Harpacticoid Species Research Articles

Benthic Harpacticoida of the Kara Sea: Species Composition and Bathymetrically Related Distribution

Data on benthic harpacticoid copepods from the Voronin Trench (central part of the Kara Sea) are reported for the first time. Harpacticoids accounted for 1–25% of total meiofauna, their abundance varied from 6 to 102 ind./10 cm2 and decreased with depth. I total, 42 nominal species have been found, 15 species are new for the Kara Sea, and at least 8 species are new for science. Several species have been recorded for Arctic waters for the first time: Cylindronannopus bispinosus, Haloschizopera clotensis, H. bathyalis, Metauntemannia pseudomagniceps, Mesocletdemus duosetosus, M. parabodini, Proameira echinipes, and Cletodes tuberculatus. The most species-rich families are Ameiridae, Argestidae, Pseudotachidiidae, Miraciidae, and Ectinosomatidae. Comparative analysis including the data obtained at shallow-water stations from the Yenisei Gulf (southern Kara Sea) revealed three assemblages occupying different habitats. The assemblage inhabiting shallow-water silts (20–62-m depth) was the poorest in regard to species diversity; shallow-water sands were richer in species number, while the deepest stations (92–698 m) were the richest. The latter assemblage had the composition of families typical for the deep-sea areas. The fauna of the Kara Sea includes by now 82 harpacticoid species, most of which have been also reported from North Atlantic and/or western Arctic waters.

A new species and new records of harpacticoids (Crustacea: Copepoda: Harpacticoida) from North-Eastern Borneo

Zooplankton samples from inland water bodies in the north-eastern part of Borneo were collected in rivers, ponds, roadside ditches, irrigation canals, rice fields, and temporary water bodies. The harpacticoid copepods (Harpacticoida) were found only in three surveyed locations. Seven species of four genera from the families Canthocamptidae and Phyllognathopodidae were identified. Four of harpacticoid species found belong to the genus Elaphoidella. A new species, Elaphoidella fatimae sp. nov., is described. It differs from all known species of the genus by combination of the following characters: posterior margins of body somites serrate at dorsal side; anal operculum rounded, with spinules; caudal rami conical; exopod of leg 5 about three times as long as wide. Six species were reported for Borneo for the first time.

Two new deep-sea species of Argestidae and Ameiridae (Copepoda: Harpacticoida) from the Eastern Mexican Pacific and Gulf of California, with proposal of a new genus of the family Argestidae

ABSTRACTA handful of benthic harpacticoid species are known from the Gulf of California. Here I describe Argestes analongises sp. n. (Argestidae), and Argestigens celibis sp. n. (Ameiridae) from the deep sea of the Tropical Eastern Pacific and Gulf of California. Argestes analongises sp. n. fits in the subfamily Argestinae (Argestidae) and was attributed to the genus Argestes by the presence of small spinules covering the body surface of, at least, the urosome, and by the presence of an extremely elongated distal seta on the sixth segment of the female antennule. This new species seems to be allied to A. angolaensis by the situation of all the caudal setae, and by the ventral position of caudal seta III. They differ in the relative length of the female caudal rami, size, shape and relative position of the sensilla-bearing tubercles associated to the anal somite, armature of the mandibular basis, shape of the exopodal and endopodal segments of swimming legs, and relative length of the setae on the female P5 endopodal lobe and position of the innermost seta of the exopod of the female fifth leg. Argestigens celibis sp. n. was attributed to the family Ameiridae based on the non-argestid maxilla, on the presence of a more or less well-developed endopodal lobe of the male fifth leg and three inner setae on the third endopodal segment of the third leg, and on the presence of the typically modified ameirid-like inner spine on the basis of the male first leg. The new species was attributed to Argestigens based on the non-prehensile endopod of first leg and presence of long inner spinules on the basis of second to fourth legs. Additionally, a new genus, Georgus gen. n., is proposed for Bodinia peterrumi, and some comments are given on the monophyly of that genus.www.zoobank.org/urn:lsid:zoobank.org:pub:4BD580B0-E856-4FBC-ABA6-B031A9B6E1F9

Mesochra rostrata Gurney, 1927 (Copepoda, Harpacticoida) in Sivash Bay (Sea of Azov): Is it a new alien species or a relict of Tethys?

