Virus and microbial loop dynamics over an annual cycle in three contrasting Antarctic lakes

1. Viral and microbial loop dynamics were investigated over an annual cycle in three contrasting saline Antarctic lakes – Highway Lake (salinity 4‰), Pendant Lake (salinity 19‰) and Ace Lake, a meromictic system (with a mixolimnion salinity of 18‰) in order to assess the importance of viruses in extreme, microbially dominated systems. 2. Virus like particles (VLP) showed no clear seasonal pattern, with high concentrations occurring in both winter and summer (range 0.89 × 10⁷ ± 0.038 to 12.017 × 10⁷ ± 1.28 mL^?1). VLP abundances reflected lake productivity based on chlorophyll a concentrations. Bacterial abundances and biomass did not correlate with VLP numbers except in Pendant Lake, the most productive of the three lakes studied. 3. Pendant Lake supported the highest bacterial biomass (range Highway: 18.44 ± 1.35 to 59.43 ± 2.80 ng C mL^?1; Ace: 14.42 ± 2.69 to 68.39 ± 2.95 ng C mL^?1; Pendant: 31.36 ± 3.94 to 115.95 ± 4.49 ng C mL^?1) so that virus to bacteria ratios (VBR) (range 30.48 ± 7.96 to 96.67 ± 8.21) were higher in Ace Lake (range 30.58 ± 3.98 to 80.037 ± 1.60) and Highway Lake (range 18.63 ± 3.12 to 126.74 ± 6.50). 4. Negative correlations occurred between VLP and cryptophytes (dominant phototrophic nanoflagellates), suggesting that they were not hosts to lytic viruses. Among the other protists only the heterotrophic nanoflagellates of Highway Lake (dominated by the marine choanoflagellate Diaphanoeca grandis) showed a positive correlation with VLP. 5. The VLP was negatively correlated with photosynthetically active radiation (PAR) and temperature, both of which increased with ice thinning and breakout, increasing viral decay. In winter VLP probably persisted in cold, dark water. 6. High VLP concentrations and high VBR (values at the upper end of those reported for marine and lacustrine systems) indicated that viruses, most of which were probably bacteriophage, are a major element within the microbial communities in extreme, saline lakes.     

Carbon dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) in summer

1. Microbial plankton dynamics in an ultra‐oligotrophic epishelf lake (Beaver Lake, Antarctica) were investigated over an austral summer (December 2002 to January 2003). The aim was to characterise carbon cycling in an environmentally extreme lake. 2. The lake had an unusual temperature profile with peak temperatures of 1.3–1.9 °C between 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom (110 m) on occasions. The ice cover underwent marked thinning and melting during the study period. 3. Chlorophyll a concentrations were consistently low, usually below 1 μg L^?1, with highest concentrations close to the lake bottom, where the photosynthetic elements showed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between 34.9 × 10⁴ L^?1 ± 33.5 (23rd December) and 130.9 × 10⁴ L^?1 ± 112.3 (4th December). Highest photosynthetic activity was usually recorded below 25 m. Rates of carbon fixation varied between 0.089 μg C L^?1 h^?1 ± 0.002 and 0.579 μg C L^?1 h^?1 ± 0.156. Primary production was limited by low temperature and orthophosphate availability. 4. Mean bacterial concentration throughout the water column ranged between 9.3 × 10⁷ L^?1 ± 1.2 (23rd December) and 14.0 × 10⁷ L^?1 ± 1.8 (28th January). Bacterial production was low, less than 10% of primary production and ranged between 2.1 ng C L^?1 h^?1 ± 0.8 and 12 ng C L^?1 h^?1 ± 0.9. Highest rates coincided with times of highest primary production. On occasion dissolved organic carbon (DOC) concentrations dropped to 20 μg L^?1, probably below accurate limits of detection, suggesting that carbon substratum and phosphorus may have limited bacterial growth. 5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of 26.6 × 10⁴ L^?1 ± 14.2 (23rd December) to 133.8 × 10⁴ L^?1 ± 33.5 (14th December). They imposed a significant grazing impact on the bacterioplankton, removing in excess of 100% of bacterial production in December. 6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below 600 μg L^?1. The ratio of DOC : POC ranged between 0.44 : 1 and 2.8 : 1 in the upper 40 m of the water column, and 1.8 : 1 and 3.7 : 1 in the lower waters. The microbial plankton contributed 1–29% of POC, thus detrital POC made up the largest fraction of the POC pool. 7. Beaver Lake is an extreme lacustrine ecosystem where heterotrophic processes occasionally appear to be carbon limited. Significant summer ice‐melt, not seen in a previous opportunistic sampling, may be having an impact on the carbon cycle.     

