Copepod Assemblages Research Articles

Zooplankton Abundance and Diversity in the Tropical and Subtropical Ocean

The abundance and composition of zooplankton down to 3000 m depth was studied in the subtropical and tropical latitudes across the Atlantic, Pacific and Indian Oceans (35 °N–40 °S). Samples were collected from December 2010 to June 2011 during the Malaspina Circumnavigation Expedition. Usually, low abundances were observed with the highest values found in the North Pacific Ocean, Benguela, and off Mauritania, and the lowest in the South Pacific Ocean. No significant differences in abundance and zooplankton composition were found among oceans, with depth being consistently the most important factor affecting their distribution. Each depth strata were inhabited by distinct copepod assemblages, which significantly differed among the strata. The contribution of copepods to the zooplankton community increased with the depth although, as expected, their abundance strongly decreased. Among the copepods, 265 species were identified but 85% were rare and contributed less than 1% in abundance. Clausocalanus furcatus and Nannocalanus minor dominated the epipelagic strata. Pleuromamma abdominalis and Lucicutia clausi were of importance in the mesopelagic layer, and Pareucalanus, Triconia, Conaea and Metridia brevicauda in the bathypelagic layer. Our results provide a global-scale assessment of copepod biodiversity and distribution, providing a contemporary benchmark to follow future ocean changes at low latitudes.

Annual and seasonal changes in the assemblage of planktonic copepods and appendicularians in Funka Bay before and after intrusion of Coastal Oyashio Water

Annual and seasonal changes in the abundance and the assemblage of planktonic copepods and appendicularians were clarified in Funka Bay. Zooplankton samples were obtained by vertical hauls with a NORPAC net (0.10-mm mesh aperture) from December to May over a 4-year period (2014–2017). Temporal fluctuations of mean abundance of copepods were small from December 2013 to May 2014 under the low water temperature condition (maximum 1.55 times difference between adjacent survey periods), while those were large in other 3 years (1.60–1.93 times). Maximum mean abundance of appendicularians in 2014 (6.0 × 104 ind./m2) was lower than those in 2015–2017 (8.6 × 104–1.4 × 105 ind./m2). Less saline (≤ 33.3) and cold Coastal Oyashio Water (COW) intruded in early February 2014, late February 2015, and late March 2016 and 2017. Phytoplankton blooms occurred in March of all 4 years. Copepods and appendicularians increased nearer periods of phytoplankton bloom than after COW intrusion. In the results of canonical correspondence analysis, the assemblage of copepods and appendicularians gradually changed from small-sized and warm-water species to large-sized and cold-water ones. Northwesterly wind speed had an effect equal to COW intrusion (82% of COW intrusion) to the change in taxonomic compositions of copepods and appendicularians.

Changes in Copepod Community Between Two Contrasting Samplings in a Highly Polluted Mediterranean Coastal Zone (Sfax Bay, Tunisia)

Changes of taxonomic composition, morphology (total length) and reproductive mode of copepod assemblages between the cold and warm periods were studied in the Southern coast of Sfax, in relation with environmental factors and pollution degree (heavy metal concentration). Salinity, temperature and heavy metal concentration seem to be the most important factors influencing the total length during both sampling periods. A total of 23 different copepod species were identified during the survey period. The copepod abundance was higher in cold (74%; 9.78 ± 10.04 A— 103 ind m-3) than in warm (67%; 7.11 ± 8.81 A— 103 ind m-3) periods. This result could be attributed to an increase of temperature and salinity in August, which favors the development of smaller copepod species. During the cold season, larger adult broadcaster of calanoids species (total length between 0.98 and 1.22 mm) such as Acartia (Acartia) danae (Giesbrecht) (Tl = 1.22 mm), Paracartia grani (Sars) (Tl = 1.12 mm) and Paracartia latisetosa (Krichagin) (Tl = 1.06 mm) were associated to low temperature and salinity. During the warm period, smaller egg-carrying species of harpacticoids (total length between 0.18 and 0.3 mm) such as Harpacticus littoralis (Sars), Tisbe furcata (Baird) and Tigriopus sp. (Norman) were associated with high temperature and heavy metal pollution. H. littoralis displayed a very high abundance of ovigerous females (Nfo = 12.8 A— 103 ind m-3, representing 87.2% of total number of females) with high number of eggs per sac (E = 26 ± 2 egg sac-1).

