Seven 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.

The community composition of zooplankton with an emphasis on copepods was assessed in the frontal zones of the Indian sector of the Southern Ocean (SO) during summer 2013. Copepods were the dominant group in both the bongo net and multiple plankton sampler across the entire region. High zooplankton abundance was recorded along each transect in the Polar Front (PF). Community structure in this front was dominated by common taxa, including Ctenocalanus citer, Clausocalanus spp., Calanoides acutus, Calanus propinquus, Calanus australis and Rhincalanus gigas, which together accounted for > 62% of the total abundance. Calocalanus spp., Neocalanus tonsus and C. propinquus were indicator species in the Sub-Tropical Front (STF), Sub-Antarctic Front and PF, respectively. A strong contrast in population structure and biovolume was observed between then PF and the STF. The community structure of smaller copepods was associated with the high-temperature region, whereas communities of larger copepods were associated with the low-temperature region. Thus, it seems probable that physical and biological characteristics of the SO frontal regions are controlling the abundance and distribution of zooplankton community structure by restricting some species to the warmer stratified zones and some species to the well-mixed zone.

Fatty acids (FA) analysis is a well-established approach for qualitatively studying feeding preferences. In the Argentinean Continental Shelf, Argentine hake Merluccius hubbsi supports the major demersal finfish fishery. The Patagonian stock of the species spawns and nurses in austral summer in the north Patagonian shelf (NPS, 43°–45°30′S). Previous studies about larval feeding in the NPS have solely focused on gut contents, indicating selectivity upon calanoid copepods. Hence, our main objective was to apply the FA approach to confirm and/or broaden M. hubbsi larval food selection. Hake larvae and copepod FA profiles overlapped significantly, dominated by the saturated FA 16:0, the monounsaturated FAs 18:1n-9 and 22:1n-9, and the polyunsaturated FA 22:6n-3. Moreover, identified markers typical of bacteria (15:0, 17:0) and dinoflagellates (18:4n-3, 22:6n-3) suggest a microbial input at the base of the NPS food web, with the latter probably acting as an intermediate step between bacteria and hake larvae. Possible direct predation upon protozoans by larvae is postulated, broadening the known trophic spectrum derived from classical diet analyses. The FA approach allowed us to clarify feeding preferences in the NPS, with data being relevant in the context of hake recruitment studies.

Removal of parasite free-living stages by predators has previously been suggested an important factor controlling parasite transmission in aquatic habitats. Experimental studies of zooplankton predation on macroparasite larvae are, however, scarce. We tested whether trematode cercariae, which are often numerous in shallow waters, are suitable prey for syntopic zooplankters. Feeding rates and survival of freshwater cyclopoids (Megacyclops viridis, Macrocyclops distinctus), calanoids (Arctodiaptomus paulseni), cladocerans (Sida crystallina) and rotifers Asplanchna spp., fed with cercariae of Diplostomum pseudospathaceum, a common fish trematode, were studied. In additional long-term experiments, we studied reproduction of cyclopoids fed with cercariae. All tested zooplankton species consumed cercariae. The highest feeding rates were observed for cyclopoids (33 ± 12 cercariae ind−1 h−1), which actively reproduced (up to one egg clutch day−1) when fed ad libitum with cercariae. Their reproductive characteristics did not change significantly with time, indicating that cercariae supported cyclopoids’ dietary needs. Mortality of rotifers and cladocerans was high (25–28% individuals) when exposed to cercariae in contrast to cyclopoids and calanoids (<2%). Cercariae clogged the filtration apparatus of cladocerans and caused internal injuries in predatory rotifers, which ingested cercariae. Observed trophic links between common freshwater zooplankters and cercariae may significantly influence food webs and parasite transmission in lentic ecosystems.

To our knowledge, there is no report on microRNA (miRNA) expression and their target analysis in relation to the type of the first feed and its effect on the further growth of fish. Atlantic cod (Gadus morhua) larvae have better growth and development performance when fed natural zooplankton as a start-feed, as compared with those fed typical aquaculture start-feeds. In our experiment, two groups of Atlantic cod larvae were fed reference feed (zooplankton, mostly copepods, filtered from a seawater pond) v. aquaculture feeds: enriched rotifers (Brachionus sp.) and later brine shrimp (Artemia salina). We examined the miRNA expressions of six defined developmental stages as determined and standardised by body length from first feeding for both diet groups. We found eight miRNA (miR-9, miR-19a, miR-130b, miR-146, miR-181a, miR-192, miR-206 and miR-11240) differentially expressed between the two feeding groups in at least one developmental stage. We verified the next-generation sequencing data using real-time RT-PCR. We found 397 putative targets (mRNA) to the differentially expressed miRNA; eighteen of these mRNA showed differential expression in at least one stage. The patterns of differentially expressed miRNA and their putative target mRNA were mostly inverse, but sometimes also concurrent. The predicted miRNA targets were involved in different pathways, including metabolic, phototransduction and signalling pathways. The results of this study provide new nutrigenomic information on the potential role of miRNA in mediating nutritional effects on growth during the start-feeding period in fish larvae.

