Cryptic mitochondrial lineages in the widespread pycnogonid Colossendeis megalonyx Hoek, 1881 from Antarctic and Subantarctic waters

Colossendeis megalonyx Hoek, 1881 is a widespread and abundant pycnogonid in the Southern Ocean which has also been reported from the South Atlantic and South Pacific Oceans. Its strictly benthic lifestyle is expected to promote genetic differentiation among populations and ultimately facilitate speciation. On the other hand, the reported eurybathy and unknown larval stages of this species may allow Colossendeis megalonyx to maintain genetic continuity between isolated shallow-water habitats by active dispersal through the deep sea or by passive rafting on floating substrates. Thus, it remains unknown whether and to which extent geographically separated populations of Colossendeis megalonyx maintain gene flow in the Southern Ocean. We sampled 96 specimens of Colossendeis megalonyx from three stations in the Atlantic Sector of the Southern Ocean and one station from the South American continental shelf (Burdwood Bank). The genetic structure of nominal Colossendeis megalonyx as well as its phylogenetic position within the genus Colossendeis were assessed using a fragment of the cytochrome c oxidase subunit 1 gene. Our data strongly support that nominal Colossendeis megalonyx consists of at least five cryptic and one pseudocryptic mitochondrial lineages, four of which appear to be geographically restricted. Two lineages occurred at locations separated by more than 1,000 km in the Antarctic, thus indicating high levels of gene flow or recent colonization. No haplotype sharing across the Polar Frontal Zone was observed. Our results strongly suggest that cryptic speciation occurred within the genus Colossendeis. The wide biogeographic distribution range of Colossendeis megalonyx and perhaps that of other Antarctic pycnogonids should therefore be regarded with caution.     

Locomotory mechanisms in Antarctic pycnogonids

Patterns of walking, modes of joint movement, and individual limb diversity were analysed with the aid of ciné film of several living Antarctic pycnogonids, including the 8-legged Colossendeis australis, C. angusta, Pallenopsis patagonica , and Nymphon sp., the 10-legged Decolopoda australis , and the 12-legged Dodecolopoda mawsoni. Appendage musculature of several of these species and also of the 10-legged Pentapycnon charcoti and Pentanymphon antarcticurn was dissected. At least two distinct morphotypes were identified: a short-legged, crawling variety ( P. charcoti ); and the more typical long-legged, large bodied, walking forms. No gross differences in musculature of joints were noted in the species examined. All joints are, at least superficially, hinge joints. The coxa-body joint is largely immobile, the coxa 1-coxa 2 joint alone exhibits promotion-remotion and all other joints are flexion-extension joints. The 8-legged forms move in an imprecise manner, there being irregularity of leg raising and lowering and where legs touch down in relation to the body and to other legs. The 10- and 12-legged forms exhibit more precise patterns of metachronal leg movements. Although legs move in a basic promotion-remotion, extension-flexion mode, there is a certain degree of twisting of a leg as it is picked up, brought forward, and set down; models indicating how such joint movement occurs were constructed. The possibility that hydrostatic pressure is employed in extension is considered and is found to be remote. Lateral placement of legs, orientated in almost all directions in the horizontal plane of the trunk, achieves a versatility of movement similar to that in crabs. Comments on pycnogonid taxonomic affinities are offered.     

Impact of temperature on UV-susceptibility of two Ulva (Chlorophyta) species from Antarctic and Subantarctic regions

The interactive effects of UV-B-exposure and increased temperature were investigated in the two green macroalgae Ulva bulbosa from Antarctica and Ulva clathrata from southern Chile in the laboratory. At seawater temperatures of 0°C, UV-induced inhibition of photosynthesis was much larger in U. clathrata than in U. bulbosa, whereas temperatures of 10°C compensated UV-effects in both species. Despite pronounced photoinhibition, damage to D1 protein in photosystem II could not be detected, indicating that photosynthetic reaction centers were unaffected by experimental UV-exposure. In addition, marked differences in the generation of oxidative stress were not detected. Under all treatments, the activity of superoxide dismutase was higher in U. bulbosa than in U. clathrata, indicating a higher degree of cold adaptation in U. bulbosa from Antarctica, resulting in a higher UV-tolerance at 0°C than in U. clathrata from southern Chile.     