Harpacticoid Mesochra rostrata Gurney, 1927 was found in Sivash Bay (Sea of Azov) for the first time in 2013. In 2015, it became the most common and abundant species of Harpacticoida in the bay. The morphological characteristics of males and females of M. rostrata found in the Sivash accord with the species description given in earlier publications. The bay population comprised adult males and females, naupliar and copepodite stages. Adult male size varied from 0.30 to 0.40 mm, and adult female size varied from 0.38 to 0.45 mm. Since 2014, a substantial increase in salinity has been observed in Sivash Bay. In August 2015, seven species of Harpacticoida were registered in the bay in total; M. rostrata dominated and was abundant in benthos (up to 56000 ind./m2), in the floating mats of filamentous green algae (up to 336 400 ind./m2), and in plankton (up to 580 ind./m3) at water salinity of 60–75 g/L. Earlier, this species was registered in the Sinai Peninsula at the water salinity not exceeding 45 g/L. M. rostrata can be considered a new invader in the Azov-Black Sea Region; the resting stage of this crustacean was brought here by wind or birds. However, it can be assumed also that the species is an aboriginal one for the Azov-Black Sea Region from times of the Tethys Ocean. In the Black and Mediterranean seas, there are some relicts of Tethys. In normal conditions, this species is rare and, possibly, can succeed only in destabilized biotopes, such as Sivash Bay nowadays during the period of a sharp increase in the water salinity.

Variability of the fauna within drifting sea ice floes in the seasonal ice zone of the Southern Ocean during the austral summer

Sea ice covering the seasonal ice zone in the Southern Ocean contains micro-organisms (sea ice biota). Studies of sea ice biota have mostly been conducted on the land-fast ice and large ice floes, despite most sea ice in the Southern Ocean being seasonal and drifting ice types. We sampled 17 drifting sea ice floes in the marginal ice zone off Adélie Land, East Antarctica, in January 2013 and 2014. We found high densities of copepods such as Harpacticoida species (18,787 ± 50,647 inds.m−3), Paralabidocera antarctica (1773 ± 6370) and their nauplii (69,943 ± 149,607), as well as foraminiferans (193,869 ± 408,721) within ice. Variability in the animal assemblages among the different ice floes was observed. Cluster analysis of samples based on the assemblage of sea ice fauna revealed two major groups, which were divided by the year of the sampling, and were dominated by harpacticoid nauplii and foraminiferans, respectively. Sea ice trajectory and drifting duration estimated from satellite data were different for both years, although the origin of the sea ice was in the same bay. This study suggests that the variability of fauna among sea ice floes may reflect the continuance period of ice formation and the trajectory from where they originated.

Species composition of freshwater zooplankton fauna from selected groundwater-dependent ecosystems in Bulacan Province (Philippines) with taxonomic notes on new locality record of harpacticoid species in the Philippines

In the Philippines, the taxonomy of freshwater zooplankton fauna from ground waters remain poorly understood, yet knowledge on this group is important to know patterns in groundwater biodiversity to develop sound conservation policies. In this study, zooplankton were studied by collecting samples from selected groundwater-dependent ecosystems in Bulacan Province. Results indicate the presence of 13 species belonging to 10 families from Rotifera, Cladocera, and Copepoda. Large portion of the samples included the copepods Mesocyclops and Thermocyclops spp together with cladocerans Ceriodaphnia cornuta and Moinodaphnia macleayi. Observation of these taxa in groundwater-dependent ecosystems suggests high surface and sub-surface hydrological connectivity in the Province. Lastly, new locality record of Elaphoidella bidens in the Philippines was establishes.

