Uwe Piatkowski

Meso- and macrozooplankton communities in the Weddell Sea, Antarctica

SummaryThe 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 μm 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.

Variability in the macrozooplankton community off the Antarctic Peninsula

SummaryThis paper presents an analysis of zooplankton net sampling surveys carried out during four expeditions to the Antarctic Peninsula region. Cluster analysis documented two to three site groupings for the epipelagic zone and one mesopelagic site cluster below 200 to 300 m depth. Analysis of species dominance, constancy, diversity and evenness indices did not allow clear designation and separation of communities in terms of these parameters.Computation of a rank correlation matrix for each season allowed the characterization of species groups. There were no perfect indicator species in the very strict sense. The main differences in the composition of the zooplankton between the site clusters were due mainly to changes in abundance rather than to presence or absence of particular species. However, the interpretation of the complex species and site groupings led to the conclusion that we can define three distinct communities: an oceanic, a neritic, and a mesopelagic community beneath 200 to 300 m. A so-called transitional cluster represents a mixing zone created by frequent occurrence of species from both the oceanic and neritic community. The location of the described oceanic and neritic community sites seem to be relatively stable with minor latitudinal changes during the seasons, while occurrence and abundance of most species changes with the time of the year. The usefulness of particular species (e.g. Euphausia superba) as indicator species also change during the year

Beak length analysis of the Southern Ocean squid Psychroteuthis glacialis (Cephalopoda: Psychroteuthidae) and its use for size and biomass estimation

Abstract A detailed analysis of beak length to body size and mass measurements was carried out for the glacial squid Psychroteuthis glacialis, which is an endemic cephalopod species in the Southern Ocean. Beak lengths (lower rostral length) were measured from 211 specimens which had been sampled in the Atlantic sector of the Southern Ocean. The basic idea was to find some calibration model in order to inter- or extrapolate missing mantle length and/or wet body mass data by means of beak lengths. The relationships between beak length and mantle length/wet body mass bear essential information for future use in biomass estimates in Southern Ocean top predators, since beaks of P. glacialis occur frequently in the stomach contents of Antarctic seabirds, seals and toothed whales. Therefore, lower rostral lengths were plotted against both mantle length and wet body mass to determine the relationship between these variables. The relationships had limited scatter and very high coefficients of determination, showing that lower rostral length is a good predictor of the squids mantle length and wet mass. A non-linear 3rd order polynomial regression of lower rostral length against mantle length was identified as the best fitted calibration model, explaining 93% (R2) of the associated variance. The relationship between lower rostral length and wet body mass was empirically well fitted through regressing ln-transformed values of lower rostral length against wet body mass, explaining 95% (R2) of the associated variance. The present investigation provides measurements for a wide size range of P. glacialis individuals compared to earlier studies, which were limited on very small data sets.

Abundance, horizontal and vertical distribution of fish in eastern Weddell Sea micronekton

SummaryThe spatial distribution and species composition of high-Antarctic ichthyonekton was investigated during the EPOS 3 cruise by RV Polarstern in the eastern Weddell Sea during January–February 1989. A multiple rectangular midwater trawl was used to collect samples from the surface to near the sea floor at 11 stations along a 245 kra transect off Halley Bay. Early larval stages of 18 species, representing about 24% of the known Weddell Sea ichthyofauna, were present in the water column. The Antarctic silver-fish, Pleuragramma antarcticum, over-whelmingly dominated the catches comprising 84.5% of the 5022 specimens caught. The abundance of this species markedly increased towards the offshore end of the transect with the highest numbers occurring near the shelf-break front associated with the westerly current of the southern limb of the Weddell Gyre. The increased abundance of P. antarcticum in continental slope waters was attributed to deflection of the East Weddell Coastal Current beyond the shelf/slope break by fringing ice shelves. Most larval and juvenile fish were found in the seasonally warmed upper 0–70 m layer of the Antarctic Surface Water where conditions occurred that appeared to be favourable to both feeding and growth. Cluster analysis indicated that inner-, central-and outer-shelf assemblages were represented and that the species composition was most effectively described by reference to water mass and depth.

A new species of Pareledone (Cephalopoda : Octopodidae) from Antarctic Peninsula Waters

During recent cruises aboard RV Polarstern in the Antarctic Peninsula region, a new species of benthic octopodid was discovered whose generic affinities based on morphological characteristics were uncertain. Molecular sequence analysis of six mitochondrial and nuclear genes allows this species to be placed with confidence within the genus Pareledone. The species is described herein and morphological diagnostic characters are provided for its identification.

