Copepod Community Structure Research Articles

Seasonal and annual change in community structure of meso-sized copepods in Tokyo Bay, Japan

Seasonal change in the meso-sized copepod community structure in the central part of Tokyo Bay was investigated from January 2006 to December 2008. Three seasonal community groups were detected, and seasonal shifts of these communities are explained by life history characteristics of indicator species and seasonal changes in the hydrographical environment. In the winter-spring community, Acartia omorii and Centropages abdominalis dominate because of high growth rates at low temperature. A shift to the early summer community is caused by a diapause of Ce. abdominalis as resting eggs and an increase in the growth and egg-production rate of Pseudodiaptomus marinus at high temperature. A shift to the summer-fall community is caused by a diapause of A. omorii at hypoxic and high temperature conditions and an increase of Temora turbinata, Paracalanus parvus and other oceanic species by an enhancement of the estuary circulation. Then, the community returns to a winter-spring one by the recovery of A. omorii and Ce. abdominalis with low temperatures and oxygenation of bottom water and by the disappearance of oceanic warm-water species at low temperature. Seasonal community shifts occurred almost regularly, but the shift from a winter-spring community to an early summer one occurred 1 month early in 2007 when the water temperature was warmer than in other years.

Interannual changes in the zooplankton community structure on the southeastern Bering Sea shelf during summers of 1994–2009

On the southeastern Bering Sea shelf, mesozooplankton plays an important role in material transfer between primary producers and fisheries resources. The biomass of mesozooplankton in this region is known to vary annually, but little is known about annual changes in community structure and species composition. In the present study, regional and long-term changes in abundance, biomass and community structure of copepods and chaetognaths on the shelf were evaluated based on NORPAC net samples collected during summers of 1994–2009. During the study period, regime shifts occurred from high interannual variability regime (1994–1999) to low interannual variability regime with high temperature (2000–2005), then to a low interannual variability regime with low temperature (2007–2009). A total of 24 calanoid copepod species belonging to 21 genera were identified from samples. Copepod abundance ranged from 150 to 834,486inds.m−2, was greatest on the Middle shelf, and was higher in cold years, than in warm years. Copepod biomass ranged from 0.013 to 150gDMm-2, and was also higher in cold years than in warm years. Based on the results of cluster analysis, the copepod community was divided into six groups (A–F). The regional and interannual distributions of each group were distinct. Interannual changes in abundance of the dominant copepod on the Outer shelf and Middle shelf were highly significant (p<0.0001), and their abundances were negatively correlated with temperature and salinity. Interannual changes in copepod community that occurred between cold and warm years are thought to have been caused by differences in the magnitude and timing of the spring phytoplankton bloom between the two regimes. Abundance and biomass of the chaetognath Parasagitta elegans ranged from 30 to 15,180inds.m-2 and from 11 to 1559mgDMm−2, respectively. Chaetognath abundance was significantly correlated with the abundance of the dominant copepods (p<0.0001). Differences in cold and warm years may also affect recruitment of walleye pollock. We conclude that on the southeastern Bering Sea shelf, the magnitude and timing of primary production, which is related to climate change, may significantly affect how it is transferred through the food web.

Diel, seasonal and man-induced changes in copepod assemblages and diversity, with special emphasis on hyperbenthic calanoid species, in a Mediterranean meromictic system (Lake Faro)

The present study focuses on variations in day and night copepod community structure in a meromictic Mediterranean ecosystem (Lake Faro). Because of the high salinity in the lake, this environment is defined as a coastal-marine rather than true-lagoon ecosystem. Copepod abundances showed wide oscillations, with marked spatial and seasonal heterogeneity. The copepod assemblage was dominated by coastal and estuarine species Paracartia latisetosa and Acartia margalefi, in late summer–autumn and spring, respectively. A remarkable change in species composition was the occurrence of the alien species Oithona brevicornis, never having been reported in this environment before. O. brevicornis is progressively replacing the congener species O. nana. The discovery of the hyperbenthic calanoid species ‘ecological group’ contributes to increased functional diversity of this ecosystem, despite their relatively low abundances. All six hyperbenthic calanoid species occurred in the plankton community only at night, with spatial distribution patterns being related to substrate more than water physico-chemical parameters. Among all hyperbenthic calanoid species, Pseudocyclops xiphophorus was the only one able to inhabit the whole lake because of its daytime habitat (fouling material, attached to submerged ropes and mooring posts, widely distributed all around the lake). In this habitat, the temporal abundance pattern resembled the night-time one in plankton community.

