Similar soft-bottom polychaete diversity in Arctic and Antarctic marine inlets

The diversity of soft-bottom polychaete assemblages in one Antarctic (Admiralty Bay) and two Arctic (Kongsfjord and van Mijenfjord) localities was compared. The data sets included 79 (Admiralty Bay), 80 (Kongsfjord) and 44 (van Mijenfjord) samples collected with use of 0.1 m² van Veen grab. The number of species per sample in Kongsfjord (mean 19.9 ± 8.0 SD) was higher than that in Van Mijenfjord (13.7 ± 8.3) or Admiralty Bay (15.7 ± 9.4). The differences in species numbers reflected differences in numbers of individuals in samples: 310.4 ind/0.1 m² ± 178.0 in Kongsfjord, 132.7 ind/0.1 m² ± 88.7 in Van Mijenfjord and 138.9 ind/0.1 m² ± 91.5 in Admiralty Bay. The Hurlbert diversity for 50 individuals (ES _[50]) was similar at all sites: 10.7 ± 3.4 in Kongsfjord, 9.7 ± 4.2 in van Mijenfjord, 10.5 ± 4.9 in Admiralty Bay. The shape of species accumulation curves was also similar for all localities. There was no significant difference (at P < 0.05) either in the total number of species or in species richness as estimated by Chao1 and Chao2 estimators. The generic and family richness at three sites was also similar. We found no substantial differences in the distribution of species among families. At both poles Terebellidae, Ampharetidae, Maldanidae, Spionidae and Polynoidae were dominant in terms of species numbers. The similarity of infaunal polychaete diversity at the polar sites studied contrasts with the substantial differences reported for epi-megafauna. Our study suggests that the patterns of diversity of polar benthic communities are shaped by patterns of habitat heterogeneity which appears to mask any historical processes.     

Seasonal variation in the diversity and abundance of pelagic larvae of Antarctic marine invertebrates

Most marine benthic macroinvertebrate species reproduce via a larval phase but attempts to explain the occurrence of different larval strategies (feeding or non-feeding, pelagic or benthic) in different habitats have been largely inconclusive. There have been very few year-round surveys of meroplankton at any latitude and in consequence fundamental data on the diversity, abundance, and timings of larval life history phases are lacking. There has been considerable debate regarding the viability of pelagic larvae in cold waters with highly seasonal primary production but there has been only one year-round study of meroplankton in the Southern Ocean, and that was outside of the Antarctic Circle. We present data from the first year-round survey of meroplankton assemblages at a location within the Antarctic Circle. We surveyed abundances of meroplanktonic larvae over 1.5 year at Rothera Point, West Antarctic Peninsula (67°34′S, 68°07′W). Larvae were collected in monthly diver-towed net samples close to the seabed at 20 and 6 m total water depths at each of three locations and were identified and counted live immediately after sampling. A total of 99 operationally defined taxonomic types representing 11 phyla were recorded but this is likely to be an underestimate of true diversity because of inherent difficulties of identification. Larvae were present in all months of the year and although planktotrophic larvae were more abundant in summer, both feeding and non-feeding types were present in all months. Comparisons of seasonal larval abundances with data from a settlement study at the same sites and from the literature show that larvae of mobile adults settle in summer regardless of developmental type, whereas sessile taxa settle in all seasons. We suggest that this is a consequence of differences in the food requirements of mobile and sessile fauna and that the availability of food for post-larval juveniles is more critical for survival than factors affecting the larval stage itself.     

Genetic diversity of Nymphon (Arthropoda: Pycnogonida: Nymphonidae) along the Antarctic Peninsula with a focus on Nymphon australe Hodgson 1902

