Two species of Drepanopus Brady (Copepoda Calanoida) with discrete ranges in the Southern Hemisphere

Morphological features, distributional records and developmentalstages of Drepanopus pectinatus Brady and D. forcipatus Giesbrechtindicate their close relationship but also corroborate the validityof their states as separate species with discrete ranges. D.pectinatus lives in inshore waters of the Crozet, Kerguelenand Heard Islands, south of the Antarctic Convergence. D. forcipatusoccurs along both the Pacific and thc Atlantic coasts of southernSouth America and around South Georgia. The distribution ofthe species in the former region, which includes the FalklandIslands, appears to be related to the extent of the continentalshelf and of the sub-Antarctic water; South Georgia lies southof the Antarctic Convergence. Significant morphometric differencesbetween both populations of D. forcipatus were found.     

Predicted Patterns of Photosynthetic Production in Maritime Antarctic Mosses

The microclimate of a moss turf of Polytrichum alpestre Hoppeand a moss carpet of Drepanocladus uncinatus (Hedw.) Warnst.is described for two sites in the maritime Antarctic. Thesemicro-climatic data, together with some additional data, arethen used in the solution of multiple regression equations describingnet photosynthetic response to variation in radiant flux densityand temperature as measured in Antarctic material of the twomosses grown under controlled conditions in the U.K. Predictionsare made of daily and seasonal courses of net photosynthesisat the Antarctic field site. The basis of acclimation of netphotosynthesis to growth temperatures through a season is discussedand the physiological basis of growth under snow is examined. Polytrichum alpestre. Hoppe, Drepanocladus uncinatus (Hedw.) Warnst., mosses, Bryophyta photosynthesis, productivity, Antarctic     

THE DISTRIBUTION OF SOME ENDEMIC ANTARCTIC NUDIBRANCHIA

The distribution of six endemic Antarctic nudibranch speciesis described, using both published data and new results fromrecent expeditions to the Atlantic sector of the South PolarSea. Notaeolidia schmekelae Wägele, 1990 is restrictedto the Weddell Sea, and N. gigas Eliot, 1905 to the AntarcticPeninsula and the Scotia Arc. N. depressa Eliot, 1905 is theonly member of the family Notaeolidiidae Odhner, 1926 with acircumpolar distribution. Localities of Pseudotritonia quadrangularisThiele, 1912 and Telarma antarctica Odhner, 1934, are knownaround the Antarctic Continent, whereas Pseudotritonia gracilidensOdhner, 1944 was only collected at the Antarctic Peninsula.The biogeographical divisions, discussed by several authors,do not coincide in all aspects with the distribution patternsof the Nudibranchia. According to my results, the AntarcticPeninsula forms a separate faunal zone, with transitional elementsof the High Antarctic and Subantarctic zone. South Georgia hasno endemic nudibranchs. (Received 30 March 1990; accepted 23 September 1990)     

THE DISTRIBUTION OF SOME ANTARCTIC NUDIBRANCHS (OPISTHOBRANCHIA)

The circumpolar distribution of the four revised species ofdoridacean nudibranchs: Aegires albus, Bathydoris hodgsoni,B. clavigera and Austrodoris kerguelenensis, is demonstrated,taking into consideration the known data from the literatureand new localities from the Atlantic sector of the Antarctic.A. albus and B. hodgsoni are restricted to the High AntarcticZone. A. kerguelenensis is widely distributed in the High Antarcticand Subantarctic Zone, whereas localities of B. clavigera arerestricted to the High Antarctic Zone and the Atlantic sectorof the Subantarctic Zone. (Received 13 November 1986;     

A field study on the physiology of digestion in the Antarctic krill, Euphausia superba, with special regard to chitinolytic enzymes