Effects of elevated CO2 and temperature on an intertidal harpacticoid copepod community

Warming and ocean acidification have been shown to have significant impacts on marine organisms. However, none studies have addressed the impact of these two stressors on harpacticoid copepod community structure. A mesocosm experiment was conducted to assess the potential interactive impact of different levels of elevated CO2 and temperature on an intertidal harpacticoid copepod community. Artificial substrate units (ASUs) colonized by meiofauna from the extreme low intertidal zone were exposed to eight experimental treatments (four pH levels: 8.0, 7.7, 7.3 and 6.7, crossed with two temperature levels: 12 and 16 °C). After 60 days exposure communities were significantly affected by both stressors. The dominant harpacticoid species were mainly affected at treatments held at pH 6.7, but with divergent biological response patterns. At pH 6.7 Tisbe sp and Ectinosoma sp2 exhibited important density reductions, while considerable density increases were observed for Amphiascus longarticulatus and Amphiascoides golikovi. This study has demonstrated that elevated levels of CO2 and ocean warming may have substantial effects on the structure of harpacticoid communities. Importantly, the increase in malformations observed at pH 6.7 indicated that we need to consider sub-lethal effects that could have consequences for populations after long periods of exposure.

Continental copepod biodiversity in North-Eastern Borneo, Malaysia

To obtain a relevant information on copepod biodiversity/distribution in continental Borneo water bodies in June 2011 about 30 different sites in Malaysian state Sabah were visited and more than 50 alcohol and formalin preserved samples in nine rivers, 10 ponds, and six near-road ditches and canals, rice fields and forest leaf litter environment were collected. In literature 16 copepod species were referred for Borneo and 10 other species for Kalimantan (Indonesean) states. After the Sabah sample analyses, the copepodspecies richnessin the Borneo island increased more than twice. The most abundant with species number genera were ranged as: Mesocyclops (13), Elaphoidella (6), Microcyclops (5), Eucyclops (4), Thermocyclops (4), Halicyclops (3) and Paracyclops (3). Species biodiversity in different sites plotted against type of water body and several environment parameters revealed significant positive correlations for number of species and both for depth and temperature in sampling site (Pearson non-parametric tests 0.6 and 0.5 respectively at p < 0.05). One way Kruscal-Walise dispersal analysis confirmed significant relationship between copepod biodiversity and water transparence/ turbidity (p < 0.05). The highest copepod biodiversity values were found in ponds (23 species), near road ditches (15), rivers with transparent water (12), lowland or swamp areas related with rivers (9). The lowest number of species were found in rivers with turbid water colored in orange with soil-erosive matter where the average number of copepod species (0.2 ± 0.08 species per site) was about 20 times less than in waters without silt particles (3.8 ± 2.8 species per site). This indicates a strong negative effect of soil erosion resulting water land-used activities and deforestation in the watershed on the biodiversity of aquatic organisms in Borneo. In one sub-urban population of Mesocyclops cf. thermocyclopoides, a trans-sexual mutation of female-sized but constructed as male armed with genicu late antennule organisms was found that possibly reflect a negative result of wide artificial hormone-based pesticide usage in this area. Keys for Harpacticoida species for Borneo and for Eucyclops species known for SEAsia, Australia and India are provided. Within practically each copepod genus studied in Borneo there are forms with problems on species identification by existing faunistic keys. This possibly indicates a necessity of new species description from this area in the nearest future.

Benthic harpacticoid copepods of Jiaozhou Bay, Qingdao

The species richness of benthic harpacticoid copepod fauna in Jiaozhou Bay, Qingdao, on the southern coast of Shandong Peninsula, has not been comprehensively studied. We present a preliminary inventory of species for this region based on material found in nine sediment samples collected from 2011 to 2012. Our list includes 15 species belonging to 15 genera in 9 families, the most speciose family was the Miraciidae Dana, 1846 (seven species); all other families were represented by single species only. Sediment characteristics and depth are determined to be important environmental determinants of harpacticoid distribution in this region. We briefly detail the known distributions of species and provide a key to facilitate their identification. Both harpacticoid species richness and the species/genus ratio in Jiaozhou Bay are lower than in Bohai Gulf and Gwangyang Bay. The poor knowledge of the distribution of benthic harpacticoids, in addition to low sampling effort in Jiaozhou Bay, likely contribute to low species richness.

