Copepods in summer platelet ice in the eastern Weddell Sea,Antarctica

Copepods in platelet-ice layers underlying fast ice and in the water column below were studied at Drescher Inlet, eastern Weddell Sea in February 1998. Three copepod species were found: Drescheriella glacialis and Paralabidocera antarctica occurred in platelet-ice layers, while Stephos longipes was only present in the water column. The distribution of all species varied considerably between station and depth. D. glacialis dominated the platelet-ice community and occurred at all five platelet-ice sampling sites, except one, with numbers of up to 26 ind. l^–1. In contrast, P. antarctica was only found in low numbers (up to 2 ind. l^–1) at one site. The total copepod abundance in the platelet ice was not associated with algal biomass, although it was strongly correlated with high ammonium concentrations (up to 9 M) in the interstitial water between the platelets. This is the first indirect evidence to support the hypothesis that zooplankton excretion can partly account for the high ammonium values often found in platelet-ice layers.     

A study on octopodids from the eastern Weddell Sea, Antarctica

A comprehensive study of octopodids in the Weddell Sea was conducted during cruise ANT XIII/3 of RV "Polarstern". The study yielded eight species of incirrate octopodids, three of which were undescribed. There appeared to be no differences in octopodid species assemblage in the two sampling areas (Kapp Norvegia and south of Drescher Inlet), supporting the theory that there is a single macrobenthic assemblage on the eastern shelf of the Weddell Sea. Six of the octopodid species belonged to the genus Pareledone, illustrating the extensive radiation of this endemic genus within the Southern Ocean. The fragmented nature of suitable habitats and disturbance caused by glaciation cycles are proposed as mechanisms for this radiation. Comparative data illustrate that both the number of octopodid species present and their abundance are greater at higher latitudes than close to the Antarctic Polar Frontal Zone.     

Summer diet of Weddell Seals (Leptonychotes weddelli) in the eastern and southern Weddell Sea,Antarctica

Summary Stomach and intestine samples from 21 adult Weddell seals were used to study the diet of these seals from the eastern and southern Weddell Sea coast from January to February 1983 and 1985. Fish occurred in all seals, squid in five, octopods in three and Euphausia crystallorophias in one seal. Pleuragramma antarcticum was the predominant fish in the diet, constituting 61.1% of otoliths in 1983 samples and 93.8% in 1985. Aethotaxis mitopteryx, Dissostichus mawsoni, unidentified Trematomus spp. and channichthyids were also recorded. Size and wet weight of P. antarcticum were calculated from uneroded otoliths, found in 6 seal stomachs with liquid food pulp, collected during early morning hours in 1985. Size distribution of P. antarcticum from individual seals was reasonably constant, ranging between 5.0 and 22.0 cm SL; adult fish from about 14.0 to 19.0 cm SL predominated. P. antarcticum in seals from the southern area had a larger median size (16.5 cm SL), than those from further east (15.5 cm SL). Calculated wet weights of all P. antarcticum from individual seal stomachs ranged between 4.7 and 16.9 kg the mean was 12.8 kg. Comparisons with net-hauls from the southern Gould Bay suggest that Weddell seals feed mainly in deeper water layers (>400 m) where adult P. antarcticum occur at higher densities.     

Shrimp (Decapoda,Natantia) occurrence and distribution in the eastern Weddell Sea,Antarctica

Summary 108 successful ground and Agassiz trawl catches were taken between 155 and 2031 m depth in the eastern Weddell Sea on board RV Polarstern in spring and summer (October–February) 1985–1989. In addition, 7 hauls were taken with a semipelagic trawl. Only 19 hauls (16.5%) contained no shrimps. The others yielded large numbers of Notocrangon antarcticus, Chorismus antarcticus, and Nematocarcinus lanceopes as well as 20 Lebbeus antarcticus and 11 specimens of an Eualus species new to science. 8 Pasiphaea scotiae were caught in a pelagic krill trawl. No reptant decapod crustaceans were detected in the study area. Shrimp densities determined from trawl catches were lower than estimates derived from underwater photography but in the same order of magnitude. Although yields of the three common shrimp species in some cases exceeded 20 kg per 0.5 h haul, shrimp stocks in the area cannot be considered to be of commercial significance. A wider geographical distribution and greater frequency of shrimps in high Antarctic waters was found than described hitherto. There was considerable variation in numbers, sex composition, occurrence at different depths, and size-frequency distributions. C. antarcticus and N. antarcticus grow to a larger size compared with individuals from the Antarctic Peninsula area. Within the area of investigation, length frequency distributions are skewed towards larger sizes at higher latitudes. In the eastern Weddell Sea larger specimens of the three common species live at greater depths than smaller individuals. Potential reasons for these differences are discussed.AWI Publication No. 124     

