Copepod Assemblages Research Articles

Hydrodynamics and zooplankton assemblages in Prydz Bay, East Antarctica, during the austral summer of 2017

Vertical distribution of zooplankton biovolume, abundance and community composition in the twilight zone are important to better understand their role in carbon and energy transfer that mediate the food web structure in the Prydz Bay. Qualitative and quantitative zooplankton studies were carried out in January 2017, using a multi plankton sampler (mouth area: 0.25 m2; 200-microns mesh size) in the ice-free domain of the Prydz Bay. In this study, we investigated the diel variation of zooplankton biovolume and community structure between the surface water layer and 500 m depth at every six hours intervals for a period of 48 h at about 68° S latitude, 74° E longitude in the Prydz Bay. Besides, relationship between the zooplankton assemblages and diffrent water masses were also discussed. We found an abrupt increase in zooplankton biovolume within the mixed layer depth on day 1 (13:15 h). Apart from high, localized contributions from chaetognaths, appendicularians and polychaete larvae, mesozooplankton was numerically dominated by copepods, and densities were highest near the surface most of the times. Two water masses were identified based on the signatures of temperature and salinity: Antarctic Surface Water (ASW) and Shelf Water (SW). ASW had a higher proportion of Calanoides acutus, Calanus propinquus and Oithona similis, while Metridia gerlachei, and Heterorhabdus austrinus were mostly encountered in SW. Our results will help to predict the short term temporal variations of copepods assemblages and other zooplanktons according to the dynamics of hydrographic features in Prydz Bay.

Copepod assemblages in the water column and drifting sea-ice floes in the ice-edge region in the Indian Ocean sector of the Southern Ocean during the austral summer

Copepod assemblages in the water column and drifting sea-ice floes in the ice-edge region in the Indian Ocean sector of the Southern Ocean during the austral summer

Temporal changes in the epipelagic copepod assemblage at Gorgona Island, Colombian Eastern Tropical Pacific ocean

Temporal variations in the hydrographic conditions of the Eastern Tropical Pacific (ETP) can modulate the assemblage structure of marine organisms, including copepods. While this taxonomic group has been widely recognized as important in the energy flow of the pelagic environment, fundamental ecological aspects are still unknown particularly possible relationships with oceanographic variations that have been described for ETP. In this paper, we evaluated the intra-annual and interannual variation of structure, richness, diversity, and similarity of the epipelagic copepod assemblage of Gorgona Island (Colombian ETP) based on samples collected during six oceanographic campaigns carried out between 2010 and 2016. We found significant changes in the oceanographic conditions and abundance of copepods between periods and years. Seven significant clusters were identified: five for each sampled period and two for the period of October 2010. Ditrichocorycaeus andrewsi, Oncaea clevei, Paracalanus parvus, and Subeucalanus pileatus were the species with the greatest contribution to group formation. Our results suggest that the intra-annual changes in the assemblage of epipelagic copepods recorded in Gorgona Island are a consequence of the displacement of the Intertropical Convergence Zone throughout the ETP during the year. This is due to the fact that during the periods of March they respond to the entry of subsurface waters from the Ensenada de Panama, and during the periods of October respond to the increase of the continental runoff on the pelagic environment of Colombian ETP.

Copepods key traits in diverse habitats of tropical waters

AbstractCopepods are the dominant marine zooplankton and perform important functions in the marine food web. However, copepod traits have not been studied in many waters. We studied the copepod community under influence of the Mekong River and the Southern Vietnamese coastal upwelling, based on their functional traits, during the southwest monsoon period in 2016. Fourteen trait categories of four key functional traits (trophic-groups, feeding-types, reproductive-strategies and diel migration) of copepod data were analyzed to investigate how environmental gradients impact on their distribution and abundance among the four defined habitats: Mekong River (MKW), upwelling (UpW), nearshore (OnSW) and offshore waters (OSW). There were seven functional groups identified in the study waters based on multiple correspondence analysis of distribution, abundance and traits of 139 copepod species. Herbivorous, current-feeding and sac-spawning copepods were dominant in all habitats with the highest abundance in OSW. Specifically, herbivorous species dominated in MKW and UpW, whereas omnivorous species dominated in OnSW and OSW. Sac-spawners dominated in all habitats, but decreased from MKW and UpW to OnSW and lowest in OSW. Cruise feeders were 2-fold higher than ambush feeders in the UpW, but the opposite was observed in the other habitats. The results suggest that impacts of Mekong River and coastal upwelling led to distinctive copepod assemblages with specific functional traits.

