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Aim Recreational boating is arguably the largest unregulated vector for the introduction and spread of marine invasive species. Hull fouling communities have been recognized to harbour non-indigenous species (NIS), but presence should not be equated with transport. In this study, we characterize the presence of NIS in hull fouling communities, determine if host vessels transport these species and evaluate the importance of recreational boating as a vector for introduction and spread. Location Coastal British Columbia (BC), Canada. Methods Dive surveys in BC marinas were conducted to record the presence of NIS and to estimate their per cent cover. In addition, a boater questionnaire survey was used to determine common travel and maintenance practices. These results were combined to investigate the potential for recreational boats to transport NIS. Results Nine NIS, including the highly invasive ascidians Styela clava and Botrylloides violaceus, and the macroalga Sargassum muticum, were found in hull fouling communities on recreational boats. Overall, per cent cover was generally low; however, niche areas were commonly fouled, even on active and otherwise clean boats. Fouling of niche areas was not related to either antifouling paint age or travel frequency, and fouling levels were highly variable among individual boats both within marinas and across regions. Main conclusions Recreational boating is a major vector contributing to the spread of marine invasive species. Our results indicate that recreational boats represent a high-risk vector both for primary introduction and secondary spread of marine NIS and should be subject to vector management regulations.

Feeding dynamics of the Antarctic salps Ihlea racovitzai and Salpa thompsoni were studied in the Lazarev Sea in fall 2004, summer 2005–2006 and winter 2006. Pigment concentrations in the guts of both species were positively correlated with ambient surface chlorophyll a (chl a). No evidence was found for salp clogging even at dense surface concentrations of up to 7 μg chl a L−1. However, gut pigment concentrations had a lower range than ambient pigment concentrations, suggesting that salps increased retention times of ingested material in low-food environments. For medium-sized I. racovitzai and S. thompsoni, estimated individual daily rations reached 7–10 and >100% of body carbon in winter and summer, respectively. Daily respiratory needs of I. racovitzai and S. thompsoni accounted for 28 and 22% of daily carbon assimilation based on pigment ingestion rates in winter, and for 2 and 1% in summer, respectively. The grazing impact of the salp populations on the phytoplankton standing stock was negligible during all seasons due to generally low salp densities. Fatty acid trophic biomarkers in the salps suggest high year-round contributions of flagellates and modest contributions of diatoms to the salp’s diet. These markers showed low seasonal variability for I. racovitzai. The more pronounced seasonality of trophic markers in S. thompsoni were likely related to their generally deeper residence depth in winter linked to a seasonal alternation of sexual and asexual generations.

The benthic fauna was investigated during the expedition ANT-XXIV/2 (2007/08) in relation to oceanographic features, biogeochemical properties and sediment characteristics, as well as the pelagic, benthic pelagic and air-breathing fauna. The results document that Maud Rise (MR) differs distinctly from surrounding deep-sea basins investigated during previous Southern Ocean expeditions (ANDEEP 2002, 2005). Considering all taxa, the overall similarity between MR and adjacent stations was low (20% Bray-Curtis-Similarity), and analyses of single taxa show obvious differences in species composition, abundances and densities. The composition and diversity of bivalves of MR are characterised by extremely high abundances of three species, especially the small sized Vesicomya spp. Exceptionally high gastropod abundance at MR is due to the single species Onoba subantarctica wilkesiana, a small brooder that may prey upon abundant benthic foraminiferas. The abundance and diversity of isopods also show that one family, Haplomunnidae, occurs with a surprisingly high number of individuals at MR while this family was not found at any of the 40 bathyal and abyssal ANDEEP stations. Similarly, polychaetes, especially the tube-dwelling, suspension-feeder fraction, are represented by species not found at the comparison stations. Sponges comprise almost exclusively small specimens in relatively high numbers, especially a few species of Polymastiidae. Water-column sampling from the surface to the seafloor, including observations of top predators, indicate the existence of a prospering pelagic food web. Local concentrations of top predators and zooplankton are associated with a rich ice-edge bloom located over the northern slope of MR. There the sea ice melts, which is probably accelerated by the advection of warm water at intermediate depth. Over the southern slope, high concentrations of Antarctic krill (Euphausia superba) occur under dense sea ice and attract Antarctic Minke Whales (Balaenoptera bonaerensis) and several seabird species. These findings suggest that biological prosperity over MR is related to both oceanographic and sea-ice processes. Downward transport of the organic matter produced in the pelagic realm may be more constant than elsewhere due to low lateral drift over MR

Eddies have some decisive functions in the dynamics of the Southern Ocean ecosystems. This is particularly true in the Indian sector of the Southern Ocean, where a region of unusually high-mesoscale variability has been observed in the vicinity of the South-West Indian Ridge. In April 2003, three eddies were studied: eddy A, a recently spawned anticyclone south of the Antarctic Polar Front (APF),; eddy B, an anticyclone north of lying between the Subantarctic Front and the APF; and eddy C, a cyclone north of the APF west of the ridge. Elevated concentrations of total Chl-a coincided with the edges of the cyclonic eddy, whereas both anticyclonic eddies A and B were characterised by low total Chl-a concentrations. Biologically, the two anticyclonic eddies A and B were distinctly different in their biogeographic origin. The zooplankton community in the larger anticyclonic eddy A was similar in composition to the Antarctic Polar Frontal Zone (APFZ) community with an addition of some Antarctic species suggesting an origin just north of the APF. In contrast, the species composition within the second anticyclonic eddy B appeared to be more typical of the transitional nature of the APFZ, comprising species of both subantarctic and subtropical origin and thus influenced by intrusions of water masses from both north and south of the Subantarctic Front. Back-tracking of these features shows that the biological composition clearly demarcates the hydrographic origin of these features.

Sub-Antarctic islands are classified as isolated, hostile, impoverished regions, in which the terrestrial and marine ecosystems are relatively simple and extremely sensitive to perturbations. They provide an ideal ecological laboratory for studying how organisms, ecological processes and ecosystems respond to a changing ocean climate in the Southern Ocean. 1hese islands are characterised by large populations of top predators and subsequently any changes in the oceanographic frontal dynamics associated with the Antarctic Circumpolar Current, either in the vicinity of these islands or further afield, may have strong implications on their foraging behaviour. The relatively easy accessibility of the Prince Edward Islands from South Africa and their location between the main frontal systems bordering the Antarctic Circumpolar Current enable high-resolution synoptic field studies to be undertaken. Such studies have provided information on the impact changes in the large-·scale ocean dynamics have on the local marine ecosystems.

The distribution and abundance of larval and postlarval fishes was investigated in the Lazarev Sea, Southern Ocean, in March and April 2004. The upper 200 m of the water column were sampled with an 8 m2 rectangular midwater trawl at 93 stations. The larval species community clustered in a diverse coastal community with high densities of Antarctic silverfish Pleuragramma antarcticum larvae and a less diverse offshore community dominated by Antarctic jonasfish Notolepis coatsi and the lanternfish Electrona antarctica. No postlarval fish were caught in coastal areas. The offshore community of postlarval fishes consisted of the deep-sea smelt Bathylagus antarcticus, and the lanternfishes Gymnoscopelus braueri, G. nicholsi and E. antarctica. The latter species clearly dominated, occurring at mean individual and wet mass densities of 0.17 individuals m–2 and 0.26 g m–2, respectively. A generalized additive model significantly related the density of postlarval E. antarctica to the abundance of Antarctic krill Euphausia superba, ocean depth and sea surface temperature. The diet of E. antarctica was dominated by copepods and euphausiid larvae. Mean energy density of E. antarctica in the upper 200 m was 2.8 kJ m–2, which is equivalent to 36% of the energy stored in Antarctic krill stocks and probably would be considerably higher if a greater depth range were considered. This suggests that E. antarctica is a major energy transmitter in the food web of the Lazarev Sea, challenging the classical krill-dominated food web paradigm of the Southern Ocean.

