Podon Leuckarti Research Articles

Mesozooplankton succession in a sub-Antarctic bay (Beagle channel, Southern tip of South America): distinctive annual patterns between two environmentally different zones

Frequent sampling of zooplankton is essential to understand their annual dynamics. However, in polar and subpolar ecosystems, such sampling is rare. This study comparatively analysed, for the first time, the annual mesozooplankton succession in the northwest nearshore and external zones of Ushuaia Bay in the sub-Antarctic Beagle Channel by monthly sampling over two years. The nearshore zone, with shallow waters and strong continental and anthropogenic influence, was characterised by the year-round occurrence of the euryhaline copepod Eurytemora americana and adventitious taxa. The mesozooplankton community exhibited pronounced monthly and year-to-year variability but, as a general seasonal trend, winter assemblages were dominated by the copepod Oithona similis and adventitious nematodes, whereas the spring–summer ones were dominated by E. americana, the cladoceran Podon leuckarti and Cirripedia nauplii. In the external zone, the copepods Drepanopus forcipatus and Ctenocalanus citer were found throughout the year. The annual succession showed a clearer seasonal pattern. Main shifts in community structure occurred in late winter–spring and late summer–autumn, when a high representation of meroplankton and appendicularians was closely associated with phytoplankton blooms. The higher temporal variability in the nearshore community was partially related to variable contributions of adventitious taxa to assemblage composition and may be also reflecting stressful conditions for plankton species linked to freshwater and urban discharges reported within the bay. This study allowed filling the temporal gaps in previous research and providing a more complete picture of the annual mesozooplankton dynamics in the Beagle Channel, generating hypotheses at the community and population levels for future research.

Spatio-temporal dynamics of mesozooplankton in the subantarctic Beagle Channel: The case of Ushuaia Bay (Argentina)

The Beagle Channel is the southernmost South American fjord. Although it has been the focus of many biological studies, more in-depth knowledge of plankton and their linkage with environmental variables is lacking. The main objective of this study was to analyse the spatio-temporal variations in mesozooplankton assemblages of Ushuaia Bay, an ecologically and economically relevant area in the middle Beagle Channel, on the basis of samples collected during summer (March), autumn (June), winter (September) and spring (December) 2012 from environmentally different sites. Mesozooplankton composition and abundance exhibited strong seasonal variations, closely associated with the late winter–springphytoplankton bloom. The appendicularian Fritillaria borealis and the cyclopoid copepod Oithona similis were the dominant species during summer and autumn, whereas meroplanktonic larvae and the cladocerans Evadne nordmanni and Podon leuckarti dominated during late winter and spring, respectively. Mesozooplankton abundance was lower at coastal sites receiving freshwater and sewage discharges. Contrary to data reported a decade earlier, small-sized omnivorous species were dominant in Ushuaia Bay in 2012. The increased abundance of these species and decrease in the abundance of calanoids (e.g. Drepanopus forcipatus and Eurytemora americana) may reflect the natural year-to-year variability in phytoplankton structure and water physico-chemical properties. However, since this bay suffers from chronic pollution, other explanations, such as the influence of eutrophication on plankton structure, should also be considered. This study provides a baseline for future research on the effects of natural and anthropogenic environmental change on the Beagle Channel, thereby expanding our knowledge of plankton in subantarctic fjords.

Spring and Summer Zooplankton Community near Tongyeong and Namhaedo in the South Sea of Korea

The monthly variations of zooplankton community were investigated at 12 stations near Tongyeong and Namhaedo in the South Sea of Korea from April to July, 2012. Zooplankton samples were collected by a plankton net (RN80) from near the bottom to the surface. Zooplankton community consisted of 97 taxa, and the mean abundance ranged from 213 inds.mSUP-3/SUP in July to 426 inds.mSUP-3/SUP in April. Copepods constituted 38.98% of zooplankton abundance, and included 39 species. Calanus sinicus, Corycaeus affinis, Paracalanus parvus s.l., copepodids, Evadne nordmonni, Podon leuckarti, cirriped nauplii, Muggiacea sp., Diphyes sp., and Zonosagitta bedoti were dominant species. Of these, Calanus sinicus was the most abundant throughout the study period, being constituted 18.6% of total zooplankton abundance. The density variations of dominant species between stations and months were correlated with the environmental factors. Zooplankton community varied with by sampling months, being influenced by monthly oceanographic variations.