Copepods of the off-shore waters of Caribbean Colombian Sea and their response to oceanographic regulators

AbstractSeven oceanographic expeditions were conducted between the years 2013 and 2018 to determine the horizontal and vertical distribution schemes in the epipelagic and mesopelagic copepod community structure of the Caribbean Oceanic ecoregion (CAO) and the oceanographic variables that regulate it. Four indicator species are suggested for the North Equatorial Current and the Caribbean Surface Water (CSW) mass (Clausocalanus furcatus, Oncaea venusta, Temora stylifera and T. turbinate) and two indicator species for deep-water masses such as the Western North Atlantic Central Water (NACW) and the Antarctic Intermediate Water (AAIW) (Mormonilla phasma and Conaea rapax). The copepod assemblage responds to local oceanographic patterns that are regulated (24%) by the variability of dissolved oxygen and temperature in the water column. The horizontal structure of the copepod assemblage in offshore waters presented a spatial sectorization. Three zones were differentiated: (1) oceanic Colombian zone; (2) influence of the Magdalena River zone; and (3) offshore north-east zone. Water mass mixing processes and migration mechanisms favour the homogeneity of the vertical assemblage of copepods in the CAO ecoregion. This study provides relevant information on the structure and density of copepod species, providing key information to describe the ecological processes and the different responses to the oceanographic factors that modulate them.

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Latitudinal changes in copepod assemblages across the South West Indian Ridge

In the South Atlantic Ocean, the Subtropical Front (STF) separates warm-water copepod assemblages of high diversity from cold-water assemblages of lower diversity. Comparable information from the southern Indian Ocean are scarce. Here we test observations made in the southwest sector of the Indian Ocean using samples collected during 2009 from along the South West Indian Ridge (SWIR, ∼27 - 42° S). Distinct assemblages were associated with the Agulhas Return Current (ARC), the Sub-Tropical Front (STF) and Sub-Antarctic Front (SAF). Sixty-nine percent of the structure of the assemblages could be attributable to the temperature at both the surface and 200 m, the salinity and the fluorescence signal of surface waters and the depth of the upper mixed layer. Forty-nine copepod genera and 132 species were recorded. While richness was greatest in waters of the ARC and lowest in the SAF, copepods were most abundant in the latter and scarcest in the former. Mean prosome length decreased with increasing latitude, and assemblages of the ARC included greater numbers of carnivorous taxa than those associated with either the STF or the SAF. As in the Atlantic, the STF markedly influenced the relative distribution range of copepod assemblages above the South West Indian Ridge.

Diel Feeding Rhythm and Grazing Selectivity of Small-Sized Copepods in a Subtropical Embayment, the Northern South China Sea

Small marine copepods are key components of the pelagic food webs in Chinese coastal waters, but very few studies have addressed their trophodynamics, with even fewer studies addressing their diel feeding rhythms. In this study, the diel feeding rhythm and grazing selectivity of the copepod assemblage in Daya Bay during September 30 to October 2, 2014, were studied based on gut pigment analysis. Small copepods (body length < 1.5 mm) including Paracalanus parvus, Temora turbinata, Acrocalanus gibber, Temora stylifera, Euterpe acutifrons, and Acrocalanus gracilis, accounted for 73.9–100% of the total copepod abundance. The copepod assemblage generally exhibited a diurnal feeding pattern, characterized by a higher gut pigment content and ingestion rate during the daytime, consistent with variation in the ambient Chl α concentration. Fifty-five percent of the phytoplankton standing stock per day was consumed by the copepod assemblage, wherein diatoms, prymnesiophytes, and cyanobacteria were the main prey items with average contributions of 19.4–32.9% to the gut pigment contents. The copepod assemblage showed a strong feeding preference for prymnesiophytes, a weak feeding preference for diatoms, and avoidance of cyanobacteria. These results suggest a strong top-down control on phytoplankton community, especially on small groups from small copepods in the Daya Bay ecosystem.