Meiobenthic Assemblages from the Southwestern Coast of the Black Sea, İğneada (Turkey)

AbstractMeiobenthic organisms were sampled for the first time from İğneada coasts, Turkey (Western Black Sea) in order to provide a base-line study on the meiobenthic community structure of the sampling area. Meiobenthos was found to be composed of 12 higher taxonomical groups: Nematoda, Harpacticoida, Polychaeta, recent hard-shelled Foraminifera, soft-shelled Foraminifera, Bivalvia, Gastropoda, Ostracoda, Turbellaria, Oligochaeta, Nemertea and Acari. Meiobenthic community was dominated by nematodes, harpacticoid copepods and hard-shelled foraminifera in the study area. Fifty two species of Nematoda, fifteen species of Harpacticoida and twelve species of living hard-shelled Foraminifera were identified. Six nematode species (

New data to the knowledge on the Harpacticoida (Crustacea, Copepoda) fauna in Poland

Harpacticoida is the least known group of Copepoda in freshwater habitats in Poland, although they are very common and very abundant in the continental waters. The last detailed taxonomic studies of Harpacticoida in Polish inland waters were carried out about 100 years ago. A faunistic and ecological review of 12 harpacticoid species from north-eastern Poland is presented herein for the first time. Two species new to the Polish fauna were recorded: Elaphoidella elaphoides (Chappuis, 1923) and Bryocamptus (Rheocamptus) spinulosus (Borutzky, 1934). Bryocamptus spinulosus is morphologically close to B. zschokkei (Schmeil, 1893). The latter species is considered to be widely distributed in Poland, yet many records of B. zschokkei might in fact refer to B. spinulosus. Distinguishing features of these species were described in detail.

A Newly Recorded Harpacticoid Species of the Genus Paramphiascella (Harpacticoida: Miraciidae) from South Korea

A harpacticoid species, Paramphiascella fulvofasciata Rosenfield and Coull, 1974, belonging to Miraciidae Dana, 1846 is newly reported from Korean waters. The species is mostly related with P. pacifica Vervoort, 1962, however, it is easily distinguished by the typical structure of male P2 in having 1 large spine and 2 setae on P2 enp-2. Korean materials represented some discrepancies from the original description of P. fulvofasciata in the detailed structures of mouth parts. The present study is a first record of the genus Paramphiascella Lang, 1944 from Korean waters.

The harpacticoid assemblages (Copepoda: Harpacticoida) in the Western Carpathian spring fens in relation to environmental variables and habitat age