Seasonal variation in community structure and body length of dominant copepods around artificial reefs in Xiaoshi Island, China

This study aims to investigate the seasonal variations in copepod community structure and prosome length of dominant species from March 2009 to January 2010 around artificial reefs in Xiaoshi Island, Yellow Sea, Weihai, China. Samples were collected using two types of plankton net (Model I and Model II) for different-sized copepods. The number of taxon was calculated from the data of both the net types, while the copepod abundance was done using the samples from Model II only. Sixteen species of planktonic copepods, including 5 dominant species, were recorded. Results reveal that Oithona similis was the first dominant species from March to June, and was replaced by Paracalanus parvus in September; both dominated the copepod community in January. Acartia hongi was the second dominant species from March to September. Centropages abdominalis was the third dominant species from March to June, and was replaced by O. similis in September and Corycaeus affinis in January. C. affinis was the fourth dominant species in September. Population density of the dominant copepods was compared with that of other similar regions. We found that the dominant species were mostly small copepods (<1 mm) except for adult Centrapages abdominalis. Seasonal variation in prosome length of O. similis, C. abdominalis, and C. affinis, and their copepodites were studied for the first time in China. For P. parvus and A. hongi, seasonal trends in prosome length variation were similar with those in Jiaozhou Bay, Yellow Sea, Qingdao, China, in a similar temperate domain. The results are helpful for future calculation of copepod biomass and production, and for investigation of the relationship between copepods and fish resources.

Community structure of harpacticoid copepods in intertidal and shallow-water habitats of Cat Ba archipelago (Vietnam, South China Sea)

The assemblage structure of harpacticoid copepods inhabiting the soft sediments of littoral and sublittoral areas of Cat Ba archipelago (South China Sea) is analysed. Three basic types of harpacticoid taxocenes were observed in the upper sublittoral. Main dominant species of taxocenes were Amphiascoides sp., Stenhelia latioperculata, Paramphiascella sp., Phyllopodopsyllus sp., Tisbe sp.1 and Amphiascoides sp. In addition, the main characteristics of harpacticoid species composition in littoral rock pools are described. A comparative analysis of shallow-water harpacticoid communities from different biotopes of the tropical region is presented, and shows that harpacticoid diversity and abundance are lowest in muddy sediments. Highest diversity and abundance are found in washed sands and silty sands with detritus. In general, the structure of muddy bottom communities is the most homogeneous throughout the tropics. Mangrove forests have no significant influence on harpacticoid taxocene structure. Harpacticoid associations of washed sands and silty sands with detritus demonstrate greater diversity and are region-specific.

Copepodid and adult Argestidae Por, 1986 (Copepoda: Harpacticoida) in the southeastern Atlantic deep sea: diversity and community structure at the species level

Drawing on the example of Argestidae Por, 1986b, community structure and large-scale distribution patterns of harpacticoid copepods at species level were examined in the three southeastern Atlantic deep-sea basins. The study was based on 30 multicorer deployments at depths from 5,035 to 5,655 m during the DIVA-2 expedition. The 1,176 adult and copepodid Argestidae from CIII onwards belong to 114 species. Some species occurred at all five stations; others appeared to be exclusive for single stations. Inclusion of copepodids revealed a higher similarity in species composition among the five stations than consideration of just adults and caused a slight shift toward dominance of single species in the sediments at most locations.

Using multitable techniques for assessing the temporal variability of species–environment relationship in a copepod community from a temperate estuarine ecosystem

This study investigated copepod assemblages' distribution patterns and determined the main hydrological and physical factors structuring it at different temporal scales. Copepod and hydrographic surveys were conducted seasonally during a one-year period, at a fixed station in Mondego estuary. Hourly samples were collected, during a diel cycle from sub-surface and 1 m above the bottom, at spring tides. Temporal variability of copepod community was analyzed using the STATICO method. Seasonal variability of the environmental conditions, linked with periods of higher freshwater flow, were the main drivers responsible for copepod community structure observed. Seasonal changes related to environmental factors showed to be strongest in spring and in winter, which accounted with higher species density. Marine and estuarine copepods showed maximal abundance in spring and summer, while the period of higher river flow, coincidently with autumn and winter, imposed changes in the copepods composition, emphasizing the changes in saline zonation within the estuary due to regime of river discharge. STATICO also emphasized the effects of physical forcing at short-term temporal scales. The stable part of the species–environment relationships resulted from the combination of a salinity gradient linked to a fresh, brackish- and marine species gradient, which was dependent on tidal cycle. The STATICO method proved to be a valuable statistical tool to get a clear representation of temporal organization of the copepod assemblages.