Copepod assemblages along a hydrothermal stress gradient at diffuse flow habitats within the ABE vent site (Eastern Lau Spreading Center, Southwest Pacific)

Copepoda is the most diverse and abundant taxon at deep-sea hydrothermal vents, contributing significantly to the biodiversity and thus is important in maintaining ecosystem functioning. To date we lack knowledge on meiofauna, specifically copepod community dynamics, in the entire region of the Eastern Lau Spreading Center. We explore abundance and diversity of copepods associated with foundation species thriving at distinct physiochemical regimes at the active vent site ABE. Diffuse flow habitats within ABE are dominated by three foundation species: (1) the snail Alviniconcha hessleri, exposed to average vent fluid temperatures of ~24 °C, (2) the snail Ifremeria nautilei at ~12 °C, and (3) the mussel Bathymodiolus septemdierum in average temperatures of ~6 °C. In each habitat, three samples were taken using a quantitative collection device (mussel-pot). Copepod abundance ranged from 1 to 30 ind. per 10 cm2, with no significant differences between the three habitats. A total of 18 copepod species were identified. In the Alviniconcha habitat, the vent endemic dirivultid copepod Stygiopontius lauensis dominated the community, representing >90% of the individuals. Species richness and Shannon diversity were significantly higher in the Bathymodiolus habitat, correlated with lower temperatures, lower hydrogen sulfide concentrations and higher oxygen concentrations. This increase in diversity was driven by a community mostly comprised of habitat generalists including genera reported from shallow coastal waters, shallow vents, and peripheral vent environments. This study provides the first quantification of biodiversity and community structure of copepods along a physiochemical stress gradient at a relatively stable Southwest Pacific vent site prospective for deep-sea mining.

Habitat-Diversity Relations between Sessile Macrobenthos and Benthic Copepods in the Rocky Shores of a Marine Protected Area

In rocky shore systems, sessile macrobenthic assemblages may act as “ecosystem engineers” for many smaller benthic organisms. Thus, the influence of macrobenthic coverage on the diversity and assemblage structure of the harpacticoid copepod fauna was investigated in the rocky shores of a Marine Protect Area (MPA) in the Ligurian Sea (NW, Mediterranean Sea). Two sampling sites were investigated in two seasons at three different depths on both sub-vertical and inclined reefs. A total of 61 species of copepods mainly represented by Miraciidae, Laophontidae, Longipediidae and Thalestridae were found. The complex micro-topography of these substrata provided a wide variety of niches for many species with different lifestyles that suggests the important role of rocky shores to ensure the functioning of coastal ecosystems. The harpacticoid assemblage structure seemed mainly influenced by season and depth. The temporal spread observed is likely one of the underlying mechanisms of niche segregation that allows many species to co-occur in this specific environment along with a subordinate spatial segregation corresponding to the depth gradient. The results seem to support the hypothesis that the different species composition of the “ecosystem engineer” (and consequently its structure changes) are relevant in structuring the copepod assemblages. The comparison with previous data on general meiofauna underlines that higher surrogacy of the taxonomic identification could be used to study rocky shore communities, but the rich diversity that these systems host can only be understood at the lower taxonomic levels. The same holds for future evaluations of impact of environmental changes (including MPA regulations) on meiofaunal assemblages.

Metabarcoding of zooplankton diversity within the Chukchi Borderland, Arctic Ocean: improved resolution from multi-gene markers and region-specific DNA databases

