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)     

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 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;     

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)     

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.     

The discovery of an Antarctic epipelagic medusan in the Mediterranean

A single specimen of the Antarctic anthomedusan Russellia mirabilisKramp 1957 has recently been collected in the AlboránSea. This is the first record for an Antarctic epipelagic organismin the Mediterranean Sea. Transport in the ballast water ofa cargo ship seems the most plausible mechanism for explainingthis rare occurrence. However, an alternative hypothesis isexplored involving a possibly complex medusan life cycle togetherwith the role of Antarctic (Intermediate and Bottom) water asdispersal mechanisms.     

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.     

Influence of Ozone-Related Increases in Ultraviolet Radiation on Antarctic Marine Organisms

Every spring for the past two decades, depletion of stratosphericozone has caused increases in ultraviolet B radiation (UVB,280–320 nm) reaching Antarctic terrestrial and aquatichabitats. Research efforts to evaluate the impact of this phenomenonhave focused on phytoplankton under the assumption that ecosystemeffects will most likely originate through reductions in primaryproductivity; however, phytoplankton do not represent the onlysignificant component in ecosystem response to elevated UVB.Antarctic bacterioplankton are adversely affected by UVB exposure;and invertebrates and fish, particularly early developmentalstages that reside in the plankton, are sensitive to UVB. Thereis little information available on UV responses of larger Antarcticmarine animals (e.g., birds, seals and whales). Understandingthe balance between direct biological damage and species-specificpotentials for UV tolerance (protection and recovery) relativeto trophic dynamics and biogeochemical cycling is a crucialfactor in evaluating the overall impact of ozone depletion.After more than a decade of research, much information has beengathered about UV-photobiology in Antarctica; however, a definitivequantitative assessment of the effect of ozone depletion onthe Antarctic ecosystem still eludes us. It is only obviousthat ozone depletion has not had a catastrophic effect in theAntarctic region. The long-term consequences of possible subtleshifts in species composition and trophic interactions are stilluncertain.     

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     

The First Record of Fossil Wood of Winteraceae from the Upper Cretaceous of Antarctica

Fossil wood of the Winteraceae from the Upper Cretaceous sedimentsof James Ross Island, Antarctic Peninsula, is described herefor the first time. The specimen is characterized by the absenceof vessels, rays of two distinct sizes and tracheids with one–threerows of circular bordered pits, mainly on the radial walls,grading to horizontally elongate and scalariform. Despite anatomicalconformity to the family Winteraceae, the fossil wood is notidentical to any one extant genus and therefore has been assignedto the fossil organ genus Winteroxylon Gottwald with which thefossil shows greatest similarity. Copyright 2000 Annals of BotanyCompany Antarctica, Cretaceous, angiosperm, wood, anatomy, Winteraceae, Winteroxylon, fossil, palaeoclimate     

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.     

A Fossil Wood Flora from King George Island: Ecological Implications for an Antarctic Eocene Vegetation

Early Tertiary sediments of the Antarctic Peninsula region continueto yield a rich assemblage of well-preserved fossil dicotyledonousangiosperm wood. The wood flora under consideration is fromthe Collins Glacier region on Fildes Peninsula, King GeorgeIsland and is derived from tuffaceous sediments of the MiddleUnit of the Fildes Formation. These deposits accumulated ina volcanic setting adjacent to a basic-intermediate stratocone.The fossil assemblage provides further evidence for the existenceof cool temperate forests, similar in composition to those foundtoday in New Zealand, Australia and, in particular, southernSouth America. This paper describes two conifer and five angiospermmorphotypes, four of which are new additions to the Antarcticapalaeoflora records. Cupressinoxylon Goeppert, which is thedominant conifer in terms of numbers, and Podocarpoxylon Gothanrepresent the conifers. The angiosperm component includes twospecies ofNothofagoxylon and two previously undescribed woodmorphotypes that exhibit greatest anatomical similarity to woodsofLuma A. Gray (Myrtaceae) and Eucryphia Cav. (Cunoniaceae).These morphotypes are described and assigned to the organ generaMyrceugenelloxylon Nishida, and Weinmannioxylon Petriella, respectively.A model based on the extant cool temperate Valdivian rainforestsis proposed and ecological reconstructions based on palaeobotanicaland geological evidence suggest that changes in the palaeovegetationreflect natural dynamics following volcanic disturbances.Copyright2001 Annals of Botany Company Fossil wood, Antarctica, Myrtaceae, Eucryphia, Nothofagaceae, Eocene, Valdivia, Tertiary     

Evolution and Diversification of Antarctic Notothenioid Fishes

Antarctica supported fossil ichthyofaunas during the Devonian,Jurassic, Cretaceous and Eocene/Oligocene. These faunas arenot ancestral to each other, nor are they related to any componentof the modern fauna. About one hundred species of notothenioidsdominate a modern fauna of over 200 species of bottom fishes.This highly endemic perciform suborder is not representedinthe fossil record of Antarctica. Notothenioids may have evolvedin situ on the margins of the Antarctic continent while graduallyadapting to cooling conditions during the Tertiary. Cladisticstudies indicate that notothenioids are a monophyletic group,but a sister group has not been identified among perciform fishes.With relatively few non-notothenioid fishes in Antarctic waters,notothenioids fill ecological roles normally occupied by taxonomicallydiverse fishes in temperate waters. There are six notothenioidfamilies: Bovichtidae, Nototheniidae, Harpagiferidae, Artedidraconidae,Bathydraconidae and Channichthyidae. Aspects of theirbiologyare briefly considered with emphasis on the Nototheniidae, themost speciose family. Evolutionary diversification within thisfamily allows recognition of species which are pelagic, cryopelagic,benthopelagic and benthic.     