Sea spiders are conspicuous, and often abundant, members of the Antarctic benthic community. Nymphonidae (Pycnogonida) in Southern Ocean waters comprise over 240 species which are often difficult to assign due to their intraspecific ‘highly variable’ morphology. In particular, Nymphon australe, the numerically dominant species in Antarctic waters is known to have a high level of phenotypic variation in external morphology and is also reported to have a circumpolar distribution. Circumpolarity seems contradictory to the pycnogonid’s brooding lifestyle and presumably limited dispersal. Here we examine the genetic diversity of several Nymphon species collected in the Antarctic Peninsular region. Concomitantly, we assess the genetic structure of N. australe to gain insight into Nymphon dispersal capacity. Cytochrome c oxidase subunit I (COI) and 16S ribosomal gene data suggest a recent common history and/or recent gene-flow of N. australe populations across nearly 800 km of the Antarctic Peninsula. Furthermore, these data support that the Antarctic Peninsula region may hold two previously unrecognized species of Nymphon. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Growth of two Antarctic lamellibranchs: Adamussium colbecki and Laternula elliptica

The growth of two Antarctic lamellibranchs, Adamussium colbecki (E.A. Smith) and Laternula elliptica (King and Broderip), has been investigated. A. colbecki is a pectinid that grows to a shell height of approximately 70 mm in 6 to 7 years; L. elliptica is a deep-burrowing form, ecologically similar to the genus Mya and grows to a shell length of approximately 90 mm in 12 to 13 years. The growth pattern of both species is accurately described by the Bertalanffy growth equation and both have smaller values of the Bertalanffy K coefficient than comparable temperate species (A. colbecki K=0.24, L. elliptica K=0.16).     

Metachronal swimming in Antarctic krill: gait kinematics and system design

Metachronal swimming, in which adjacent appendages stroke in sequence, is widespread among crustaceans inhabiting the transitional flow realm in which both viscosity and inertia effects are important. However, the design and operation of this propulsion system in response to various hydrodynamic, energetic, and behavioral needs have not been well investigated. We examine free-swimming Antarctic krill (Euphausia superba) as a model species and identify three distinct behavioral swimming gaits. The pleopod kinematics of these gaits, hovering, fast-forward swimming, and upside-down swimming, are quantified via image analysis of high-speed video. Pleopod stroke amplitude and frequency were found to vary significantly among these swimming modes. In order to increase swimming speed, krill were found first to increase stroke amplitude and secondarily to increase beat frequency. The kinematics of these distinct swimming modes provide insight as we consider multi-appendage metachronal swimming from a design standpoint. The ratio of the distance between adjacent appendage bases and appendage length is identified as a key parameter in metachrony, the value of which is constrained to a narrow range for a wide variety of species.     

Fire shapes and the adequacy of fire-spread models

It has been suggested that shapes of burned areas resulting from fires spreading under uniform fuel and meteorological conditions may be described as ellipses, double ellipses, or ovoids. The adequacy of these shapes (together with simulation outputs) as bases for fire spread models was tested by finding the best fits of each shape to maps of experimental fires and comparing the results with fits given by a rectangle (an unlikely fire shape). Each of the models (ellipse, double ellipse, ovoid, simulation model, and even the rectangle) provided adequate approximations to the fire contours used in the tests. The parameter trends found implied that the fires examined tended to become more nearly elliptical in shape and to have higher eccentricity as they grew.     

Renal function in Antarctic teleost fishes: Serum and urine composition

The urine and serum compositions in 11 species of Antarctic teleost fishes were studied. The body fluids of these fishes were hypoosmotic to seawater. Both urine and serum osmoconcentrations were conspicuously greater than those of temperate species. The elevated serum osmolality was due to increased levels of NaCl, while elevated urine osmolality was due chiefly to increased concentrations of magnesium and chloride. The kidney was unable to form a urine hyperosmotic to serum under field conditions. The renal tubular epithelium secreted magnesium and calcium against a concentration gradient, while effectively preventing the renal excretion of significant amounts of sodium and potassium. Bladder urine of Antarctic teleosts may often be supercooled by as much as 0.8°C. Coelomic fluid and the integument probably act as a barrier in preventing ice propagation in the supercooled bladder urine, since they both contain glycoprotein “antifreeze” agents.     

