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Copepods play an important role in marine ecosystems as key prey species of important commercial fishes. However, there is very limited data for the Seto Inland Sea, especially after the late 1990s. In the present study, we described the abundance and biomass of copepods over a 3-year period in Harima-Nada, eastern Seto Inland Sea, Japan. In Harima-Nada, the dominant species were Paracalanus spp., Oithona spp., and Microsetella spp. by abundance of both nauplii and copepodites. In terms of biomass, Paracalanus spp. and Microsetella spp. dominated with Calanus sinicus instead of Oithona spp. Copepod adult assemblages based on body carbon weight were classified into three seasonal clusters. The representative species of each cluster were Microsetella norvegica, Paracalanus parvus s.l., and C. sinicus for groups 1, 2, and 3, respectively. It was considered that the copepod nauplii densities of Harima-Nada are insufficient to saturate the survival rate of Japanese anchovy larvae. The biomass of dominant copepods seems to be almost the same as previous studies, but C. sinicus, which is representative of group 3 and an important prey item for the sand lance, is expected to become more unstable in the future.

Successful feeding on preferred prey could be important for the survival of fish larvae. However, high taxonomic resolution of prey types from damaged gut contents is difficult to achieve through morphological classification, especially for fragile organisms or immature stages. In this study, <10 mm early post-larvae of Japanese sardine Sardinops melanostictus and Pacific round herring Etrumeus teres were collected from Tosa Bay (Japan) during their main spawning periods. Diet and plankton communities present in the environment were investigated using molecular operational taxonomic units (MOTUs) clustered using eukaryoticmetagenetic data fromthe 18S V9 region. There were no clear differences in the diets of the co-existing fish species. Fragile protists and gelatinous metazoans occasionally represented large proportions of gut content; however, copepods comprised the majority of the prey items. Among the copepods, the Calanidae MOTU derived fromthe large copepod Calanus sinicus was most consumed, followed by the Paracalanidae MOTU identified as small Paracalanus parvus s.l. The C. sinicus MOTU largely dominated intermediate (0.5–1.0 mm) and large (1.0–2.0 mm) environmental mesoplankton communities, whereas the P. parvus s.l. MOTU was the most dominant in small-sized (0.1–0.5 mm) communities. Early post-larvae fish were considered to prefer eggs or nauplii of C. sinicus, which was the second-dominant MOTU in small-sized communities. These results suggested that both food availability and developmental stages of copepods determined prey preference.

In the Humboldt Current System (HCS) off northern Chile (23° S), 6 samplings were conducted in 2013 and 2014, each at 8 depths ranging from 5 to 80 m, to study the role of environmental variability on the abundance and vertical distribution of the eggs of dominant copepods, with special emphasis on hypoxia associated with the oxygen minimum zone (OMZ). The highest levels of abundance of Acartia tonsa and Paracalanus cf. indicus eggs were in surface waters above the OMZ. The distribution of eggs of both species correlated positively with chlorophyll a and stratification (Brunt-Väisälä frequency). Calanus chilensis eggs were found at greater depths, and their distribution did not correlate with any abiotic variables, whereas the distribution of C. chilensis females was associated with subsurface water upwelling due to a positive correlation with Ekman transport and salinity. The vertical distribution of copepod eggs in the HCS can be explained by abiotic variability, the sinking velocities of the eggs and the resuspension effect of upwelling vertical velocities, all of which may retain the eggs of smaller copepods in waters above the OMZ while C. chilensis eggs sink more rapidly, reaching the OMZ in less than 2 d. The survival of early-stage copepods is vital for the success of populations; therefore, any changes in conditions, like upwelling intensification, shoaling, and expansion of OMZs due to climate change, can affect the productivity of the pelagic realm in coastal upwelling ecosystems.

The Paracalanus parvus species complex is one of the most dominant and ecologically important copepod groups in the waters around Japan. However, the overall taxonomic classification of the species complex has not been sufficiently defined to date. In this study, both genetic and morphological analyses were performed on specimens of the P. parvus species complex collected along the \"O-line\", a monitoring line located at 138°E, south of Japan. Among the individuals collected, P. nanus specimens were clearly distinguishable morphologically, whereas other specimens could be classified into three reproductively isolated species. These distinctions are based on genetic analyses of the mitochondrial cytochrome oxidase subunit I (mtCOI) and nuclear large subunit (nLSU) ribosomal RNA. By comparing the genetic and morphological data with findings from previous studies, these three species were identified as P. tropicus, P. indicus, and an as-yet undescribed species (Paracalanus sp. (NWP)). The latter possesses a humped forehead and was found to be a dominant species within the surveyed continental slope area. As a distinguishing characteristic, the humped forehead was not consistently useful as it was prominent in only about half of the individuals collected. Morphological discrimination between this species and P. indicus was only made possible by comparing the relative length of exopod segment 3 on swimming leg 4. Despite morphological similarities among member species, ecological studies on the P. parvus species complex conducted around Japan may mostly concern the undescribed species, Paracalanus sp. (NWP), considering that P. indicus was found only in warmer waters in this study.

