Meiofauna densities, nematode biomass, nematode genus diversity, sediment grain size, organic matter, and pigments for the surface layers of two sites in summer (November 2009) and winter (august 2010)

The meiobenthic community of Potter Cove (King George Island, west Antarctic Peninsula) was investigated, focusing on responses to summer/winter conditions in two study sites contrasting in terms of organic matter inputs. Meiofaunal densities were found to be higher in summer and lower in winter, although this result was not significantly related to the in situ availability of organic matter in each season. The combination of food quality and competition for food amongst higher trophic levels may have played a role in determining the standing stocks at the two sites. Meiobenthic winter abundances were sufficiently high to infer that energy sources were not limiting during winter, supporting observations from other studies for both shallow water and continental shelf Antarctic ecosystems. Recruitment within meiofaunal communities was coupled to the seasonal input of fresh detritus for harpacticoid copepods but not for nematodes, suggesting that species-specific life history or trophic features form an important element of the responses observed.

Community structure and biodiversity in marine benthic communities during experiments, 2011

A mesocosm experiment was conducted to quantify the effects of reduced pH and elevated temperature on an intact marine invertebrate community. Standardised faunal communities, collected from the extreme low intertidal zone using artificial substrate units, were exposed to one of eight nominal treatments (four pH levels: 8.0, 7.7, 7.3 and 6.7, crossed with two temperature levels: 12 and 16°C). After 60 days exposure communities showed significant changes in structure and lower diversity in response to reduced pH. The response to temperature was more complex. At higher pH levels (8.0 and 7.7) elevated temperature treatments contained higher species abundances and diversity than the lower temperature treatments. In contrast, at lower pH levels (7.3 and 6.7), elevated temperature treatments had lower species abundances and diversity than lower temperature treatments. The species losses responsible for these changes in community structure and diversity were not randomly distributed across the different phyla examined. Molluscs showed the greatest reduction in abundance and diversity in response to low pH and elevated temperature, whilst annelid abundance and diversity was mostly unaffected by low pH and was higher at the elevated temperature. The arthropod response was between these two extremes with moderately reduced abundance and diversity at low pH and elevated temperature. Nematode abundance increased in response to low pH and elevated temperature, probably due to the reduction of ecological constraints, such as predation and competition, caused by a decrease in macrofaunal abundance. This community-based mesocosm study supports previous suggestions, based on observations of direct physiological impacts, that ocean acidification induced changes in marine biodiversity will be driven by differential vulnerability within and between different taxonomical groups. This study also illustrates the importance of considering indirect effects that occur within multispecies assemblages when attempting to predict the consequences of ocean acidification and global warming on marine communities.

Effects of elevated CO2 and temperature on an intertidal meiobenthic community

In the near future, the marine environment is likely to be subjected to simultaneous increases in temperature and decreased pH. The potential effects of these changes on intertidal, meiofaunal assemblages were investigated using a mesocosm experiment. Artificial Substrate Units containing meiofauna from the extreme low intertidal zone were exposed for 60 days to eight experimental treatments (four replicates for each treatment) comprising four pH levels: 8.0 (ambient control), 7.7 & 7.3 (predicted changes associated with ocean acidification), and 6.7 (CO2 point-source leakage from geological storage), crossed with two temperatures: 12 °C (ambient control) and 16 °C (predicted). Community structure, measured using major meiofauna taxa was significantly affected by pH and temperature. Copepods and copepodites showed the greatest decline in abundance in response to low pH and elevated temperature. Nematodes increased in abundance in response to low pH and temperature rise, possibly caused by decreased predation and competition for food owing to the declining macrofauna density. Nematode species composition changed significantly between the different treatments, and was affected by both seawater acidification and warming. Estimated nematode species diversity, species evenness, and the maturity index, were substantially lower at 16 °C, whereas trophic diversity was slightly higher at 16 °C except at pH 6.7. This study has demonstrated that the combination of elevated levels of CO2 and ocean warming may have substantial effects on structural and functional characteristics of meiofaunal and nematode communities, and that single stressor experiments are unlikely to encompass the complexity of abiotic and biotic interactions. At the same time, ecological interactions may lead to complex community responses to pH and temperature changes in the interstitial environment.