The diet and feeding pattern of scyphomedusa Stomolophus meleagris (Rhizostomeae) was studied, by comparing stomach samples from different developmental stages and environmental zooplankton with the aim to determine diet composition, trophic niche breadth, selectivity and feeding overlap of this edible jellyfish species. Samplings were performed during April and December 2010 and in January 2011, in the coastal lagoon Las Guásimas (27°49′–27°54′N 110°40′–110°35′W), central Gulf of California, which consisted of zooplankton tows and jellyfish collections for stomach content. More than 39 prey items were identified in the gut contents (N = 69), from which eight taxa formed over 90% of the total. Fish eggs were considered main prey (58.6%), copepods (10.8%), veliger larvae of gastropod (13.0%) and bivalve (12.7%) were secondary prey while cirriped and decapod larvae were incidental prey (<3%). However, these proportions varied significantly between small, medium and large size classes of medusa as well as number and type of prey increasing as a function of medusa size. Values of Levin's index confirmed S. meleagris is a specialist predator and Pearre's index showed positive selection of fish eggs, gastropods, bivalves and cirripeds while selectivity was negative for copepods and appendicularians. The relative timing of these changes suggests that ontogenetic processes are closely related with shift in the diet, which indicates increasing predation pressure during development of the medusoid stage of this species, thus emphasizing their ecological importance in coastal ecosystems.

A twelve-month investigation was undertaken on how copepod community structure varied in relation to environmental factors in the Coleroon estuary, south-east India. Sampling was monthly, from Station 1 in the sea to Station 4 in the Vettar backwaters. Canonical correspondence analysis (CCA) was applied to elucidate the environmental factors affecting the copepod community. A total of 104 copepod species in 38 genera and 26 families were recorded, with the Calanoids, Acartia erythraea and Oithona brevicornis being the most dominant. At all four stations, both these species loaded near the intercept of CCA axes 1 and 2, perhaps reflecting that they were autochthonous. Most species occurred in distinct seasonal patterns. Abundances ranged from 13 × 103 to 215 × 103 (ind. m−3). Coleroon waters showed high diversity (bits/ind.), from 5.29 at Station 3 to 4.97 at Station 4. Abundance correlated positively with temperature and salinity and negatively with rainfall, dissolved oxygen concentration (DO) and pH. Species diversity correlated strongly with abundance (P < 0.01). Abundance and diversity were highest during the summer, and both correlated positively with salinity. Temperatures (air and water), salinity, pH and DO varied in the ranges 26–36°C, 25–34.2°C, 9–38, 7.0–8.7 and 3.0–6.8 ml l-1, respectively. Nitrate, nitrite, phosphate and silicate (µM) varied in the ranges: 4.7–64.5, 0.4–14.1, 0.2–12.9 and 9.3–148, respectively.

The distribution of subterranean copepods may reflect the persistence of cave assemblages in relation to the environmental health of the overlying landscape. Areas supporting groundwater fauna were established by modelling the persistence of seven copepod species using a geographical information system (GIS). Environmental drivers were found to influence subterranean copepod distribution in the caves of the Romanian Carpathians. Habitat-based modelling, using ordinary least squares regression and geographically-weighted regression to identify the significant predictors explaining copepod habitat suitability, predicted suitable areas for the selected taxa. The most constant predictor was land cover, a measure of human impact and climate change, followed by precipitation and altitude. The model performed well for the majority of analysed taxa, and the areas predicted as suitable for narrowly distributed taxa overlapped with observed distributions. GIS facilitated the prediction of suitable habitat, and also enabled spatial autocorrelation to be tested. The results of this study demonstrate the importance of sustainable management of the terrestrial surface in limestone areas in conserving copepod biodiversity.