Tropical cyclones (TCs) are discrete events that affect ecology of estuaries. On 26 May 2021, TC Yass (category-1) disrupted the Muriganga estuary (ME), West Bengal coast, India. Authors assessed short-term cyclone-mediated changes of the copepod community by sampling three stations on the ME before and after TC Yass. Copepod and water samples collected on November 2020, and January and April 2021 were assumed as pre-Yass samples. Post-Yass samples were collected between 4 and 22 June 2021 once in every 6 days. It was hypothesized that diversity, total abundance and dominance of the copepods of the ME were impacted by TC Yass. Post-Yass the ME turned polyhaline from its meso-haline characteristic. Post-Yass species richness was higher than the pre-Yass period. Pre-Yass Bestiolina similis was the most abundant species, and species such as Paracalanus parvus and Acartiella tortaniformis co-dominated the copepod community. Post-Yass, Acartiella tortaniformis was the most abundant species of the copepod community followed by Oithona brevicornis and Paracalanus parvus . Post-Yass, total abundance of cyclopoid copepods was higher than the pre-Yass. Spatial heterogeneity of the copepods, which was observed during the pre-Yass was lost in the post-Yass period. Those changes in composition and abundances may have cascading consequences for the ecology of the copepods in the ME. Such changes could be traced through a high frequency sampling (e.g., daily to weekly) starting within the first week of a TC impact followed by a medium (e.g., monthly interval) frequency sampling based on the intensity of a TC, resident time of water in an estuary and the complexity of its copepod community.

Two new species of Paracalanidae, Giesbrecht, 1893 , have been described. Paracalanus brasiliensis sp. nov. and Bestiolina brasiliensis sp. nov. were registered in four estuaries on the central coast of Brazil. Paracalanus brasiliensis sp. nov. females differ from their congeners mainly with regard to body size, the structure of swimming legs 1–4, absence of bristles in the coxopodites, spinules between the spines in the third segment of the exopodite, and the shape of the seminal receptacles. The uniformity of the number of spinules and their location on the anterior face of the second exopodite of legs 2–3 and the absence of spinules on the endopodite of legs 3–4 differentiate Bestiolina brasiliensis sp. nov. females from other Bestiolina Andronov, 1991 , species. In the males of both species, the main diagnostic features (swimming leg seta, spine formula, and ornamentation) are generally observed in females with a few additional characteristics. Genetic divergence analyses based on partial mitochondrial COI (mtCOI) sequences revealed no genetic divergence between Paracalanus brasiliensis sp. nov. and Paracalanus sp. E. sensu Cornils and Held ( 2014 ), demonstrating that they are mutually conspecific. mtCOI sequence data from Bestiolina brasiliensis sp. nov. identified a clade with high bootstrap support that separated the specimens in this study from other Bestiolina species. The present report provides the first morphological description of females and males of both Paracalanus brasiliensis sp. nov. and Bestiolina brasiliensis sp. nov. and presents molecular evidence for species specificity. Matters regarding the validity of these species are also discussed.

Trophic preference (i.e., food resources and trophic levels) of different copepod groups was assessed along a salinity gradient in the temperate estuarine Gwangyang Bay of Korea, based on seasonal investigation of taxonomic results in 2015 and stable isotope analysis incorporating multiple linear regression models. The δ13C and δ15N values of copepods in the bay displayed significant spatial heterogeneity as well as seasonal variations, which were indicated by their significant relationships with salinity and temperature, respectively. Both spatial and temporal variations reflected those in isotopic values of food sources. The major calanoid groups (marine calanoids and brackish water calanoids) had a mean trophic level of 2.2 relative to nanoplankton as the basal food source, similar to the bulk copepod assemblage; however, they had dissimilar food sources based on the different δ13C values. Calanoid isotopic values indicated a mixture of different genera including species with high δ15N values (e.g., Labidocera, Sinocalanus, and Tortanus), moderate values (Calanus sinicus, Centropages, Paracalanus, and Acartia), and relatively low δ15N values (Eurytemora pacifica and Pseudodiaptomus). Feeding preferences of different copepods probably explain these seasonal and spatial patterns of the community trophic niche. Bayesian mixing model calculations based on source materials of two size fractions of particulate organic matter (nanoplankton at < 20 µm vs. microplankton at 20–200 µm) indicated that Acartia and Centropages preferred large particles; Paracalanus, Calanus, Eurytemora, and Pseudodiaptomus apparently preferred small particles. Tortanus was typically carnivorous with low selectivity on different copepods. Labidocera preferred marine calanoids Acartia, Centropages, and harpacticoids; on the other hand, Sinocalanus and Corycaeus preferred brackish calanoids Paracalanus and Pseudodiaptomus. Overall, our results depict a simple energy flow of the planktonic food web of Gwangyang Bay: from primary producers (nanoplankton) and a mixture of primary producers and herbivores (microplankton) through omnivores (Acartia, Calanus, Centropages, and Paracalanus) and detritivores (Pseudodiaptomus, Eurytemora, and harpacticoids) to carnivores (Corycaeus, Tortanus, Labidocera, and Sinocalanus).