Harpacticoids are an important component of meiofaunal assemblages in springs. No information so far has been available on harpacticoid assemblages of the Western Carpathian spring fens, unique biotopes of high conservation value which cover a very long gradient of mineral content of groundwater, due to the variable geological background setting. Spring fens are isolated habitats of different age which can be assessed by radiocarbon dating of their basal sediment layers. This enables to test a possible effect of habitat age on species composition and species richness. In this study, we examined harpacticoid assemblages in 50 permanent tree-less spring fens (helocrenes) in the Western Carpathians (Slovakia and Czech Republic) in terms of species composition, total abundance, species density, and species richness. We tested mainly the effect of 12 explanatory variables describing water chemistry and temperature, climatic conditions, amount of nutrients, organic carbon, sediment structure, habitat age and size, using Canonical Correspondence Analyses (CCA) with stepwise forward selection. For the computation of species richness rarefaction was used. In total, 20 harpacticoid species were recorded with the total median density of 950 individuals in m −2 . Three significant explanatory variables, Ellenberg Indicator Values of plant community for nutrients, in situ measured pH, and average January temperature, explained together 19.0% (adj. 13.7%) of the total variance in the species composition data. The relationships of harpacticoids to these three explanatory variables were species specific and no uniform response of the total assemblage to the environmental variables was found (in terms of total abundance and number of species). The only exception was the influence of overall unfavourable conditions in the mineral-poor acidic Sphagnum -fens. Pilocamptus pilosus was significantly associated with a higher amount of nutrients and warmer climate. Nutrient enrichment was clearly indicated by a decrease or absence of crenophile Bryocamptus cuspidatus , and accompanied by an increase in ubiquitous Attheyella crassa . Moraria brevipes was confined to low pH, B. cuspidatus showed a high tolerance for low pH, whereas Bryocamptus echinatus preferred alkaline conditions. Despite a significant correlation between habitat age and species density we found no clear evidence that any colonisation driven process could influence the number of harpacticoid species within the tested time scale. We hypothesize that rather other habitat characteristics connected with age, i.e. habitat heterogeneity and stability, may be determinant for species richness. The occurrence of some species (e.g. P. pilosus , B. cuspidatus ) was clearly geographically limited, but due to the spatial structuring of significant environmental variables no conclusion on dispersal limitations could be made.

Harpacticoida (Copepoda) of the northern East Sea (the Sea of Japan) and the southern Sea of Okhotsk: diversity, taxocenes, and biogeographical aspects

Based on novel data and a literature review, an inventory of Harpacticoida from the northern part of the East Sea and the southern part of Sea of Okhotsk is compiled. A total of 151 species belonging to 70 genera and 26 families, of which 16 species are deemed to be new to science, are recognized from the region. Twelve harpacticoid species assemblages are described from marine and brackish water soft sediments and the phytal zone. Estuarine faunas were similar throughout the East Sea and Sea of Okhotsk, both in species composition and dominant-taxon structure. Conversely, the fauna of marine soft sediment and phytal zones differed greatly throughout this region. This distinction may have been caused by differences in dispersal rates or by differences in environmental conditions. The distribution of littoral and sublittoral harpacticoids was determined primarily by climatic factors and the temperature of surface waters. Three basic sub-regions were distinguished within the survey area: Korean, which includes many tropical taxa (39%) and a smaller amount (about 20%) of boreal taxa; Primorye, where boreal and subarctic-arctic species (>40%) predominate, and representatives of the tropical complex are rare (17%); and Soya, with a mix of tropical (22%) and boreal (31%) faunal elements. The faunas of the Korean and the Primorye sub-regions are distinct, whereas that of the Soya has intermediate features.

Trophodynamics of estuarine intertidal harpacticoid copepods based on stable isotope composition and fatty acid profiles

Trophic interactions at the basis of food webs, for instance between meiofauna, primary producers and bacteria, are key drivers of benthic energy fluxes. Yet both qualitative and quantitative information about meiofaunal resource utilization under in situ conditions is scant. By means of natural stable isotope ratios of carbon and nitrogen and of fatty acid (FA) profiles, we examined the variability of in situ resource utilization of a range of harpacticoid copepod species from 5 stations in an estuarine intertidal area. These stations, located in different habitats, differed in sediment granulometry, resource availability, presence/absence of vegetation and other environmental variables, as well as in copepod species composition. Our goal was to describe interspecific differences among harpacticoid species, as well as spatio-temporal variability within species. Despite differences in resource availability between habitats, delta C-13 data clearly point at microphytobenthos (MPB) as the major carbon source to the harpacticoid assemblages at all 5 stations. Small differences in carbon isotopic ratios between co-occurring species indicate some degree of resource differentiation, whereas both the delta N-15 and FA composition suggest that several harpacticoid species obtain MPB carbon indirectly, perhaps through feeding on bacteria or ciliates. For a limited number of species, such as Paraleptastacus spinicauda, clear dietary contributions of suspended particulate matter and bacteria were found, and MPB appeared to have only a small or no contribution. Even in vegetated salt-marsh stations, Spartina anglica detritus did not appear to contribute to copepod diets. The delta C-13 of Cletodidae were highly depleted, reflecting a contribution of methane-derived carbon.

