David K. A. Barnes

Biodiversity: Invasions by marine life on plastic debris

Colonization by alien species poses one of the greatest threats to global biodiversity. Here I investigate the colonization by marine organisms of drift debris deposited on the shores of 30 remote islands from the Arctic to the Antarctic (across all oceans) and find that human litter more than doubles the rafting opportunities for biota, particularly at high latitudes. Although the poles may be protected from invasion by freezing sea surface temperatures, these may be under threat as the fastest-warming areas anywhere are at these latitudes.

Environmental constraints on life histories in Antarctic ecosystems: tempos, timings and predictability

Knowledge of Antarctic biotas and environments has increased dramatically in recent years. There has also been a rapid increase in the use of novel technologies. Despite this, some fundamental aspects of environmental control that structure physiological, ecological and life‐history traits in Antarctic organisms have received little attention. Possibly the most important of these is the timing and availability of resources, and the way in which this dictates the tempo or pace of life. The clearest view of this effect comes from comparisons of species living in different habitats. Here, we (i) show that the timing and extent of resource availability, from nutrients to colonisable space, differ across Antarctic marine, intertidal and terrestrial habitats, and (ii) illustrate that these differences affect the rate at which organisms function. Consequently, there are many dramatic biological differences between organisms that live as little as 10 m apart, but have gaping voids between them ecologically.

The spatial structure of Antarctic biodiversity

Patterns of environmental spatial structure lie at the heart of the most fundamental and familiar patterns of diversity on Earth. Antarctica contains some of the strongest environmental gradients on the planet and therefore provides an ideal study ground to test hypotheses on the relevance of environmental variability for biodiversity. To answer the pivotal question, “How does spatial variation in physical and biological environmental properties across the Antarctic drive biodiversity?” we have synthesized current knowledge on environmental variability across terrestrial, freshwater, and marine Antarctic biomes and related this to the observed biotic patterns. The most important physical driver of Antarctic terrestrial communities is the availability of liquid water, itself driven by solar irradiance intensity. Patterns of biota distribution are further strongly influenced by the historical development of any given location or region, and by geographical barriers. In freshwater ecosystems, free water is also crucial, with further important influences from salinity, nutrient availability, oxygenation, and characteristics of ice cover and extent. In the marine biome there does not appear to be one major driving force, with the exception of the oceanographic boundary of the Polar Front. At smaller spatial scales, ice cover, ice scour, and salinity gradients are clearly important determinants of diversity at habitat and community level. Stochastic and extreme events remain an important driving force in all environments, particularly in the context of local extinction and colonization or recolonization, as well as that of temporal environmental variability. Our synthesis demonstrates that the Antarctic continent and surrounding oceans provide an ideal study ground to develop new biogeographical models, including life history and physiological traits, and to address questions regarding biological responses to environmental variability and change.

Links between the structure of an Antarctic shallow-water community and ice-scour frequency

Ice is a major structuring force in marine and freshwater environments at high latitudes. Although recovery from scouring has been quantified in time, the frequency of scouring in the Antarctic has not. We placed grids of markers at 9–17xa0m depth at two sites, to study ice-scouring over 2xa0years at Adelaide island (Antarctic Peninsula). We quantified the time scale of scour frequencies, and linked this to community mortality, age and diversity. Markers were hit from zero to at least three times in 2xa0years. At the least disturbed site (South Cove) 24% of markers were destroyed per year, whereas in North Cove 60% of markers were destroyed. There were significant differences in scouring frequency between our two sites: a given area in North Cove was on average hit twice as often as one in South Cove. Compared with near shore environments elsewhere, faunas of both sites were characteristic of high disturbance regimes, exhibiting low percent cover, diversity, ages and a high proportion of pioneers. Aspects of the encrusting communities studied reflected the differences between site disturbance regimes. North Cove was scoured twice as often, and bryozoan communities there had half the number of species, two-thirds the space occupation and twice the mortality level of those in South Cove. Maximum age in North Cove bryozoans was also half that in South Cove. Although there are natural disturbance events that rival ice-scouring in either frequency or catastrophic power at lower latitudes, none do both nor across such a wide depth range. We suggest that ice scour effects on polar benthos are even more significant than the same magnitude of disturbance at lower latitudes as recovery rates of high latitude communities are very slow. Climate warming seems likely to increase iceloading of near shore polar waters, so that some of the world’s most intensely disturbed faunas may soon suffer even more disturbance.

Macroplastics at sea around Antarctica.

UNLABELLEDnMore so than at any previous time, there is a heightened awareness of the amount of plastic in the environment, its spread to even remote localities and the multiple influences of this on organisms. In the austral summer of 2007/08 Greenpeace and British Antarctic Survey ships (MV Esperanza and RRS James Clark Ross respectively) conducted the first co-ordinated joint marine debris survey of the planets most remote seas around East and West Antarctica to reveal floating macroplastics. With observations also made from the ice patrol vessel HMS Endurance in the same season and seabed samples collected from the RRS James Clark Ross, this was the widest survey for plastics ever undertaken around Antarctica.nnnMAIN FEATURESnThe 2008 visit of RRS James Clark Ross to the Amundsen Sea breached two last frontiers; the last and most remote sea from which biological samples and plastic debris have been reported. A plastic cup and two fishing buoys were seen in the Durmont DUrville and Davis seas while two pieces of plastic packaging and a fishing buoy were observed in the Amundsen Sea. Agassiz trawls revealed rich biodiversity on the Amundsen (and south Bellingshausen) seabed but no sunken plastic pieces. We found no microplastics in five epibenthic sledge samples (300 microm mesh) from the Amundsen seabed. The seabeds immediately surrounding continental Antarctica are probably the last environments on the planet yet to be reached by plastics, but with pieces floating into the surface of the Amundsen Sea this seems likely to change soon. Our knowledge now touches every sea but so does our legacy of lost and discarded plastic.