DNA-based analyses have become powerful tools for characterizing the metazoan biodiversity of diverse marine ecosystems. Metabarcoding (i.e., large-scale taxonomic identification of complex samples via high-throughput sequencing of a DNA barcode region) frequently uses hypervariable regions of the nuclear eukaryotic 18S ribosomal RNA (rRNA) gene. However, species-level taxonomic identification is hampered by the conservative nature of the 18S gene in comparison to the mitochondrial cytochrome oxidase I (COI) barcode gene. Additionally, metabarcoding relies on reference DNA sequence databases for classification of millions of unknown sequence reads and molecular operational taxonomic units (OTUs); databases that are at present depauperate for marine zooplankton taxa. Here, we characterized the mesozooplankton community for the Chukchi Borderland (CBL) region, western Arctic Ocean, through metabarcoding analysis of the V4 and V9 hypervariable regions of 18S rRNA and a portion of COI. Characterization of zooplankton diversity for the epipelagic and upper mesopelagic layers (0–500 m) was based upon 17 metazoan taxonomic categories encompassing 24 orders in 14 classes. Taxonomic classification using the V4 and V9 markers was most reliable for orders, with copepods dominating OTU counts. To increase taxonomic resolution and allow detection of species, V4, V9, and COI OTUs were classified against DNA sequence databases for the Arctic Ocean for the subclass Copepoda. The geographic region-specific databases for 18S rRNA and COI resulted in the detection and identification of 6 genera and 49 species of copepods representing 23 families, a marked increase in the taxonomic classification of the 18S rRNA markers. The greatest copepod species diversity was captured with V4 (34 species) followed by COI (28 species) with the least copepod diversity detected by V9 (5 species). Our results demonstrate the power of using multiple gene markers, with DNA reference databases that are specific to the geographic region of interest, providing more accurate metabarcoding biodiversity measures for the copepod assemblages compared to universal metazoan sequence reference databases. Results from this study highlight the need for continued DNA barcode sequencing to increase species representation in the reference sequence databases that are crucial for accurate characterization of mesozooplankton communities.

Effects of cyclone Fani on the copepod community of the Ganges River estuary of India.

A cyclone temporarily disrupts copepod community structure of an estuary, and during the community rebuilding process, omnivorous copepods dominate. This hypothesis was tested after cyclone Fani affected the Ganges River estuary of India on 5 May 2019. Copepod assemblages and environmental parameters were collected before (25 February 2019), after (24 August 2019) and immediately after (daily between 8 and 14 May 2019) cyclone Fani from three sites of the estuary. Immediately after cyclone Fani, spatial heterogeneity of the estuarineenvironment was washed away, salinity and temperature levels of the estuaryincreased, pH level declined, while the total dissolve solids remained constant at high levels of concentration. Copepod diversity and abundance were drastically reduced by cyclone Fani with the exception of the omnivorous Bestiolina similis, which tolerated a wide variability of the environment and dominated the community. Led by small and medium-sized copepods, within days, the community recovered from its initial disruption. Immediately after cyclone Fani, medium-sized omnivorous copepod Acartiella tortaniformis became the second most abundant species replacing the small-sized herbivorous Paracalanus parvus. Changes in species composition and abundance hierarchy observed immediately after cyclone Fani lasted for a few months. The intensity of cyclones is increasing in the Indian Sundarban; therefore, following a cyclone, more severe and prolong disruptions of the copepod community are likely. Institutionalized monitoring of the cyclone-mediated ecological changes of the Ganges River estuary is therefore strongly recommended.

Surface cyclopoid copepod assemblages in relation to environmental conditions near undisturbed coral reefs of Minicoy, southeastern Arabian Sea, a part of the Indian Ocean

AbstractThe cruise conducted in the spring inter‐monsoon (pre‐monsoon) of April 2015 in the frame of a funded project epitomized an open ocean survey that allowed procuring a quasi‐synoptic picture of cyclopoid copepod community structure in 18 open ocean stations of the Minicoy Island, Lakshadweep archipelago, off the southwestern Indian coast, based on the analysis of standing stock and composition in the integrated 0–10 m water column. The main objective was to explore the community structure of cyclopoid copepods prevailing here and which environmental variable influences the same. It is witnessed that sea surface temperature (SST) (30.42 ± 0.19°C), sea surface salinity (SSS) (33.56 ± 1.15 psu), and dissolved oxygen (DO) (4.32 ± 0.06 ml/L) with SSS and DO are the best matching variables diversifying cyclopoid copepod species (av. abundance 700 ± 386 no. of individuals/100 m3). Average zooplankton biomass (0.03 ml/m3) and abundance (8,989 ± 3,866 no. of individuals/100 m3) were also observed. Fifty‐one cyclopoid copepod species belonging to four families and seven genera were identified, with the dominance of high saline species such as Sapphirina, Copilia, Farranula, and Oncaea. An abundance biomass curve (ABC) plot analysis indicated an undisturbed community with normal environmental conditions. TAXDTEST (taxonomic distinctness) depicted a diverse condition where all points clustered together within a 95% confidence level. Our results indicate that the cyclopoid copepod assemblage near Minicoy Island is a diverse, undisturbed community and hypothesize that the stable environmental conditions during pre‐monsoon (spring inter‐monsoon) preferred the diversification of cyclopoid copepods with the prevalence of high saline species. The data evolved could be used as a standard reference/benchmark to detect any deviation from an undisturbed/diverse community status of Minicoy Island in the looming scenario of climate change in and around the Indian Ocean.