Abundance and feeding ecology of Antarctic phaeodarian radiolarians

Phaeodarian radiolarians were sampled from the upper 200 m along a transect through the ice-edge zone in the Weddell Sea in the austral autumn (March 1986) and at several stations in the western Antarctic Peninsula region in the austral winter (June 1987). Abundances of phaeodarians reached 3 132 m^-3 and were similar to or higher than maximum abundances of polycystine radiolarians, foraminiferans, and acantharians, and similar to or less than those of the heliozoan Sticholonche sp. Phaeodarians varied in abundance and species composition both seasonally and/or geographically. In contrast to the more numerous ciliates and flagellates that were most abundant in the upper 100 m, phaeodarians were most abundant from 100 to 200 m and showed no distinct pattern related to the ice edge. Electron microscopical examination of food vacuoles showed that phaeodarians are omnivorous generalists, feeding on a variety of food ranging in size from bacteria to large protozoans in both regions and seasons. Algal cells consumed in addition to diatoms and dinoflagellates included Chlorella-like cells and members of the recently described chrysophyte order Parmales. Scales of prasinophytes were common. Phaeodarians are consumed by the non-selective particlefeeding salp Salpa thompsoni. Thus, phaeodarians link microbial food webs to macrozooplankton and increase the complexity of the Antarctic food web.     

Plasticity of biometrical and mechanical properties of Echinocardium cordatum spines according to environment

We investigated the plasticity of spines of the burrowing heart urchin Echinocardium cordatum inhabiting sandy beaches. This urchin has very specialized spines which play specific roles in feeding and locomotion. Biometrical and mechanical properties of the spine skeleton of individuals from a wave-exposed intertidal site and a protected subtidal site (Brittany, France) were compared and related to sediment grain size, food supply and urchin small-scale distribution and burrowing depth. The intertidal site was characterized by coarser sand; the urchins were more scattered and more deeply buried than in the subtidal site. Intertidal urchins were bigger than subtidal urchins but showed similar resource allocation. Spines of intertidal urchins were longer than those of subtidal urchins, their architecture was reinforced and they presented a higher fracture force and stiffness. These spine differences would be essentially due to passive plasticity, but could also be adaptative at a certain extent.     

Mitochondrial energetics of benthic and pelagic Antarctic teleosts

Antarctic fauna are highly adapted to the frigid waters of the Southern Ocean. This study describes the in vitro temperature sensitivity of oxygen consumption rates measured in liver mitochondria from the pelagic notothenioid Pleuragramma antarcticum between 5 and 35 °C. Oxygen fluxes were measured after the addition of millimolar levels of pyruvate, malate, succinate and glutamate (state II, LEAK) and saturating levels of ADP [state III, oxidative phosphorylation (OXPHOS)]. State III respiration significantly decreased above 18.7 °C. A comparison of the oxidative capacities among P. antarcticum and other notothenioids showed significant differences in state III respiration, where benthic species exhibited about 50 % lower rates than P. antarcticum. In addition, state III respiration rates normalized per milligram of mitochondrial protein of P. antarcticum were up to eight times higher than state III rates reported in the literature for other notothenioids. The comparatively high respiration rates measured in this study may be explained by our approach, which engaged both complexes I and II under conditions of oxidative phosphorylation. State III rates of independently activated complexes I and II were found to range from 42 to 100 % of rates obtained when both complexes were activated simultaneously in the same species. The remarkable tolerance of P. antarcticum OXPHOS toward warmer temperatures was unexpected for an Antarctic stenotherm and may indicate that thermal sensitivity of their mitochondria is not the driving force behind their stenothermy.     

Locomotory activity and behaviour of the Antarctic teleostNotothenia coriiceps

The activity and behaviour of a free-living Antarctic fish,Notothenia coriiceps Richardson (formerlyN. neglecta), was investigated using a high-sensitivity, underwater TV camera at Signy Island, South Orkney Islands. Detailed observations of the 33 cm TL (total length) fish were made over a period of 6 d in austral summer (February 1992), for a total 69.5 h. Natural light at 2.5 m depth allowed viewing from 1 h before sunrise to 1 h after sunset. The fish stayed in a territory within 3 m of a small cave for >98% of the time, and made between 1 to 148 swims d^-1, of which 92.5% were brief (<15 s) feeding attempts. On average, 1.7% of each day was engaged in locomotion, including 1.2% swimming and 0.5% manoeuvring. Swimming was generally slow, at <2 body lengths s^-1, and labriform and subcarangiform modes were used alternately or in combination. Activity level (swims or displays per hour) was unaffected by tide, but was lower for 3 d when a wind speed >16 knots prevailed indicating that large waves reduced activity. A suspected diurnal activity rhythm was not statistically significant. The fish is an ambush-predator, and it took most of its prey from the water column but some off macroalgae or the seabed. Ventilation rate was slightly higher after activity, and peaked after an encounter with anotherN. coriiceps.     