Mesozooplankton assemblages and their relationship with environmental variables: a study case in a disturbed bay (Beagle Channel, Argentina)

This study focused on the seasonal and spatial analysis of the mesozooplankton community in a human-impacted subantarctic bay in Argentina and aimed to detect assemblages associated with environmental variability. Mesozooplankton samples and environmental data were obtained in the Ushuaia Bay (UB) seasonally, from August 2004 to June 2005, and spatially, from coastal (more polluted), middle (less influenced) and open sea water (free polluted) sampling stations. Remarkable seasonal changes on the mesozooplankton community were observed. Nitrogenated nutrients, chlorophyll a, salinity and temperature were the prevailing environmental conditions likely associated with the different mesozooplankton assemblages found in the bay. The copepods Eurytemora americana, Acartia tonsa, Podon leuckarti and Nematoda were particularly observed on the northwest coast of the bay, characterized by the highest level of urban pollution, eutrophicated by sewage and freshwater inputs from the Encerrada Bay which is connected to it. The stations situated in the northeast area, mostly influenced by freshwater input from rivers and glacier melting, showed low mesozooplankton abundances and an important contribution of adventitious plankton. The copepods Ctenocalanus citer, Clausocalanus brevipes and Drepanopus forcipatus were mostly observed at the stations located near the Beagle Channel, characterized by open sea and free polluted waters. Our findings suggest that the variations observed in the mesozooplankton assemblages in the UB seem to be modulated by environmental variables associated with the anthropogenic influence, clearly detected on the coast of the bay. Certain opportunistic species such as A. tonsa and E. americana could be postulated as potential bioindicators of water quality in subantarctic coastal ecosystems.

Seasonal changes in the distribution and abundance of marine cladocerans of the Northwest Alboran Sea (Western Mediterranean), Spain

The annual cycle of marine cladocerans was studied over six years from 1994 to 1999 within the frame of the monitoring Project ECOMALAGA at a nine stations in the NW of the Alboran Sea, with the aim of assessing seasonal patterns and interannual trends in distribution and abundance of marine cladocerans. Seven species (Penilia avirostris, Evadne nordmanni, Evadne spinifera, Pseudoevadne tergestina, Pleopis polyphemoides, Podon leuckarti and Podon intermedius) were detected in the northwest Alboran Sea. Total cladoceran relative abundance varied from 0 to 89 % of the total cladocerans. The abundance of cladocerans was higher in summer-autumn than in winter-spring (7012 - 4711.100 and 743 - 217.100m-3 , respectively). The species composition was very different in terms of seasonality. P. polyphemoides, P. leuckarti and P. intermedius appeared mostly during the spring. P. tergestina, E. spinifera and E. nordmanni predominantly occurred during the winter. P. avirostris occurred mostly during the summer and autumn.

Trophic interactions of pelagic crustaceans in Comau Fjord (Chile): their role in the food web structure