The winter diet and daily ration of four small size classes of estuary-associated fishes, Rhabdosargus holubi , Gilchristella aestuaria , Glossogobius callidus and Monodactylus falciformis , from the temporarily open/closed Igoda Estuary were investigated. The diet of G. callidus was dominated by gammarid amphipods and copepods. Copepods accounted for 70% by volume of the stomach contents of M. falciformis and 50% in G. aestuaria . Plant material and copepods were the most prominent food items in the stomach contents of R. holubi . All species except G. aestuaria showed a diel pattern in feeding activity. Gut evacuation rates ranged between 0.3 and 2.5 h –1 for incubations, and from 0.1–0.4 h –1 in situ . Daily ingestion rates, estimated using an in situ stomach content analysis technique, ranged between 4.0% and 10.2% body dry mass. Keywords: fish diet, diel feeding pattern, daily ration, gut evacuation rate, estuaries African Journal of Aquatic Science 2008, 33(1): 83–86

Eulerian time-series were completed at three sites on the south eastern shelf of the Sub-Antarctic Prince Edward Islands (PEI), from 9 to 27 April 2000, to investigate the spatial and temporal variability of mesozooplankton communities in relation to on-shelf hydrodynamics. Surface temperature and phytoplankton biomass were recorded daily at all three sites, while two Bongo net tows and vertical temperature profiles were collected daily at two sites. Con- trary to predictions of on-shelf water retention at low ambient current velocities, cross-correlation analysis iden- tified a northward advection of *8.23 cm s -1 over the study area. Day to day changes in both physical and bio- logical parameters were associated with cross-shelf advection. However, sea temperature had a narrow range of 6.2-7.4C, while average between sample Bray-Curtis similarity in zooplankton communities was high, exceeding 75%. The relatively consistent average sample biomass amounted to *494 tonnes dry weight of mesozooplankton per day being advected onto the south eastern sector of the PEI shelf. We hypothesise that the observed stability of both physical and biological parameters was due to the Sub- Antarctic Front, with its high volume transport and steep physical gradients, being far to the north of the islands. Spatial and temporal variability of hydrodynamics on the PEI shelf, and particularly its relationship to shifting frontal positions, is highlighted as a future research area necessary to quantify the gross delivery of allochthonous biomass to the PEI ecosystem.

Long-tenn variation in krill (Euphausia superba) and salp (mainly Salpa thompsoni) stocks was compared to environmental changes in the Atlantic and Indian sectors of the Antarctic. Environmental conditions examined were air temperature, water temperature, salinity, and sea-ice extent from 1926 to 1938 and from 1982 to 2000. The long-term pattern of krill was opposite to that of salp: krill stock decreased while salp stock increased concurrently. Krill stock was about three-fold higher from 1926 to 1938 than from 1982 to 2000, but salp was about four -fold lower in 1926-1938 than in 1982-2000. A wanning trend was observed in the environmental data, and the long-term variation in krill and salp stocks was affected by this trend.

The macrozooplankton of the Cosmonaut Sea, Indian sector of the Southern Ocean, were investigated during the austral summers (January/February) of 1987, 1988, 1989 and 1990. Macrozooplankton samples were collected with Bongo and MT nets in the top 200 m of the water column, along with integrated temperature and salinity. Multivariate analysis of macrozooplankton density data identified a consistent division between the assemblage structure of the neritic and oceanic zones, the latter being characterized by a number of species unique to the continental shelf including Euphausia crystallorophias, Pleuragramma antarcticum and Notothenia kempi. Samples collected in the oceanic zone were all located within the Coastal Current (CC), south of the Southern Boundary of the Antarctic Circumpolar Current (ACC). However, in both 1987 and 1988 water masses of ACC origin had been injected into the CC. These intrusions were an important but inter-annually variable source of mesoscale spatial variability, being associated with distinct macrozooplankton assemblage structure and densities. Inter-annually there was considerable variation in macrozooplankton densities and biomass. Densities, dominated by Eukrohnia hamata, Thysanoessa macrura and Euphausia superba (krill), averaged ∼250 ind.1000 m−3 from 1987 to 1989, but reached >750 ind.1000 m−3 in 1990, largely due to higher densities of E. hamata. Biomass was dominated by krill, and total levels reflected the decline in biomass of this species from 1986 to 1990. A number of significant correlations were identified between species densities and temperature and/or salinity. However, the wide biogeographic ranges of most species indicated that these correlations were largely spurious. Overall, the differences between macrozooplankton assemblages in ACC and CC water masses within years, and the differences in macrozooplankton densities between years, most likely reflected the different histories of spatially or temporally separated water masses that were structured by a combination of bottom-up and top-down processes. Comparison of the data from this study with other regions in the Antarctic demonstrated that there is considerable circumpolar consistency in the taxonomic composition of Antarctic macrozooplankton communities, although the densities and proportional contribution of species varies both spatially and temporally. The occurrence of a krill-dominated assemblage, characterized by low densities of other species, indicates that this species has a significant top-down impact on zooplankton communities. The spatial and temporal variation in krill biomass may therefore be a significant determinant of both mesoscale and circumpolar variation in the contribution of other taxonomic groups to Antarctic zooplankton assemblages. Locally, the decline in krill biomass in the Cosmonaut Sea between 1987 and 1990 indicated a weaker connection with the Cooperation Sea to the east, where the opposite trend was observed, than previously thought. Separation between these two seas is probably facilitated in part by the anti-cyclonic gyres observed in both regions.

The chemical composition, metabolism, and feeding ecology of the cydippid ctenophore Callianira antarctica (Chun 1897) were investigated during autumn and winter 2001 and 2002 in the vicinity of Marguerite Bay, an embayment on the western Antarctic Peninsula shelf. C. antarctica had relatively high carbon (C) and nitrogen (N) values (average: 8.4% C and 1.8 % N (% dry weight, DW)), further suggesting that polar ctenophores are more C-rich than tropical species. Winter oxygen consumption and ammonium excretion rates ranged from 0.059 to 0.411 µl O2 mg -1 DW h -1 and 0.043 to 2.22 nmol N mg -1 DW h -1 , respectively, at 0°C. Calanoid copepods, larval and juvenile Antarctic krill Euphausia superba and a mixture of prey were offered to ctenophores during feeding incuba- tions. Ingestion rates based on preliminary feeding experiments were linearly related to prey densi- ties, with rates ranging from 9 to 39 prey ind. -1 d -1 and from 3.5 to 4.0 prey ind. -1 d -1 for 1 larger and 1 smaller C. antarctica, respectively. Daily rations varied between 22 and 136% of body C for the larger ctenophore and 6 to 22% of body C for the smaller individual. Digestion time (median: 11.5 h) was dependent on prey elemental content and prey number, and was independent of ctenophore size. Gut content analyses indicated that C. antarctica preyed predominantly on larval euphausiids and copepods. Diver observations, net collections, and diet analyses suggest that this species is an opportunistic predator that feeds both during the day and night, and appears to be well adapted to the prey patchiness found in Antarctic waters.