Heterogeneity shapes invasion: host size and environment influence susceptibility to a nonnative pathogen.

Theoretical study of invasion dynamics has suggested that spatial heterogeneity should strongly influence the rate and extent of spreading organisms. However, empirical support for this prediction is scant, and the importance of understanding heterogeneity for real-world systems has remained ambiguous. This study quantified the influence of host and environmental heterogeneity on the dynamics of a 19-year disease invasion by the exotic and fatal pathogen, Phytophthora lateralis, within a stream population of its host tree, Port Orford cedar (Chamaecyparis lawsoniana). Using dendrochronology, we reconstructed the invasion history along a 1350-m length of infected stream, which serves as the only route of pathogen dispersal. Contrary to theoretical predictions, the temporal progression of the disease invasion was not related to a host's downstream spatial position, but instead was determined by two sources of heterogeneity: host size and proximity to the stream channel. These sources of heterogeneity influenced both the epidemic and endemic dynamics of this pathogen invasion. This analysis provides empirical support for the influence of heterogeneity on the invasion dynamics of a commercially important forest pathogen and highlights the need to incorporate such natural variability into both invasion theory and methods aimed at controlling future spread.     

Mega-epibenthic communities in Arctic and Antarctic shelf areas

Mega-epibenthic shelf assemblages were investigated off Northeast Greenland and in the Weddell, Bellingshausen and Amundsen Seas in the Antarctic using underwater video. In the Arctic a total of 94 taxa represented by more than 100 000 individuals were identified. Echinoderms, particularly brittle stars, were the most important elements of the mega-epibenthic fauna on the shelf off Northeast Greenland. Multivariate analyses of the species distribution revealed a conspicuous depth zonation in which an assemblage on the shallow banks can be clearly distinguished from that in the troughs. Between these a transitional zone with a heterogeneous benthic fauna was found. Physical disturbances are supposed to be responsible for the pronounced dominance patterns observed on the shallow banks. The fauna in the troughs, which consists of more than 50% suspension feeders, is diverse but low in numbers of individuals. In the Antarctic more than 115 000 individuals belonging to 169 taxa were analyzed. Obvious faunal differences exist between the stations in the Weddell Sea and the Bellingshausen/Amundsen Seas. Assemblages of suspension feeders dominated by sponges and bryozoans are prevalent on the shelf of the eastern Weddell Sea, but almost absent in the Bellingshausen and Amundsen Seas. These assemblages seem to be restricted to areas where bottom currents provide favourable feeding conditions. However, motile deposit feeders are more abundant in both regions where there is a soft bottom substrate with presumably slow bottom currents and reduced horizontal transport of organic particles. Received: 22 January 1999 / Accepted: 7 June 1999     

Growth and productivity of the high Antarctic Bryozoan Melicerita obliqua

We analysed growth of the Antarctic bryozoan Melicerita obliqua (Thornely, 1924) by x-ray photography and stable isotope analysis. M. obliqua colonies form one segment per year, thus attaining maximum length of about 200 mm within 50 years. In the Weddell and Lazarev Seas, annual production/biomass ratio of M. obliqua is 0.1 yr⁻¹, which is in the range of other Antarctic benthic invertebrate populations. Production amounts to 3.34 mg C_orgm⁻² yr⁻¹ and 90.6 mg ash m⁻² yr⁻¹ on the shelf (100 to 600 m water depth), and to 0.13 mg C_orgm⁻² yr⁻¹ and 36.8 mg ash m⁻² yr⁻¹ on the slope (600 to 1250 m water depth). Received: 27 February 1998 / Accepted: 8 May 1998     