Predation on cephalopods by Antarctic fur seals, Arctocephalus gazella, at two localities of the Scotia Arc, Antarctica

Abstract The cephalopod remains from 206 Antarctic fur seal (Arctocephalus gazella) scats collected at Mossman Peninsula, South Orkney Islands (nu2009=u2009105) and at Stranger Point, South Shetland Islands (nu2009=u2009101) contained 148 beaks (57 lower and 91 upper). The lower beaks were sorted and measured. Identification of 33 of the lower beaks that were collected at Mossman Peninsula revealed two squid species, Brachioteuthis ?picta (nu2009=u200926) and Psychroteuthisglacialis (nu2009=u20097), with lower rostral lengths (LRL) of 2.0–3.5u2009mm, and 1.0–2.5u2009mm, respectively. Identification of 15 of the lower beaks collected at Stranger Point revealed the same squid species, with the LRL of B. ?picta ranging from 3.0–3.4u2009mm (nu2009=u20099), and that of P. glacialis from 2.0 to 3.5u2009mm (nu2009=u20096). Estimated squid sizes and wet masses indicate that Antarctic fur seals feed on the small sub-adult squid which inhabit the surface layers. We have compared the squid diet estimated for the seals with that reported for its congeners in lower latitudes and other Antarctic seals, and conclude that cephalopods do not form an important food resource for Antarctic fur seals.

Occurrence of the cephalopod Martialia hyadesi (Teuthoidea : Ommastrephidae) at the Kerguelen Islands in the Indian Ocean sector of the Southern Ocean

In the Atlantic sector of the Southern Ocean, data from vertebrate predators and commercial fisheries suggests that the distribution of the ommast rephid squid Martialia hyadesi is related to the Antarctic Polar Frontal Zone, but it spreads further to the north in some years (Rodhouse, in press). A mass stranding of M. hyadesi occurred on Macquarie Island in 1971 (OSullivan et al. 1983) suggesting that its distribution is c ircumpolar (Rodhouse and Yeatman 1990). However, apart from a single beak collected from the s tomach of a wandering albatross at Mar ion Island (Imber and Berruti 1981) its presence has not, until now, been confirmed in the Indian Ocean sector and in particular it is not included in the list of cephalopods from the Kerguelenian Province (Lu and Mangold 1978). M. hyadesi is a major prey item of the grey-headed albatross, Diomedea chrysostoma, and the southern elephant seal, Mirounoa leonina, at South Georgia (Rodhouse et al. 1990; Rodhouse et al., unpublished data) and is present in the diet o f several other predators in the Scotia Sea area including the wandering albatross, Diomedea exulans (Rodhouse et al. 1987) and the giant petrels, Macronectes halli and M. gioanteus (Hunter 1983). It occasionally occurs as a significant by-catch in the lllex argentinus fishery on the Pa tagonian Shelf and has been taken during commercial squid jigging trials in the Scotia Sea at the Antarctic Polar Frontal Zone (Rodhouse, in press). It appears to have potential for commercial exploitation in the sub-Antarctic waters of the Atlantic sector of the nSouthern Ocean (Rodhouse 1990). nIn view of the ecological importance of M. hyadesi to Antarctic predators, and the likelihood that it will be commercially exploited in the future, it is important to nthoroughly establish its geographical range, and in particular to confirm its circumpolar distribution.

Benthoctopus rigbyae, n. sp., a new species of cephalopod (Octopoda; Incirrata) from near the Antarctic Peninsula

ABSTRACT Among the many octopods collected during recent Antarctic trawling surveys were 93 specimens of an undescribed octopod with biserial suckers. Although most similar in appearance to the sub-Antarctic Benthoctopus levis (Hoyle 1885), these octopods differed in several morphological characters, including arm length, web depth, and details of the hectocotylus. Furthermore, molecular evidence supports the separation of the present material from known species. We therefore describe a new species named Benthoctopus rigbyae. These octopods attain mantle lengths of at least 105 mm (400 mm total length), and they are common at depths of 250–600 m throughout the South Shetland Island chain off the Antarctic Peninsula. We present some information on the biology of this species.