Grazing experiments were used to study the trophic interactions among plankton components in a stratified fjord of southern Chile. A strong pycnocline (7–10 m) separating the low-salinity layer from the deeper, high-salinity, marine layer, affected the composition, abundance and distribution of phytoplankton and zooplankton every season. Nanoflagellates averaging 59% were consistently the main components of the plankton biomass in both layers. The microphytoplankton contribution was always higher within the marine layer. Cladocerans and some small copepods showed a vertical gradient with greater abundances in the low-salinity layer, whereas medium-large copepods and euphausiids were more abundant below the pycnocline. Podon leuckarti averaged an ingestion rate of 3.1 µg C ind.−1 day−1, consisting mostly of particles from the nanoplankton size spectrum. Given significant clearance on ciliates and athecate dinoflagellates plus high ingestion rates of heterotrophic nanoflagellates it seems that this species selects for microzooplankton and that heterotrophic components are important in their diet. Calanus australis ingested 15 µg C ind.−1 day−1 on average, covering a wide spectrum of prey sizes (5–65 µm equivalent spherical diameter) and diversity, with active selection for ciliates. The average ingestion rate for Euphausia vallentini was 78.7 µg C ind.−1 day−1, including wide variety of prey sizes but no apparent selectivity. The potential grazing impact (11%) on primary productivity, together with high abundances, feeding selectivity on nanoplankton and production of unconsolidated fecal material indicate that cladocerans could have a double positive feedback effect on the microbial loop, thereby having an important impact by modifying the composition and structure of the planktonic community in Comau Fjord in spring-summer.

시화호 중형동물플랑크톤 군집의 시공간적 변동

The purpose of this study was to investigate the temporal and spatial variability of taxonomic groups and major species of the mesozooplankton community in Lake Shihwa, Korea. Monthly collections were carried out at five stations in Lake Shihwa for a period of one year. The mesozooplankton community showed distinct seasonal variability with water temperature and salinity. Major mesozooplankton species in each seasonal community were derived from non-metric MDS and SIMPER as follows: winter community (Acartia hongi and Eurytemora pacifica), spring community (Acartia hudsonica and Polychaeta larvae), summer community (Acartia sinjiensis, Pavocalanus crassirostris, Evadne tergestina and Cirripedia nauplii) and fall community (Paracalanus indicus and Podon leuckarti). The succession of the seasonal species, A. hudsonica and A. sinjiensis, was the most remarkable event during the seasonal changes of the mesozooplankton community. The species response curve of these species fitted with the logistic regression in relation to water temperature and salinity. The curve also correctly represented the characteristics of the occurrence of A. hudsonica and A. sinjiensis in Lake Shihwa.

Distribution, diversity and biomass of summer zooplankton from the coastal Canadian Beaufort Sea

Composition, abundance, biomass and distribution of zooplankton in the coastal Canadian Beaufort Sea were studied in the summer of 2005 and 2006. Data were collected from two cross-shelf transects (11 stations in each). Sampling was conducted with vertical hauls using a conical net of 153-μm mesh size. Our results revealed that there are three ecological zones, Intense Plume, Diffuse Plume and oceanic, which are primarily shaped by the highly variable Mackenzie River plume. The Intense Plume Grouping was located at stations influenced greatly by the Mackenzie River, where Podon leuckarti, Pseudocalanus spp., Copepoda nauplii and Limnocalanus macrurus were most abundant. The Diffuse Plume Grouping, that was located in the transitional zone between the river plume and the ocean, had the highest diversity. This grouping was characterised by high abundance of Copepoda nauplii, Polychaeta larvae, Pseudocalanus and L. macrurus. The Oceanic Grouping, located farthest from shore beyond the 85-m depth contour, was mainly inhabited by marine taxa—Calanusglacialis, C. hyperboreus, Triconia (Oncea) borealis and Microcalanus spp.—and had the greatest overall zooplankton abundance and biomass of all groupings.

Inter-annual variability in abundance and community structure of zooplankton south and north of Iceland in relation to environmental conditions in spring 1990-2007