Debris accumulation on oceanic island shores of the Scotia Arc, Antarctica

Abstract. The oceanic islands in the Southern Ocean can be considered amongst the remotest shores as, not only are they uninhabited (except for small research stations) and geographically isolated, but they are also enclosed by the oceanographic barrier of the Polar Frontal Zone. We survey island shores in the Scotia Arc mountain chain linking Antarctica to South America, including South Georgia, the South Sandwich archipelago and Adelaide Island off the west coast of the Antarctic Peninsula, and compare our findings to literature reports from two other Scotia Arc island groups (South Orkney and South Shetland archipelagos). The presence of marine pollution (in the form of beached debris) in this region is significant, both as a measure of mans influence on this isolated environment, and due to direct dangers posed to the fauna. This paper reports the results of surveys of beached marine debris at various times in the last decade for each island group. The majority (>70%) of the items recovered were anthropogenic in origin and most of these were synthetic (plastic or polystyrene). Debris densities varied from zero to 0.3 items m–1 but were typically lower than those reported from other regions of the globe. At some localities (South Georgia), marine-debris data showed a close relationship with local fishery activity, whilst at others (South Sandwich Islands) debris appeared to have a more distant origin. Unlike oceanic debris in warm (non-polar) water localities, there was no evidence of any colonisation by biota. Debris accumulation may provide a useful indirect measure of local fishery activity and compliance with CCAMLR regulations, as well as monitoring the state of the oceans and island shores.

Climate change and glacier retreat drive shifts in an Antarctic benthic ecosystem

Climatic change in the Antarctic Peninsula has driven profound shifts in the seabed. The Antarctic Peninsula (AP) is one of the three places on Earth that registered the most intense warming in the last 50 years, almost five times the global mean. This warming has strongly affected the cryosphere, causing the largest ice-shelf collapses ever observed and the retreat of 87% of glaciers. Ecosystem responses, although increasingly predicted, have been mainly reported for pelagic systems. However, and despite most Antarctic species being benthic, responses in the Antarctic benthos have been detected in only a few species, and major effects at assemblage level are unknown. This is probably due to the scarcity of baselines against which to assess change. We performed repeat surveys of coastal benthos in 1994, 1998, and 2010, analyzing community structure and environmental variables at King George Island, Antarctica. We report a marked shift in an Antarctic benthic community that can be linked to ongoing climate change. However, rather than temperature as the primary factor, we highlight the resulting increased sediment runoff, triggered by glacier retreat, as the potential causal factor. The sudden shift from a “filter feeders–ascidian domination” to a “mixed assemblage” suggests that thresholds (for example, of tolerable sedimentation) and alternative equilibrium states, depending on the reversibility of the changes, could be possible traits of this ecosystem. Sedimentation processes will be increasing under the current scenario of glacier retreat, and attention needs to be paid to its effects along the AP.

Ice scour disturbance in Antarctic waters

The West Antarctic Peninsula is one of the fastest warming regions on Earth, and, as a consequence, most maritime glaciers and ice shelves in the region have significantly retreated over the past few decades. We collected a multiyear data set on ice scouring frequency from Antarctica by using unique experimental markers and scuba diving surveys. We show that the annual intensity of ice scouring is negatively correlated with the duration of the winter fast ice season. Because fast ice extent and duration is currently in decline in the region after recent rapid warming, it is likely that marine benthic communities are set for even more scouring in the near future.

Ecophysiological strategies of Antarctic intertidal invertebrates faced with freezing stress

Recent studies have revealed a previously unanticipated level of biodiversity present in the Antarctic littoral. Here, we report research on the ecophysiological strategies adopted by intertidal species that permit them to survive in this environment, presenting cold-tolerance data for the widest range of invertebrates published to date from the Antarctic intertidal zone. We found significant differences in levels of cold tolerance between species within this zone. However, and contrary to expectations, intraspecific comparisons of subtidal and intertidal groups of eight species found significant differences between groups in only three species. One species, the nemertean Antarctonemertes validum, showed evidence of the presence of antifreeze proteins (thermal hysteresis proteins), with 1.4°C of thermal hysteresis measured in its haemolymph. We found a strong inverse relationship across species between mass and supercooling point, and fitted a power law model to describe the data. The scaling exponent (0.3) in this model suggests a relationship between an animal’s supercooling point and its linear dimensions.

Low heat shock thresholds in wild Antarctic inter-tidal limpets (Nacella concinna)

Heat shock proteins (HSPs) are a family of genes classically used to measure levels of organism stress. We have previously identified two HSP70 genes (HSP70A and HSP70B) in sub-tidal populations of the Antarctic limpet (Nacella concinna). These genes are up-regulated in response to increased seawater temperatures of 15°C or more during acute heat shock experiments, temperatures that have very little basis when considering the current Antarctic ecology of these animals. Therefore, the question was posed as to whether these animals could express HSP70 genes when subjected to more complex environmental conditions, such as those that occur in the inter-tidal. Inter-tidal limpets were collected on three occasions in different weather conditions at South Cove, Rothera Point, over a complete tidal cycle, and the expression levels of the HSP70 genes were measured. Both genes showed relative up-regulation of gene expression over the period of the tidal cycle. The average foot temperature of these animals was 3.3°C, far below that of the acute heat shock experiments. These experiments demonstrate that the temperature and expression levels of HSP production in wild animals cannot be accurately extrapolated from experimentally induced treatments, especially when considering the complexity of stressors in the natural environment. However, experimental manipulation can provide molecular markers for identifying stress in Antarctic molluscs, provided it is accompanied by environmental validation, as demonstrated here.