Demersal fish community structure, distribution and trophic relationships on the slope (depth range 200–1500 m) of the sub-Antarctic Prince Edward Islands and surrounding sea rises were investigated during a pilot survey conducted in April 2001 onboard fishing vessel MV Iris. A total of 56 fish taxa were collected during the survey, of which 44 were identified to the species level, seven to the genus level and five to the family level. Among the identified taxa, 36 constituted new records for the area investigated. Total catch per unit effort (cpue) during the survey ranged from 1·1 to 241·2 individuals h−1. Both average fish diversity and total cpue positively correlated with trawling depth. Overall, mean sampling depth and near-bottom temperature explained 56% of total fish cpue. Hierarchal cluster analysis identified three distinct fish assemblages with pronounced dominant species. Major shifts in fish community composition occurred at 500–600 m and 800–900 m depth strata and could probably be a result of physical and biological vertical zonation. Analysis of the diet of selected fish species showed that they were generalist feeders, consuming predominantly pelagic, including epipelagic, meso- and benthopelagic, prey. Diets of six species and nitrogen stable isotope signatures of 22 species revealed that with a few exceptions most fishes occupied the fourth trophic level and were tertiary consumers. Wide variability in carbon isotopic signatures is discussed with respect to alternative, e.g. possible importance of high Antarctic and chemoautotrophic v. photoautotrophic sub-Antarctic primary production, organic matter sources at the base of deep-sea food webs.

The seasonal dietary composition and estimates of daily consumption rate of Lepidonotothen larseni and Gobionotothen marionensis juveniles were obtained for the first time using fish collected near sub-Antarctic Prince Edward Islands during April 1999–2003. The diet of L. larseni consisted mainly of pelagic prey, with copepods and arrow worms making up the most significant prey groups and accounting for 46% and 40% of prey mass, respectively. The diet of G. marionensis was more diverse than that of L. larseni and was composed mainly of benthic prey, including bottom-dwelling decapods (Nauticaris marionis) and sedentary polychaetes, which accounted for 54% and 30% of prey mass, respectively. During the present study, dietary overlap between juveniles of L. larseni and G. marionensis was very low (

Underway sampling and measurements of pH, f CO 2 , oxygen and Chlorophyll a (Chl a ) were performed in the surface waters from Cape Town (South Africa) to Queen Maud Land (Antarctica) in the Atlantic sector of the Southern Ocean during the austral summer 1997/1998. From direct measurements of these parameters and from calculated f CO 2 the oceanic carbon dioxide system was studied and related to hydrological and biological parameters. f CO 2 was in general undersaturated relative to the atmosphere and showed a large variability with values ranging from 313 to 377 μatm with a mean value of 346±13 μatm. The undersaturation was more pronounced in areas associated with fronts where high Chl a and high pH in situ values were observed. Using shipboard wind speed data, estimates of the CO 2 flux were made along the transect and during three mesoscale surveys on the northward return transect in the area of the Spring Ice Edge (SIE), the Winter Ice Edge (WIE) and in the Antarctic Polar Front (APF). The undersaturation observed during the transect caused the ocean to act as a sink for CO 2 with a mean sea–air flux for the entire transect of −3±5 mmol m −2 d −1 with a large variability between −20 mmol m −2 d −1 (oceanic uptake) to 1.3 mmol m −2 d −1 (oceanic source). The lowest f CO 2 values (largest oceanic uptake of CO 2 ) were found at the southern boundary of the APF at 53°S, which coincided with a supersaturation in oxygen and high pH values. Oxygen concentrations were measured from 50°S to 63°S and varied between 324 and 359 μmol kg −1 with a mean value of 347±9 μmol kg −1 . In general only small deviations from equilibrium oxygen saturation were observed (mean value=99±2%). However, in the SIE oxygen was clearly undersaturated, probably an effect of upwelling of oxygen poor deep water which had not yet been compensated for by biological production. Three weeks later, the ice edge had retreated in the SIE region and the Chl a concentration had increased three-fold, suggesting the start of a phytoplankton bloom. This was also seen in the oxygen concentration which had increased and showed supersaturation. This coincided with an increased oceanic uptake of CO 2 in the SIE during the mesoscale survey.

Zooplankton grazing impact using the gut fluorescence technique was investigated in the top 200 m water layer along the 6°E meridian between 49°50′ and 60°25′S at six Biostations during a Scandinavian/South African Joint Global Ocean Flux Study (December 1997–January 1998) on board the SA Agulhas . Copepods were found to be the most conspicuous grazers along the entire transect, generally accounting for ≈40% of total zooplankton grazing. Pelagic pteropods, Limacina helicina and Clio sulcata , were the second most important grazers within the Seasonal Ice Edge (SIE) region, while the tunicate Salpa thompsoni and euphausiids, mainly Euphausia superba and E. frigida , were the second and third most important consumers of the phytoplankton production within the Winter Ice Edge (WIE) and Antarctic Polar Front (APF) regions. The overall ingestion rates of the zooplankton community ranged from 24 to 277 mg C m −2 day −1 . The lowest and highest ingestion rates were recorded within the SIE and APF regions. The zooplankton grazing impact was low within the SIE region accounting for

A number of parameters of biogeochemical interest were monitored along a north-southerly transect (S 43-S 63degrees) in the Atlantic Sector of the Southern Ocean from the 8th to the 20th of December 1997. Changes in total dissolved inorganic carbon (C-T) and total alkalinity (A(T)) were mostly dependent on temperature and salinity until the ice edge was reached. After this point only a weak correlation was seen between these. Highest mean values of C-T and A(T) were observed in the Winter Ice Edge (WIE) (2195 and 2319 mumol kg(-1), respectively). Lowest mean AT (2277 mumol kg(-1)) was observed in the Sub-Antarctic Front (SAF), whereas lowest mean CT concentration (2068 mumol kg(-1)) was associated with the Sub-Tropical Front (STF). The pH in situ varied between 8.060 and 8.156 where the highest values were observed in the southern part of the Antarctic Polar Front (APF) and in the Summer Ice Edge (SIE) Region. These peaks were associated with areas of high chlorophyll a (chl a) and tribromomethane values. In the other areas the pH in situ was mainly dependent on hydrography. Bacterial abundance decreased more than one order of magnitude when going from north to south. The decrease appeared to be strongly related to water temperature and there were no elevated abundances at frontal zones. Microphytoplankton dominated in the SAF and APF, whereas the nano- and picoplankton dominated outside these regions. Volatile halogenated compounds were found to vary both with regions, and with daylight. For the iodinated compounds, the highest concentrations were found north of the STF. Brominated hydrocarbons had high concentrations in the STF, but elevated concentrations were also found in the APF and SIE regions. No obvious correlation could be found between the occurrence of individual halocarbons and chl a. On some occasions trichloroethene and tribromomethane related to the presence of nano- and microplankton, respectively.

Zooplankton abundance, biomass and community structure in the top 300 m layer were studied along the 6°E meridian between 49 and 65°S during a Scandinavian/South African Joint Global Ocean Flux Study (December 1997–January 1998) onboard the S.A. Agulhas. Along the transect, total abundance and biomass of zooplankton ranged from 8 to 384 ind m−3 and 1.4 to 64.1 mg DW m−3, respectively. The general pattern in zooplankton distribution observed was an increase in density between Spring Ice Edge and the Antarctic Polar Front (APF) regions. Copepods numerically dominated zooplankton along the entire transect accounting for 68–97% of the total abundance and 24–90% of the total zooplankton standing stock. Other important contributors to total biomass, particularly within the Winter Ice Edge (WIE) and APF regions, were cnidarians and ctenophores (up to 50%), pteropods (up to 35%), tunicates (up to 30%), chaetognaths (up to 25%) and euphausiids (up to 23%). Numerical analyses identified three major zooplankton groupings, coinciding with the three regions of investigation. A dramatic change in the zooplankton composition occurred at the APF region as several copepod and euphausiid species were found on either side of the front only. A second change in the species composition was observed at the WIE, emphasizing the ecological importance of the frontal zone associated with the winter ice edge.

