Ctenocalanus Vanus Research Articles

Spatio-temporal changes in diversity and community structure of planktonic copepods in Sagami Bay, Japan

Seasonal changes in diversity and community structure of planktonic copepods at a shelf site in Sagami Bay, Japan was studied in relation to cross-shelf interaction of species components. Seasonal mesozooplankton samples were collected from the shelf station (St. M) of the north-west part of Sagami Bay from 1995 to 1997. Vertical multi-layered samples were collected near the center of Sagami Bay (St. P) in June 1996. A total 185 copepod species were identified from the two stations. We observed a clear seasonal succession in calanoid diversity and community structure at St. M from a simple shelf water community (>11 species) during spring blooming periods to highly diverse and mixed communities (ca 20–30 species) of shelf water species coupled with various Kuroshio Current species during late summer to autumn. Cluster and non-metric multidimensional scaling ordination analyses showed two distinct calanoid community groups. One group, which included samples of St. M and the surface layer of St. P, consisted of shelf water species, such as Calanus sinicus, Ctenocalanus vanus, Paracalanus spp., and Kuroshio species, such as, Canthocalanus pauper, Scolecithrix danae, etc. The other cluster was restricted to the samples collected from mid and deep layers at St. P, which consisted of meso- and bathypelagic species and Oyashio species (cold-current species, such as Neocalanus cristatus, Pseudocalanus spp., Eucalanus bungii and Metridia pacifica). In the mid and deep layers at St. P, the population of dormant copepodid stage V (CV) of Eucalanus californicus and C. sinicus were dominant. The deep CV population of C. sinicus might be ecologically discriminated from the surface and shelf water population due to their larger body length and dormant life cycle. E. californicus was also collected at the shelf site during each spring bloom period, whereas the population might descend into the mid- and deep-layers of the central bay before summer. Our results suggest that the seasonal fluctuation of community structure in the shelf water was controlled by both physical (Kuroshio Current) and biological factors, i.e., spring bloom and ontogenetic vertical migration of E. californicus. In particular, transport and diffusion processes of Kuroshio Current in Sagami Bay played a key role in controlling the shelf water calanoid community.

Summer mesozooplankton distribution in coastal waters of central Greece (eastern Mediterranean). II. Species assemblages

Mesozooplankton distribution was investigated over an intensive grid of 124 stations in coastal and pelagic waters of central Greece (eastern Mediterranean) during July 1998. The complex topography of the area consisted of various semi-enclosed gulfs as well as open-sea areas and provided excellent fieldwork for determining species assemblages, their relationships to environmental parameters and the distribution and abundance patterns of the copepod species.Three coastal and one pelagic group of stations were revealed by cluster analysis. Inverse analysis of species affinities defined distinct ‘coastal’ and ‘pelagic’ species assemblages. All coastal areas were dominated by a small number of species (e.g. Penilia avirostris, Podon spp., Ctenocalanus vanus, Paracalanus parvus and Centropages typicus) all belonging to the ‘coastal’ assemblage. Differences among these coastal areas were mainly due to small changes in relative abundance of a common-species list. On the contrary, pelagic stations were characterized by higher species diversity, low dominance and the presence of characteristic epipelagic and mesopelagic species of the Mediterranean Sea (e.g. Calocalanus spp., Haloptilus longicornis, Lucicutia flavicornis, Mecynocera clausi, Farranula rostrata, Mesocalanus tenuicornis and Oncaea mediterranea).The observed differences in taxonomic composition and abundance of zooplankton were related to the marked differences in salinity values observed between the eastern and western part of the surveyed area. Bathymetry, temperature and fluorescence were also related with the inshore–offshore gradient of the zooplankton community observed in the pelagic areas as well as with the discrimination of the zooplankton communities of the various semi-enclosed gulfs of the region.