Endo- and exochitinase activities were determined in the stomachand midgut gland of the Antarctic krill, Euphausia superba.along a transect west of the Antarctic Peninsula. Activitieswere compared with the digestive enzymes protease, cellulase(1,4-ß-D-glucanase) and laminarinase (1,3-ß-D-glucanase)The chlorophyll and protein contents in the surface water ofthe corresponding stations were determined. Enzyme activitieswere characterized by high individual and spatial variations.Chitinolytic activity in the stomach correlated well with alldigestive enzymes investigated. In the midgut gland, a correlationwith cellulase and laminannase was evident. The amount of chlorophylla and phytoplankton protein in the surface water was not correlatedwith enzyme activity. Specific enzyme activity was higher inthe stomach than in the midgut gland. showing individual ratiosfor each enzyme. Elevated endochitinase activity in the stomachsuggests that chitinous food is digested to oligomers in thestomach, while the subsequent degradation to amino sugars occurspredominantly in the midgut gland.     

Swimming in formation in krill (Euphausiacea), a hypothesis: dynamics of the flow field, properties of antennular sensor systems and a sensory-motor link

The act of swimming in formation by species such as Euphausiasuperba, Antarctic krill, is assumed to be regulated by a sensitivityto the characteristic and spatially elaborate flow field producedby this species of shrimp. We used a related species, Meganyctiphanes,North Atlantic krill, to visualize the flow field produced bytethered shrimps in an aquarium. In this situation, the propulsionjet flow some centimeters behind the shrimp is surrounded bya vortex ring of recoiling water motion from which, if the vortexis also produced by unrestrained swimming shrimp, a followingshrimp hypothetically can draw forces of lift and propulsionto decrease energy expense in long-distance migration. Two antennularsensitivities to water vibration in frequency ranges 5–40and 40–150 Hz were calibrated, and the activity of connectedinterneurons was traced into the abdominal pleopod-carryingsegments. Water oscillation of 3–10 Hz frequency, appliedto the antennules, was shown to entrain a closely synchronouspleopod beat in the stimulated specimens.     

SOME OBSERVATIONS ON THE DIET AND DISTRIBUTION OF NUDIBRANCHS AT SIGNY ISLAND, ANTARCTICA

Observations were made on the diet and distribution of eightspecies of nudibranchs found in Borge Bay, Signy Island, Antarctica.Specimens from seven sites were examined in situ on four separateoccasions during 1992 and 1993 using SCUBA. A small collectionfor identification was also made Six of the eight species presentwere identified, and the first ecological data for at leastone species (Charcotia granulosa) were recorded. Notaeolidiagigas was feeding principally on hydroids of the genus Tubulariaover the entire depth range surveyed (3–36 m), and wasmost abundant in shallow water, whereas Truomella belli wasonly found at deeper sites, mostly on an octocoral of the genusAscolepis. Charcoaa granulosa and Pseudotritoma gracilidensappeared to be specialist bryozoan feeders and, as has beenfound at other locations, Austrodoris kerguelenesis specialisedon the demosponge Dendnlla antarcnca. Two unidentified aeolidspecies occurred almost entirely on particular hydroids andthe prey of Tritonia antarctica was not apparent. The physicalsize of Antarctic nudibranchs may have important implicationsto the type of prey and feeding strategy used by different species. (Received 11 May 1995; accepted 3 December 1995)     

Unusual swimming mechanism in Calycopsis borchgrevinki (Hydrozoa)

Calycopsis borchgrevinki (Browne, 1910) from Antarctic waterswas studied histologically. The entire bell is enclosed in achitin-like skin, supported by chitin-like rods in the radialmesogleal fibres. In the tentacles a thick mesogloea is presentwithout chitinous structures. The gonads are embedded in thestomach folds. It is postulated that these characters are adaptationsto ecological conditions in Antarctic waters.     