Meso- and macrozooplankton communities in the Weddell Sea,Antarctica

Summary The present paper describes composition and abundance of meso- and macrozooplankton in the epipelagic zone of the Weddell Sea and gives a systematic review of encountered species regarding results of earlier expeditions. Material was sampled from 6 February to 10 March 1983 from RV Polarstern with a RMT 1+8 m (320 and 4500 m mesh size). In agreement with topography and water mass distribution three distinct communities were defined, clearly separated by cluster analysis: The Southern Shelf Community has lowest abundances (approx. 9000 ind./1000 m³). Euphausia crystallorophias and Metridia gerlachei are predominating. Compared with the low overall abundance the number of regularly occurring species is high (55) due to many neritic forms. Herbivores and omnivores are dominating (58% and 35%). The North-eastern Shelf Community has highest abundances (about 31 000 ind./1000 m³). It is predominated by copepodites I–III of Calanus propinquus and Calanoides acutus (61%). The faunal composition is characterized by both oceanic and neritic species (64). Fine-filter feeders are prevailing (65%). The Oceanic Community has a mean abundance of approximately 23 000 ind./1000 m³, consisting of 61 species. Dominances are not as pronounced as in the shelf communities. Apart from abundant species like Calanus propinquus, Calanoides acutus, Metridia gerlachei, Oithona spp. and Oncaea spp. many typical inhabitants of the Eastwind Drift are encountered. All feeding types have about the same importance in the Oceanic Community.     

Phytoplankton biomass,P-I relationships and primary production in the Weddell Sea,Antarctica, during the austral autumn

An investigation into the changing phytoplankton biomass and total water column production during autumn sea ice formation in the eastern Weddell Sea, Antarctica showed reduced biomass concentrations and extremely low daily primary production. Mean chlorophyll-a concentration for the entire study period was extremely low, 0.15±0.01 mg.m⁻³ with a maximum of 0.35 mg.m⁻³ found along the first transect to the east of the grid. Areas of low biomass were identified as those either associated with heavy grazing or with deep mixing and corresponding low light levels. In most cases phytoplankton in the <20-μm size classes dominated. Integrated biomass to 100 m ranged from 7.1 to 28.0 mg.m⁻² and correlated positively with surface chlorophyll-a concentrations. Mean P^Bmax (photosynthetic capacity) and α^B (initial slope of the photosynthesis-irradiance curve) were 1.25±0.19 mgC. mgChla ⁻¹.h⁻¹ and 0.042±0.009 mgC.mgChla ⁻¹.h⁻¹.(μmol.m⁻².s⁻¹)⁻¹ respectively. The mean index of photoadaptation,I _k, was 32.2±4.0 μmol.m⁻².s⁻¹ and photoinhibition was found in all cases. Primary production was integrated to the critical depth (Z _cr) at each production station and ranged from 15.6 to 41.5 mgC.m⁻².d⁻¹. It appears that, other than grazing intensity, the relationship between the critical depth and the mixing depth (Z _mix) is an important factor as, ultimately, light availability due both to the late season and growing sea ice cover severely limits production during the austral autumn.     

Summer phytoplankton distributions in the Weddell Sea

Summary The quantitative composition of phytoplankton was studied along a transect of 14 hydrographic stations, between the southern coast of the Weddell Sea and the Antarctic Peninsula, during the austral summer of 1984–1985. The most apparent feature of the phytoplankton distribution was the presence of a bloom of Phaeocystis at a frontal zone over the shelf break, and the marked contrast between a southern region, with high phytoplankton biomass, and a poorer region north of the shelf break. The most widely distributed diatom genus was Nitzschia (Fragilariopsis section). The phytoplankton assemblage of the southern region included the silicoflagellate Distephanus speculum, the diatom Rhizosolenia alata and several heterotrophic dinoflagellates such as Protoperidinium antarcticum and P. applanatum. The northern assemblage could be characterized by the abundance of flagellates and small dinoflagellates, and by diatoms such as Chaetoceros criophilum, Corethron criophilum Nitzschia kerguelensis and other Nitzschia species of the Fragilariopsis section.     