Summer coastal zooplankton biomass and copepod community structure near the Italian Terra Nova Base (Terra Nova Bay, Ross Sea, Antarctica)

The structure of the zooplankton biotic community and of copepod population in the coastal area of Terra Nova Bay (Ross Sea, Antarctica) was investigated during the 10th Italian Antarctic Expedition (1994/1995). Zooplankton biotic community consisted mainly of pteropods (Limacina helicina and Clione antarctica), Cyclopoid (Oithona similis), Poecilostomatoid (Oncaea curvata) and Calanoid (Ctenocalanus vanus, Paraeuchaeta antarctica, Metridia gerlachei and Stephos longipes) copepods, ostracods, larval polychaetes and larval euphausiids. Zooplankton abundance ranged from 48.1 ind m � 3 to 5968.9 ind m � 3 , and copepod abundance ranged from 45.2 ind m � 3 to 3965.3 ind m � 3 .T he highest peak of zooplankton abundance was observed between 25 m and the surface and was mainly due to the contribution of O. similis, O. curvata and C. vanus. Zooplankton biomass ranged from 5.28 mg m � 3 to 13.04 mg m � 3 dry weight; the maximum value was observed between 25 m and the surface. Total lipid content varied from 216.44 to 460.73 mg g � 1 dry weight.

Spatial patterns of mesozooplankton distribution in the Southwestern Atlantic Ocean (34°–41°S) during austral spring: relationship with the hydrographic conditions

Abstract The mesozooplankton community was analysed in a large region of the Argentine Shelf (34°–41°S) on the main spring spawning ground of the anchovy (Engraulis anchoita), and its spatial pattern was related to the hydrographic conditions. Copepods smaller than 1 mm dominated the community. Three faunistic areas were identified by cluster analysis: northern coastal area (NCA), southern coastal area (SCA), and shelf area (SA), each with distinct physical conditions. The NCA, influenced by the Río de la Plata estuary, had relatively high temperature, the lowest salinity, and the highest stratification values. The SCA had the highest salinity and a vertically homogeneous water column. The SA, vertically stratified, was influenced by the Río de la Plata estuary and by Subantarctic shelf waters and had the lowest temperature values and the greatest depths. Canonical correlation analysis was used to analyse the relationship between zooplankton and physical variables and four zooplankton assemblages were identified. Group A included the copepods Calanus australis, C. simillimus, Clausocalanus brevipes, Centropages brachiatus, Drepanopus forcipatus, Oithona atlantica, and O. helgolandica, and was preferentially distributed in the SA. Group B, composed of the copepods Acartia tonsa and Corycaeus spp. and the cladoceran Pleopis polyphemoides, showed a strong preference for the NCA. Group C included Labidocera fluviatilis, Ctenocalanus vanus, Paracalanus spp., Calanoides cf. carinatus, Euterpina acutifrons, Oithona nana, and the cladoceran Evadne nordmanni, and was preferentially distributed in coastal areas (NCA and SCA). Group D only included the cladoceran Podon intermedius and was mainly located in high salinity waters of the SCA. Small, omnivorous, fast-reproducing species (groups B, D, and most of C) are better adapted to warmer variable and less productive coastal areas, whereas larger herbivorous species (most of group A) seem to better exploit colder stratified and more productive shelf waters. The mesozooplankton community provides adequate food for E. anchoita larvae in coastal areas and for adults in shelf waters.

Interannual variability in copepod community composition at a coastal station in the northern California Current: a multivariate approach

Abstract We sampled a single station in the coastal zone off Newport OR ( 9 km from shore; 60 m water depth) on 206 occasions during 12 years: 1969–1973, 1983 and 1996–2001. We used cluster analysis, ordinations, and indicator species analysis (ISA) to describe temporal variations in copepod community composition. Copepod community structure during summer was distinctly different from winter. Cluster analysis showed that the transition between winter and summer communities occurred early March/April in the 1970s, late (May/June) in the late 1990s, but in (March/April) since spring 2000. Seven copepod assemblages were identified: four were found during the summer upwelling season, two during large El Nino events, and one during winter. Interannual variations in the composition of the summer assemblages was seen: most sampling dates from the summers of 1970, 1973, 2000 and 2001 clustered into one group, and dates from 1971, 1972, and 1999 clustered into a second group. The 1983 and 1998 El Nino events clustered together, but subdivided into “early El Nino” and “late El Nino” communities. The summer of 1969 corresponded with a weak El Nino event but clustered differently from both the other El Nino events and other summer clusters. Samples collected during the 1972 El Nino event clustered with “normal” summers. Non-metric multidimensional ordination analysis showed that two axes accounted for 87% of the variability in community composition; Axis 1 was associated with the influence of El Nino events and seasonal downwelling, and Axis 2 was associated with upwelling-induced productivity. ISA showed Centropages abdominalis, Acartia longiremis, and Microcalanus pusillus as indicators of upwelling; Corycaeus anglicus, Calanus pacificus, and Ctenocalanus vanus as good indicators of El Nino; and Ctenocalanus vanus, Clausocalanus, and Calocalanus styliremis as good indicators of winter conditions.