Interannual variability in the distribution of the phytoplankton standing stock across the seasonal sea-ice zone west of the Antarctic Peninsula

The spatial distribution of phytoplankton cell abundance, carbon(C) biomass and chlorophyll a (Chl a) concentration was analysedduring three summers (1996, 1997 and 1999) in a seasonal sea-icearea, west of the Antarctic Peninsula. The objective of thestudy was to assess interannual variability in phytoplanktonspatial distribution and the mechanisms that regulate phytoplanktonaccumulation in the water column. Phytoplankton C biomass andChl a distributions were consistent from year to year, exhibitinga negative on/offshore gradient. The variations in C concentrationhad a close and non-linear relationship with the upper mixedlayer depth, suggesting that the vertical mixing of the watercolumn is the main factor regulating phytoplankton stock. Themagnitude of C gradients was 5-fold higher during 1996 thanduring 1997 and 1999. This was ascribed to interannual variationsin the concentration of diatom blooms in the region influencedby sea-ice melting. Vertical distribution of the phytoplankton,as estimated from Chl a profiles, also varied along an on/offshoregradient: Chl a was distributed homogeneously in the upper mixedlayer in coastal and mid-shelf stations and concentrated inthe deep layer (40–100 m) occupied by the winter waters(WW, remnants of the Antarctic surface waters during summer)in more offshore stations. The region with a deep Chl a maximumlayer (DCM layer) was dominated by a phytoplankton assemblagecharacterized by a relatively high concentration of diatoms.The extent of this region varied from year to year: it was restrictedto pelagic waters during 1996, extended to the shelf slope during1997 and occupied a major portion of the area during 1999. Itis hypothesized that iron depletion in near surface waters dueto phytoplankton consumption, and a higher concentration inWW, regulated this vertical phytoplankton distribution pattern.Furthermore, we postulate that year-to-year variations in thespatial distribution of the DCM layer were related to interannualvariations in the timing of the sea-ice retreat. The similaritybetween our results and those reported in literature for otherareas of the Southern Ocean allows us to suggest that the mechanismsproposed here as regulating phytoplankton stock in our areamay be applicable elsewhere.     

ANATOMY OF PSEUDOTRITONIA THIELE, 1912 AND NOTAEOLIDIA ELIOT, 1905 (GASTROPODA: OPISTHOBRANCHIA: NUDIBRANCHIA) FROM SIGNY ISLAND, ANTARCTICA

Several species of nudibranch molluscs are abundant amongstthe rich benthic hard substratum communities found close tothe British Antarctic Survey base at Signy Island, in the Atlanticsector of the Antarctic. Over the austral summer 1992/1993,two of the authors (LWB and DKAB) were able to collect someof the lesser known species of Nudibranchia at depths between3 and 40 metres, using SCUBA. New information on morphologyand anatomy of two of these species, Pseudotritonia gracilidensOdhner, 1944 (Charcotiidae, Arminoidea) and Notaeolidia gigasEliot, 1905(Notaeolidiidae, Aeolidoidea) are presented in thispaper. The validity of the species Notaeolidia gigas is strengthened. (Received 9 February 1994; accepted 18 September 1994)     

A deployment method for in situ oceanic primary production measurement

A launch, suspension and recovery technique for oceanic, insitu, ¹⁴C productivity measurements is described. Ship's timefor deployment of 125 ml incubation bottles at several depthsdown to 100 m is approximately 10 minutes but another half houris required for water sampling and laboratory manipulations.Relocation from up to 9 nautical miles (16.7 km) is by inexpensiveVHF telemetry transmitters and recovery is by grappling fromthe ship. The method was tested in the Scotia Sea, The Antarctic,during the cruise John Biscoe 2 (1980). It was found feasibleto launch experiments in winds of up to 30 knots (15.4 m s^–1)and recover in a wind of 40 knots (20.6 m s^–) on occasion.Eleven experiments were performed in 15 days.     