The SWEDARP 1997/98 expedition aboard the S.A. Agulhas focused on three study areas along the 6°E meridian: 60°S, the location of the spring ice edge; 56°S, the location of the winter ice edge; and 50.5°S, the Antarctic Polar Front. This intensive study was preceded by a north–south transect through the area measuring surface water properties while under way. An extensive measurement programme included hydrography, tracers, nutrients, organic carbon, trace metals, bacteria, and primary and secondary producers (including production and grazing rates). Analysis of the results from the three study areas does not identify a single factor limiting primary production: water column stability and the optical regime, and probably iron supply contributed to the control of primary production. The study area acted as a sink for atmospheric CO2 at the time of measurement, while analysis of water column carbon inventories indicated a net CO2 source integrated over the spring season.

Size-fractionated chlorophyll- a (Chl- a ), primary production and biogenic carbon flux in the vicinity of the Winter Ice-edge Zone (WIE), Spring Ice-edge Zone (SIE) and Antarctic Polar Front (APF) were investigated in the eastern Atlantic sector of the Southern Ocean during a collaborative Scandinavian/South African Antarctic cruise conducted in late austral summer (December 1997/January 1998). Microphytoplankton (>20 μm) dominated integrated Chl- a biomass in the SIE and at the APF, comprising >50% of the total at all stations. Within the WIE, nanophytoplankton (2–20 μm) dominated total integrated Chl -a biomass comprising on average 36% of the total. Total integrated primary production ranged between 316 and 729 mg C m −2 d −1 at stations occupied in the region of the SIE, and between 292 and 317 mg C m −2 d −1 within the WIE. At stations occupied in the region of the APF, total integrated production ranged between 708 and 926 mg C m −2 d −1 . The contribution of various size fractions to total productivity generally displayed the same pattern as integrated Chl -a biomass. Microphytoplankton formed the most important contributor to total production at all stations in the SIE and at two stations in the region of the APF. Within the WIE, nanophytoplankton dominated total daily production. The elevated primary production rates in the region of the SIE and APF appear to be related to favourable light environment and the availability of iron. In the SIE, the partitioning of carbon between the microbial loop and classical food web was similar. Grazing activity by metazoans resulted in 1.5% of total daily production being transported to depth. In the region of the WIE and APF, the classical food web represented the main sink for daily primary production. Within the SIE and APF, the grazer-mediated carbon flux corresponded to 8.4% and 15.4% of the total production, respectively. The low rates of biologically mediated carbon flux resulting from grazing by zooplankton in the SIE can be related to the size structure of the phytoplankton assemblages and the absence of larger macrozooplankton in the region. As a consequence of the low grazing activity, the sinking of dead/senescent phytoplankton cells appears to be the major route for the transfer of carbon from the surface waters to depth in the SIE. Results of the investigation suggest that the efficiency of the biological pump in the three regions of investigation was largely determined by the zooplankton community composition and the structure of the local phytoplankton community.

Spatial distribution and feeding ecophysiology of the Antarctic krill, Euphausia superba, and the tunicate, Salpa thompsoni, were investigated along the 6°E meridian between 49 and 65°S. Krill and salps displayed pronounced spatial segregation along the transect. Salps clearly dominated north of the 56°S parallel, while krill dominated south of it. Overlap in krill/salp distribution occurred only at ≈56°S. This region coincided with the northernmost expansion of the subsurface cold water layer and with the Winter Ice Edge (WIE) region suggesting a clear biotopical separation of these key-stone species in the Antarctic pelagic food web. Krill and salp grazing rates determined using the in situ gut fluorescence technique were low (

Spatial and temporal dynamics of carbon and nitrogen stable isotope signatures of the bottom-dwelling caridean shrimp Nauticaris marionis were measured during April and May between 1984 and 2000 in the vicinity of Marion Island (the Prince Edward Islands, Southern Ocean). There was one trophic-level enrichment in bulk δ15N and δ13C signatures between small ( 20 mm) specimens of N. marionis, suggesting distinct trophic differentiation among major shrimp size groups. Both δ15N and δ13C values of N. marionis increased with the depth, reflecting changes in their diet. There were no clear temporal trends in bulk δ15N signatures of N. marionis. However, compound-specific δ15N measurements of amino acids indicated that N. marionis from the inter-island realm occupied the trophic level of second order carnivores, while similarly sized shrimps in the near-shore realm were at the trophic level of first order carnivores. Compound-specific measurements also identified a change in the source of inorganic nitrogen at the base of the food web between the inter-island and near-shore realms. In contrast to the bulk δ15N values, a significant shift in bulk δ13C values of N. marionis was observed between 1984 and more recent years. This temporal change appears to be linked to changes in the overall productivity of the Prince Edward Island inter-island system, which could be linked to global climate change.

Mesozooplankton surveys were conducted in April/May for four consecutive years (1996-1999) in the vicinity of the Prince Edward Islands (PEIs), Southern Ocean. The PEIs are located in the Polar Frontal Zone, directly in the path of the east-flowing Antarctic Circumpolar Current. Zooplankton were collected by oblique tows using a Bongo net fitted with 300 μm mesh. The abundance, biomass and average side of the mesozooplankton in the upstream (USR), inter-island (IIR) and downstream (DSR) regions indicated that some groups and species were significantly affected by their interaction with the shallow shelf waters of the PEIs. Total mesozooplankton abundance and biomass were typically highest in the DSR, but no consistent pattern was evident in the USR and IIR, Copepods, euphausiids and fish were generally of a low average size in the IIR. This small size was largely attributed to the reduced abundance, or complete absence, of mesopelagic species from the shelf region. Of total biomass, the mesopelagic species Euphausia longirostris, Euphausia similis, Pleuromamma abdominalis, Paraeuchaeta biloba and Oncaea antarctica together contributed an average of 16% to the USR, 2% to the HR and 15% to the DSR. Conversely, epipelagic species showed no consistent pattern of abundance and biomass distribution between regions. The low incidence of mesopelagic species over the island shelf was attributed mainly to reduced advection of deep water into the shelf region (average depth = 200 m), rather than predation, particularly during the through-flow mode between the islands. This resulted in substantial regional differences in euphausiid community structure. The epipelagic species Euphausia vallentini and Thysanoessa vicina completely dominated the IIR, comprising on average 89% of total euphausiid biomass in this region. However, predation may be important, during the water-trapping mode between the islands. Advection of zooplankton into the IIR appeared to be affected by the proximity of the Subantarctic Front (SAF). In 1996, when the SAF was far north of the PEIs, reduced current velocities resulted in some degree of water retention over the shelf and an increased predation impact. Conversely, when the SAF was close to the PEIs in 1999, more large plankton were transported over the island shelf. High current velocities and productivity associated with the SAF appear to increase the biomass and size of allochthonous zoopilankton/nekton advected info the IIR. and consequently may have increased the availability of prey to land-based predators. The long-term southward movement of the SAF recently observed in the vicinity of the PEIs may therefore have important implications for the ecosystem of these islands.