Calanoid copepods assemblages in Pearl River Estuary of China in summer: Relationships between species distribution and environmental variables

To study the relationships between species distribution and environmental variables, calanoid copepods were classified and enumerated, and environmental variables were analyzed along 91 sites of the Pearl River Estuary (China) and adjacent waters. The 91 sites were divided into 3 groups based on surface salinity: the Inner area had salinity level below 10‰ and was mostly located in the Pearl River Estuary, the Coastal area had salinity between 10‰ and 32‰ and was almost located along the coastline, while the Offshore area had salinity level higher than 32‰ and was mainly located in the open area. Indicator Species Analysis was conducted to identify the indicator species within each group from among all calanoid copepods taxa. We found that the Inner area was characterized by Acartiella sinensis, Pseudodiaptomus poplesia and Pseudodiaptomus inopinus, the coastal area was characterized by Temora turbinata and Subeucalanus subcrassus, and the Offshore area was characterized by Paracandacia truncata, Subeucalanus subtenuis, Euchaeta rimana, Pareucalanus attenuatus, Rhincalanus cornutus, Cosmocalanus darwini, Centropages gracilis, Undinula vulgaris, Nannocalanus minor and Paraeuchaeta russelli. Canonical Correspondence Analysis (CCA) was used to identify relevant biotic and abiotic parameters that can best explain the distribution of calanoid copepods. CCA showed that during the summer of 2006, salinity, nutrient variables, especially SiO 3–Si, NO 3–N and DTN, Depth and Chl a were the environmental variables that strongly impacted the distribution and community structure of calanoid copepods.

Patterns of copepod diversity in the Chilean coastal upwelling system

The copepod community structure from the Northern and Central/southern upwelling regions off Chile was studied and compared. The derived community descriptors were species abundance (N), species richness (R) and the Shannon-Wiener diversity index (H′). These descriptors were related to distinct habitats and conditions, sea surface temperature (SST) and depth of the upper boundary of the oxygen minimum zone (OMZ). From 159 samples, obtained between 2002 and 2008, a total number of 118 species were found of which the calanoids Paracalanus indicus, Acartia tonsa and Eucalanus inermis, along with the cyclopoid Oithona similis, and the poecilostomatoids Triconia conifera and Oncaea media were the dominant species. H′ was higher in the northern region, but no differences in N and R were detected between regions. N was higher in the epipelagic vs the deep habitat, but R and H′ did not differ. N, R and H′ correlated positively to SST and negatively to OMZ depth. The ascent of the OMZ to the upper layer forced by upwelling was proposed as a mechanism that aggregates and increases copepod diversity in the food-rich photic zone. All these findings suggest a fundamental role of upwelling variation for modulating copepod dynamics and community structure in this highly productive but strongly variable marine ecosystem.

Effects of the copepod community structure on fecal pellet flux in Kagoshima bay, a deep, semi-enclosed embayment

Seasonal changes in the shape and size composition of fecal pellets were investigated with sediment trap samples from 50 and 150 m in Kagoshima Bay to evaluate how the mesozooplankton community affects fecal pellet flux. Deep vertical mixing was evident in March, and thermal stratification was developed above 50 m in June, August and November. Chlorophyll a, suspended particulate organic carbon (POC) and copepod abundance were uniform throughout the water column during the seasonal mixing and concentrated above 50 m in the stratified seasons. Calanoids were the most predominant copepods in March and poecilostomatoids composed more than 45% of the copepod community in June, August and November. Fecal pellet fluxes at 50 and 150 m were the highest in March, nearly half of POC flux. The relative contribution declined considerably in the other months, especially for less than 4% of POC flux in August. The decline was corresponded to the predominance of cyclopoids and poecilostomatoids. Cylindrical pellets dominated the fecal matters at both depths throughout the study period, while larger cylindrical pellets nearly disappeared at 150 m in June, August and November. Copepod incubation revealed that cylindrical and oval pellets were egested by calanoids and the other copepods, respectively. We suggest that cylindrical fecal pellets produced by calanoid copepods contribute to feces flux but the predominance of poecilostomatoids and/or cyclopoids decreases feces flux via the increase of oval pellets and fragmentation of larger cylindrical pellets.