Diversity and environmental control of benthic harpacticoids of an offshore post-dredging pit in coastal waters of Puck Bay, Baltic Sea

Placer extraction in Puck Bay, a shallow (3 m depth) area of the Baltic Sea, resulted in the formation of post-dredging pits. Such dredging activities led to a considerable local disturbance of the soft-bottom communities. Topography and sedimentary characteristics of the disturbed area have been radically changed. It is therefore a matter of concern as to whether these alterations to the environment resulted in any serious permanent changes to the biological communities in the affected areas. Benthic copepod assemblages were examined 10 years after termination of placer digging in one of the post-dredging pits and compared with the fauna in a natural depression (Kuźnicka Hollow) and on the shallow sandy bottom surrounding the pits. Samples were collected on four occasions in 2001–2003. This study has generated ecological information on the status of harpacticoid species inhabiting the dredged and undredged areas in the vicinity. Analyses of data showed that the sampling stations differed significantly, during all the sampling events, in harpacticoid abundance, taxonomic composition and Shannon–Wiener diversity index. The natural depression and the shallow sandy bottom of Puck Bay were found to support specific harpacticoid assemblages. Interstitial and sand-burrowing species (e.g. Paraleptastacus spinicauda) dominate the shallow sandy bottom, and the Kuźnicka Hollow is inhabited mainly by epibenthic and silt-burrowing species (e.g. Halectinosoma curticorne, Tachidius discipes, Microarthridion littorale). The post-dredging pit assemblage showed the presence of epibenthic species, e.g. Tachidius discipes, Dactylopusia euryhalina, and Stenhelia palustris, passively transported into the pit by wave action and currents, possibly with algal mats and/or plant remains. The taxonomic composition and occurrence of harpacticoid species in the post-dredging area is therefore random and accidental.

To add six new species freshwater crustaceans (Cyclopoida, Harpacticoida-Copepoda) to the fauna of inland freshwater zooplankton of Vietnam

Based on analysis of many samples collected from Ca river and other waters belonging to Nghean province, one species of Cyclopoida: Halicyclops aequoreus (Fischer, 1860) and five species of Harpacticoida as Tachidius (Neotachidius) triangularis Shen et Tai, 1963; Elaphoidella coronata (Sars, 1904); Onychocamptus mohammed (Blanchard et Richard, 1891); Enhydrosoma bifurcarostratum Shen et Tai, 1965; and Stenhelia (Delavalia) ornamentalia Shen et Tai, 1965 that are firstly determined. All of these species are described in detail in the paper. Among these five species of Harpacticoid, only one Elaphoidella coronata distributed in mountainous waters, four remain species only distributed in blackish waters of estuarine area. Up to now, 12 species of inland freshwater harpacticoid-copepods are recorded in Vietnam. The amount of species of harpacticoid-copepods determined as above that are sure not enough to compare with the real in nature of Vietnam.

Harpacticoida (Copepoda) fauna and the taxocenes structure of brackish lagoons and estuaries of the Russian far east

On the basis of original data and literature sources, the species composition of Harpacticoida (Copepoda) in the plankton of the brackish waters of four Far Eastern regions was described: Khabarovsk krai, Sakhalin Island, Kamchatka Peninsula, and the Commander Islands. The compiled list includes 32 harpacticoid species of 22 genera and 10 families. The representatives of the typical brackish families Canthocamptidae and Ectinosomatidae account for about one-third of the total. Six of the species are new to science: 4 species of Halectinosoma, Amphiascus sp. 1, and Schizopera sp. 1. Cosmopolitan species constitute the major portion of the fauna (38% of the total number), while a smaller proportion is typical of endemics (25%), as well as species with the arctic (12%), tropical (9%), and North American (9%) types of areas. There are 17 types of harpacticoid taxocenes of the observed water bodies. Also, the influence of the salinity and temperature on these species complexes was characterized. The hypotheses about the cosmopolitanism of the brackish water fauna and the intrazonality of the estuarine harpacticoid taxocenes structure were tested. It is shown that the structure of the genera dominance in the taxocenes allocated for the temperature latitudes of the Far East demonstrates significant similarity with the arctic and tropical regions.