Food and feeding dynamics of the larval Antarctic fishNototheniops larseni

The feeding dynamics of larvae of the Antarctic fishNototheniops larseni were analyzed from data collected over three years in Bransfield Strait and adjacent waters (Antarctica). Seasonal feeding was examined from 1977/1978 (November–March). The diel feeding cycle was investigated during a 96 h station established in February 1976, while food selection was analyzed using larvae and zooplankton samples collected in February 1982. Hatching occurs in early spring, and larvae fed on eggs of calanoid copepods and on cyclopoid copepods. Copepod eggs were the principal food near the pack ice, and cyclopoids in open waters. Cyclopoids were the staple food in summer. Eggs of the Antarctic krillEuphausia superba were ingested selectively and formed major portions of the larval summer diet in neritic (Joinville Island) and oceanic (Elephant Island) spawning areas ofE. superba. In the fall, copepods predominated in the diets. Most abundant and most frequently ingested prey in summer and fall wereOncaea spp. Feeding commenced at dawn and continued at least until dusk. Krill eggs were taken chiefly during morning hours and egg incidence declined during the day, suggesting that eggs were ingested soon after spawning. Prey size at the onset of feeding was estimated as 0.130 to 0.330 mm. Size-selective feeding was evident in small larvae, while in larger larvae median prey length remained constant. High feeding incidence among yolk-sac larvae in spring, high overall feeding incidence in summer, and size-selective foraging of small larvae suggested favorable feeding conditions in the 1977/1978 season. Yolk-absorption times in Antarctic fish larvae vary on a scale of weeks and may be further retarded due to early feeding. Hence, year-to-year variability of yolk incidence inN. larseni indicated variable biotic environments of early feeding larvae rather than temporal shifts of hatching periods. As hatching periods are constant between years in contrast to the variable retreat of the pack ice and subsequent onset of the production cycle in space and time, maternal yolk reserves are probably utilized to compensate for such variations.     

Food web of an Antarctic midwater ecosystem

The diets of 93 species of plankton and micronekton taken in the upper 1000 m of Croker Passage (Gerlache Strait) in the austral fall, 1983, were examined and the principal features of the food web were characterized. Most species were small particle feeders, with phytoplankton and debris (of phytoplankton and krill) being the principal diet components. Krill remains were found in the guts of the majority of species examined, with the krill playing a greater role in the form of molts and debris than as living prey. Carcinores fed mostly on copepods, coelenterates and salps. Some of the larger species fed on live krill. No-hierarchical cluster analysis of diet information supported the concept of resource partitioning and determined the arrangement of the species into 21 feeding groups. Cluster analysis groupings tended to be along genetic lines with closely related and morphologically similar species having similar diets. These analyses were based on collections made in the austral fall (March–April, 1983) when phytoplankton standing crop was low, most zooplankton species had descended into the mesopelagic zone, and some of the more abundant species, such as Calanoides acutus, had ceased feeding. Because the trophodynamics of Antarctic ecosystems is strongly pulse-induced, it is essential to examine the food web at different periods in the seasonal cycle.     

Metabolic cold adaptation in Antarctic fishes: evidence from enzymatic activities of brain

To evaluate the concept of metabolic cold adaptation (MCA) in fishes, we compared - in brain, red muscle, and white muscle of Antarctic notothenioid fishes and tropical/subtropical fishes - the activities of two enzymes of ATP-generating pathways, citrate synthase (CS), an indicator of citric acid cycle activity (aerobic metabolism), and lactate dehydrogenase (LDH), an indicator of potential for ATP production through anaerobic glycolysis. Brain was chosen because, unlike locomotory muscle, its metabolic activity is not likely to be influenced by a species' level of activity or nutritional status, so MCA should be readily observed if present. CS and LDH activities in brain exhibited a high level of MCA, but compensation to temperature was not complete (48% for CS; 46% for LDH). CS and LDH activities in red and white muscle varied widely among species, according to the general level of locomotory activity. The 'mode of life'-related enzymatic activities in locomotory muscle show that study of MCA at the level of whole organism metabolism is fraught with difficulties and experimental ambiguities. In contrast, the low variation among species within each group in enzymatic activities in brain, and the large differences between groups in CS and LDH activity, show that brain is an excellent study system for evaluating metabolic compensation to temperature.