INTRODUCTION: Many marine planktonic crustaceans such as copepods have been considered as widespread organisms. However, the growing evidence for cryptic and pseudo-cryptic speciation has emphasized the need of re-evaluating the status of copepod species complexes in molecular and morphological studies to get a clearer picture about pelagic marine species as evolutionary units and their distributions. This study analyses the molecular diversity of the ecologically important Paracalanus parvus species complex. Its seven currently recognized species are abundant and also often dominant in marine coastal regions worldwide from temperate to tropical oceans. RESULTS: COI and Cytochrome b sequences of 160 specimens of the Paracalanus parvus complex from all oceans were obtained. Furthermore, 42 COI sequences from GenBank were added for the genetic analyses. Thirteen distinct molecular operational taxonomic units (MOTU) and two single sequences were revealed with cladistic analyses (Maximum Likelihood, Bayesian Inference), of which seven were identical with results from species delimitation methods (barcode gaps, ABDG, GMYC, Rosenberg’s P(AB)). In total, 10 to 12 putative species were detected and could be placed in three categories: (1) temperate geographically isolated, (2) warm-temperate to tropical wider spread and (3) circumglobal warm-water species. CONCLUSIONS: The present study provides evidence of cryptic or pseudocryptic speciation in the Paracalanus parvus complex. One major insight is that the species Paracalanus parvus s.s. is not panmictic, but may be restricted in its distribution to the northeastern Atlantic.

During this research, the average surface temperature, salinity, dissolved oxygen, and pH were 24.65 ± 1.53 (°C), 34.21 ± 0.07 (PSU), 6.85 ± 0.18 (mg/L), and 8.36 ± 0.03, respectively. Based on these environmental parameters, stations were arranged into three groups. Group A represents stations located around Keelung Island with the relative highest average dissolved oxygen, lowest average temperature, and pH values. Instead, the lowest average dissolved oxygen and highest average temperature, salinity, and pH values were recorded at the offshore stations. Keelung Island area was charged by cold water masses, which were driven by the Northeast monsoon, and stations in group C were affected by the Kuroshio Current. Kueishan Island area was mainly affected by mixed water masses resulting from the Kuroshio intrusion and monsoon-derived cold water. In this study, a total of 108 copepod species were identified, with an average abundance of 774.24 ± 289.42 (inds. m−3). Most species belong to the orders Calanoida and Poecilostomatoida, with an average relative abundance (RA) of 62.96% and 30.56%, respectively. Calanoid copepodites were the most dominant group, with a RA of 28.06%. This was followed by Paracalanus aculeatus, with a RA of 18.44%. The RA of Clausocalanus furcatus and Canthocalanus pauper was 4.80% and 3.59%, respectively. The dominant species P. aculeatus, C. pauper, Paracalanus parvus, and Temora turbinata were positively correlated with dissolved oxygen and negatively correlated with temperature in the surface waters. pH showed a negative correlation with P. parvus and T. turbinata, while the temperature was negatively correlated with these two dominant species. Indicator species were selected by an indicator value higher than 50%. Temora turbinata, Calanopia elliptica, C. pauper, Euchaeta concinna, Temora discaudata, Acartia pacifica, Macrosetella gracilis, Corycaeus speciosus, and P. parvus were considered as monsoonal cold water indicator species in Group A. Indicator copepod species for the Kuroshio Current were Farranula concinna, Copilia mirabilis, Candacia aethiopica, Corycaeus agilis, Farranula gibbula and Acrocalanus monachus in the study area. Paracandacia truncata, Oncaea clevei, P. aculeatus, and Centropages furcatus were considered suitable indicators for mixed water masses.

We measured the monthly egg production rate (EPR) of Paracalanus parvus s. l. (P. parvus) at a fixed station in Busan Harbor from January 2020 to December 2021 to elucidate the seasonal variation in the EPR and the factors involved. Over the 2 years, the monthly EPR ranged from 0.5 to 47.0 eggs female−1 d−1 (average 13.3 eggs female−1 d−1). The seasonal mean EPR was high in spring (April to June) and summer (July to September) and low in autumn (October to December) in both years. Egg hatching success was high (average 94%). Monthly nauplii production in the P. parvus population ranged from 9 to 37,123 ind. m−3 d−1 (average 4605 ind. m−3 d−1), with a peak in March and May in 2020 and in April in 2021. The monthly EPR of P. parvus was more dependent on chlorophyll-a concentration than on water temperature. Nauplii production was dependent on the abundance of adult females, while the chlorophyll-a concentration had a positive effect on nauplii production. In this study, while there was no clear seasonal variation in the abundance of adult females, the EPR showed a clear pattern of seasonal variation. These results imply that for monitoring potential environmental changes in Busan Harbor, measuring the EPR of copepods may be a better indicator than copepod abundance.