Oxygen hypothesis of polar gigantism not supported by performance of Antarctic pycnogonids in hypoxia

Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (−1.8–0°C) for several million years and contain spectacular examples of gigantism. Pycnogonids from 12 species, spanning three orders of magnitude in body mass, were collected from McMurdo Sound, Antarctica. Individual sea spiders were forced into activity and their performance was measured at different experimental levels of dissolved oxygen (DO). The oxygen hypothesis predicts that, all else being equal, large pycnogonids should perform disproportionately poorly in hypoxia, an outcome that would appear as a statistically significant interaction between body size and oxygen level. In fact, although we found large effects of DO on performance, and substantial interspecific variability in oxygen sensitivity, there was no evidence for size×DO interactions. These data do not support the oxygen hypothesis of Antarctic pycnogonid gigantism and suggest that explanations must be sought in other ecological or evolutionary processes.     

Sedimentation of biogenic siliceous particles in Antarctic waters from the Atlantic sector

Sediment traps were deployed in the Drake Passage, Bransfield Strait and west of South Orkney Islands (Powell Basin) during December 1980/ January 1981, December 1983, and between March and December 1983, respectively.Most of the trapped material is biogenic opal except in the lower half of the water column in Bransfield Strait where large amounts of resuspended aluminosilicates and quartz grains were present. Frustules and skeletons of siliceous microorganisms (diatoms, silicoflagellates, radiolarians, chrysophycean cysts), fragments and moults of crustaceans and tests of foraminifera were found. Quantitatively diatoms are the dominant constituent of the trapped biogenic material.Alteration of diatom assemblages in the water column is due to mechanical breakdown by grazing zooplankton. It mainly affects large frustules (e.g. Corethron criophilum Castracane) in the uppermost part of the water column. Dissolution of frustules occurs mostly at the sediment/water interface and leads to the enrichment of strongly silicified valves [e.g. Nitzschia kerguelensis (O'Meara) Hasle, Thalassiosira antarctica Comber (resting spores)].At the Bransfield Strait site a large part of biogenic opal was incorporated into fecal pellets of krill and copepods. The bulk of pellet content consists of fragmented diatom frustules (1–10 μm in size). Most intact valves found in the sediments have settled through the water column by means other than fecal pellet transport: e.g. settling as solitary particles or incorporated into or attached to “Marine Snow” or “Large Amorphous Aggregates”.     

First record of lithodid crabs from Antarctic waters off the Balleny Islands

Four specimens of Neolithodes brodiei Dawson and Yaldwyn (1970) have been obtained for the first time from bottom trawls deployed in Antarctic waters off the Balleny Islands (about 67°S) in March 2004. The Lithodidae constitute the only anomuran crab family so far known to be able to thrive under high-Antarctic conditions, and lithodids in the Ross Sea have previously only been recorded off Scott Island. The new record of N. brodiei, commonly found in waters off New Zealand, clearly extends its geographic range into the Southern Ocean. The significance of this finding with respect to the biodiversity and distribution of the Lithodidae from the Southern Ocean is briefly discussed.This revised version was published online in November 2004 with corrections to Figure 2.     

The diversity, distribution and ecology of diatoms from Antarctic inland waters

Diatoms are abundant and diverse in many Antarctic freshwaters, with a general trend of decreasing diversity moving southwards. They form an important component of many benthic algal communities in streams and standing waters but are generally less common in the phytoplankton. Diatoms are excellent ecological indicator species and, because their remains are preserved in many sedimentary environments, there appears to be a great potential for palaeoenvironmental reconstruction and the examination of past diversity. A lack of taxonomic precision and consistency, coupled with the insufficient collection from some geographical areas, makes the estimation of the number of Antarctic diatom species problematic.     

Two new species of Heterokrohnia (Chaetognatha) from Antarctic waters

Summary Two new species of the genus Heterokrohnia, H. longidentata and H. fragilis, are described and compared with the other three known Heterokrohnia species, H. mirabilis Ritter-Záhony 1911; H. bathybia Marumo and Kitou 1966 and H. involucrum Dawson 1968. The species have been found at great depths (1,000 m–2,000 m) near Elephant Island, north of the Antarctic Peninsula.     