An 18 year zooplankton time series from two standard sections differing in hydrographic conditions (Subarctic Water north of Iceland and Atlantic water south of Iceland) was examined in relation to hydrography and phytoplankton dynamics, and large-scale climatic changes in the North Atlantic Ocean, particularly the North Atlantic Oscillation (NAO). The long-term mean zooplankton abundance was higher in south (∼160 000 individuals m−2) than that in north of Iceland (∼120 000 individuals m−2). Abundance fluctuated markedly between years. Copepods (mainly Calanus finmarchicus and Oithona spp.) dominated the zooplankton, comprising >60–70% of the plankton in most years. Among the copepods, C. finmarchicus was more abundant in south of Iceland (∼20–70%) than to the north (∼10–60%). Abundance and community structure were related to environmental variables using regression and multivariate techniques (principal component analysis and redundancy analysis). Temperature and salinity were the most important environmental variables in explaining the differences in species composition in north and south of Iceland, with species and groups like Podon leuckarti and cirripede larvae being relatively abundant to the south, and C. hyperboreus to the north of Iceland. A significant year-to-year variability in community structure was observed both to the south and to the north, with salinity and used nitrate dictating the variability to the south and temperature to the north (Monte Carlo permutation tests, P < 0.05). In neither region was a unidirectional temporal trend in species composition.

Spatial and temporal distribution patterns of Cladocera in the Argentine Sea

The geographical and seasonal distribution of Cladocera was studied in the Argentine Sea, from the Rio de la Plata River (34°S) to the Patagonian area (47°S). The cladoceran community included six species, which were found in the plankton especially in spring and summer and were absent during winter. Evadne nordmanni and Podon intermedius were the most widely distributed species, from 34°S to 44°S, in coastal and mid-shelf waters (MSW). Their Temperature-Salinity ranges of occurrence were around 8–21.7°C and 18–36.4‰. High numbers of E. nordmanni and P. intermedius were observed in the weakly stratified waters of the northpatagonian tidal front (42°S–45°S) compared to the other sectors of the frontal system. Pleopis polyphemoides mainly appeared north of 39°S in waters influenced by the Rio de la Plata estuary (18–36.5‰) and it showed preference for warm waters. Podon leuckarti was present only in a few samples from cold coastal and MSW between 38°S and 44°S and seemed to be a stenohaline species (33.4–34.2‰). Penilia avirostris and Pseudoevadne tergestina were found north of 39°S particularly in coastal and MSW, but also in tropical and subtropical waters. Their Temperature-Salinity ranges of occurrence were 14–20.5°C and 27–36.5‰. Although the highest densities of Cladocera were found in neritic waters, our data suggests that some species may also inhabit oceanic waters. During early spring, E. nordmanni, P. polyphemoides, P. intermedius, and P. leuckarti were the first species to appear in the plankton in coastal waters off the Buenos Aires province, followed by P. avirostris and P. tergestina which gradually replaced the previously mentioned species and were dominant during the following summer. All species were absent during autumn and winter.

Geographical and seasonal variations in mesozooplankton abundance and biomass in relation to environmental parameters in Lake Shinji–Ohashi River–Lake Nakaumi brackish-water system, Japan

We measured the abundance and biomass of the major taxonomic groups of mesozooplankton at six stations in Lake Shinji–Ohashi River–Lake Nakaumi brackish-water system, Japan, monthly for three full years (1995–1997), except for one station (for 1 year and 9 months). Over the entire area, copepods overwhelmingly dominated the zooplankton community both in terms of abundance (mean: 87.9%) and biomass (83.4%). The remaining taxa were cladocerans (i.e. Diphanosoma brachyurum, Evadone tergestina, Penilia avirostris, Podon leuckarti and Podon polyphemoides), appendicularians ( Oikopleura dioica and Oikopleura longicauda), chaetognaths ( Sagitta crassa) and the larvae of benthos (e.g. polychaetes, bivalves, gastropods and malacostracans). The geographical and seasonal variations of the mesozooplankton community were therefore principally explained by the variations of the copepod community. The geographical difference in copepod species composition was associated with salinity preference or tolerance of respective species. In Lake Shinji, where the salinity was lowest (mean: 4.0), Sinocalanus tenellus was monospecifically abundant with sporadic occurrence of Pseudodiaptomus inopinus. In Ohashi River (mean salinity: 9.9), Acartia hudsonica, Acartia sinjiensis, Eurytemora pacifica and Oithona davisae added to the community. At central and southeast Lake Nakaumi and in Honjo District, where mean salinity ranged from 16.4 to 21.7, these four species became more important than S. tenellus and P. inopinus. At the entrance of Sakai Strait, where the salinity was highest (mean: 24.0), Paracalanus spp. constituted a significant component. Due to large temperature fluctuation with season, the copepods showed remarkable seasonal variations in abundance and biomass, with enormous annual peaks in winter–spring. These annual peaks might be attributed to scarce occurrence of predators.