Mesozooplankton community structure and grazing impact in the Polar Frontal Zone of the south Indian Ocean during austral autumn 2002

Mesozooplankton community structure and grazing impact were investigated at 13 stations in the Polar Frontal Zone during the second Marion Offshore Variability Ecosystem Study (MOVES II), conducted during April 2002. Total integrated chl- a biomass ranged between 11.17 and 28.34 mg chl- a m-2 and was always dominated by nano- and picophytoplankton (<20 µm). Throughout the study, small copepods, mainly Oithona similis and Ctenocalanus vanus, numerically dominated the mesozooplankton community, composing up to 85% (range 30–85%) of the total abundance. Grazing activity of the four most abundant copepods ( O. similis, C. vanus, Calanus simillimus and Clausocalanus spp.), constituting up to 93% of total mesozooplankton abundance, was investigated using the gut fluorescence technique. Results of gut fluorescence analyses indicated that Calanus simillimus and Clausocalanus spp. exhibited diel variability in gut pigments with maximum values recorded at night. In contrast, O. similis and Ctenocalanus vanus did not demonstrate diel variation in gut pigment contents. Ingestion rates of the four copepods ranged from 23.23 to 1462,02 ng(pigm.)ind-1day-1. The combined grazing impact of the four copepods ranged between 1 and 36% of the phytoplankton standing stock per day, with the highest daily impact occurring at stations occupied in the vicinity of the Antarctic Polar Front (~35.86% at station 23). Among the copepods, O. similis and Ctenocalanus vanus represented the most important consumers of phytoplankton biomass, collectively responsible for up to 89% (range 15–89%) of the total daily grazing impact. Carbon specific ingestion rates of the copepods varied between 42 and 320% body carbon per day.

Onshore-offshore variations in copepod community structure off the Oregon coast during the summer upwelling season

During the summer of 1994, 1996, and 1997, we conducted hydrographic and plankton surveys of the upper 70 m in the nearshore, the continental shelf, and off-shelf oceanic waters off Oregon, USA. Copepod densities and biomass were estimated along 4 transects from each cruise. The on-shelf copepod biomass was 2.8 times greater than off-shelf biomass. Nonmetric multidimen- sional scaling identified an on-shelf and an off-shelf copepod community. The change in community composition usually occurred at or slightly offshore of the continental shelf break, defined here as 180 m water depth. Indicator-species analysis identified the subarctic neritic species, Calanus mar- shallae, Pseudocalanus mimus, and Acartia longiremis, as good indicators of continental shelf waters. 'Warm water' species Mesocalanus tenuicornis, Calocalanus styliremis, Clausocalanus spp., and Ctenocalanus vanus were indicators of off-shelf waters. The copepod communities off the coast of Oregon during the summer upwelling season reflect the origins of the dominating currents within each habitat. The coastal copepod community is subarctic neritic in origin, consistent with southward coastal flows. The offshore copepod community is a mixture of species with origins in the Transition Zone as well as species that are typical of the coastal region of the California Current off central and southern California. We speculate that the central and southern California Current species are pre- sent in offshore waters of Oregon in summer because they are transported north with the Davidson Current in winter but, with the initiation of the upwelling season in spring, they are transported into offshore waters where they establish viable populations.

Mesozooplankton features in a frontal area off northern Patagonia (Argentina) during spring 1995 and 1998

Hydrography and spatial patterns of mesozooplankton communities in a frontal area off northern Patagonian were investigated in spring 1995 and 1998. Differential wind/tidal relative forcing appeared to drive along-shelf variations in the physical structure of the front and hence, planktonic patterns. Approaching the northern border of the system, the conspicuous presence of Oithona helgolandica , cladocerans and appendicularians, and the low fecundities of calanoid copepods suggest that a high proportion of the primary production may be channelled through microheterotrophic processes. Towards the southern area, calanoids dominated over cyclopoids, `large´ species ( Drepanopus forcipatus, Calanoides cf. carinatus ) were abundant, and copepod fecundities were high and steady, suggesting that there may be a more classical-like herbivorous food web. Paracalanus parvus and Ctenocalanus vanus occurred over the whole system but seemed to be key species in mixed and weakly stratified waters. Copepods peaked in stratified waters away from the front itself, while the abundance of eggs and nauplii was highest in weakly stratified waters next to the front. Apparently, the general heating occurring over the region in spring 1998 strongly affected both the physical and biological structure of the system. Unlike in 1995, a massive bloom of gelatinous zooplankton took place in 1998 and a bloom of the phagotrophic dinoflagellate Noctiluca sp. occurred in the northern area. Co-occurring copepod populations were depressed and their reproductive patterns seemed to be highly disrupted. Present observations stress the significance of variable external forcing in driving satisfactory habitat conditions for juvenile fish in the area.