(Table 1) Number of alleles per locus and heterozygosity of Arctic charr (Salvelinus alpinus) populations in Iceland

The ecological theory of adaptive radiation predicts that the evolution of phenotypic diversity within species is generated by divergent natural selection arising from different environments and competition between species. Genetic connectivity among populations is likely also to have an important role in both the origin and maintenance of adaptive genetic diversity. Our goal was to evaluate the potential roles of genetic connectivity and natural selection in the maintenance of adaptive phenotypic differences among morphs of Arctic charr, Salvelinus alpinus, in Iceland. At a large spatial scale, we tested the predictive power of geographic structure and phenotypic variation for patterns of neutral genetic variation among populations throughout Iceland. At a smaller scale, we evaluated the genetic differentiation between two morphs in Lake Thingvallavatn relative to historically explicit, coalescent-based null models of the evolutionary history of these lineages. At the large spatial scale, populations are highly differentiated, but weakly structured, both geographically and with respect to patterns of phenotypic variation. At the intralacustrine scale, we observe modest genetic differentiation between two morphs, but this level of differentiation is nonetheless consistent with strong reproductive isolation throughout the Holocene. Rather than a result of the homogenizing effect of gene flow in a system at migration-drift equilibrium, the modest level of genetic differentiation could equally be a result of slow neutral divergence by drift in large populations. We conclude that contemporary and recent patterns of restricted gene flow have been highly conducive to the evolution and maintenance of adaptive genetic variation in Icelandic Arctic charr.

Nannofossil assemblages of mid-Pliocene sediments from the equatorial Atlantic

Downcore cyclic variation in high-resolution nannofossil abundance records from mid-Pliocene equatorial Atlantic ODP Sites 662 and 926 demonstrate the direct response by several Pliocene taxa (notably Discoaster, Sphenolithus and Florisphaera profunda) to orbitally forced climatic variation. In particular, these records display strong obliquity and precessional signals reflecting primarily high latitude, Southern hemisphere changes influencing upwelling intensity and local low-latitude, insolation-driven climatic changes (via the productivity and/or turbidity influence of Amazon-sourced terrigenous material) at Sites 622 and 926 respectively. In seasonal studies of coccolithophorid assemblages, only part of the variation observed can be explained by abiotic processes, so it is perhaps not surprising that in this study few Pliocene nannofossil taxa demonstrate significant correlations with each other or with physical environmental parameters. Only some variance in nannofossil abundances can be explained by the primary controls of temperature and productivity. The rest is attributed to nonlinear responses to climatic changes; biotic processes such as grazing, predation, viral infection and competition, and/or, abiotic factors for which there is no readily available proxy (e.g. salinity). The lack of strong, consistent intra- and inter-relationships of the nannoflora and the environment reflects an ecologically complex, differentiated original community producing a complex integrated signal transmitted into the fossil record.

Living benthic foraminifers from the central Arctic Ocean

Fifty short sediment cores collected with a multiple corer and five box cores from the central Arctic Ocean were analysed to study the ecology and distribution of benthic foraminifers. To work out living faunal associations, standing stock and diversity, separate analyses of living (Rose Bengal stained) and dead foraminifers were carried out for the sediment surface. The size fractions between 63 and 125 µm and >125 µm were counted separately to allow comparison with former Arctic studies and with studies from the adjacent Norwegian-Greenland Sea, Barents Sea and the North Atlantic Ocean. Benthic foraminiferal associations are mainly controlled by the availability of food, and competition for food, while water mass characteristics, bottom current activity, substrate composition, and water depth are of minor importance. Off Spitsbergen in seasonally ice-free areas, high primary production rates are reflected by high standing stocks, high diversities, and foraminiferal associations (>125 µm) that are similar to those of the Norwegian-Greenland Sea. Generally, in seasonally ice-free areas standing stock and diversity increase with increasing food supply. In the central Arctic Ocean, the oligotrophic permanently ice-covered areas are dominated by epibenthic species. The limited food availability is reflected by very low standing stocks and low diversities. Most of these foraminiferal associations do not correspond to those of the Norwegian-Greenland Sea. The dominant associations include simple agglutinated species such as Sorosphaerae, Placopsilinellae, Komokiacea and Aschemonellae, as well as small calcareous species such as Stetsonia horvathi and Epistominella arctica. Those of the foraminiferal species that usually thrive under seasonally ice-free conditions in middle bathyal to lower bathyal water depth are found under permanently ice-covered conditions in water depths about 1000 m shallower, if present at all.