Vertical changes in abundance, biomass and community structure of copepods down to 3000 m in the southern Bering Sea

Vertical changes in abundance, biomass and community structure of copepods down to 3000 m depth were studied at a single station of the Aleutian Basin of the Bering Sea (53°28′N, 177°00′W, depth 3779 m) on the 14th June 2006. Both abundance and biomass of copepods were greatest near the surface layer and decreased with increase in depth. Abundance and biomass of copepods integrated over 0–3000 m were 1,390,000 inds. m −2 and 5056 mg C m −2, respectively. Copepod carcasses occurred throughout the layer, and the carcass:living specimen ratio was the greatest in the oxygen minimum layer (750–100 m, the ratio was 2.3). A total of 72 calanoid copepod species belonging to 34 genera and 15 families occurred in the 0–3000 m water column (Cyclopoida, Harpacticoida and Poecilostomatoida were not identified to species level). Cluster analysis separated calanoid copepod communities into 5 groups (A–E). Each group was separated by depth, and the depth range of each group was at 0–75 m (A), 75–500 m (B), 500–750 m (C), 750–1500 m (D) and 1500–3000 m (E). Copepods were divided into four types based on the feeding pattern: suspension feeders, suspension feeders in diapause, detritivores and carnivores. In terms of abundance the most dominant group was suspension feeders (mainly Cyclopoida) in the epipelagic zone, and detritivores (mainly Poecilostomatoida) were dominant in the meso- and bathypelagic zones. In terms of biomass, suspension feeders in diapause (calanoid copepods Neocalanus spp. and Eucalanus bungii) were the major component (ca. 10–45%), especially in the 250–3000 m depth. These results are compared with the previous studies in the same region and that down to greater depths in the worldwide oceans.

Species diversity and community structure of pelagic copepods in the marine lakes of Palau

Community structure and diversity patterns of pelagic copepods were investigated for the coastal areas and in the marine lakes of the Palau islands in the West Pacific. We conducted field surveys during 2004–2007 and collected zooplankton samples from eight coastal areas and 16 marine lakes. The marine lakes in the islands of Palau are limnologically classified into two types, meromictic and holomictic lakes. Species diversity indices (Margalef’s species richness d′, Shannon–Wiener index H′, and Simpson’s dominance) were measured at each sampling site. The copepod community structure was analyzed using multivariate analyses, hierarchical cluster analysis, and non-metric multidimensional scaling (MDS) from the PRIMER package. A total of 36 copepod taxa were identified to the genus or species level from Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida. Multivariate analysis based on the Bray–Curtis similarity index revealed that copepod assemblages could be classified into three different groups according to their habitat: (I) meromictic lakes, (II) holomictic lakes with an exceptionally shallow and flat basin (type A holomictic lakes), (III) holomictic lakes with a deep basin (type B holomictic lakes), and all coastal areas. The meromictic lakes were characterized by markedly decreased species diversity (d′ = 0.15, H′ = 0.41) in which only two brackish-water species, Bestiolina similis and Oithona dissimilis, were dominant. Type A holomictic lakes were characterized by relatively low levels of species diversity (d′ = 1.25, H′ = 1.35). In contrast, type B holomictic lakes were characterized by relatively high levels of species diversity, which was comparable to that of coastal areas. This result indicated that zooplankton assemblages in the type B holomictic lakes were closely related to a coastal community. The present study showed that the species diversity of pelagic copepods varies according to the level of isolation and the local environmental conditions for each marine lake.

Spatial distribution and community structure of copepods in a central Mediterranean key region (Egadi Islands—Sicily Channel)

During an autumn oceanographic cruise in October 2004, 87 zooplankton samples were collected from 12 sites, located along inshore–offshore sections around the Egadi Island Archipelago, a central Mediterranean key region. Zooplankton samples were taken by the electronic multinet BIONESS, equipped with a multi-parameter probe system in order to measure simultaneously physico-chemical and biological factors (temperature, salinity, dissolved oxygen and fluorescence). Three different water masses were identified from physico-chemical parameter analysis: MAW (0–50 m) widespread all around the study area; a water mass, which is most likely a mixture of western and eastern-origin waters, up to 300 m depth; and LIW in the 300–600 m layer, with a core salinity of 38.72–38.74 at the most offshore stations. Spatial diversity patterns of copepod assemblage were examined using species richness and Shannon–Wiener diversity indices. 107 copepod species were identified. Four major sample groups were identified by cluster analysis, differing in species composition and abundances in relation to the depth and in-offshore environments. They seemed to be only partly related to the different water masses and significantly correlated to temperature and salinity. In the entire study area, the copepod abundances were markedly lower than those reported for other regions of the Mediterranean Sea, but the species richness was relatively high, and similar to the richest Mediterranean areas. This is probably due to geographical position of the Egadi Island Archipelago at the entrance of Sicily Channel, where water mass exchange between Eastern and Western basins occurs.