Vertical and geographic distribution of copepod communities at late summer in the Amerasian Basin, Arctic Ocean

Zooplankton plays a pivotal role in linking primary production to higher level consumers in the food webs of marine ecosystems. The distribution of zooplankton is affected by general water conditions, monsoons, currents, and spatial and temporal factors. In the Arctic Ocean, the sea surface is naturally covered with ice. Under ice, water masses interplay to create complex environments that facilitate the transport and distribution of zooplankton, thus altering community structures at geospatial and vertical scales. The present study investigated the species composition and copepod community structures by using geospatial and multiple depth scales, and using multivariate analyses to evaluate the relation of sampling stations and layers. During July–August 2010, zooplankton samples were collected and the temperature and salinity of seawater measured from three stations in the Canada Basin and two stations in the Makarov Basin of the Arctic Ocean (maximum distance of approximately 1400 km). A total of 55 copepod species (including 25 species that were solely identified to the generic level) and 7 taxa of copepodites, altogether belonging to 28 genera, 11 families, and 2 orders were identified, and significant differences were detected in copepod community structures among sampling strata and at geospatial scales. Numerically, Calanus hyperboreus, Calanus copepodite, Calanoida copepodite, Calanus glacialis, and Metridia longa were the most dominant species and taxa. At the local scale, copepod compositions responded differently at each of the sampling stations. At the geospatial scale, the distance between stations MS03 and ICE explained variations in the pattern of dominant species and of copepod community richness. Our study demonstrated varied spatial distribution which indicates that (1) the abundance of copepods at 0–200 m was significantly higher than at other strata, (2) vertical strata affected the distribution of copepod communities, and (3) the interplay of North Pacific and Atlantic waters shaping the copepod assemblage structure at geospatial scales in the Arctic Ocean. The results of our research provide base data for Arctic zooplankton biodiversity and biogeographic distribution.

Epipelagic copepod assemblage in the Gerlache Strait (Antarctica) during the 2015 austral summer

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

Key Drivers for Copepod Assemblages in a Eutrophic Coastal Brackish Lake

The copepod assemblages and abiotic parameters were investigated at 11 stations in a large coastal lake (Lake Manzalah, Nile Delta) from 2009–2010 in order to verify any impacts of eutrophication and salinity on the copepod species composition. The environmental conditions and the copepod assemblages appeared to have changed in comparison with previous studies, possibly because of increasing eutrophication and invasions of non-indigenous species (NIS). The aim of the present study was the identification of species which can be used as ecological indicators of high trophic status. Among the nine copepod species of Lake Manzalah, Acartia tonsa, Mesocyclops ogunnus, and Apocyclops panamensis were reported for the first time. Acartia tonsa, a well-known NIS for the Mediterranean, numerically dominated the copepod assemblages in some portions of the lake. The distribution of Acanthocyclops trajani and Thermocyclops consimilis was insensible to eutrophication because they can stand high levels of nutrients and hypoxia. Compared with previous reports, the copepod assemblage of Lake Manzalah was richer in species. The invasions of NIS, in addition to the heterogeneous progress of eutrophication in the lake, created an environmental mosaic with many species in total, but with single areas suitable for only a small number of them.

Spatial structuring of zooplankton communities through partitioning of habitat and resources in the Bay of Bengal during spring intermonsoon

Despite advances in oceanographic investigations in the Indian Ocean, zooplankton ecology is still poorly known from the open waters of the Bay of Bengal. In order to understand the vertical and horizontal distribution of zooplankton in the Bay of Bengal during spring intermonsoon, stratified sampling was conducted using a multiple plankton net. We found that higher zooplankton biomass was often associated with mesoscale cold-core eddies. The biomass in the mixed layer was less in the central bay and the near absence of organisms beneath this layer was attributed to the very low dissolved oxygen levels, including suboxia in the northern extent. The copepod diversity was severely reduced here and only a few species specialized to thrive in minimum oxygen concentrations were found in this zone. However, Pleuromamma indica is another copepod that seems to have adapted to the oxygen minimum zone, as seen from its increased numbers and its strong vertical migrating ability to cross the low oxygen barrier. Highly diverse copepod assemblages comprising 129 identified species were found to be vertically structured, mostly through partitioning of habitat and food resources.