The impact of nitrate on the groundwater assemblages of European unconsolidated aquifers is likely less severe than expected.

In this study, we analyzed the structure of the stygobiotic copepod assemblages of an unconsolidated European aquifer (VO), in southern Italy, that has been subject to persistent nitrate contamination for over 15 years. To this end, we monitored 25 bores where groundwater was contaminated only by nitrate, and no other chemical pollutants were reported as being above detection limits from 2009 to 2014. We monitored these bores three times, namely in autumn 2014 and in spring and autumn 2015. We expected that the chronic exposure to high nitrate concentrations had a significant and evident impact on the stygobiotic copepod assemblages. Unexpectedly, the assemblages were highly diversified. The stygobiotic species richness (SSR) accounted 17 species, a value that exceeded the European mean value (SSR = 12 species). However, the species density was only 0.6 species/km2, lower than the European mean value (= 1.6 species/km2). Moreover, the juvenile copepods were numerically less abundant than the adults and the biomass-abundance model showed signs of alteration of the structure of the copepod assemblages. This study highlighted that (i) nitrates, even at high concentrations, probably have a less severe impact on groundwater assemblages of unconsolidated aquifers than expected and (ii) the analysis of population traits and biomasses can detect signs of alteration of these assemblages that would, otherwise, not be visible from the analysis of the sole species richness and abundances.

Diversity and functional groups of copepods as a tool for interpreting trophic relationships and ecosystem functioning in estuaries

We examined trophic relationships in estuarine planktonic food webs by focusing on the assemblages and functional groups of copepods and their effects on prey and predator. We also studied the relationship between biodiversity and ecosystem functioning in estuaries using different taxonomic and functional diversity indices of copepod assemblages and copepod biomass as a proxy of ecosystem functioning. We collected samples every 2 months over a 2-year period in four Brazilian estuaries. Taxonomic diversity indices showed a positive and negative relationship with chaetognath densities and ecosystem functioning, respectively. The functional indices were negatively related to the effect of predator diversity on prey. Different functional groups of copepods were positively correlated with chaetognath density, consistent with their generalist feeding habits. Thus, multifaceted approaches that use different indices and functional groups are recommended to provide a more realistic view of the trophic relationships and ecosystem functioning in estuaries.

Environmental influences on zooplankton diversity in the Kavaratti lagoon and offshore, Lakshadweep Archipelago, India

The present study aimed to analyse the influence of physico-chemical properties on zooplankton assemblages and species diversity in a lagoon system. The study was carried out in coral reef lagoon of Kavaratti Island, Lakshadweep Archipelago, India during the monsoon of the year 2017. Zooplankton assemblages, distributed among 56 taxonomic units, were found to be dominated by copepods (63.27%, 34 taxa) followed by cladocerans (11.14%, 7 taxa), ostracods (9.87%, 2 taxa), ciliates (6.23%, 6 taxa), chaetognaths (4.32%, 3 taxa), leptomedusae, (1.25%, 1 taxa), and appendicularians (3.92%, 3 taxa). Copepods assemblages showed maximum density of 14326 ind m−3 from S1, in which leptomedusea was the lowest abundant taxa (284 ind m−3). Shannon–Wiener-index between 3.725–3.860 attested to the fact that the species diversity and richness predominated in lagoon than that in offshore. Canonical Correspondence Analysis revealed the environmental parameters influencing the abundance and occurrence zooplankton community in the study area.

Coastal eutrophication as a potential driver of functional homogenization of copepod species assemblages in the Mediterranean Sea

• Passive ambushing copepods were favored as Chl a increased. • Generalist feeders were favored as Chl a increased showing trophic homogenization. • Trait-based approaches are useful to study the effect of eutrophication on copepods. Eutrophication as a consequence of anthropogenic nutrient enrichment is one of the major threats to biodiversity in nearshore and coastal marine waters, and consequently, for ecosystem functioning. This study explores changes in the biological organization of copepod assemblages along a Chl a gradient through an upscaling analysis of regional datasets from the coastal waters of the Mediterranean Sea. Results show that omnivorous copepods using passive and/or ambush feeding strategy are favored as Chl a increases, and copepod community shifts towards trophic homogenization by favoring generalist feeders against specialists. To our knowledge, this is the first report of functional homogenization of copepods as the result of eutrophication. The present study also demonstrates the potential use of trait-based approaches to explore the effect of human disturbances on marine copepod assemblages in marine ecosystems.