The paramyxean parasite Marteilia refringens infects several bivalve species including European flat oysters Ostrea edulis and Mediterranean mussels Mytilus galloprovincialis. Sequence polymorphism allowed definition of three parasite types ‘M’, ‘O’ and ‘C’ preferably detected in oysters, mussels and cockles respectively. Transmission of the infection from infected bivalves to copepods Paracartia grani could be experimentally achieved but assays from copepods to bivalves failed. In order to contribute to the elucidation of the M. refringens life cycle, the dynamics of the infection was investigated in O. edulis, M. galloprovincialis and zooplankton over one year in Diana lagoon, Corsica (France). Flat oysters appeared non-infected while mussels were infected part of the year, showing highest prevalence in summertime. The parasite was detected by PCR in zooplankton particularly after the peak of prevalence in mussels. Several zooplanktonic groups including copepods, Cladocera, Appendicularia, Chaetognatha and Polychaeta appeared PCR positive. However, only the copepod species Paracartia latisetosa showed positive signal by in situ hybridization. Small parasite cells were observed in gonadal tissues of female copepods demonstrating for the first time that a copepod species other than P. grani can be infected with M. refringens. Molecular characterization of the parasite infecting mussels and zooplankton allowed the distinguishing of three Marteilia types in the lagoon.

In order to determine the influence of lentic habitats and macrophyte stands on the plankton development and seston flux, an investigation of zooplankton was carried out in the karst Jankovac flow-through system (Papuk Nature Park, Croatia). The system was characterized by low abundance (1–116 ind.L−1) and high diversity of identified zooplankton. Eighty-six taxa were recorded, comprising 57 rotifers, 15 cladocerans, 8 copepods and 6 members of other groups of organisms. The spatial oscillations of environmental parameters and biocoenosis assemblage revealed statistically significant differences between lotic and lentic habitats, as well as between vegetated and non-vegetated stations. These differences mainly respond to higher concentration of food resources and zooplankton/zooseston abundance and biomass in lentic, especially vegetated, habitats. This is also proved by results of principal component analysis (PCA), which suggested that the main drivers of development of the planktonic community were the food resources and the avoidance of flow velocity. Accordingly, shoreline areas with submerged macrophyte stands of Hippuris vulgaris L. were the most productive parts, represented by highest zooplankton abundance, biomass and biodiversity. Flow velocity significantly affected crustaceans assemblage, so that higher abundances of the larger cladocerans and copepods were achieved in vegetated stations with low flow velocity, while rotifers showed to be rheotolerance organisms. On the other hand, the longitudinal discontinuum of the stream channel by two man-made reservoirs could offer new habitats to enrich seston with organic particles and bioseston. The results of our study pronounce the need for further monitoring of this hydrosystem, especially considering biodiversity and microhabitats conservation.

Baited traps with a 5 mm diameter opening were deployed 9 cm off the seabed in the Cape d'Aguilar Marine Reserve, Hong Kong. In contrast to analogous studies from boreal waters, lysianassoids accounted for 0.5% of the total number of trapped hyperbenthos. Species of Tisbe (Copepoda: Tisbidae), Ceradocus (Gammaridea: Melitidae), Nebalia (Leptostraca: Nebaliacea), unidentified benthic ostracods, Neanthes cricognatha (Polychaeta: Nereidae) and a species of Lepidepecreum (Amphipoda: Lysianassoidea) were caught in a decreasing order of numerical importance. A spatial segregation of trapped fauna was identified between the reserve's shallow Lobster Bay (<–2 m Chart Datum (CD)) and deeper-waters (between –6 and–17 m CD) outside it. Ceradocus sp. monopolized the trapped fauna in the former area, while the other species were caught almost exclusively from the latter. Insignificant Ceradocus sp. catch differences between baited and control traps suggested that they functioned only as ‘habitat traps’ for this species. Almost all other organisms attracted to the bait were hyperbenthic scavengers. Their absence from the shallows might be due to the coarser and lower organic contents of the sediments, also related to faster flow rates here. Finally, we confirm that in subtropical Hong Kong, lysianassid amphipods are not as significant hyperbenthic scavengers as they are in boreal waters.