Diel patterns of zooplankton community structure in nearshore waters of different substrates off Tinggi and Sibu Islands, Malaysia, with special reference to copepods

The relationship between zooplankton community structure and selected environmental conditions was investigated by simultaneous two-day consecutive sampling in the waters overlying coral and sand sites off Sibu Island and a seagrass site off Tinggi Island, Johor, Malaysia. A total of 129 taxa were identified, 60 non-copepod taxa and 69 copepod species in all samples. Uni- and multi-variate analyses reveal distinct coral, sand, seagrass copepod assemblages with indicator copepod species and attributes of their size fractions. Small fraction (100–335 µm) samples contained greatest number of individuals, few rare species and were densest at onshore depths, and the opposite for large fraction (>335 µm) samples but were densest at nighttime and most species rich in the coral site at night. Higher species diversity at offshore stations is due likely to ecotonal effects of overlapping oceanic and nearshore communities. This study demonstrates the usefulness of uni- and multi-variate analyses in identifying patterns in zooplankton community structure in representative shallow tropical habitats, and the need for accurate zooplankton taxonomy, nighttime and daytime and onshore and offshore sampling, and size fractionation of samples.

Chemoautotrophic food availability influences copepod assemblage composition at deep hydrothermal vent sites within sea knoll calderas in the northwestern Pacific

Chemoautotrophic food availability influences copepod assemblage composition at deep hydrothermal vent sites within sea knoll calderas in the northwestern Pacific

Do the presence and physiological stage of algal mats affect the meiobenthic community in a tropical estuary?

The effects of compacted algal mats growing attached to sediments on the abundance and community structure of intertidal sediment meiofauna and harpacticoid copepod assemblages were evaluated on a tropical estuarine mudflat. Differences in fauna based on the presence of algae (within vs. outside the algal patches) and the physiological stages of the algae (live vs. decomposing algal patches) were compared. In general, lower densities occurred within algal patches for most meiofaunal groups, except for harpacticoids, which showed an increase in number in the live algal patches (LAP). Non-metric MDS analysis clearly distinguished both meiofauna community and harpacticoid assemblage in relation to the presence of algae and the physiological stage. Organic matter, carbohydrates, proteins and photosynthetic pigments were higher within algal patches and highly correlated with meiofauna variables. One species of harpacticoid (Cletocamptus sp.1) dominated the LAP samples and thus reduced species richness and diversity of harpacticoids in these samples. The species Robertsonia mourei occurred exclusively in decomposing algal patches (DAP) and probably is an opportunistic species within the DAP samples. Strong differences regarding live and decomposing algae samples highlighted the importance of physiological stage in understanding meiofaunal responses to algal mats.

Assessing environmental effects of the bay scallop Argopecten irradians culture in China: Using abiotic and biotic indicators

This study aims to identify the effect of biodeposition from a non-indigenous scallop (bay scallop) farm on sediment organisms in a semi-closed bay in Bohai Sea, China. Sediment characteristics, the meifauna community, and harpacticoid copepod assemblages were investigated before aquaculture and during the high biodeposition period at three scallop farms: Sandy-Shallow (SS), Muddy Shallow (MS), and Muddy Deep (MD), and their correspondent control sites. Total organic carbon and total nitrogen did not accumulate under the scallop farms. Although sedimentary bioavailable organic matter (biopolycarbon and Chlorophyll a) can accumulate under the scallop farms, all sediment characteristics were within the range of a meso-oligotrophic state. Bioindicators showed a location-specific response. Only in Farm SS the meiofauna community differed from the control site as there was a larger proportion of nematodes. The density and diversity of harpacticoid copepods were enhanced by scallop farms in MD, while a slight reduction of copepod density was found at SS due to the scallop farming. The overall results suggested that this non-indigenous scallop farming had minimal detrimental effect on the benthic environment in Laizhou Bay. Also, the bioavailable organic matter, the entire meiofauna community and harpacticoid copepod assemblages were useful tools for assessing of the potential environmental impact of shellfish farming

Mesozooplankton distribution, especially copepods, according to water masses dynamics in the upper layer of the Southwestern Atlantic shelf (26°S to 29°S)