A new species of Hormathia (Actiniaria, Hormathiidae) from the eastern Weddell Sea, Antarctica

A new species of sea anemone in the genus Hormathia, is described and illustrated based on forty-two specimens collected during the Polarstern cruises ANT XV/3 and ANT XVII/3 in the Weddell Sea. The main features of the new taxon are the crown of flattened and hooked tubercles at the distal end of the scapus, the regular arrangement of pointed tubercles along the column and the cnidom. The new species shares the pointed tubercles, at least in the upper part of the scapus, with two other species of Hormathia in the southern hemisphere: Hormathia spinosa Hertwig 1882 and H. pectinata Hertwig 1882 Received in revised form: 27 December 2000 Electronic Publication     

The post-moult diet of Emperor Penguins (Aptenodytes forsteri) in the eastern Weddell Sea,Antarctica

The diet of emperor penguins Aptenodytes forsteri was studied during late austral summer at Drescher Inlet, eastern Weddell Sea, Antarctica. Antarctic krill Euphausia superba was a major component of the food, accounting for 75% of all prey items. Emperor penguins appear to feed on krill during shallow dives under the fast sea ice. Fish, mainly nototheniids, accounted for less than 20% by number of all prey. An evaluation of the main prey types in terms of mass indicated, however, that fish represented up to 75% approximately of prey mass. Feeding experiments were performed on captive penguins and showed that squid beaks can accumulate for up to 3 weeks within the stomach without any clear signs of erosion. The lack of cephalopod soft parts in the samples makes it likely that all squid beaks were derived from animals captured some time previously. Squid seems to be a very minor dietary component of emperor penguins at the Drescher Inlet.     

Vernal abundance,structure and development of epipelagic copepod populations of the eastern Weddell Sea (Antarctica)

Summary Pelagic copepod populations under the pack ice of the Antarctic Weddell Sea were sampled with a 50 m net between October 2 and December 7, 1986, to study their abundance and developmental stage composition before and at the onset of the vernal phytoplankton bloom. Subadult stages and adult females were incubated to estimate rates of development and egg production. Copepod densities in the upper 200 m were highest for the small-sized species Oithona similis, Oncaea curvata and Ctenocalanus citer. About 95% of the copedite stages belonged to these species, dominated by Oithona. The copepodids were outnumbered by the nauplii in all species, except in Oncaea. The stage distribution in the small-sized species was bimodal with peaks in N3 and C4. The larger species Calanus propinquus and Metridia gerlachei showed peaks in nauplii only. Eggs were relatively abundant in all small and large species. Animals smaller than 1 mm not only were more abundant than the larger ones, but also had a higher total potential respiration. Eggs were produced by incubated females in sea water virtually without food at 0°C. Eggs hatched, and Oithona nauplii developed at a rate of about 7 days per stage. Copepodite stages did not develop significantly. Reproduction in the most abundant species commonly occurred before the algal spring increase when food levels were very low. Maintenance of a stable stage distribution at the expense of a high juvenile mortality seemed to be characteristic for the overwintering strategy of Antarctic copepods.     

Phyto- and protozooplankton biomass during austral summer in surface waters of the Weddell Sea and vicinity

Summary Phyto- and protozooplankton were sampled in the upper 10 m of the water column in austral summer during a cruise of RV Polarstern from January 6 to February 20 1985 in the eastern Bransfield Strait vicinity and in the northern, southeastern (off Vestkapp, twice: I and II) and southern Weddell Sea (Vahsel Bay across the Filchner Depression to Gould Bay). The plankton assemblages are discussed in relation to physical, chemical and biological factors in the different geographical areas in summer. Phytoplankton biomass (Phytoplankton carbon, PPC) ranged from 4–194 g carbon/l and consisted on average of 65% diatoms and 35% autotrophic flagellates. Whereas in the northwest phytoplankton assemblages were dominated by small nanoflagellates (78% of PPC), higher biomass of diatoms (54–94% of PPC) occurred at the other sampling sites. In general autotrophic flagellates and small pennate diatoms dominated at oceanic stations; in neritic areas large centric diatoms prevailed. Chlorophyll a concentrations ranged from 0.25–3.14/g chl a/l with a mean of 1.13/gmg chlorophyll a/l and an average phytoplankton carbon/chlorophyll a ratio of 39. Protozooplankton biomass (Protozooplankton carbon, PZC) ranged from 0–67 g carbon/l and consisted of 49% ciliates, 49% heterotrophic dinoflagellates and 2% tintinnids. Heterotrophic dinoflagellates were more important in the northern investigation areas (58%–84% of PZC). Ciliates dominated the protozooplankton in the southeast and south (56%–65% of PZC); higher abundances of tintinnids were observed only in the south (11% of PZC). The most remarkable feature of the surface waters was the high protozooplankton biomass: protozooplankton amounted to 25% on an average of the combined biomass of PPC plus PZC for the entire investigation period. Protozoan biomass in the southeastern and southern Weddell Sea occasionally exceeded phytoplankton biomass. Temperature, salinity, and inorganic nutrients were generally lower in the southern regions; at most of these stations a meltwater layer occurred in the upper meters of the water column. We suggest that this physical regime allows a well developed summer system with a high proportion of heterotrophic microplankton. In the eastern Bransfield Strait, in the northern Weddell Sea and close to the coast off Vestkapp (I), however, early summer conditions occurred with less protozooplankton contribution.Contribution no. 427 from the Alfred-Wegener-Institute for Polar and Marine Research     