A mass death event of the pelagic tunicate Salpa thompsoni, which occurred in April 2002 in Potter Cove near the Argentinean/German Antarctic station Jubany (62°14′S–58°40′W), King George Island, South Shetland Islands, is described. Salps appeared on the beach 2 days after very strong (>80 km.h−1) winds were registered, which accumulated particulate material in the inner part of the cove and probably also re-suspended bottom sediments. The sharp increase in particulate-matter concentrations in Potter Cove caused clogging of salp mucous filtering nets, and probably a combination of clogging, winds and tides caused dying salps to be washed out onto the beach.

Kelp beds are thought to provide a refuge for a variety of marine organisms by damping waves, changing hydrodynamic flow, offering substrata for epiphytic species, and altering the abundances of predators and prey. At the sub-Antarctic Prince Edward Islands, a typical flow-through system, kelp beds have the potential of acting as a prime habitat for a variety of pelagic species that would otherwise be swept away and lost from the island ecosystem. The current study investigates the effects of kelp beds on the abundance and composition of zooplankton and microphytoplankton, with the main aim of determining whether kelp beds act as a repository for larval stages in general, and for the swimming prawn, Nauticaris marionis, in particular. Salinity gradients created by freshwater run-off indicated that kelp beds at Marion Island retain surface water and restrict water exchange with the open ocean. Both the abundance and diversity of zooplankton were greatest within the kelp beds. This was partially due to the high abundance of kelp-associated species, but also to the apparent retention of naupliar larvae within the kelp canopy. Unlike the larvae of ostracods and copepods, caridean zoeae were rare, indicating that kelp beds are not a prime habitat for larvae of N. marionis. The larval retention mechanism for this species, therefore, remains unknown. Apart from retaining water and certain species of zooplankton, chlorophyll a/phaeopigment ratios confirmed the existence of a substantial detrital pool within the kelp beds. This retention of detritus may explain the observed importance of kelp-derived matter in the diet of many nearshore animals. In contrast to the zooplankton, kelp beds seemed to have little effect on the abundance and composition of microphytoplankton, and chlorophyll a values were low at all stations.

The composition, biomass, feeding and predation impact of carnivorous macrozooplankton (>2cm) on mesozooplankton (0.2-2cm) 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

Mesozooplankton community structure was investigated in four consecutive years from 1996 to 1999, during late austral summer (April/May), in the vicinity of the Prince Edward Islands. Sampling was carried out using a Bongo net with a mouth area of 0.25 m 2 , and fitted with 300 μm mesh. Surveys were of high resolution, with net tows being separated by ±10–20 km. Zooplankton species composition demonstrated a high degree of similarity between net tows, containing a mix of sub-Antarctic and Antarctic species. However, variation in species abundance levels showed that within each year of study the region was characterised by the presence of different zooplankton communities. These communities differed by as much as an order of magnitude in total zooplankton density. Analysis of physical variables indicated that zooplankton communities were associated with different water masses, identifiable by their physical characteristics. Sea temperature was the most important physical variable, accounting for as much as 69% of the variation in community structure. Communities were often not spatially discrete, and many stations demonstrated a high degree of similarity despite wide spatial separation. The heterogeneity in the biological and oceanographic environment extended to a small scale, on the order of 10 km. This is indicative of the oceanographic complexity of the region. The complex oceanography associated with shallow topography, including seamounts, islands, and frontal zones, indicates that small-scale spatial heterogeneity in zooplankton communities may be an important factor to consider when modelling these ecosystems.

The feeding biology of three euphausiid species, Euphausia vallentini (adults and juveniles), Euphausia longirostris , and Nematoscelis megalops , was investigated in the vicinity of the Prince Edward Archipelago during austral autumn (April/May) of 1998 and 1999, using the gut fluorescence and gut fullness techniques, to assess diel feeding patterns and estimate daily rations. The results showed clear diel feeding patterns for both E. vallentini adults and juveniles. High feeding activity occurred during dark hours in E. longirostris , while N. megalops did not show distinct diel feeding pattern. E. longirostris had the highest gut pigment levels, averaging 15.2 and 57.1 ng pigm ind −1 in 1998 and 1999, respectively. A similar pattern was observed for E. vallentini : 3.2 versus 6.5 ng pigm ind −1 in juveniles and 4.4 versus 21.9 ng pigm ind −1 in adults. Low average gut pigment levels were found for N. megalops during both years (range 2.0–4.5 ng pigm ind −1 ). Gut evacuation rates varied between 0.45 and 0.99 h −1 for E. vallentini adults, 0.47 and 1.36 h −1 for E. vallentini juveniles, 0.41 and 1.08 h −1 for N. megalops . A single measurement of 0.94 h −1 was made for E. longirostris . Ingestion rates for E. vallentini ranged from 0.24 to 1.82 μg pigm ind −1 d −1 for adults and from 0.98 to 1.92 μg pigm ind −1 d −1 for juveniles. The highest individual ingestion rates were found for E. longirostris (between 1.24 and 3.65 μg pigm ind −1 d −1 ), and the lowest for N. megalops (0.23 μg pigm ind −1 d −1 ). These ingestion rates were combined with data from the gut fullness technique to estimate the contribution of herbivory to the total daily carbon uptake.

Phytoplankton dynamics in the open waters of the ice-edge zone of the Lazarev Sea were investigated over 12 consecutive days during a drogue study conducted in austral summer (December/January) 1994/1995. Throughout the study, the upper water column (

Mesozooplankton community structure in the vicinity of the Prince Edward Islands (PEIs) was investigated during six surveys conducted in late austral summer (April/May) from 1996 to 1999. Zooplankton samples were collected by oblique tows using a Bongo net fitted with 300-μm mesh. Surface temperature, average temperature and chlorophyll a were measured in conjunction with each net tow. The positions of the Sub-Antarctic Front (SAF) and the Antarctic Polar Front (APF), in relation to the islands, were determined by CTD and/or XBT transects to the west of the islands (upstream). Both fronts were characterized by a high degree of latitudinal variation. Changes in position of the fronts occurred rapidly, the SAF moving up to ∼120 km in a 2-week period. Consequently, the oceanographic environment in the vicinity of the PEIs was subject to a high degree of intra- and inter-survey variation. The positions of the SAF and APF appeared to have a significant impact on phytoplankton biomass in the vicinity of the PEIs, possibly through the alteration of local oceanographic flow dynamics. Water retention over the island shelf in 1996, associated with location of the SAF far to the north of the PEIs, corresponded to enhanced chlorophyll-a concentrations (∼1.54 mg m−3). Conversely, when the fronts were close to the islands, as in 1997 and 1999, higher current velocity limited water retention and chlorophyll-a concentrations in the inter-island region were relatively low (∼0.4 mg m−3). Cluster analyses showed that, in many instances, there was greater similarity among zooplankton communities from different surveys than among communities within surveys, indicating that short-term variability exceeded inter-annual variability. The population structure of the copepod Calanus simillimus indicated that there was inter-annual variation in the timing of the biological season. Differences in the population structure of species, and consequently their contribution to abundance and biomass, may therefore have been an important contributor to inter-annual variation in community structure. Evidence is provided of a long-term southward shift in the position of the SAF. It is postulated that this may affect the PEIs by increasing the proportion of allochthonous energy input, because the PEIs now lie in the path of the front, altering the tropho-dynamics of the island ecosystem. Lower mesozooplankton biomass associated with warmer sub-Antarctic water may have important negative consequences for higher trophic levels that depend on mesozooplankton for food.