Heterokrohnia longicaudata,a new species of chaetognatha from Antarctic waters

Summary A new bathypelagic species of the genus Heterokrohnia, H. longicaudata, is described and separated from the other five previously described Heterokrohnia species, H. mirabilis Ritter-Záhony 1911, H. bathybia Marumo and Kitou 1966, H. involucrum Dawson 1968, H. longidentata Kapp and Hagen 1985 and H. fragilis Kapp and Hagen 1985. The new specimen has been found at great depths (2,350m–1,000m) near Elephant Island, in the atlantic sector north of the Antarctic Peninsula.     

Composition and significance of picophytoplankton in Antarctic waters

Filter fractionated picophytoplankton from Antarctic coastal waters (summer 2001) represented only 7–33% of total phytoplankton, even though total stocks were low (average Chl a = 0.32 μg l⁻¹, range = 0.13–1.03 μg l⁻¹). Though all cells passed a 2 μm filter, electron microscopy revealed most cells were over 2 μm, principally Parmales, Phaeocystis sp., and small diatoms. CHEMTAX analysis of HPLC pigment data suggested type 8 haptophytes (e.g. Phaeocystis sp. plus Parmales and pelagophytes) contributed 7–58% of picoplanktonic chlorophyll a, type 6 haptophytes (e.g. coccolithophorids) 18–59%, diatoms 0–18% (mostly type 2 diatoms, e.g. Pseudonitzschia sp., 0–15%), prasinophytes 0–17%, with cell fragments of cryptophytes 0–40%, and dinoflagellates 0–11%. Only stocks of type 8 haptophytes and prasinophytes differed significantly due to successional changes. Zeaxanthin concentrations exceeded estimates from previous cyanobacterial counts and may derive from non-photosynthetic bacteria.     

Structures of grasping spines and teeth in three species of chaetognaths from Antarctic waters

The shape and surface structures of the grasping spines and teeth of the Antarctic chaetognaths Eukrohnia hamata, Sagitta gazellae and S. marri collected in Bransfield Strait, were studied by scanning electron microscopy. The characters of arrangement, shape, curvature, surface, edges, and tips of hooks and teeth are described and discussed.     

Ammonia-oxidizing Archaea in the Arctic Ocean and Antarctic coastal waters

We compared abundance, distributions and phylogenetic composition of Crenarchaeota and ammonia-oxidizing Archaea (AOA) in samples collected from coastal waters west of the Antarctic Peninsula during the summers of 2005 and 2006, with samples from the central Arctic Ocean collected during the summer of 1997. Ammonia-oxidizing Archaea and Crenarchaeota abundances were estimated from quantitative PCR measurements of amoA and 16S rRNA gene abundances. Crenarchaeota and AOA were approximately fivefold more abundant at comparable depths in the Antarctic versus the Arctic Ocean. Crenarchaeota and AOA were essentially absent from the Antarctic Summer Surface Water (SSW) water mass (0–45 m depth). The ratio of Crenarchaeota 16S rRNA to archaeal amoA gene abundance in the Winter Water (WW) water mass (45–105 m depth) of the Southern Ocean was much lower (0.15) than expected and in sharp contrast to the ratio (2.0) in the Circumpolar Deep Water (CDW) water mass (105–3500 m depth) immediately below it. We did not observe comparable segregation of this ratio by depth or water mass in Arctic Ocean samples. A ubiquitous, abundant and polar-specific crenarchaeote was the dominant ribotype in the WW and important in the upper halocline of the Arctic Ocean. Our data suggest that this organism does not contain an ammonia monooxygenase gene. In contrast to other studies where Crenarchaeota populations apparently lacking amoA genes are found in bathypelagic waters, this organism appears to dominate in well-defined, ammonium-rich, near-surface water masses in polar oceans.     

A metaproteomic assessment of winter and summer bacterioplankton from Antarctic Peninsula coastal surface waters