THE FUNCTIONAL MORPHOLOGY OF THE ANTARCTIC BIVALVE THRACIA MERIDIONALIS SMITH, 1885 (ANOMALODESMATA: THRACIIDAE)

The functional morphology of the Thraciidae is poorly understood.Although some morphological aspects of several members havebeen described, only Trigonothracia jinxingae from Chinese watersis known in detail. Thracia meridionalis is the only representativeof the family in Antarctic waters, and is common in AdmiraltyBay, King George Island, where it inhabits muddy sediments.Thracia meridionalis shares many features with Tr. jinxingaethat are typical of most Anomalodesmata, i.e. a secondary ‘ligament’of thickened periostracum, extensively fused mantle margins,ctenidia of type E, a ctenidial-labial palp junction of categoryIII, a stomach of type IV and simultaneous hermaphroditism.Thracia meridionalis is, however, strikingly different fromTr. jinxingae in a number of ways, such as the presence of afourth pallial aperture, statocysts of type B₃, heterorhabdicctenidia, direct communication between the mantle chambers,a deep-burrowing habit (individuals lying on the left shellvalve), siphons that retract into mucus-lined burrows, a stomachwith extensive sorting areas, a rectum which passes over thekidneys and separate male and female gonadial apertures. Thereis, therefore, a greater range of morphological diversity withinthe Thraciidae than previously suspected. (Received 27 April 2004; accepted 30 November 2004)     

Diel patterns of photosynthate biosynthesis by phytoplankton in permanently ice-covered Antarctic lakes under continuous sunlight

Diel patterns of photosynthate biosynthesis by Antarctic freshwaterphytoplankton growing under the variable but continuous sunlightof summer were found to be similar in many respects to thosereported from other aquatic environments where light/dark periodsalternate. Lipid synthesis by freshwater phytoplankton in LakesVanda and Fryxell predominated during periods when solar radiationand photosynthesis were most intense; the inverse was generallytrue of the protein and polysaccharide fractions. The majorphotosynthetic end-products in both lakes were protein and polysaccharide,which together accounted for 60–81% of the total cellularcarbon incorporation. Less than 4% of the carbon was incorporatedinto lipid in Lake Vanda; >12% appeared in the lipid fractionin Lake Fryxell. The Lake Fryxell populations showed evidenceof photoinhibition of complete photosynthesis during ‘midday’when irradiance was most intense. I_k values, computed from thephotosynthesis irradiance relationships in Lake Fryxell, corroborateother studies suggesting that the phytoplankton populationsin permanently ice-capped Antarctic lakes are among the mostshade-adapted yet reported.     

An Overview of the Ecology of Antarctic Seals

Four species of seals occupy the pack-ice region of the oceanssurrounding the Antarctic Continent. These seals include thecrabeater (Lobodon cardnophagus), leopard (Hydrurga leptonyx),weddell (Leplonychotes weddellii), and ross (Ommatophoca rossii),and are true seals with special adaptations for living in thepack-ice region. Two other seal species, the southern elephantseal (Mirounga leonina) and the fur seal (Arctocephalus gazella)(the only eared seal of this region) generally occur furtherto the north and use land rather than ice during the periodof birth of young. This paper reviews the status of these species,and examines the generalecology of the four species that inhabitthe pack-ice zone. In general, the four species that occupythe pack-ice zone have specialized in habitats and habits sothat little overlap in dietsor habitat use exist among thesespecies. The exception is the interaction between the leopardand the crabeater which occupy the same regions and eat krill(Euphausia superba), particularly during the winter. The impactof the potential harvest of krill by man on these species isdiscussed. Further, the impact that recovery of the large baleenwhales that feedin this region during the summer is discussedwith regard to the changes that might occur as competition forkrill by the large vertebrate species increases.     

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.     

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.     

FAECAL PRODUCTION AND AN ESTIMATE OF FOOD INTAKE IN THE WILD OF THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL)

The Antarctic limpet Nacella concinna is common in shallow watersaround the Antarctic Peninsula, and has a mean density of 125individuals/m² at Signy Island (Picken, 1980). In the australsummer 1986/87 ammonia excretion and faecal egestion were measuredas part of a programme to develop a detailed individual energybudget for this species. Ammonia production was measured in 102 individuals ranging from3 to 720 mg dry weight. For a standard limpet of 200 mg dryweight, ammonia excretion was 0.13 µg-at/hr. Comparedwith previous measures of oxygen uptake these data suggest anO:N atomic ratio of between 15 and 25. The relationship betweenammonia excretion and dry weight could be expressed by a powercurve with a weight exponent of 0.82 (SE 0.042). Faecal production was measured in limpets freshly sampled fromthe field, and placed in dean seawater for 4 days. During thistime faecal production decreased (since the limpets were notfeeding), although only data from the first 24 hours were used.Again the relationship between faecal egestion and dry weightcould be expressed by a power curve, although this time theweight exponent was 0.94 (SE 0.101). The ash content of thefaecal strings increased significantly with the size of thelimpet, possibly because larger limpets were ingesting a greaterproportion of substrate during feeding. If this is so, thenthis would also explain the weight exponent dose to 1.0, ratherthan the value of about 0.8 to be expected from metabolic measures(since larger limpets would be passing relatively more faecalmaterial). If assimilation efficiency is known, then food intake in thewild may be estimated from a measurement of faecal egestionand faecal organic content (Clarke et at., 1988). Applying typicalvalues of assimilation efficiency for limpets (40 to 60%) suggestsa daily food intake in Nacella of 2 to 3% body weight per day.This is a quite typical figure for a grazing limpet, and suggeststhere is no resource limitation for Nacella at Signy in summer.