Variability of Primary Production in an Antarctic Marine Ecosystem as Estimated Using a Multi-scale Sampling Strategy

A major objective of the multidisciplinary Palmer Long TermEcological Research (LTER) program is to obtain a comprehensiveunderstanding of various components of the Antarctic marineecosystem—the assemblage of plants, animals, ocean, seaice, and island components south of the Antarctic Convergence.Phytoplankton production plays a key role in this polar ecosystem,and factors that regulate production include those that controlcell growth (light, temperature, nutrients) and those that controlcell accumulation rate and hence population growth (water columnstability, advection, grazing, and sinking). Several of thesefactors are mediated by the annual advance and retreat of seaice. In this study, we examine the results from nearly a decade(1991–2000) of ecological research in the western AntarcticPeninsula region. We evaluate the spatial and temporal variabilityof phytoplankton biomass (estimated as chlorophyll-a concentration)and primary production (determined in-situ aboard ship as wellas estimated from ocean color satellite data). We also presentthe spatial and temporal variability of sea ice extent (estimatedfrom passive microwave satellite data). While the data recordis relatively short from a long-term perspective, evidence isaccumulating that statistically links the variability in seaice to the variability in primary production. Even though thismarine ecosystem displays extreme interannual variability inboth phytoplankton biomass and primary production, persistentspatial patterns have been observed over the many years of study(e.g., an on to offshore gradient in biomass and a growing seasoncharacterized by episodic phytoplankton blooms). This high interannualvariability at the base of the food chain influences organismsat all trophic levels.     

Diurnal variations in mean volume backscattering strength of an Antarctic krill (Euphausia superba) patch

A series of acoustic transects and quantitative net hauls wasmade in a large patch of Antarctic krill (Euphausia superba)just north of South Georgia. The krill went through a diurnalpattern of dense swarming in daytime and dispersion after dark.This was accompanied by an 8 dB change in mean volume backscatteringstrength.     

Seasonal Variation in Respiratory and Photosynthetic Parameters in Three Mosses from the Maritime Antarctic

Carbon fixation under controlled conditions was measured inthree mosses from the maritime Antarctic using an infra-redgas analysis system. Gas exchange parameters were determinedduring each season in 1993 and 1994 using the Arrhenius equationand a hyperbolic tangent function applied to respiration andphotosynthesis, respectively. Environmental data was collectedin 1994 for comparison. All seasonal variations were greaterinBrachythecium than in the species from less hydric habitats.Respiration rates were highest in summer and lowest in winterat all temperatures inBrachythecium, but there was little changeinChorisodontium orAndreaea . There was some seasonal variationin the initial slope (K_p) of the photosynthesis-irradiance curvein all species, although the environmental data suggested thatthis was of little ecological importance. In all species seasonalchanges in the maximum rates of photosynthesis (GP_max, NP_max)were observed, generally with a pattern of summer maxima, althoughthere were some interannual differences. These changes are consideredto be the most important in affecting the overall annual productivityof the mosses. There were no seasonal variations in the optimumtemperatures for either gross or net photosynthesis, or forthe irradiance at the onset of light saturation (I_k). The resultshave important implications for the use of models to estimatethe productivity of the Antarctic flora based upon present orpredicted climate data. Antarctica; bryophytes; mosses; carbon exchange; irradiance; photosynthesis; productivity models; respiration; seasonal variation; temperature     

Foraging and provisioning in Antarctic fur seals: interannual variability in time-energy budgets

This study examined three competing hypotheses to explain howlactating Antarctic fur seals (Arctocephalus gazella) respondto changes in the level of resource availability. Antarcticfur seals have episodic bouts of suckling (1-3 days), alternatingwith foraging trips (3-10 days). Foraging time budgets variedsignificantly (p <.001) among 8 consecutive years at BirdIsland, South Georgia. Foraging trip duration increased during periodsof relative food shortage. Time spent ashore was more consistentamong years than foraging trip duration but declined duringa year of particularly low food availability. In 4 of the 8years, there was a significant positive correlation betweentime spent ashore and foraging trip duration. In the other years,the relationship was close to statistical significance. Energydelivery to pups during suckling bouts followed an asymptoticpower function. Energy gain during foraging trips was estimatedfrom diving behavior, which suggested that the energy gain functionwas linear. Distance traveled during foraging trips was correlatedwith foraging trip duration, and long foraging trips were associatedwith reduced foraging intensity. There was support for the hypothesisthat lactating Antarctic fur seals compensate for reduced resources byincreasing the foraging trip duration rather than working harderand increasing their energy expenditure. However, there wasmost support for the hypothesis that lactating Antarctic furseals adjust time spent ashore as well as foraging trip duration,possibly to maximize the delivery of food to their offspring.Lactation appears to impose constraints on provisioning of offspringthat differ from those of seabirds foraging in the same environment andoften on the same prey.     