Objective. Unravelling the determinants of parasite life-history traits in natural settings is complex. Here, we deciphered the relationships between biotic, abiotic factors and the variation in 4 life-history traits (body size, egg presence, egg number and egg size) in the fish ectoparasite Tracheliastes polycolpus. We then determined the factors affecting the strength of the trade-off between egg number and egg size. Methods. To do so, we used 4-level (parasite, microhabitat, host and environment) hierarchical models coupled to a field database. Results. Variation in life-history traits was mostly due to individual characteristics measured at the parasite level. At the microhabitat level (fins of fish hosts), parasite number was positively related to body size, egg presence and egg number. Higher parasite number on fins was positively associated with individual parasite fitness. At the host level, host body size was positively related to the individual fitness of the parasite; parasites were bigger and more fecund on bigger hosts. In contrast, factors measured at the environmental level had a weak influence on life-history traits. Finally, a site-dependent trade-off between egg number and egg size existed in this population. Conclusion. Our study illustrates the importance of considering parasite life-history traits in a hierarchical framework to decipher complex links between biotic, abiotic factors and parasite life-history traits.

A new species of calanoid copepod, Centropages uedai sp. nov., is described from the neritic waters of the northern Red Sea. This species is characterized by: (1) symmetry of a globular female genital double-somite that is ornamented with an anterior irregular group of spinules as well as transverse and dorsolateral rows of spinules on each side; (2) second exopodal segment of female leg 5 bearing a strong trough medial process serrated along the distal 4/5 of its posterior margin; (3) second exopodal segment of male right leg 5 serrated laterally along distal 1/5 of its medial process; (4) third exopodal segment of male right leg 5 with medial seta bifurcated at its tip and with hyaline ridge on both sides; and (5) second exopodal segment of male right leg 4 asymmetrical with undulating, thicker and longer lateral spine than left leg. The new species does not belong to any known species groups of the genus.

Fatty acids composition of two marine copepods, Acartia tonsa and Centropages brachiatus, and lipid profiles of natural food assemblages were studied during the austral summer 2006 at three upwelling sites in the coastal upwelling zone off Chile, along with oceanographic conditions. Fatty acids of food supply were assessed for the picoplankton, nanoplankton and microplankton size fractions. There were marked differences in upwelling conditions among locations, as well as in their food supply in terms of quantity and quality. Differences in fatty acid composition were also found, both among food assemblages and between copepod species. Essential polyunsaturated fatty acids (PUFA; linoleic acid) and monounsaturated fatty acids (MUFA; oleic acid) dominated the picoplankton and nanoplankton size fractions of food, and they were highly represented in both species of copepods, indicating these size fractions were the major contributors to their diet. These fatty acids can thus be considered as useful trophic markers for copepods. Variation in lipid profiles between species depended on sampling sites, whereas differences in lipid composition among sampling sites were attributed to distinct upwelling conditions, which drive the changes in food quality, such that trophic response is highly dependent on food offer. Variation in fatty acids compositions of copepods may thus act as an indicator of upwelling variability. Our findings suggest that lipid transfer from primary producers to primary consumers can have a crucial role for carbon cycling in the marine food web, and that picoplankton and nanoplankton fractions are the key items of copepod diet in this upwelling system.

The summer spatial distribution of the phytoplankton community in the Gulf of Gabès (Tunisia, eastern Mediterranean Sea), together with environmental factors, were studied during a preliminary study conducted in July 2005 aboard the RV ‘Hannibal’. The phytoplankton community, which showed a decrease in concentration along a coastal–open sea gradient, was dominated by Dictyochophyceae (41%) followed by Dinophyceae (25%), Bacillariophyceae (16%), Cyanobacteriae (17%) and Euglenophyceae (1%). The phytoplankton found along the coast was dominated by opportunistic species (e.g. Dictyocha fibula) associated with high nutrient availability. In the open sea, phytoplankton development seemed influenced by Atlantic hydrodynamics. In addition, the Gulf of Gabès is characterized by an oligotrophic status with a summer stratification that impacted on species composition especially in off-shore areas. The coupling of phytoplankton dynamics to nutrients, ciliates and copepods showed the potential role played by ciliates not only as predators of phytoplankton but also as prey for filter-feeding copepods accounting for the increased fisheries productivity of the Gulf of Gabès.

We studied the summer spatial distribution of the copepod community in both the neritic and oceanic areas of the Gulf of Gabès (Tunisia, eastern Mediterranean Sea) coupled with environmental factors. Copepods were the most abundant zooplankton throughout the sampling period, contributing 78% of the total zooplankton. A total of 14 copepod families were identified in all stations, with an overwhelming abundance of Acartiidae and Oithonidae (39.05 and 39.09% of total abundance, respectively). Abundance of Acartia clausi and chlorophyll-a concentrations were negatively correlated with salinity, suggesting that this species probably escaped the high coastal salinity (38 psu). Significant correlation determined between A. clausi and tintinnids at 50 m isobaths indicates that these planktonic ciliates probably served as a substantial food link towards higher trophic levels of this area. Conversely, Oithona nana which was well adapted to high chlorophyll-a concentrations and high salinity along the coast, showed significant correlations with Dictyochophyceae, Dinophyceae, Bacillariophyceae and Euglenophyceae, suggesting that this small copepod was capable of feeding on a wide selection of phytoplankton preys.