The relative trophic positions of Euphausia vallentini (juveniles and adults), E. lon- girostris (adults) and Nematoscelis megalops (adults) were investigated using samples collected in the vicinity of the Prince Edward archipelago during austral autumn (April/May) of 1998 on voyage 87 of the MV 'SA Agulhas'. Gut content analysis and stable nitrogen isotope measurements (δ 15 N) were performed on the same individuals. For comparative purposes, nitrogen isotope ratios of the copepod Calanus simillimis, the hyperid amphipod Themisto gaudichaudi and the fish Cerato- scopelus warmingi were also analysed. The results of the gut content analysis for E. vallentini juve- niles showed that there was a high contribution of phytoplankton to the diet. Stable nitrogen isotope analysis supported this and indicated that E. vallentini juveniles occupied a similar trophic position to that of the copepod (mean δ 15 N values of 2.38 and 1.72‰ respectively). E. vallentini adults were found to be omnivorous, but the contribution of carnivory to the diet was difficult to determine. High phytoplankton and low mesozooplankton contributions to the diet from the gut content analysis sug- gested a predominantly herbivorous diet. However, the stable nitrogen isotope results showed that E. vallentini adults were closely grouped with T. gaudichaudi (mean δ 15 N values of 3.66 and 4.13‰ respectively), indicating a high degree of omnivory and a relatively large heterotrophic contribution to the diet. Irrespective of the degree of carnivory, a dietary shift with an increase in size was evident for this species. The gut content analysis of E. longirostris showed that this species consumed large amounts of both phytoplankton and metazoan prey. However, the stable nitrogen isotope analysis indicated a high degree of carnivory (mean δ 15 N = 6.88‰). Although the gut content analysis showed that N. megalops had a lower contribution of mesozooplankton to the diet compared to that of E. lon- girostris, the stable isotope analysis showed that these 2 species occupied a similar position (N. mega- lops mean δ 15 N = 6.83‰). The findings of this study support findings in the literature and show that E. vallentini juveniles are herbivorous and N. megalops adults are carnivorous. However, adults of E. vallentini and E. longirostris appear to have higher contributions of heterotrophic carbon to their diets than has been assumed and may occupy higher trophic positions than initially predicted.

Oceanographic environment, chlorophyll- a (chl-a), plankton composition and spatial dynamics were investigated during two large-scale surveys conducted in April/May 1989 and 1997 within the Antarctic Polar Front Zone (APFZ) around the Prince Edward Islands. On both occasions, substantial disturbances in the flow pattern of the Antarctic Circumpolar Current (ACC) were demonstrated particularly downstream of the islands. In this region, enhanced cross frontal and zonal mixing were generated by the intrusion of foreign water masses from outside the APFZ. This may have been promoted by the differences in the flow intensity of the ACC in the vicinity of the islands which is affected by the Subantarctic Front (SAF) location near the island plateau. Distribution of chl-a was generally uniform throughout both surveys with values ranging from 0.1 to 0.2 and from 0.2 to 0.3 mg m −3 during 1989 and 1997, respectively. Although a single phytoplankon community was identified during both surveys, quantitative distribution of the surface phytoplankton showed a good consistency with spatial patterns of water masses. Community structure and distribution of meso- and macrozooplankton/micronekton confirmed that extensive cross-frontal mixing occurred in the downstream region of the islands. While no substantial differences between the inter-island and offshore assemblages of mesozooplankton were found, a distinct inter-island macroplankton community was identified. Zooplankton community structure clearly indicated the intrusion of subtropical species into the region during the 1997 survey. The extent of modifications in the APFZ planktonic realms in the vicinity of the Prince Edward Islands may be influenced by the effect of the flow regime, in particular by the speed at which the incident current, the ACC, approaches and interacts with the island group.

The composition, biomass, distribution and grazing impact of dominant components of the meso- and macrozooplankton community were investigated along a transect occupied in the Atlantic sector of the Southern Ocean during the second cruise of the South African Antarctic Ecosystem Study conducted in late austral summer (Jan.–Feb.) 1993. Total zooplankton abundance along the transect ranged from 6 to 161 ind. m−3, and biomass levels ranged from 4. 2 to 80.5 mg DWt m−3. Elevated abundances and biomass were recorded at stations occupied in the vicinity of the Marginal Ice Zone (MIZ), the Antarctic Polar Front (APF) and Subantarctic Front (SAF). Throughout the investigation mesozooplankton, comprising mainly copepods, dominated numerically and by biomass accounting for >80% of the total. South of the APF, the copepods Calanus propinquus, Calanoides acutus and Metridia gerlachei numerically dominated zooplankton counts, while north of the front the zooplankton community was dominated by the copepods Calanus simillimus, Rhincalanus gigas and Lucicutia ovalis. Grazing impact of the six most abundant zooplankton taxa, accounting for up to 90% of all zooplankton counted at each station, demonstrated large spatial variability ranging from 0.01 to 18% of the chlorophyll (chl-a) standing stock or up to 89% of the daily phytoplankton production (DPP). The highest grazing impact along the transect was recorded within the Polar Front Zone where zooplankton removed between 4 and 18% of the chl-a standing stock or between 53 and 89% of DPP daily. Outside this region, zooplankton grazing generally corresponded to

Variability in the oceanographic parameters and macrozooplankton and micronekton composition, densities and distributional patterns were investigated during a repeat survey conducted between the Prince Edward Islands in April 1998. Results of this study demonstrated the occurrence of pronounced water pulses along the inter-island trench. The location of the Subantarctic Front to the north of the island plateau, through its interactions with the island group, appeared to have a marked effect on the mesoscale dynamics of physical and biological parameters between and around the islands. Seawater temperature and salinity accounted for >40% of the variation in the zooplankton distribution during the trench studies. A total of 41 macroplankton and micronekton taxa, consisting of subantarctic, subtropical and Antarctic species, were identified. Numerical analyses revealed two major groupings of stations corresponding to an offshore and inshore region. Although there was no evidence for quantitative differences in macroplankton densities between the inshore surveys, offshore plankton biomass was at least three- to eightfold higher than during the trench surveys. The importance of water pulses in carrying stocks of large plankton between the islands appeared to be minimal, at least during the time when the investigation took place.

Sub-Antarctic bottom-dwelling caridean shrimps Nauticaris marionis were collected in April/May between 1984 and 1997 over the shelf region of the Prince Edward Islands (37 °50′E, 46 °45′S). N. marionis is a partially protandric hermaphrodite. Hatching probably occurs just before April each year, but may persist until May. During the 1st year N. marionis seem to survive in undetected localities, moult into juveniles, and then settle amongst the benthos from the plankton beginning probably after November. Diel vertical migration then occurs up to an unknown larger size. The vast majority of juveniles develop into males, most of which transmutate into females by April/May of their 3rd year. Reproduction can occur before all male secondary characteristics have been lost. A minority of individuals develop directly into females without passing through a male phase. Individuals older than 5 years are undetectable using samples of the sizes analysed, but they may well persist in the population. The von Bertalanffy growth parameters for N. marionis are tentatively identified as k=0.2353/year, L ∞=12.6 mm, t 0=−0.2828 years and WW ∞=2.03 g. Sex-reversal in N. marionis at Marion Island may be affected by the changing environment as sexual differentiation is probably determined during the planktonic stage.