Metabolism and elemental composition of aggregate and solitary forms of Salpa thompsoni (Tunicata: Thaliacea) in waters off the Antarctic Peninsula during austral summer 1999

Oxygen consumption, ammonia excretion and phosphate excretionrates were measured on the aggregate form (aggregated sexualblastozooid generation) and solitary form (solitary asexualoozooid generation) of Salpa thompsoni sampled from waters offthe Antarctic Peninsula from December 1999 to February 2000,in conjunction with body composition analysis (water, ash, carbon,nitrogen and phosphorus). The specific metabolic rates of S.thompsoni were weight-independent. No significant differencesbetween the aggregate and solitary forms were observed for theweight-specific rates with the exception of the oxygen consumptionrate on phosphorus weight. Metabolic loss estimated for theaggregate and solitary forms was 3.0 and 3.5% day^–1 forbody carbon, 1.6 and 1.8% for body nitrogen, 3.9 and 10.6% forbody phosphorus, respectively. Contents of carbon (6.0% of dryweight for the aggregate form and 5.1% for the solitary form),nitrogen (1.5 and 1.3%) and phosphorus (0.15 and 0.11%) tendedto decrease with the increase of dry weight. All mean valuesof each body constituent (water, ash, C, N and P) for the aggregateand solitary forms were not significantly different in the samedry weight ranges.     

Comparative nutrient status and competitive interactions of two Antarctic diatoms (Corethron criophilum and Thalassiosira antarctica)

The nutrient status of two common Antarctic diatoms (Corethroncriophilum and Thalassiosira cf. antarctica) was analysed bystudying the growth response in enrichment bioassays and byestimates of the cell quotas of Si, N and P after size-fractionationof net plankton samples Corethron had higher biomass-specificN-quotas; Si- and P-quotas were quite similar between both species.Corethron was Si-limited in five enrichment experiments andnot nutrient limited in five experiments. Thalassiosira wasnot nutrient limited in six experiments, N-hmited in four experimentsand Si-limited in one experiment Droop-kinetics of Si-limitedgrowth of Corethron and of N-hmited growth of Thalassiosirawere obtained by combining the growth rates in the bioassaysand the cell quotas from the natural populations. The minimalSi-quota of Corethron was 0 041 mol Si/mol C, the saturatingcell quota was 0.158 mol Si/mol C respectively The minimal N-quotaof Thalassiosira was 0 0223 mol N/mol C, the saturating cellquota was 0.208 mol N/mol C Corethron was N-saturated at cellquotas of >0 106 mol N/mol C; Thalassiosira was Si-saturatedat cell quotas of <0 132 mol Si/mol C. As the better competitorfor N and the poorer one for Si, Corethron became more importantwith increasing Si N ratios, while Thalassiosira became moreimportant with decreasing Si:N ratios in the water     

Agglutinated loricae of some Baltic and Antarctic Tintinnina species (Ciliophora)

The abundance and species composition of diatoms adhering tothe loricae of four agglutinated Tintinnina species, Laackmanniellanaviculaefera, Codonellopsis gaussi, Cd.balechi and Tintinnopsislobiancoi, were determined. Diatoms from the Fragdariopsis group,F.cylindrus and F.pseudonana, dominated on tintinnid loricaefrom the Antarctic waters, whilst Thalassiosira spp. were predominanton loricae from the Baltic Sea. Although tintinnids utilizeddiatoms in the environment, it is not a rule that they use onlythese which are dominant. Our results suggest that certain diatomsare actively selected and agglutinated by particular tintinnidspecies.     

Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.