Copepod Assemblage Dynamics in a Snowmelt-Dominated Estuary

What limits secondary production in the estuaries of snowmelt-dominated basins? Due to substantial differences in their annual hydrographs, zooplankton dynamics in these estuaries are expected to differ from better-studied pluvial systems. We hypothesized that water residence time limited zooplankton production in the undammed, snowmelt-dominated estuary of the Fraser River, Canada. We sampled zooplankton and associated environmental variables bi-weekly to monthly in slough and channel areas of the estuary over a 33-month period. Annual mean copepod abundance at channel stations was low (2005 ± 238 ind. m−3) in comparison to other studied estuaries, with minima occurring during spring, concurrent with the freshet. Higher abundances (11,905 ± 3606 ind. m−3) observed at slough stations were attributed to estuarine copepods. Differences in abundance and species composition between slough and channel areas, and the coincidence of seasonal minima with the freshet, suggest that the low water residence time of this system limits zooplankton density and production. Heavy channelization of the Fraser River Estuary has further reduced water residence time in the estuary, likely affecting prey availability to fish and invertebrate predators. Given that peak river discharge in snowmelt-dominated basins occurs during the relatively short spring-summer growing season, the impacts of channelization on zooplankton production in the estuaries of snowmelt-dominated basins may be greater than in river-dominated estuaries subjected to different flow regimes.

Oceanographic influence on coastal zooplankton assemblages at three IMOS National Reference Stations in Western Australia

Knowledge about the coastal zooplankton of the south-eastern Indian Ocean is limited, with few studies having compared assemblages across the latitudinal range of the western seaboard of Australia. The dominant oceanographic feature in this region is the Leeuwin Current, which transports warm, lower-salinity, tropical waters southward along the shelf-edge. This study examined data collected by Australia’s Integrated Marine Observing System at three coastal National Reference Stations located at 22°S 114°E, 32°S 115°E and 34°S 122°E. Spatial and temporal patterns in zooplankton abundance, composition and diversity were investigated, and differences in assemblage structure, particularly with respect to copepods, were related to oceanographic conditions. Clear dissimilarities among copepod assemblages were observed, becoming weaker in winter owing to enhanced connectivity of species driven by alongshore and cross-shelf transport in the Leeuwin Current. Both physical and biogeochemical factors were significant in structuring copepod assemblages, with seawater density, incorporating temperature and salinity, exerting the greatest influence. The results suggest that both broad-scale latitudinal gradients and mesoscale events contribute to variation in zooplankton assemblages in these waters. This study provides the first detailed comparison of zooplankton assemblages among the north-west, south-west and southern coastal waters of Western Australia, and enhances understanding of the processes influencing zooplankton distribution and structure.

Potential of A Trait-Based Approach in the Characterization of An N-Contaminated Alluvial Aquifer

Groundwater communities residing in contaminated aquifers have been investigated mainly through taxonomy-based approaches (i.e., analyzing taxonomic richness and abundances) while ecological traits have been rarely considered. The aim of this study was to assess whether a trait analysis adds value to the traditional taxonomy-based biomonitoring in N-contaminated aquifers. To this end, we monitored 40 bores in the Vomano alluvial aquifer (VO_GWB, Italy) for two years. The aquifer is a nitrate vulnerable zone according to the Water Framework Directive. The traditional taxonomy-based approach revealed an unexpectedly high biodiversity (38 taxa and 5725 individuals), dominated by crustaceans, comparable to that of other unpolluted alluvial aquifers worldwide. This result is in contrast with previous studies and calls into question the sensitivity of stygobiotic species to N-compounds. The trait analysis provided an added value to the study, unveiling signs of impairments of the groundwater community such as low juveniles-to-adults and males-to-females ratios and a crossover of biomasses and abundances curves suggestive of an intermediate alteration of the copepod assemblages.