Zooplankton in shelf waters is dominated by a highly diverse assemblage of copepods, followed by a variety of organisms sorted according to the environmental conditions. Epipelagic copepod, chaetognath and cladoceran species assemblages in the upper 100 m layer, together with mesozooplankton major groups were characterized in relation to dynamics of the water masses in the subtropical domain of the Brazilian shelf. Water samples for nutrients and chlorophyll, measurements of temperature, salinity and fluorescence (Rosette/CTD) and zooplankton samples were collected in four transects (26°S to 29°S), ~ 250 km long, across the shelf, during early summer. Intrusions of the cold South Atlantic Central Water (~ 15 m) was evidenced by the large abundance (> 3000 ind.m-3) of the small copepod Oncaea venusta, highlighting the role of small omnivorous copepods in the coastal upwelling at ~ 26°S. Low-salinity waters (< 34.5) were observed up to 120 km off the bay area at ~ 29°S, together with a high abundance of Temora turbinata. At the slope, the dominance of the Tropical Water increased the prevalence of Clausocalanus furcatus. The chaetognath Flaccisagitta enflata and the cladoceran Penilia avirostris in the inner shelf and the cladoceran Evadne spinifera in the outer shelf were also dominant species in the area. Zooplankton assemblages were related to different oceanographic scenarios, associated with coastal upwelling, coastal and estuarine plumes, shelf and slope areas. These assemblages were mainly comprised of epipelagic and tropical species; however, the recurrent presence of copepod, cladoceran and chaetognath cold-water species reinforced the transitional character of the area. In addition, there was a clear cross-shelf gradient, with an increasing contribution of large copepods, siphonophores, salps and euphausiids toward the ocean. The characteristic tropical species assemblages emphasise the dominant role of small metazoans in the pelagic food webs driven by the dynamics of the water masses. The species assemblages also established the species distribution baseline in the subtropical Brazilian shelf.

Seasonal dependence on seagrass detritus and trophic niche partitioning in four copepod eco-morphotypes

Benthic copepods dominate meiofaunal communities from marine phytodetritus, both in terms of numerical abundance and species diversity. Nevertheless, ecological factors driving copepod co-existence and population dynamics are still largely unknown. Here, we aimed to explore feeding habits of four copepod species commonly found in Mediterranean seagrass detritus accumulations, representing distinct eco-morphotypes (planktonic, phytal, epibenthic and mesopsammic). Joint use of fatty acid and stable isotope trophic markers showed that co-occurring harpacticoid copepods have diversified diets. Contrary to what was expected, microphytobenthos does not serve as their main food source. Instead, we found evidence from both techniques that major food items include heterotrophic biomass, macro-epiphytes and, depending on eco-morphology and season, of seagrass detritus-derived organic matter. Isotopic niches suggested that eco-morphotypes showed resource segregation. This segregation varies temporally, and partial overlap occurs between niches of phytal and epibenthic eco-morphotypes in some seasons. Our results highlight that, contrary to what is often assumed for meiofaunal consumers, considerable trophic diversity exists among copepod assemblages. They also indicate that, through multiple non-exclusive possible mechanisms, copepods could constitute a major link between seagrass detritus and associated biomass and higher trophic levels (namely macroinvertebrates and juvenile fish).

Anthropogenic Impacts on Coral Reef Harpacticoid Copepods

The number of studies demonstrating the susceptibility of benthic reef communities to anthropogenic impacts is growing. However, for some of the components of reef fauna, such as meiobenthic harpacticoid copepods, information is still lacking. Here, different diversity and taxonomic distinctness indexes and multivariate analyses were used to test whether the assemblage of harpacticoid copepods colonizing Artificial Substrate Units (ASUs) is an appropriate tool for the identification of reefs subjected to different levels of anthropogenic pressure. Furthermore, we also evaluate if diffused, persistent, anthropogenic impacts generate the homogenization and simplification of Harpacticoida assemblages. Six reefs were organized into two groups along the coast, depending on their proximity to very large urban centers. ASUs were used for meiofauna colonization and, for each reef, 320 Harpacticoida individuals were separated for identification at the species level. Abiotic parameters were analyzed, and significant differences were found between the two groups of reefs, with an increase in dissolved inorganic nutrients found in areas near large urban centers. Both the multivariate analyses and the indexes of diversity showed a clear separation between the reefs closer to the urban zones and those further away, as a response to the anthropogenic pressure. As hypothesized, in the impacted reef areas, there was a strong simplification and homogenization of the harpacticoid copepod assemblages. However, the results of the indexes, based on taxonomic distinctness, suggest that there was no phylogenetic signal of anthropogenic impact on coral reef harpacticoid copepods.