The feeding dynamics and predation impact of the hyperiid amphipod, Themisto gaudichaudi, on the zooplankton community in the waters surrounding the Prince Edward Archipelago were investigated at 30 stations in late austral summer (April/May) 1998. Ingestion rates of T. gaudichaudi were estimated using two approaches, the gut fullness index and in vitro incubations. Throughout the investigation mesozooplankton, comprising copepods, pteropods and chaetognaths, numerically and by biomass dominated Bongo samples. Zooplankton abundances and biomass ranged from 8 to 271 ind. m−3 and between 1.01 and 7.47 mg dwt m−3, respectively. Densities of T. gaudichaudi during the study were low, never exceeding 0.4 ind. m−3. Gut content analysis (n=61) indicates that T. gaudichaudi is a non-selective, opportunistic carnivore generally feeding on the most abundant copepod and chaetognath species. Peaks in feeding activity were recorded at sunrise and sunset, corresponding to their diel vertical migration patterns. Daily rations estimated from in vitro incubations and gut fullness index were equivalent to 1.2–8.7% and between 11.5 and 19.8% of body dry weight, respectively. The predation impact of T. gaudichaudi averaged over the upper 300 m of the water column was low, accounting for

Net sampling and continuous acoustic measurements within the Antarctic Polar Frontal Zone (APFZ) and in the vicinity of the Prince Edward Islands were conducted during austral autumn (April/May) 1997 to describe the composition and distribution of macrozooplankton and micronekton, and to investigate their relations to the prevailing oceanographic regime in the area. Two major circulation patterns associated with the Subantarctic (SAF) and Antarctic Polar (APF) Fronts existed in the oceanic environment surrounding the Prince Edward Islands, promoting high cross-frontal mixing both upstream and downstream of the islands. Average abundance and biomass of macroplankton/micronekton in the top 300-m layer were 21 ind. 1000 m−3 and 467 mg DW 1000 m−3, respectively. Pelagic crustaceans (euphausiids and amphipods), fish, chaetognaths and gelatinous zooplankton dominated numerically and by biomass. Continuous acoustic measurements displayed elevated pelagic biomass at the SAF and APF. Although four groupings of stations were identified using cluster analysis, a single macroplankton/micronekton community was recognized in the top 300-m layer throughout the offshore area of the APFZ. A modification of the APFZ community was observed within the inter-island region. Subantarctic species dominated zooplankton samples throughout the APFZ, although subtropical species were also well represented at stations occupied in the northern region of the APFZ. A biological response reflected in macroplankton community composition, resulting from an extensive cross-frontal mixing, was observed within the APFZ around the Prince Edward Islands.

A novel approach was used to estimate the heterotrophic carbon component in the diet of the Antarctic krill Euphausia superba. Over 200 specimens from seven samples collected in the Lazarev Sea (January 1993 and 1995), at the Antarctic Polar Front (January 1993), and around South Georgia (February/March 1994) were dissected, and the total carbon content of their stomachs was estimated with a CHN-analyser. Gut-pigment contents were also measured by the gut-fluorescence technique in specimens collected at the same time, and the equivalent amount of their gut carbon was then subtracted from the total organic carbon content of guts from the same samples. The remaining carbon was assumed to originate entirely from heterotrophic food sources. This heterotrophic component accounted for a substantial proportion of the total food consumed by Antarctic krill, ranging from 17.4 to 98.9% of the mass of the gut contents (mean = 78.8% ± 21.2 SD). The results make an important contribution to the elucidation of the energy budget of krill and its daily carbon ration. With a few exceptions, previous estimates were largely calculated from a solely autotrophic carbon source, and were unable to account for the metabolic requirements of E. superba. Krill plays an important role in Antarctic food webs, as it often constitutes ≃50% of the total biomass of the zooplankton, and produces fast-sinking, dense faecal pellets which are important in the vertical transport of organic carbon from the euphotic layer to the deep ocean. High consumption rates of smaller heterotrophic organisms by krill suggest that this large microphage may be more important than previously believed in re-packaging micro- and mesozooplankton into a longer-lasting and more easily sequestered carbon pool.

The results of a macro-scale oceanographic survey conducted in the upstream and downstream regions of the Prince Edward Islands in austral autumn (April/May) 1989 are presented. During the investigation, the Subantarctic Front, upstream of the islands, was shown to lie initially south at 46°38′S, while downstream, the front remained in a northern position of approximately 46°S. Surface expressions of the front show that the Subantarctic Front forms a zonal band, while the subsurface expressions (200 m) show a distinct meander in both regions. In the upstream region of the islands, the northern branch of the Antarctic Circumpolar Current, the Subantarctic Front, influenced by the shallow bathymetry, was deflected around the northern edge of the islands. Water masses in this region were shown to modify gradually from Subantarctic Surface Water (7°C, 33.75) to Antarctic Surface Water (5°C, 33.70) as the Polar Frontal Zone was crossed. Downstream of the islands a wake was formed resulting in the generation of broad, cross-frontal meanders. As a consequence, warm Subantarctic Surface Water from north of the Subantarctic Front was advected southwards across the Polar Frontal Zone, while cooler waters, which had been modified in the transitional band of the Polar Frontal Zone, were advected northwards. In the downstream region a warm eddy consisting of Subantarctic Surface Water was observed. Its generation is possibly due to baroclinic instabilities in the meandering wake. Zooplankton species composition and distribution patterns during the investigation were consistent with the prevailing oceanographic regime. Four distinct groupings of stations were identified by numerical analysis. These corresponded to stations found north of the Subantarctic Front, within the warm eddy, located in the Polar Frontal Zone, and those stations associated with the meander. The groupings were separated by the Subantarctic Front, which appears to represent an important biogeographic boundary to the distribution of warm-water zooplankton species. Warm eddies in the downstream region of the islands may represent an effective mechanism for transporting warm water species across the Subantarctic Front.

The composition, biomass, distribution and predation impact of carnivorous zooplankton were investigated along a transect from SANAE to Cape Town during the second cruise of the South African Antarctic Marine Ecosystem Study (SAAMES II) in January–February 1993. The carnivore component of the pelagic community consisted mainly of six groups: amphipods, euphausiids, decapods, fish, chaetognaths and jellyfish. Amongst these, euphausiids (mainly Thysanoessa macrura and Nematoscelis megalops ), chaetognaths ( Sagitta gazellae and Eukrohnia hamata ) and myctophids were the most prominent groups throughout the transect. Jellyfish were abundant within the Marginal Ice Zone (MIZ), while mesopelagic/interzonal decapods exhibited a peak in biomass north of the Subtropical Convergence (STC). Generally, carnivores comprised 10 to 30% of total zooplankton biomass. In frontal regions, such as the Antarctic Polar Front (APF) and the STC, their contribution to total zooplankton biomass decreased to ≤6%. Carnivores overwhelmingly dominated the zooplankton stock between the Subantarctic Front (SAF) and the STC, accounting for 42 to 96% of the total. Gut content analysis showed that all the species investigated are opportunistic predators, generally consuming the most abundant mesozooplanktonic groups. Chaetognaths and euphausiids exhibited the highest impact on secondary standing stock along the transect. Total daily predation impact varied considerably along the transect but generally accounted for x =12%) of the total stock, were found in the region between the SAF and the STC, in conjunction with the high densities of chaetognaths. Carnivores may potentially contribute a regional downward flux of faeces equivalent to ≤5% of the local mesozooplankton stock per day.