Predation impact of carnivorous macrozooplankton in the vicinity of the Prince Edward Island archipelago (Southern Ocean) in austral autumn 1998

The composition, biomass, feeding and predation impact of carnivorous macrozooplankton (>2 cm) on mesozooplankton (0.2–2 cm) in the sub-Antarctic waters of the southwest Indian Ocean were investigated at 19 stations in austral autumn (April/May) 1998. Zooplankton abundances and biomass ranged from 6.9 to 95.2 ind m−3 and between 1.8 and 18.1 mg Dwt m−3, respectively. Throughout the investigation, mesozooplankton comprising mainly copepods numerically and by biomass dominated net samples. Among the copepods, Calanus simillimus, Clausocalanus brevipes, Ctenocalanus vanus, and Oithona spp. dominated. The carnivore component of the macrozooplankton consisted mainly of five groups: decapods, amphipods, chaetognaths, euphausiids and gelatinous zooplankton. Among these, chaetognaths (Eukrohnia hamata and Sagitta gazellae) and euphausiids (Nematoscelis megalops and Euphausia longirostris) were the most prominent. Collectively, the carnivorous macrozooplankton comprised between 11% and 72% of total zooplankton biomass. Total predation impact of the carnivorous macrozooplankton varied considerably but generally accounted for <5% (range 0.7–44%) of the total mesozooplankton standing stock. Tentative calculations suggest that carnivorous macrozooplankton may contribute, via vertical migrations and production of fast sinking faecal pellets, to a downward flux of carbon equivalent to up to 9% of the total mesozooplankton stock per day within the Antarctic Polar Frontal Zone. As a consequence, carnivorous macrozooplankton may increase the localised efficiency of the biological pump.

Distribution patterns of epipelagic copepods off Rio de Janeiro (SE Brazil) in summer 1991/1992 and winter 1992

The spatial distribution of copepod populations on the eastern continental shelf off Rio de Janeiro State, Brazil, was analysed in relation to the hydrographic regime in December–January (summer 1991/92) and July (winter 1992). Advection of cold and nutrient-rich South Atlantic Central Water (SACW) onto the shelf was a prevailing circulation mechanism in both seasonal cruises. The SACW occupied a larger proportion of bottom layers in summer as compared to winter, but only in the latter a well-defined upwelling event was recorded off Cape Frio. Two calanoid copepods were representative of shelf areas influenced by SACW intrusions: Calanoides carinatus, which occurred mainly during summer and Ctenocalanus vanus, recorded at high densities in both periods. Paracalanus quasimodo was the dominant copepod at inner- and mid-shelf stations both in summer and winter, followed by Temora spp. and Oncaea spp. These coastal species peaked at the upwelling site. A highly diversified and comparatively less abundant copepod assemblage, dominated by Clausocalanus furcatus and Oithona plumifera, was recorded in outer-shelf stations occupied by the oligotrophic Tropical Waters of the Brazil Current. We conclude that regional and seasonal contrasts in copepod species composition and abundance are controlled to a great extent by the advection and upwelling of the SACW onto the shelf.