Suitability of cuticular pores and sensilla for harpacticoid copepod species delineation and phylogenetic reconstruction

Cuticular organs have not been described systematically in harpacticoids until recently, and they have never been used as characters for reconstructing phylogenetic relationships in any crustacean group. We survey cuticular pores and sensilla on somites in ten Miraciidae species, belonging to six genera, from Korea, Australia, and Russia. Nine species belong to the subfamily Stenheliinae, while the outgroup belongs to the subfamily Diosaccinae. We aim to compare phylogenetic trees reconstructed for these harpactioids based on: 1) cuticular organs (with 76 characters scored, 71% of them phylogenetically informative); 2) traditionally used macro-morphological characters (66 scored, 77% of them informative); and 3) mtCOI DNA data. All analyses suggest that cuticular organs are useful characters for harpacticoid species delineation, although not as sensitive as some fast-evolving molecular markers. Reconstructed cladograms based on all three datasets show very high bootstrap values for clades representing distinct genera, suggesting that cuticular organs are suitable characters for studying phylogenetic relationships. Bootstrap values for the more basal nodes differ among the different cladograms, as do the sister-group relationships they suggest, indicating that cuticular organs probably have different evolutionary constraints from macro-morphological characters. Cuticular organs could be quite useful in the study of old museum specimens and fossil crustaceans.

Community structure of mesozooplankton in coastal waters of Sundarban mangrove wetland, India: A multivariate approach

Spatial and temporal distribution of community structure and seasonal distribution of mesozooplankton (MZ; 20–200μm) in the context of environmental parameters were studied in the coastal waters of Indian Sundarban wetland formed at the confluence of Hugli (Ganges) River estuary, India. The work has been aimed for better understanding of its ecological characteristics in terms of the most dominant mesozooplankton group in a tropical mesomacrotidal setting. Samples were collected from four sampling sites of different hydrodynamic set up using a ring trawl net (Hydro-Bios No. 438 700, mesh size 200μm) equipped with a calibrated flowmeter and both water and plankton samples were analyzed by standard methods. Distribution of MZ showed bimodality with two peak periods, primary peak during April coinciding with maximum number of copepod species (974ind.m−3) and the secondary one during August. Copepod was the most dominant taxon where the calanoids formed bulk of the biomass representing 33 species of 7 genera, while cyclopoids formed the next dominant group comprising 4 species of 3 genera followed by 4 monogeneric harpacticoid species. Results of correlation matrix revealed that two copepod families Acartiidae and Pseudodiaptomidae maintain negative relationship with other six families indicating that they form a group by themselves. Results of multiple regression analysis reveal that salinity, chlorophyll-a and transparency are the potential hydrological factors in the distribution and existence of the dominant copepods and total chaetognaths. An overall high diversity index values (max. 3.21) was associated with high richness index (4.39) and high evenness index (0.96) at the site of the mouth of the estuary. In terms of feeding guild, the herbivore copepods were dominant followed by omnivores. Cluster analysis confirmed an overall dominance of the calanoid copepod Bestiolina similis as a solitary group for all the sites. The chaetognath Sagitta bedoti was perennial in distribution where the contribution of juvenile form (recognized as Stage I) was dominant. Among the other MZ, hydromedusae, ctenophore, sergestid and mysid were also encountered contributing insignificant part of the total density. A long-term decadal change in copepod community was pronounced which might be due to climate-induced environmental changes which also modulate the physicochemical characteristics of water.