Dieter Gerdes

Short-term variations in particulate matter sedimentation off Kapp Norvegia, Weddell Sea, Antarctica: relation to water mass advection, ice cover, plankton biomass and feeding activity

SummaryA multi-cup sediment trap was deployed at 250m in the shelf area off Kapp Norvegia, Weddell Sea (630 m water depth) to determine the relative importance of water mass advection, sea ice movement, phytoplankton biomass and plankton feeding. Short-term fluctuations in sedimentation were determined using a sampling frequency of 2.7 days over 54 days during January and February 1988. Three periods of enhanced sedimentation were associated with water mass exchange, settling of diatoms following break-up of ice cover and release of fecal matter by krill feeding on particulate matter derived from phytoplankton and ice algae. An initial sedimentation pulse (28 Jan) was mainly due to sinking pelagic diatoms and krill fecal strings containing algae released from sea ice passing over the trap position. The δ13C-composition of the sedimented organic carbon was about-24‰. The isotope ratio decreased sharply by about 5.5‰ at the end of the first pulse indicating the source of sinking matter becoming pelagic diatoms of the retreating ice-edge. At this time the diatom Corethron criophilum contributed a very high proportion of the organic flux causing an increase of the opal/Corg ratios. The second pulse (6 Feb) was due to empty diatom frustules, minipellets and small planktonic aggregates. Much of the organic carbon was transported by round fecal pellets. During the third pulse (14 Feb), round fecal pellets transported even more; the percentage of C. criophilum to the diatom organic carbon flux was more than 80% (>2mg C m−2 day−1).

QUANTITATIVE INVESTIGATIONS ON MACROBENTHOS COMMUNITIES OF THE SOUTHEASTERN WEDDELL SEA SHELF BASED ON MULTIBOX CORER SAMPLES.

A total of 233 multibox corer samples from 36 stations along the southeastern Weddell Sea shelf and upper continental slope between Atka Bay (70°S) and Gould Bay (78° S), covering a depth range from 170 to 2,037 m, provided biomass and abundance data for analysis of faunal communities. Twenty-eight major taxa were distinguished. Based on these data, 3 different macrobenthos communities could be identified by means of cluster analysis. Hexactinellid sponges, polychaetes and echinoderms were most abundant. Biomass values have been found to be in the range of 94 mg up to 1.6 kg wet weight per sqm. According to TWINSPAN, the sampled stations can be divided into two groups each consisting of two major subgroups. Peracarid crustaceans, polychaetes and bivalves are commonly distributed in the area of investigation whereas others such as sponges, brachiopods, pantopods and asteroids are more confined to Kapp Norvegia and Halley Bay. Biomass values of these latter taxa off Kapp Norvegia were generally higher than in the Halley Bay area.

Spatial and temporal variability of the benthic assemblages associated to the holdfasts of the kelp Macrocystis pyrifera in the Straits of Magellan, Chile

Macrocystis pyrifera (L.) C. Agardh is a characteristic macroalga in the Magellan region covering almost 30% of the shallow coastal waters. The focus of this study was to analyse the spatial and seasonal patterns in macrofauna communities associated to the holdfasts of Macrocystis pyrifera at two study sites in the Straits of Magellan, South Chile. In total, 114 species from 10 major taxa were isolated from the holdfasts. MDS clearly separated the holdfast fauna collected in different seasons, with autumn and winter collections being richer in terms of species richness and abundance as compared to the spring and summer situation. MDS also clearly separated the holdfast associated faunas of the two study sites, Bahía Laredo and Fuerte Bulnes. The community structure and species composition of the associated macro-invertebrates and vertebrates appeared rather heterogeneous, probably due to the extremely heterogeneous environmental conditions along the entire coastline of the Subantarctic Magellan region.

High Antarctic macrobenthic community production

Abstract Production and productivity ( P / B ratio) of the high Antarctic Weddell Sea and Lazarev Sea macrozoobenthos are estimated by an empirical multiple non-linear model (artificial neural network) based on biomass data and other biotic and abiotic parameters. Average community production decreases with depth from 4.8 g C m −2 year −1 (100–300 m) to 0.1 g C m −2 year −1 (1500–4300 m). Community P / B ratio increases with depth from 0.18 year −1 to 0.55 year −1 . Taking into account the effects of water depth on production and of temperature on P / B ratio, Antarctic communities show no evidence of unique characteristics with respect to overall energy flow.

Meiofauna response to iceberg disturbance on the Antarctic continental shelf at Kapp Norvegia (Weddell Sea)

The impact of iceberg scouring on meiofauna communities, especially nematodes, was studied on the Kapp Norvegia shelf in the Weddell Sea, Antarctica. Three stations with different stages of recolonisation following scour were selected on the basis of seafloor video images, sediment characteristics and faunal occurrences. These stations comprised a fresh scour, an older scour, and an undisturbed control site where a sponge spicule mat covered the sediment with dense epifauna. Meiofaunal abundance and taxonomic diversity of meiofauna groups were significantly reduced in the fresh scour. The highest abundance and diversity were found in the older scour as compared with the undisturbed site. The abundance and diversity of nematodes also decreased due to scouring. The abundance in the older scour recovered to the level of the undisturbed site whereas the diversity remained low. Scouring also changed the nematode community structure, with the suborders Desmoscolecina and Leptolaimina as the most sensitive groups. In addition, scouring resulted in the decrease of selective deposit feeders and the Maturity Index. The low diversity and the change in nematode generic composition in the older scour compared with the undisturbed site, despite the complete recovery in terms of abundance, suggest that the deep continental shelf nematode community in this area is sensitive to iceberg disturbance.