Copepod community structure and abundance in a tropical mangrove estuary, with comparisons to coastal waters

Zooplankton, sampled at five stations from the upper Sangga estuary (7 km upstream) in Matang Mangrove Forest Reserve (MMFR), Malaysia, to 16 km offshore, comprised more than 47% copepod. Copepod abundance was highest at nearshore waters (20,311 ind m−3), but decreased toward both upstream (15,572 ind m−3) and offshore waters (12,330 ind m−3). Copepod abundance was also higher during the wetter NE monsoon period as compared to the drier SW monsoon period, but vice versa for copepod species diversity. Redundancy analysis (RDA) shows that copepod community structure in the upper estuary, nearshore and offshore waters differed, being influenced by spatial and seasonal variations in environmental conditions. The copepods could generally be grouped into estuarine species (dominantly Acartia spinicauda Mori, Acartia sp1, Oithona aruensis Fruchtl, and Oithona dissimilis Lindberg), stenohaline species (Acartia erythraea Giesbrecht, Acrocalanus gibber Giesbrecht, Paracalanus aculateus Giesbrecht, and Corycaeus andrewsi Farran) and euryhaline species (Parvocalanus crassirostris Dahl, Oithona simplex Farran, and Bestiolina similis (Sewell)). Shifts in copepod community structure due to monsoonal effects on water parameters occurred at the lower estuary. Copepod peak abundance in mangrove waters could be associated with the peak chlorophyll a concentration prior to it. Evidence of copepod consumption by many species of young fish and shrimp larvae in the MMFR estuary implies the considerable impact of phytoplankton and microphytobenthos on mangrove trophodynamics.

Seasonal variability of planktonic copepods (Copepoda: Crustacea) in a tropical estuarine region in Brazil

The Caravelas River estuary and adjacent coastal region were studied during the rainy and dry seasons of 2003-2004 to assess the copepod community structure. Abiotic and biotic parameters were measured, and the total density, frequency and percentage of copepod taxa were determined for each sampling period. Copepod densities showed significant differences between sampling periods, with higher densities in the rainy seasons (Mean: 90,941.80 ind.m-3; S.D.: 26,364.79). The sampling stations located to the north and south, in the coastal region adjacent to the Caravelas River estuary presented the lowest copepod density values. The copepod assemblage was composed mainly of estuarine and estuarine/coastal copepods. The seasonal variations in temperature and salinity influenced the abundance of species during the rainy and dry seasons, with the following dominant species alternating: Paracalanus quasimodo Bowman, 1971 in the rainy season of 2003, Parvocalanus crassirostris Dahl, 1894 in the dry season of 2003 and Acartia lilljeborgii Giesbrecht, 1892 in the rainy and dry seasons of 2004. Non-parametric multidimensional scaling indicated differences in copepod assemblages between sampling periods, but not between sampling stations.

Seasonal variability of community structure and breeding activity in marine phytal harpacticoid copepods on Ulva pertusa from Pohang, east coast of Korea

Seasonal changes in community structure and reproductive status of phytal harpacticoid copepods in the shallow sublittoral bottom at two sites (Masan-ri and Guryongpo) in Pohang (Korea) are described monthly over a period of 1 year (October 1996 to September 1997). A total of 36 harpacticoid species was identified and the numerically dominant copepods were made up of the families Porcellidiidae and Tisbidae. Although the number of species did not show a seasonal trend, total harpacticoid density revealed a favorable distribution for the warmer season (spring and summer) at both sites. Multiple linear regression analyses showed that univariate indices such as density, evenness and diversity are closely associated with certain environmental parameters. For example, the dominant species fluctuated seasonally in abundance and their maximum densities were found to be temperature- (+ with Porcellidium ofunatense) and nutrient-dependent (+ with Scutellidium longicauda acheloides, + with Zaus unisetosus, and − with P. wandoensis). In addition, the dominant species appeared to breed year round and their reproductive indices are significantly correlated with some environmental parameters such as temperature (−), pH (+), and phosphate (+). Three species ( S. l. acheloides, P. wandoensis, and P. ofunatense) showed maximum density two or three months after their reproductive activity reached a maximum. Overall, the seasonal changes in a phytal harpacticoid community could be explained by combinations of environmental parameters supporting the complexity and biodiversity for this specific group of species in coastal ecosystems.