Diel Vertical Migration of the Marine Cladoceran Podon leuckarti:Variations with Reproductive Stage

Diel vertical migration (DVM) of the marine cladoceran Podon leuckarti was investigated with reference to their reproductive stages and size. Males and females, except for gamogenic females with an advanced resting egg (GA), aggregated at the near-bottom layer or at the surface during the day and dispersed into the water column at night. Both the near-bottom aggregation and the surface aggregation during daytime are suggested to be behavior that reduces the predation risk from visual predators. However, GA aggregated in the near-bottom layer during daytime and avoided the surface layer. The near-bottom aggregation might be more effective behavior for GAs to reduce risk of visual predation than the surface aggregation because of the conspicuous resting egg they carried. These results show that carrying an advanced resting egg influenced the DVM of P. leuckarti.

Seasonal cycle of zooplankton southwest of Iceland

Seasonal variations in biomass, abundance and species composition of zooplankton in relation to environmental parameters and chlorophyll a were studied in both the Coastal water [salinity] (S) <35.0‰] and the Atlantic water (S > 35.0‰ southwest of Iceland. The sampling was carried out at approximately monthly intervals from February to November 1991. The mean temperature of the upper 50 m of the water column varied greatly during the year. Lowest temperatures were recorded in March–April (5–7δC) and the highest in July–August (11–12δC). The spring bloom of the phytoplankton probably occurred earlier in the Coastal water (early May) than in the Atlantic water (mid-to late May) and in neither water mass was there an autumn peak in the standing stock of chlorophyll a. The seasonal variations in both biomass and abundance of total zooplankton followed more or less those of the most abundant zooplankters, and were characterized by a seasonal low during the winter and two maxima during the summer (May–June) and early autumn (July–September). In the Coastal water, Calanus finmarchicus was the most abundant species (˜33% of the total zooplankton), followed by Temora Iongicornis (˜27%), Evadne nordmanni (˜17%), Podon leuckarti (˜8%) and Pseudocalanus spp. (˜6%). On the other hand, in the Atlantic water the plankton were completely dominated by C.finmarchicus (˜92%), while euphausiid eggs and larvae ranked second (˜3%) and third (˜2%), respectively. The annual mean dry weight biomass was about one and a half times greater in the Coastal water (˜6 g m−2 than in the Atlantic water (˜4 g m−2 Further, the annual mean abundance was approximately four times higher in the Coastal water (˜120 000 individuals m−2 compared to the Atlantic water (˜32 000 individuals m−2 This is presumably reflecting the higher production of the zooplankton community in Coastal water compared to Atlantic water.

Feeding habits of marine cladocerans in the Inland Sea of Japan

Natural food items of five species of marine cladocerans, Evadne nordmanni, E. tergestina, Penilia avirostris, Podon leuckarti and P. polyphemoides, were investigated in the Inland Sea of Japan between April 1986 and May 1987. Gut content examination with SEM (scanning electron microscopy) revealed that feeding was largely limited to centric diatoms and a few exceptions of pennate diatoms and dinoflagellates. No animal remains were detected, and some unidentified materials were also found. Phytoplankton smaller than 35 μm in size (cell diameter in centric diatoms and longest dimension in others) was found most frequently in the gut of cladocerans. The role of grazing of marine cladocerans in trophodynamic pathways of the pelagic realm is discussed.