A new bryozoan genus from the Weddell Sea,Antarctica

Summary Brettiopsis gen.nov. is erected within the family Scrupariidae. Its affinities with the genera Brettia, Leiosalpinx, Brettiella, Bugulella and Scruparia are briefly discussed. Its type species, Brettia triplex Hastings, is redescribed on the basis of new material collected in the southern part of the Weddell Sea by the RV Polarsirkel. Bivalved brood chambers, previously unknown in this species, are described and illustrated.     

Summer phytoplankton succession in Ellis Fjord, eastern Antarctica

Spring phytoplankton communities in the water column of EllisFjord are characterized by diatoms originating from the bottomsea-ice strand community. Upon ice breakout in early summer,these are replaced by blooms of the phytoflagellates, Phaeocystispouchetii, Cryptomonas cryophila, Pyramimonas gelidicola, silicoflagellatcsand dinoflagellates. The narrow entrance of the fjord and thedevelopment of summer stratification is probably limiting theavailability of nutrients and containing the magnitude of thesmall bloom (maximum 2.8 10⁶ cells l^–1).     

Oocyte development and gonad production of Nematocarcinus lanceopes (Decapoda: Caridea) in the eastern Weddell Sea, Antarctica

 Nematocarcinus lanceopes Bate 1888 is the only decapod that occurs in large numbers on the continental slope of the Weddell Sea, Antarctica. Histological examination of the female gonads and analyses of oocyte growth indicate a biannual reproduction cycle with seasonal occyte maturation in this species. Vitellogenic development is estimated to take 2 years and culminates during summer. Females spawn three times, every 2nd year, while they grow from 27 to 34 mm carapace length. Based on these results the calculated female gonad production is 184 g wet mass (70.5 g dry mass)/total catch, which is high compared to shrimp populations on the continental shelf of the Weddell Sea. Seasonal reproductive patterns of N. lanceopes seem to reflect oscillating food conditions in the Antarctic Weddell Sea. This mode of reproduction differs from all other Nematocarcinidae, which release eggs the whole year round. The ability to adapt the reproductive cycle to a seasonal productivity pattern may have been an important factor in extending the distribution range of the deep-water genus Nematocarcinus into Antarctic waters. Received: 3 January 1996/Accepted: 28 April 1996     

Fishes of the eastern Ross Sea,Antarctica

Antarctic fishes were sampled with 41 midwater and 6 benthic trawls during the 1999–2000 austral summer in the eastern Ross Sea. The oceanic pelagic assemblage (0–1,000 m) contained Electrona antarctica, Gymnoscopelus opisthopterus, Bathylagus antarcticus, Cyclothone kobayashii and Notolepis coatsi. These were replaced over the shelf by notothenioids, primarily Pleuragramma antarcticum. Pelagic biomass was low and concentrated below 500 m. The demersal assemblage was characteristic of East Antarctica and included seven species each of Artedidraconidae, Bathydraconidae and Channichthyidae, ten species of Nototheniidae, and three species each of Rajidae and Zoarcidae. Common species were Trematomus eulepidotus (36.5%), T. scotti (32.0%), Prionodraco evansii (4.9%), T. loennbergii (4.7%) and Chaenodraco wilsoni (4.3%). Diversity indices were highest for tows from 450 to 517 m (H=1.90–2.35). Benthic biomass ranged from 0.7 to 3.5 t km^–2. It was generally higher in tows from 450 to 517 m (0.9–2.0 t km^–2) although the highest biomass occurred at an inner-shelf station (238 m) due to large catches of T. eulepidotus, T. scotti and P. evansii.     

Potential impact of the main benthic amphipods on the eastern Weddell Sea shelf ecosystem (Antarctica)

As they represent one of the most diversified taxonomic groups on Antarctic bottoms, amphipods are likely to play a complex role in biogeochemical fluxes that occur within benthic ecosystems. The aim of this paper is to present, using both digestive tract analyses and relative species abundance data, the impact of amphipod feeding on different potential preys of the Weddell Sea. The study is based on data obtained for 29 representative amphipod species collected at 130 stations distributed along the eastern shelf of the Weddell Sea (depth range: 60-2,000 m) during three summer cruises, from 1989 to 1998. Sedimenting plankton particles (10-27%), crustaceans (22-32%) and fish carrion (5-18%) are the main food resources. Other abundant potential preys, such as molluscs or tunicates, do not seem to be consumed. Variations in the proportions of the different preyed food items are observed, mainly related to differences in relative amphipod species composition in samples. Presented results will help in refining ecological models of the prospected area, but also underline the need for accurate and reliable measurements of the feeding rates of Antarctic benthic organisms.     