Diversity and community structure of harpacticoid copepods associated with cold-water coral substrates in the Porcupine Seabight (North-East Atlantic)

The influence of microhabitat type on the diversity and community structure of the harpacticoid copepod fauna associated with a cold-water coral degradation zone was investigated in the Porcupine Seabight (North-East Atlantic). Three substrate types were distinguished: dead fragments of the cold-water coral Lophelia pertusa, skeletons of the glass sponge Aphrocallistes bocagei and the underlying sediment. At the family level, it appears that coral fragments and underlying sediment do not harbour distinctly different assemblages, with Ectinosomatidae, Ameiridae, Pseudotachidiidae, Argestidae and Miraciidae as most abundant. Conclusions on assemblage structure and diversity of the sponge skeletons are limited as only two samples were available. Similarity analysis at species level showed a strong variation in the sediment samples, which did not harbour a distinctly different assemblage in opposition to the coral and sponge samples. Several factors (sediment infill on the hard substrates, mobility of the copepods, limited sample sizes) are proposed to explain this apparent lack of a distinct difference between the microhabitats. Coral fragments and sediment were both characterised by high species diversity and low species dominance, which might indicate that copepod diversity is not substantially influenced by hydrodynamical stress. The additive partitioning of species diversity showed that by adding locations species richness was greatly enhanced. The harpacticoid community in the cold-water coral degradation zone is highly diverse and includes 157 species, 62 genera and 19 families. Information from neighbouring soft-bottom regions is necessary to assess whether total species diversity is increased by the presence of these complex habitat-providing substrates.

Copepod community structure related to environmental factors from a summer cruise in the Gulf of Gabès (Tunisia, eastern Mediterranean Sea)

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.

Seasonal variation in the copepod community structure from a tropical Amazon estuary, Northern Brazil

The main purpose of this study was to investigate the seasonal variation of copepod community structure during the months of July, September and November 2003 (dry season) and January, March and May 2004 (rainy season) in the Curuçá estuary, northern Brazil. Samples were collected during neap tides via gentle 200microm mesh net tows from a small powerboat. Measurements of surface water conductivity were accomplished in situ using an electronic conductivimeter and salinity was later obtained through the transformation of the conductivity values. Salinity varied seasonally from 7.2 +/- 0.1 to 39.2 +/- 1.8 (mean +/- standard deviation) and was influenced mainly by differences in the amount of rainfall between the studied sampling seasons. In total, 30 Copepoda taxa were identified and Acartia tonsa comprised the most representative species throughout the entire studied period followed by Acartia lilljeborgii, Subeucalanus pileatus and Paracalanus quasimodo. In the present study, the density values, ecological indexes and copepod species dominance presented a clear seasonal pattern, showing that the studied area may be considered seasonally heterogeneous in relation to the investigated parameters.

Community structure and vertical distribution of oncaeid copepods in Tosa Bay, southern Japan

Community structure and vertical distribution of oncaeid copepods were investigated at an offshore site in Tosa Bay, southern Japan. Samples were collected with a 0.063 mm closing type net from eight discrete layers between the surface and 500 m depth in August and November 2005. A total of 45 species and three form variants belonging to the genera Triconia, Oncaea, Spinoncaea, Conaea and Epicalymma were identified. The greatest number of species was consistently found in the lower epipelagic zone, at 50–100 m. The vertical distribution patterns of oncaeid copepods were similar between August and November, with the highest abundances in the upper epipelagic zone above the thermocline. The oncaeid maxima corresponded with the depth where appendicularians occurred in high numbers. Dominant species in the water column (0–500 m) were O. venusta small form, O. media, O. scottodicarloi, O. waldemari, O. zernovi, O. tregoubovi, S. ivlevi, S. tenuis and T. conifera. The vertical succession of species composition was almost the same between August and November, although several species showed a downward shift of their depth-range to some extent in November. The oncaeid copepod community could be differentiated into three distinct groups according to the depth layers, each corresponding to different hydrographic conditions in the water column.