Biology of the threespine stickleback,Gasterosteus aculeatus, and the blackspotted stickleback,G. wheatlandi, during their marine pelagic phase in the Bay of Fundy, Canada

Two species ofGasterosteus were collected from the surface waters of 48 stations in the Bay of Fundy from 1979–1982. Densities varied widely according to locality and time of year (range: 1 fish 0.2 m−2 to 1 fish 26.3 m−2 of sea surface) but peaked within 30 km of the New Brunswick/Maine coast in July and August. A few adults were caught as far as 100 km from the coast in winter. Guts ofG. wheatlandi were significantly fuller (63.3 ± 0.6%) than those ofG. aculeatus (44.6 ± 0.1%) but there were no differences between male and female guts within species. Quantitatively, gut contents were very similar between species, consisting primarily of (99.4%): calanoid copepods (Centropages typicus Kroyer andEurytemora cfamericana Williams), copepod nauplii, cladocerans (Podon leuckarti Sars andP. polyphemoides Leuckart) and planktonic eggs (in decreasing order of importance).Gasterosteus wheatlandi ate significantly more calanoids thanG. aculeatus but all other prey types were eaten in similar amounts. Within species, there were no differences in the numbers of each prey type eaten over time. The most abundant calanoid species caught alongside the fishes in the sampling nets did not occur in the sticklebacks' diets; probably they were too large to be ingested.Gasterosteus aculeatus bred in inshore, brackish water ponds in late April. By late July most juveniles had migrated out into the Bay but a few remained until early September.Gasterosteus wheatlandi bred later in the brackish water ponds (late May) and juveniles began migrating into the Bay in early August; a few remained in the ponds until early September. Adults were found in the Bay alongside juveniles suggesting that individuals of both species may survive for a second year. In both species, growth rates of juveniles were greater in brackish water than in the sea.

Length-weight relationships of important zooplankton from the Inland Sea of Japan

Measurements of dry weight, carbon- and nitrogen contents together with the body length of important zooplankton from the Inland Sea of Japan were made using freshly caught specimens. The values of the former three parameters were found to be highly correlated to length, and species specific regression equations were calculated for 10 species of Copepoda (Calanus sinicus, Euchaeta plana, E. concinna, Centropages abdominalis, Sinocalanus tenellus, Acartia clausi, A. tsuensis, Tortanus forcipatus, Oithona brevicornis andO. similis), 3 species of Cladocera (Podon leuckarti, P. polyphemoides andPenilia avirostris), 1 species of each of Mysidacea (Neomysis japonica), and Natantia (Acetes japonicus), and two forms of Chaetognatha (Sagitta crassa andS. crassa f.naikaiensis).

The food of larval turbot Scophthalmus maximus L. from the west central North Sea

An examination was made of the gut contents of the larvae of turbot 3·5–16·9 mm in length, from off the northeast coast of England. All the larvae contained a wide variety of planktonic crustaceans the most important of which were the cladocerans Podon leuckarti and Evadne nordmanni and copepodites of five species of calanoid copepods. Oikopleura dioica was also taken. Phytoplankton was found in the stomachs of some of the smaller larvae. It was estimated that the larvae ate 28·0% of their body weight each day.

The occurrence of marine Cladocera on the west coast of Sweden

The present paper is based on a 3-year field study of marine Cladocera in the waters off Gothenburg on the Swedish west coast. The group mainly occurred from May to September, when there was a temperature stratification of the waters. The dominant species, Evadne nordmanni Loven, may occur in large numbers during the entire warm period, both in offshore and inshore waters. The species Podon leuckarti G.O. Sars, P. intermedius Lilljeborg, and Pleopis (=Podon) polyphemoides (Leuckart) occurred separately both in time and space. The occurrence of different species may primarily be regulated by abiotic factors, e.g. temperature and currents, but may also be modified by competition for food between closely related species. During the early summer, the populations of E. nordmanni and Podon leuckarti seem to be comprised of specimens brought in by the sea, while the estuarine species Pleopis polyphemoides seems to be more indigenous within the area.