Reef coral diversity and global change

Regional anthropogenic processes such as pollution, dredging, and overfishing on coral reefs currently threaten the biodiversity of stony corals and other reef-associated organisms. Global climate change may interact with anthropogenic processes to create additional impacts on coral diversity in the near future. In order to predict these changes, it is necessary to understand the magnitude and causes of variation in scleractinian coral diversity throughout their 240 million year history. The fossil record documents long periods of speciation in corals, interrupted repeatedly by events of mass extinction. Some of these events relate clearly to changes in global climate. Diversity in reef corals has increased since their last period of extinction at the end of the Cretaceous (65 My bp ), and is still rising. During the last 8 million years, the fragmentation of the once pantropical Tethys Sea separated corals into two major biogeographical provinces. Periods of glaciation also have caused major changes in sea level and temperature. Accumulated evidence supports the theory that relative habitat area and changing patterns of oceanic circulation are mainly responsible for the two observed centres of recent coral diversity at the western tropical margins of the Atlantic and Pacific oceans. At predicted rates of climate change in the near future, coral reefs are likely to survive as an ecosystem. Increases in sea level may actually benefit corals and lead to regional increases in diversity if new habitat area on back reefs is opened to increased water circulation and thus coral dispersal. Rising temperature may cause higher rates of coral mortality and even local extinction in isolated, small populations such as those on oceanic islands. The effects of increases in ultraviolet radiation (UV) are largely unknown, but likely to be negative. UV may damage planktonic coral propagules in oceanic surface waters and thus decrease rates of gene flow between coral populations. This may result in increased local extinctions, again with the strongest impact on widely separated reefs with small coral populations. The largest threats to coral diversity are regional anthropogenic impacts, which may interact with global climate change to exacerbate rates of local species extinctions. Centres of high reef coral diversity coincide with human population centres in south-east Asia and the Caribbean, and thus the greatest potential for species loss lies in these geographical areas.     

Is the evaporative water loss of Knot Calidris canutus higher in tropical than in temperate climates?

To test whether Knot Calidris canutus wintering in the tropics suffer higher rates of water loss through evaporation than do Knot wintering at temperate latitudes, we tried to develop a physically realistic model to predict evaporative heat loss from air temperature, wind and humidity. In separate experiments, involving respirometry and double-labelled water, we tried to estimate relevant parameters. In both sets of experiments, we were able to show significant effects of air temperature on evaporative water loss only. Knot which were able to eat and drink had an evaporative water loss three times that of postabsorptive Knot unable to drink when in a metabolic chamber. Water turnover rates of Knot feeding on bivalves under simulated field conditions were high and did not correlate with predicted evaporative water loss. Over 32 experimental bird-days, the average contribution of predicted evaporative water loss to daily water turnover was 20%. A comparison of predicted evaporative water loss in the north-temperate Dutch Wadden Sea and in the tropical Banc d'Arguin in Mauritania in midwinter showed that Knot wintering in the tropics may need only marginally more water for evaporative cooling than Knot wintering in the Dutch Wadden Sea. Knot foraging on intertidal invertebrates are able to maintain high water turnover rates with little need to drink seawater.     

How to prioritize rat management for the benefit of petrels: a case study of the UK, Channel Islands and Isle of Man

Rats have been introduced to islands throughout the world. They have caused breeding failures, population declines and complete extirpation of vulnerable bird species. Such impacts can be difficult to diagnose in situations where extirpation occurred prior to the vulnerable species being recorded. Mitigating the impacts of rats on seabirds depends on quarantine measures for islands where rats are currently absent, and eradication or control campaigns on those where they are present. These measures can be challenging in terms of both costs and practicalities, and so can seldom be applied to all islands within a given region. Hence a prioritization exercise is often required to identify those islands where management would be most cost-effective. In this review we present a case study of rat management in the UK, Channel Islands and Isle of Man. We review rat management for the study area to date and present a simple scoring approach to prioritize islands for eradication campaigns, including those where the procellariiform priority species are currently absent. We recommend further research into rat management for the study area and on the applicability of this approach elsewhere in the world.