A metaproteomic survey of surface coastal waters near Palmer Station on the Antarctic Peninsula, West Antarctica, was performed, revealing marked differences in the functional capacity of summer and winter communities of bacterioplankton. Proteins from Flavobacteria were more abundant in the summer metaproteome, whereas winter was characterized by proteins from ammonia-oxidizing Marine Group I Crenarchaeota. Proteins prevalent in both seasons were from SAR11 and Rhodobacterales clades of Alphaproteobacteria, as well as many lineages of Gammaproteobacteria. The metaproteome data were used to elucidate the main metabolic and energy generation pathways and transport processes occurring at the microbial level in each season. In summer, autotrophic carbon assimilation appears to be driven by oxygenic photoautotrophy, consistent with high light availability and intensity. In contrast, during the dark polar winter, the metaproteome supported the occurrence of chemolithoautotrophy via the 3-hydroxypropionate/4-hydroxybutyrate cycle and the reverse tricarboxylic acid cycle of ammonia-oxidizing archaea and nitrite-oxidizing bacteria, respectively. Proteins involved in nitrification were also detected in the metaproteome. Taurine appears to be an important source of carbon and nitrogen for heterotrophs (especially SAR11), with transporters and enzymes for taurine uptake and degradation abundant in the metaproteome. Divergent heterotrophic strategies for Alphaproteobacteria and Flavobacteria were indicated by the metaproteome data, with Alphaproteobacteria capturing (by high-affinity transport) and processing labile solutes, and Flavobacteria expressing outer membrane receptors for particle adhesion to facilitate the exploitation of non-labile substrates. TonB-dependent receptors from Gammaproteobacteria and Flavobacteria (particularly in summer) were abundant, indicating that scavenging of substrates was likely an important strategy for these clades of Southern Ocean bacteria. This study provides the first insight into differences in functional processes occurring between summer and winter microbial communities in coastal Antarctic waters, and particularly highlights the important role that ‘dark'' carbon fixation has in winter.     

A new octocoral genus (Cnidaria: Anthozoa) from Antarctic waters

Sphaeralcyon weddellensis gen. nov. et sp. nov. is described and illustrated from three colonies collected in the eastern Weddell Sea on the Polarstern cruises ANT V/3 and ANT VI/3. The new genus is compared with three closely related alcyoniid genera, all having capitate or mushroom-shaped colonies and dimorphic polyps. Sphaeralcyon is readily distinguishable from Malacacanthus by the presence of sclerites (absent in the latter genus), and from Anthomastus by sclerite shape, mainly in the form of tuberculate spheroids, and by the horny periderm on the stalk (absent in Anthomastus). Sphaeralcyon also differs from Verseveldtia in the set of sclerites, which are elongate spiny rods and a different type of tuberculate spheroid, and in the presence of eight-points as anthocodial armature (absent in Verseveldtia). The discovery of this new genus lends further support to the notion that diversity in benthic communities in Antarctica is higher than suggested by previous studies. Accepted: 6 December 1999     

Winter aspects of the ichthyoplankton community in Antarctic Peninsula waters

Summary Ichthyoplankton was sampled from the Antarctic Peninsula area of the South Polar Ocean in early winter (May and June 1986). A total of 153 eggs from two species and 1368 larvae or juvenile stages from 12 species were obtained. These included pelagic species, and demersal species with a long pelagic larval or juvenile phase. Most abundant were larvae of Pleuragramma antarcticum and Notothenia kempi, and eggs of Notothenia neglecta. The distribution of notothenioid and paralepidid larvae was apparently unaffected by ice cover, whereas myctophid larvae were confined to ice-free waters. Areas where newly hatched Chionodraco hamatus occurred coincided with dense aggregations of Euphausia superba (Krill) furcilia larvae which is a potential food resource during winter. The hatching of icefish larvae during winter is apparently independent of the seasonal production cycle. Epipelagic eggs of Notothenia neglecta were found during the spawning season, which suggests that eggs ascend to the surface after demersal spawning and that development takes place near the sea surface during winter. Larvae of Notothenia kempi were chiefly confined to shelf and slope waters to the west of the Antarctic Peninsula, with larger larvae found in coastal shelf areas. Pleuragramma antarcticum occurred in the coastal waters off the Biscoe Islands, in the Gerlache Strait, and in the northern Bransfield Strait. The smallest larvae were found in the northern Bransfield Strait, whereas those at the Biscoe Islands and in Gerlache Strait waters were larger and of a similar size. A cyclonic gyre to the west of the Antarctic Peninsula observed in the austral summer was likely to have affected the larval drift of Pleuragramma antarcticum and Notothenia kempi. Differences in the timing of spawning and hatching and the vertical distribution of these larvae will lead to different transport and spatial distribution patterns. It is hypothesized that early winter conditions do not imply severe limitations on the year-class success of larval fish. Dispersal and increased mortality may occur during the second half of the winter.