The feeding dynamics and oxygen uptake of the bottom-dwelling caridean shrimp Nauticaris marionis were studied during the April/May 1984, 1996 and 1997 cruises to Marion Island (Prince Edward Islands, Southern Ocean). N. marionis is thought to have an opportunistic feeding mode. Prey composition varied considerably between the years and sites investigated. Overall, benthic (mainly hydrozoans and bottom-dwelling polychaetes) and, at times, pelagic (largely euphausiids and copepods) prey items dominated in the stomachs of N. marionis both by occurrence and by volume. Generally, pelagic prey contributed more to the diets of smaller shrimps, while benthic prey was a more important component in the guts of larger specimens. Wet, dry and ash-free dry weight were determined for specimens used in respiration experiments. The respiration rates of N. marionis females with carapace length 6.6–11.1 mm ranged from 80 to 250 μl O2 individual−1 · h−1, or from 0.588 to 2.756 μl O2 · mg−1 dry weight h−1. Regression analyses showed highly significant correlations between oxygen consumption and carapace length for N. marionis. Daily ingestion rates estimated using an in situ gut content analysis technique (4.4% of body dry weight) and an energy budget approach (average 4.7% of body dry weight, range 2.0–7.5%) showed good agreement with each other.

This review summarizes the main research findings of the multi-year oceanographic and biological studies conducted in the vicinity of the Prince Edward Archipelago during the period 1976 to 1990. The Prince Edward Islands represent a flow-through system on the mainstream of the Antarctic Circumpolar Current. Although there are no taxonomic differences between the pelagic communities of the upstream, inter-island and downstream regions, these mesoscale subsystems may operate differently. The mesoscale oceanographic and biological processes appear to be affected by the position of the Subantarctic Front (SAF) in the vicinity of the islands. Both the rich benthic community, which is supported by the local enhancement of primary production, and the strong advection of zooplankton/micronekton from the upstream region provide the food resources necessary for the survival of the huge community of land-based predators present on the islands. Collectively this is termed the `life-support system'. Future studies should concentrate on the meridional shifts in the position of the SAF and its influence on background productivity upstream and downstream of the Prince Edward Archipelago.

Pour estimer les changements saisonniers de regime alimentaire d'Euphausia crystallorophias en relation avec son bilan energetique, une etude a ete menee au printemps en en ete austral 1994/1995 dans la region de plateau continental de la Mer de Lazarev. Dans les 300 m superficiels, les concentrations de larves, de juveniles et de sub-adultes/adultes d'E. crystallorophias variaient respectivement de 27 a 1689, de 4 a 86, et de 2 a 9 ind. 1000 m -3 . Aux stations ou des essaims d'adultes etaient presents, les valeurs moyennes d'abondance atteignaient 450-689 ind. 1000 m -3 . L'analyse des tubes digestifs montre qu'en decembre le micro- et le mesozooplancton etaient les composants dominants du regime d'E. crystallorophias, representant en moyenne 75% du nombre total des constituants alimentaires identifiables. En janvier cependant, la composante heterotrophe du regime diminuait en revanche fortement et les cellules phytoplanctoniques representaient 68% du nombre total des particules alimentaires. Ceci suggere qu'E. crystallorophias est susceptible de presenter un comportement principalement carnivore pendant le printemps austral. A l'apparition de la poussee phytoplanctonique printaniere, cette espece semble en revanche capable de passer a un regime omnivore veritable.

Cross-frontal changes in the microphytoplankton, zooplankton and micronekton species composition and biomass were investigated in two sectors of the Subtropical Convergence region (STC) to evaluate patterns in the pelagic community in areas of contrasting hydro- dynamic structure. The first sector was south of Africa (±20°E, winter 1993) where the frontal zone is relatively permanent and intense. The other sector was in the mid-Atlantic ocean (±2°E, summer 1994) where the STC is ephemeral and weak. Higher biological diversity and weaker zonation patterns were observed in the mid-Atlantic sector, relative to the sector south of Africa. This indicates that the boundaries of the STC were more relaxed in the former region, suggesting that the structure in the mid-Atlantic community is less controlled by hydrodynamic forcing. In both sectors, species of Antarctic and subtropical origin were present on both sides of the convergence, suggesting that cross-frontal mixing was prevalent. Changes in the relative proportion of microphytoplankton, micro- and mesozooplankton in both regions appear to reflect the seasonality of sampling, rather than regional differences in the pelagic food web structure. Despite the marked contrast in the intensity of the hydrographic front between the two sectors, higher phytoplankton, zooplankton and mesopelagic fish abundances were consistently associated with the Subtropical Convergence, reflecting the importance of this region in the pelagic production of the south Atlantic Ocean.

The predation impact of the two chaetognaths Eukrohnia hamata and Sagitta gazellae on mesozooplankton standing stock were investigated in three depth layers during two 24 h stations occupied in the vicinity of Marion Island in late austral summer (April/May) 1986. The zooplankton community at both stations was dominated by small copepods (Oithona spp., Microcalanus spp.), which accounted for >95% of total zooplankton abundance. Chaetognaths comprised 95% of the total chaetognath stock. The general trend in both species was decreasing abundance with increasing depth, which appeared to be correlated to the distribution of copepods (r2 = 0.45; P

Trophodynamics and predation impact of the 2 dominant chaetognaths Eukrohnia hamata and Sagitta gazellae were investigated at 19 stations in the vicinity of the Prince Edward Islands and at a 24-h station occupied at the sub-Antarctic Front in late summer (April/May) 1996. During the entire investigation, the zooplankton assemblages were numerically dominated by copepods with densities ranging from 21 to 170 ind. m−3. Amongst the copepods, Clausocalanus brevipes, Metridia gerlachei and M. lucens dominated accounting for >90% of the total. Generally, chaetognaths were identified as the second most important group composing at times up to 30% (mean = 14.7%) of total zooplankton abundance. Of the two chaetognath species, E.␣hamata was generally numerically dominant. Gut content analysis showed that both chaetognath species are opportunistic predators generally feeding on the most abundant prey, copepods. No feeding patterns were evident during the 24-h station, suggesting that both species feed continuously. The feeding rates of E. hamata ranged from 0 to 0.50 prey ind. day−1 and between 0 and 0.90 prey ind. day−1 for S. gazellae. The maximum total predation impact of E. hamata was equivalent to 5.2% of the copepod standing stock or up to 103% of copepod production per day. For S. gazellae the predation impact was lower, reaching a level of 3.2% of the copepod standing stock or 63% of the daily copepod production. Chaetognaths can, therefore, be regarded as an important pelagic predator of the Prince Edward Islands subsystem.

The consumption of fishery waste by the Antarctic bottom-dwelling fish, Trematomus hansoni, is described in the Cosmonaut Sea. The study indicates that T. hansoni is able to switch its feeding habits at the time of fishery operations by incorporating fishery waste into the diet.

The diet of Cygnodraco mawsoni Waite 1916 and Gymnodraco acuticeps Boulenger 1902 (Pisces: Bathydraconidae) was studied in the Cooperation and Cosmonaut seas in the depth range 200–400 m during the summer 1988. Stomach content analysis showed that both species are piscivorous predators but with different feeding habits. Cygnodraco mawsoni fed mostly on young notothenioid fish, regularly complementing these with pelagic, Euphausia superba, and benthic crustaceans, such as amphipod gammarids and mysids. In contrast, G. acuticeps relied mostly on mesopelagic fish of the family Myctophidae. Although C. mawsoni and G. acuticeps occupy similar depths in the Cosmonaut Sea, different feeding habits appear to limit the probability of interspecific competition for food.

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