In an environment seriously impaired by human interference (draining the reservoir), ecological relationships in a community of copepods and their impact on the transmission of the tapeworm Proteocephalus neglectus La Rue. 1911 were studied. The impairment of the environment resulted in changes in the species composition of the copepod community and in the increased diversity of the copepod species, as well as in a multiple inversion of the dominant and subdominant relationships of the two most numerous copepod species (Cyclops vicinus and Eudiaptomus zachariasi). The structure of the developmental stages of the copepod community, the seasonal dynamics of the number of copepods and the abundance of P. neglectus procercoids have changed. The predominant species in the copepod community and the most susceptible intermediate host of P. neglectus (C. vicinus) was not infected. The infection of copepods decreased by 95% and that of the definitive hosts (Oncorhynchus mykiss) by 97·5% compared with the index values recorded in the previous year.

Previously undescribed cystophorous cercariae which develop in sporocyst germinal sacs in the tectibranch opisthobranch Philine denticulata (Adams) are shown to be cercariae of Hemiurus luehei Odhner, 1905 (Hemiuridae), a common stomach parasite of clupeid and salmonid fishes off the Atlantic coast of Europe, in the Baltic and the Mediterranean Sea. The free-swimming cercariae are seized by calanoid copepods. Temora longicornis (Müller) and Acartia tonsa Dana acted as suitable experimental intermediate hosts. Pressure by the copepod mouth appendages causes delivery tube eversion and the injection of the cercarcial body into the haemocoel. Sagitta sp. was found naturally infected with a metacercaria of H. luehei. The cystophorous cercaria and metacercaria are described using light and scanning electron microscopy. Adults from herring were examined under the stereoscan electron microscope.

We studied the prevalence and intensity of the parasitic copepod Myicola ostreae in 2 closely related oysters Crassostrea angulata and C. gigas and their F1 hybrids. The effects on host and host reaction were also analysed to better understand host-parasite relationships between copepods and bivalve molluscs. Full reciprocal crosses were carried out between C. angulata and C. gigas and the progenies were reared in the wild in Ria Formosa Lagoon (Portugal), allowing natural infestation by M. ostreae. Prevalence and intensity were significantly higher in C. angulata than in C. gigas. The parasite level of F1 hybrids was similar to C. angulata and significantly higher than in C. gigas. The results of our study support a hypothesis of dominantly inherited susceptibility to M. ostreae infestation. Moreover, copepods were observed on the gill surface of C. gigas engulfed by a capsule-like structure. Histological analyses revealed that the copepods were surrounded by a massive agglomerate of haemocyte-like cells encircled by a thin layer of fibroblast-like cells. This encapsulation response was not observed in C. angulata or in F1 hybrids. These results suggest that the differential susceptibility to M. ostreae between C. angulata and C. gigas may be ascribed to host defence factors.

We investigated crustacean zooplankton communities and their relationships to environmental factors in 13 lakes of Yunnan-Guizhou plateau to determine whether there is a consistent relationship between trophic indicators and crustacean zooplankton biomass or size structure. The lakes showed a wide range of trophic status, with total phosphorus (TP) ranging from 0.013 to 0.268 mg.L−1, and chlorophyll a from 0.9 to 76.26 μg.L−1. Continuous stocking with exotic planktivorous fish had taken place on a wide scale in these plateau lakes. About 36 species of Crustacea were found, of which Cladocera were represented by 20 taxa (12 genera), and Copepoda by 16 taxa (13 genera). Canonical correspondence analysis partitioned these species into two clusters. Physicochemical features and food-webs of different lakes seemed to be the key factors determining zooplankton species composition and distribution patterns. Between the 13 lakes, there was no significant relationship between cladocerans and chlorophyll a suggesting phytoplankton biomass was little controlled by macrozooplankton. The positive correlation between chlorophyll a and copepods suggested the high copepods biomass or size structure caused by the invasion of exotic planktivorous fish had a negative effect on water quality.