Zooplankton assemblages and influence of environmental parameters on them in a Mediterranean coastal area

Temporal dynamics of zooplankton communities and assemblages, as well as the influence of environmental factors on them, were studied in Saronikos Gulf (Aegean Sea, Greece). Different multivariate techniques (hierarchical clustering, multidimensional scaling and correspondence analysis) were applied on a 2 year data set of zooplankton species composition, based on samples collected at five stations of the study area. A clear discrimination of two communities was revealed, the first one in the semi-enclosed polluted northern part (Elefsis Bay) and the second in Saronikos Gulf proper. Within the latter community, five assemblages were distinguished: (i) the coastal winter assemblage characterized by Ctenocalanus vanus, Oithona similis, Clausocalanus pergens and Fritil- laria pellucida; (ii) the psychrophilic assemblage influenced by the open sea and characterized by Oithona plumifera and Clausocalanus jobei; (iii) the spring assemblage characterized by Evadne nordmanni and Cenlropages typicus; (iv) the coastal thermophilic assemblage characterized by Penilia avirostis, Evadne tergestina and Temora stylifera; (v) the thermophilic assemblage influenced by the open sea and characterized by Clausocalanus furcatus. Both zooplankton and environmental data were treated by multiple correspondence analysis which revealed the importance of some environ- mental factors on zooplankton community composition (eutrophication-pollution, temperature, water mass circulation, hydrology and topography).

Structure and grazing impact of the mesozooplankton community during late summer 1994 near South Georgia, Antarctica

Mesozooplankton abundance, community structure and grazing impact were determined during late austral summer (February/March) 1994 at eight oceanic stations near South Georgia using samples collected with a Bongo and WP-2 nets in the upper 200-m and 100-m layer, respectively. The zooplankton abundance was generally dominated by copepodite stages C3–C5 of six copepod species: Rhincalanus gigas, Calanus simillimus, Calanoides acutus, Metridia spp., Clausocalanus laticeps and Ctenocalanus vanus. Most copepods had large lipid sacs. All copepods accounted for 41–98% of total zooplankton abundance. Juvenile euphausiids were the second most important component contributing between 1 and 20% of total abundance. Pteropods, mainly Limacina inflata, were important members of the pelagic community at two sites, accounting for 44 and 53% of total abundance. Average mesozooplankton biomass in the upper 200 m was 8.0 g dry weight m−2, ranging from 4.3 to 11.5 g dry weight m−2. With the exception of Calanussimillimus, gut pigment contents and feeding activity of copepod species were low, suggesting that some species, after having stored large lipid reserves, had probably started undergoing developmental arrest. Daily mesozooplankton grazing impact, measured using in situ gut fluorescence techniques and in vitro incubations, varied widely from <1 to 8% (mean 3.5%) of phytoplankton standing stock, and from 5 to 102% (mean 36%) of primary production. The highest grazing impact was found northeast of the island co-incident with the lowest phytoplankton biomass and primary production levels.

Relationships between hydrography, phytoplankton production, biomass, cell size and species composition, and copepod production in the southern Benguela upwelling system in April 1988

Hydrography and plankton were sampled along a cross-shelf transect off the Olifants River. South Africa, in April 1988, during a relaxation phase of upwelling. Chlorophyll concentrations were similar across the shelf, 3–5 μg chl a·ℓ−1. Midshelf, c. 80 per cent of the chlorophyll a was in cells > 10 μm, but nearshore 90 per cent was in cells < 10 μm. Large cells (diatoms) dominated midshelf waters and small cells (flagellates) nearshore waters. Smaller copepods (Paracalanus parvus, Ctenocalanus vanus, Centropages brachiatus and Oithona spp.) were most abundant shorewards of the 130 m isobath; larger ones (Calanus australis and Rhincalanus nasutus) were most abundant farther offshore. Calanoides carinatus was equally abundant at all stations. Primary production averaged 2,4 g C·m−2·day−1 at the large-cell stations and 1,5 g C·m−2·day−1 at the small-cell stations. In all, 69 and 29 per cent of the production was in the > 10 μm size fraction and 15 and 48 per cent in the fraction <2 μm at the large- and small-cell stations respectively. Rates of egg production of female C. australis, C. carinatus, C. brachiatus and P. parvus averaged 43 per cent of maximum at the large-cell stations but only 8 per cent of maximum at the small-cell stations. Growth rates of small juvenile copepods (<5–10 μg dry mass) were at their maximum, but those of larger individuals were less than maximum, suggesting food-limitation of growth. Rates of copepod production were similar in both water types, 4,1 and 3,6 mg C·m−3·day−1. Food-chain efficiency (FCE), the ratio of secondary to primary production, ranged from 3,5 to 12,5 per cent. Copepods consumed 12–42 per cent of the primary production. The FCE and the absolute proportion of phytoplankton consumed were dependent upon which sizes of phytoplankton were assumed eaten by the grazers.