Stomach contents of the Antarctic Silverfish Pleuragramma antarcticum from the southern and eastern Weddell Sea (Antarctica)

Summary The stomach contents of 142 Pleuragramma antarcticum from the southernmost part of the Weddell Sea (Gould Bay: 77°19S) and from the eastern coast (72°–74°S) were analyzed. The fish were collected in February 1983 and stored frozen. Size range of the investigated specimens was from 6.4 cm SL (7.3 cm TL) to 21.9 cm SL (24.1 cm TL). The fish were caught by bottom trawl (Gould Bay) and Agassiz Trawl and pelagic RMT-m net in the upper 300 m layer at the eastern coast, respectively. Thirty-six stomachs were empty or contained sand only. The most important prey in terms of biomass were euphausiids, which occurred in 49 stomachs at a mean number of 2. Their dry weight was estimated to be 15–50 times that of the next important food items, which were copepods, gastropods and gammarids. Krill (Euphausia superba) constituted up to 14% of the euphausiids in the diet of fish caught in the eastern Weddell Sea. The rest was usually made up by Euphausia crystallorophias. This species was taken with preference even when the abundance of E. superba in accompanying plankton catches was 16 times higher. In the Gould Bay, gastropods were frequently eaten despite high numbers of copepods in the plankton, whereas in the eastern Weddell Sea, copepods were abundant both in plankton and in the stomach content. The almost complete absence of the early stages of fish in the diet of Pleuragramma antarcticum in the southern and eastern Weddell Sea is due to a pronounced vertical segregation of fish of different sizes. This distribution pattern is thought to be an adaptive mechanism to avoid intraspecific predation, as 90% of the ichthyoplankton in that area is Pleuragramma antarcticum.     

Sipuncula of the southeastern Weddell Sea (Antarctica)

Sipunculans collected during the EPOS (European Polarstern Study) leg 3 cruise (13.1.89–10.3.89) to the Weddell Sea shelf area from depths ranging from 186 to 2037 m are recorded. Seven species in three genera are recognized; Nephasoma capilleforme and Phascolion convestitum have not been recorded hitherto in Antarctica. Significant morphological characters as shown by light (LM) and electron (SEM) photographs are described and illustrated. Antarctic distribution maps of the species collected and a checklist of the sipunculan species south of the Antarctic Convergence with depths and bibliographic references are included.     

Phytoplankton biomass and primary production in the marginal ice zone of the northwestern Weddell Sea during austral summer

During the austral summer of 1995, distributions of phytoplankton biomass (as chlorophyll a), primary production, and nutrient concentrations along two north-south transects in the marginal ice zone of the northwestern Weddell Sea were examined as part of the 8th Korean Antarctic Research Program. An extensive phytoplankton bloom, ranging from 1.6 to 11.2 mg m⁻³ in surface chlorophyll a concentration, was encountered along the eastern transect and extended ca. 180 km north of the ice edge. The spatial extent of the bloom was closely related to the density field induced by the input of meltwater from the retreating sea ice. However, the extent (ca. 200 km) of the phytoplankton bloom along the western transect exceeded the meltwater-influenced zone (ca. 18 km). The extensive bloom along the western transect was more closely related to local hydrography than to the proximity of the ice edge and the resulting meltwater-induced stability of the upper water column. In addition, the marginal ice zone on the western transect was characterized by a deep, high phytoplankton biomass (up to 8 mg Chl a m⁻³) extending to 100-m depth, and the decreased nutrient concentration, which was probably caused by passive sinking from the upper euphotic zone and in situ growth. Despite the low bloom intensity relative to the marginal ice zone in both of the transects, mean primary productivity (2.6 g C m⁻² day⁻¹) in shelf waters corresponding to the northern side of the western transect was as high as in the marginal ice zone (2.1 g C m⁻² day⁻¹), and was 4.8 times greater than that in open waters, suggesting that shelf waters are as highly productive as the marginal ice zone. A comparison between the historical productivity data and our data also shows that the most productive regions in the Southern Ocean are shelf waters and the marginal ice zone, with emerging evidence of frontal regions as another major productive site. Accepted: 27 September 1998