These trends remained stable in the tropic and subtropic regions (WARM and NPSG), but decreased sharply in the Kuroshio extension and Pacific subarctic gyres regions (KURO and PSAG). A null model revealed the assembly rules of copepod assemblage significantly varied with latitude: environmental filtering was dominant in the KURO and PSAG, whereas both environmental filtering and limited similarity played important roles in the WARM and NPSG, in addition to the neutral process. Our results suggested that with ocean warming, a northward shift in the distribution range of specific functional groups (such as large carnivores) might significantly alter the biodiversity and ecosystem function of zooplankton communities in the Kuroshio extension region. This study highlights the importance of a traits-based approach in the study of biodiversity and ecosystem function in pelagic ecosystems at large scales.

Copepods and mixotrophic Rhizaria dominate zooplankton abundances in the oligotrophic Indian Ocean

The large, tropical oligotrophic gyres of the world's oceans are understood to be relatively unproductive, with low phytoplankton and zooplankton biomass, and inefficient food webs, although data are scarce. Here we investigate changes in the zooplankton assemblage along a 15 °C temperature gradient from 20 stations on the 110°E transect as part of the second International Indian Ocean Expedition. To ensure that we reflect most of the zooplankton biodiversity, we used a 100 μm mesh net to capture the small copepod and microzooplankton components that are important and often overlooked in tropical systems. Further, to obtain a synoptic view, we towed the Continuous Plankton Recorder between stations across 30° of latitude. We found that copepod assemblages clustered into four groups, with the most distinct being at the highest latitudes south of the sub-tropical Front. As the ocean temperature increased from south to north along the transect, zooplankton abundance and diversity also increased. The dominant copepod species changed accordingly and were predominantly those with the ability and/or preference to selectively feed on microzooplankton. Although copepods were the most abundant taxon, the proportion of microzooplankton, particularly, mixotrophic Rhizaria, was consistently high. Thus, our study found a highly mixotrophic system supporting secondary production in the oligotrophic Indian Ocean.

Environmental stability and long-term variability of harpacticoid copepod assemblages

Harpacticoid copepods of the Chernaya Bay (White Sea) intertidal zone were collected in 45 surveys carried out from spring to autumn over a 25-year period (1996–2020) at three sites that differed in sediment properties. There were no significant long-term trends or seasonal cycles in total abundance. Regarding the species composition, the differences between sites were the most important source of variability over the whole period while the fine-scale (within-habitat) variability was low. Epibenthic species prevailed in fine silty sand, both burrowing and epibenthic species prevailed in medium sand, and interstitial and burrowing species prevailed in coarse sand. A comparison of the data on harpacticoid assemblages from a number of geographically remote loci corroborated the generality of this pattern. In a temporal dimension, the structure of each community was stable until the early 2000s, when the proportion of epibenthic, burrowing and interstitial species changed following changes in sediment properties (increasing siltation at sandy sites and decreasing siltation at the silty site). At each site, there was an increasing long-term trend in diversity (both in total richness and in expected species number). This increase was particularly apparent at sandy sites because of the appearance of epibenthic species. We suggest that sediment composition is the key factor determining the composition of harpacticoid assemblages in space and time. The “ecomorphological profile”, i.e., the proportion of species with different lifestyle and morphological traits, is a useful and informative indicator for describing and typifying these assemblages.