Growth and age of the Antarctic bryozoan Cellaria incula on the Weddell Sea shelf

We analysed growth of the arborescent Antarctic cheilostoine bryozoan Cellaria incula by stable carbon and oxygen isotope analysis. The growth of one complete branch of C. incula takes one year, i.e. owing to the bifurcate colony structure two new branches grow froin each branch of the previous generation, The maximum age of a C. incula colony is likely to be more than 14 years. Annual production-to-biomass ratio is 0.67, the highest value hitherto measured for any benthic invertebrate south of 62s. Comparatively fast growth and high productivity identi@ C. zncula as a pioneer species which is able to quickly occupy spatial niches produced by iceberg scouring on the Antarctic shelf.

Distribution patterns and biodiversity in polychaete communities of the Weddell Sea and Antarctic Peninsula area (Southern Ocean)

During the expedition EASIZ II with RV ‘POLARSTERN’ in 1998 a multibox corer yielded 151 quantitative samples from 26 stations between 120 and 2415 m water depth for benthic community analysis. From this material a total of 235 polychaete species out of 37 families was determined. Forty-seven species are new to science. The polychaete fraction contributed 41.9% to total benthic abundance and 6.5% to total benthic biomass at these stations. Overall mean polychaete abundance (ind m −2 ) and biomass (g wet weight m −2 ) at the stations were 1617 and 49, respectively. Multidimensional scaling procedure clearly grouped the stations into south-eastern Weddell Sea shelf stations, deep-water stations, and stations mostly around the Antarctic Peninsula. Differences between these groups existed in terms of polychaete abundance and biomass as well as species composition, diversity, and evenness.

A seafloor crater in the German Bight and its effects on the benthos

Abstract In 1963 a deep crater was formed about 65 m below sea level in the western part of the German Bight, due to a gas eruption caused by drilling carried out from the platform ’Mr. Louie’. The study area is situated in a sandy to muddy bottom area inhabited by an Amphiura filiformis association (sensu Salzwedel et al. 1985). The crater, sometimes called ’Figge-Maar’, functions as a sediment trap, concentrating particles and organisms from the water column, thus leading to extreme sedimentation rates of about 50 cm, on average, per year. Crater stations, compared with stations situated in the vicinity, show enrichments of juveniles. Echinoderms, especially the subsurface-dwelling heart urchin Echinocardium cordatum and ophiuroids are responsive to enrichment. Other species that are typical of the Amphiura filiformis association are shown to be unable to cope with the special conditions in the crater.

Seasonality and spatial variability in the reproduction of two Antarctic holothurians (Echinodermata)

SummarySeasonality in the reproduction of Ekmocucumis steineni and Psolus dubiosus (Holothuroidea) from the Antarctic shelf was investigated. The material was collected in spring (October/November) and autumn (mainly February) in the southeastern Weddell Sea. For E. steineni differences between both seasons in relative female fecundity and relative gonad weight were found in both sexes. Large yolky oocytes (0.3–1.0 mm in diameter) forming 1–3 cohorts were present in spring, nearly none in autumn. A delayed or prolonged spawning is possible, depending on the locality. No seasonal differences were found in P. dubiosus, a brood-protecting species with a lower fecundity and larger eggs (≤1.5 mm in diameter). A longer spawning phase in P. dubiosus than in E. steineni (October to January) is suggested. Both species are suspension feeders and their intestines were more filled with organic material in autumn than in spring. However, the occurrence of mature oocytes was not directly linked with the seasonal availability of food. The size-frequency distribution of the entire material in the study area was heterogeneous, indicating differences in long-term environmental conditions. The data show an evolutionarily more evolved high Antarctic mode of reproduction in P. dubiosus with a prolonged reproductive period than in E. steineni which has a distinct annual spawning cycle.

Organic enrichment and structure of macrobenthic communities in the glacial Baker Fjord, Northern Patagonia, Chile

In this study we describe community parameters such as densities, biomasses, species composition, feeding modes and normalized biomass size-spectra (NBSS) of macrobenthic invertebrate communities from three stations located in the Baker Fjord obtained on four seasonal campaigns in 2008 and 2009. The macrobenthic communities were dominated by small-bodied polychaetes (Paraonidae, Capitellidae and Cirratulidae) characterized by continuous year-round breeding, short life-spans, and fast turnover rates, which in turn regulated the standing stock in the communities. Principal component analysis and multiple-regression analysis demonstrate the distribution of macrobenthic communities in the study area to be mainly controlled by few local environmental conditions. Macrofaunal densities, diversity and feeding modes were significantly correlated with the total organic carbon (TOC; R 2 = 0 . 74 ; P < 0.001) and chlorophyll-a (Chl-a; R 2 = 0 . 55 ; P < 0.05) content in the sediments. This study also suggests that feeding modes and NBSS can be used to detect and follow possible changes caused by natural perturbations such as glacial lake outburst floods or anthropogenic stressors associated with ecological impacts generated by the construction and operation of hydroelectric power stations in the Baker River.