The spring mesozooplankton variability and its relationship with hydrobiological structure over year-to-year changes (2003–2013) in the southern Bay of Biscay (Northeast Atlantic)

Mesozooplankton can be considered the most important secondary producers in marine food webs because they hold an intermediate position between the phytoplankton assemblage and the upper trophic levels. They also are a robust indicator of climatic and hydrological conditions. We conducted an analysis of the interannual variability of the spring mesozooplankton assemblage, as sampled by the PELGAS fisheries survey in the southern part of the Bay of Biscay (Northeast Atlantic Ocean) between 2003 and 2013. We examined hydrology and trophic drivers to explain the variability. Our results revealed that the subsurface temperature, the subsurface salinity, the biomasses of subsurface pico-, nano-, and microphytoplankton, and the copepod assemblage exhibited a recurrent spatial pattern that was driven mainly by freshwater and nutrient inputs from the main rivers. The mesozooplankton assemblage was dominated by copepods (82%), composed of coastal, neritic, and oceanic copepod genera that paralleled the various hydrological fronts converging in the southern Bay of Biscay. The copepod community displayed high temporal-variability; there were three periods of abundant adult copepods throughout the southern Bay of Biscay. The copepod community was structured primarily around the drive for resource control, especially by the microphytoplankton biomass (24.3% of the total variability), and to a lesser extent by hydrological features (13.7% of the total variability).

Vertical distribution and structure of copepod (Arthropoda: Copepoda) assemblages in two different seasons down to 1,200 m in the tropical Southwestern Atlantic

The vertical distribution of copepod assemblages, ascertained from the surface down to 1,200 m, was investigated during two sampling periods (rainy and dry seasons), at four depths, in the oligotrophic waters of the southwestern Atlantic Ocean. Total density, diversity, and richness differed among sampling depths. Copepod density decreased with depth in the two sampling periods, with a maximum at 1 m and a slight decrease at 800 m. Higher diversities were observed at 250 m and 1,200 m during the rainy season and at 1 m and 1,200 m during the dry season. The maximum number of species was found at 1,200 m during the rainy season and at 1 m during the dry season. Various copepod assemblages were delimited in the water column in the two sampling periods. The deeper copepod assemblages occupied a wider range of depths. Salinity and temperature influenced the structure of copepod assemblages and reflected the hydrographic characteristics of the water masses in the region. Candaciapachydactyla (Dana, 1849), Scolecithrixdanae (Lubbock, 1856), and Agetuslimbatus (Brady, 1883) were the indicator species found at 1 m. The effects of different environmental factors on the copepod assemblages suggest that these consortia occupy distinct niches in the ocean.

Spatial variability of copepod species distribution in the eastern Arabian Sea in pre-monsoon conditions

This work examines the spatial variability among mesozooplankton abundance and copepod species diversity along the continental margin prior to the onset of southwest monsoon in the eastern Arabian Sea during the year 2011. The eastern Arabian Sea experiences seasonal hypoxia during the receding phase of monsoon that corresponds to low copepod abundance in the slope region. Collectively, fifty copepod species were identified over the continental margin where the diversity index (H′) ranged between 2.59 and 3.73. Bray–Curtis cluster analysis clustered the stations into three groups that corresponded to the continental shelf, slope and break reaches of the eastern Arabian Sea. This spatial variability among the groups is mainly ascribed to changes in the relative contributions of the prevailing species. The distinct genera of the continental shelf were Microsetella spp. and Temora turbinata; at the slope region, Oncaea spp. and at shelf-break, Pleuromamma indica. Overall, herbivorous copepods were numerically abundant at the continental shelf and carnivores at the slope. The discrepancy between the distributions of herbivorous versus carnivorous copepod assemblages may be attributed to environmental factors such as ambient water dissolved oxygen and phytoplankton biomass.

Small-scale distribution of the mesozooplankton in a tropical insular system

Abstract In the present work, spatial and seasonal fluctuations of the abundance and diversity of mesozooplankton are presented, with special attention being given to copepod assemblages from coastal area of the Fernando de Noronha Archipelago (FNA) (3°50'24''S and 32°24'48''W). Sampling was carried out during the dry and rainy seasons of two consecutive years (July and December 2013) and (June and November 2014). A total of 37 mesozooplankton taxa were recorded, being the copepods the most diversified group (15 taxa). The Subclass Copepoda dominated in both periods sampled, comprising 53% and 86% of the total abundance in the dry and rainy season respectively. The species considered abundant were: Calanopia americana, Undinula vulgaris, Oithona plumifera and Corycaeus speciosus. The rainy season favored a significant increase in the abundance of mesozooplankton and copepods. However, a low value of the Shannon-Wiener diversity index was observed in this same seasonal period. This was explained by the dominance of the species C. americana and U. vulgaris in the studied area. Spatial differences have not been verified. The copepod assemblages was composed mostly by species considered as predator-carnivours of greater importance on the pelagic trophic web, indicators of oligotrophic conditions and components of a major portion of fish food items. Thus, we suggest that a spatially homogeneous mesozooplankton community characterizes the coastal area of Fernando de Noronha Archipelago with variations related mainly to the seasonal factor.

Copepod assemblage structure (Crustacea: Copepoda) along a longitudinal environmental gradient in a tropical river-floodplain system, Brazil

Abstract Aim: In this study, we analyzed the structure of the copepod community along a longitudinal axis of the last undammed stretch of the Upper Paraná River floodplain, downstream of Porto Primavera reservoir. We hypothesized that (i) copepod assemblage would show an increase in the abundance of organisms, species richness and specific diversity with the distance from the Porto Primavera reservoir, due to the arrival of species from adjacent lakes and tributaries; (ii) copepod abundance and species richness would be higher in tributaries and adjacent lakes located at the floodplain, which show higher environmental heterogeneity and function as a species source; and (iii) spatial patterns of copepod assemblage structure are related to the environmental gradient, since copepods show a rapid response to the variation of environmental conditions. Method Sampling was performed quarterly from August 2013 to July 2014, at the subsurface of the pelagic region. Sampling sites were located along the Paraná River, in seven of its tributaries, and in eight lakes located in its floodplain. Results We identified 29 species belonging to two families: Cyclopidae (21 species) and Diaptomidae (eight species). On contrary of our first hypothesis, ANOVA results showed a significant decrease in copepod abundance in the downstream direction. Similarly, the tributaries showed higher values of ecological attributes in the upstream stretch. RDA results showed that in axis 1, the Paraná River and the lakes were positively correlated with conductivity, pH, temperature and suspended organic matter, characterized by the most abundant copepod species. The tributaries, on the other hand, were negatively correlated with turbidity, total nitrogen, total phosphorus and depth. Axis 2 showed a positive correlation of the Paraná River with conductivity and suspended organic matter, and a higher abundance of Argyrodiaptomus azevedoi, Notodiaptomus iheringi, N. henseni, N. cearensis and N. cf. spinuliferus. On the other hand, the lakes were positively correlated with temperature and pH and also with a higher abundance of Thermocyclops minutus and T. decipiens. Conclusion We highlight the importance of the maintenance of the ecological integrity of the Upper Paraná River floodplain, especially of its tributaries, in order to support the high biodiversity registered in the last undammed stretch. Furthermore, we highlight the importance of manipulation of water levels in reservoirs located upstream of this stretch, a necessary condition to maintain the hydrological connectivity between floodplain habitats and the main river.

Water quality affects the structure of copepod assemblages along the Sfax southern coast (Tunisia, southern Mediterranean Sea)

The Sfax southern coast (Gulf of Gabes, Mediterranean Sea) has been under increased anthropogenic pressure for many years. In the present study we investigated the effects of this anthropisation on the spatial distribution of copepod assemblages in relation to the physicochemical features of seawater at 20 stations sampled on 19 March 2013. Copepods represented 73% of total zooplankton abundance. Small planktonic copepods (&lt;1.45mm), including pollution-tolerant species (e.g. Oithona nana, Paracalanus parvus, Harpacticus littoralis and Tisbe battagliai), proliferated exclusively in stations of ~0.5-m depth characterised by high coastal anthropogenic inputs. The largest copepod species were dominated by Calanus helgolandicus (1.45–2.5mm) in the offshore zone in depths of ~3m. Substantial numbers of Oithona plumifera (7.5%) were found at depths between 0.5 and 3m. Copepod diversity was significantly higher in the southern zone, which is less affected by sewage, than in the northern zone, which was subjected to higher pressure (Shannon–Wiener index H′=1.5–2.5 and ≤1.5 bits individual–1). A shift in the planktonic copepod community between the two zones was linked to deterioration of water quality, with higher phosphorus levels, turbidity and chemical oxygen demand (COD) in the northern zone.