Anthropogenic effects on the marine environment adjacent to Palmer Station, Antarctica

Localized contamination from research-related activities and its effects on macrofauna communities in the marine environment were investigated at Palmer Station, a medium-sized Antarctic research station. Relatively low concentrations of polycyclic aromatic hydrocarbons (PAHs; 32–302 ng g-1) and total petroleum hydrocarbons (TPHs; 0.9–8.9 μg g-1) were detected in sediments adjacent to the sewage outfall and pier, where most human activities were expected to have occurred, and at even lower concentrations at two seemingly reference areas (PAHs 6–30 ng g-1, TPHs 0.03–5.1 μg g-1). Elevated concentrations of PAHs in one sample taken in one reference area (816 ng g-1) and polychlorinated biphenyls (353 ng g-1) and dichloro-diphenyl-trichloroethane (3.2 and 25.3 ng g-1) in two samples taken adjacent to the sewage outfall indicate spatial heterogeneity of localized sediment contamination. Limpet (Nacella concinna) tissues collected adjacent to Palmer Station had high concentrations of PAHs, copper, lead, zinc and several other metals relative to outlying islands. Sediment and limpet tissue contaminant concentrations have decreased since the early 1990s following the Bahía Paraíso spill. Natural sediment characteristics affected macrofaunal community composition more than contamination adjacent to Palmer Station, presumably because of the low overall contamination levels.

Temporal succession of a macrofaunal community associated with kelp fragment accumulations in an in situ experiment

A large part of the production of Laminaria hyperborea kelp forests is not directly consumed by grazers, but is exported during storm events or natural annual blade erosion. Drifting kelp fragments are transported and can accumulate temporarily over subtidal benthic habitats. The decay process is particularly slow (>6 mo for complete decay during spring-summer) and L. hyperborea fragments are able to maintain their primary production function for several months. If they accumulate in low subtidal habitats, fragments can have a long residence time, thus modifying habitat structure. Based on a 6 mo cage experiment, we investigated macrofaunal colonization and community succession within accumulations of L. hyperborea fragments on a low subtidal (-10 m) sandy bottom ecosystem. Stable isotope (δ13C and δ15N) measurements were carried out to describe the structure and development of the trophic food web and the role of detritus as a food source. Kelp tissues were rapidly and abundantly colonized by macrofauna, and a classical ecological succession occurred, with changes in species dominance and increase in diversity during decay. The food web was based on 2 main sources: particulate organic matter from the water column and decaying kelp tissues. Kelp contributed significantly to the diet of numerous species that are commonly consumed by local predators (fish, shrimp). Following community succession, diets diversified and the food web became more complex during the decay process. Our results indicate that drift kelp accumulations structure their associated communities and food web during the whole decay process.

Mangrove benthic macrofauna: drivers of community structure and functional traits at multiple spatial scales

Environmental processes acting at multiple spatial scales influence the structure and function of macrofaunal communities in marine habitats. However, the relative contributions of small- and large-scale factors in shaping faunal communities are still poorly understood. We investigated the relative contributions of climate, geophysical and soil properties, and forest structure on structural and functional characteristics of Brazilian coastal mangrove macrofauna. We found that macrofaunal community structure is mainly driven by large-scale factors, such as minimum air temperature and runoff, which significantly differed among the coastal settings investigated. Conversely, annelid assemblage functional traits were correlated with small-scale factors such as aboveground biomass, subsurface root biomass, soil bulk density, and soil phosphorus. Annelids with diversified and more complex functional traits (e.g. with respect to appendages, segments, parapodia) preferentially inhabited sites with low subsurface root biomass, while annelids with a slender body plan were more common at sites with dense root mats. Thus, while climate and geophysical conditions drive benthic macrofaunal community structure at larger spatial scales (i.e. coastal setting) in this system, vegetation and soil factors at smaller spatial scales (i.e. site) were more related to annelid functional characteristics.

Carbon processing by the benthic ecosystem and benthic C fixation in methane-rich sediments on the South Georgia margin

As bottom water warms, destabilisation of gas hydrates may increase the extent of methane-rich sediments. The authors present an assessment of organic carbon processing by the benthic community in methane-rich sediments, including one of the first investigations of inorganic C fixation in a non-hydrothermal vent setting. This topic was previously poorly studied, and there is much need to fill the gaps in knowledge of such ecosystems. The authors hypothesized that benthic C fixation would occur, and that a high biomass macrofaunal community would play a substantial role in organic C cycling. Experiments were conducted at a 257 m deep site off South Georgia. Sediment cores were amended with13C and15N labelled algal detritus, or13C labelled bicarbonate solution. In the bicarbonate experiment, labelling of bacteria-specific phospholipid fatty acids provided direct evidence of benthic C fixation, with transfer of fixed C to macrofauna and dissolved organic carbon (DOC). In the algae experiment, macrofauna played an active role in organic carbon cycling. Compared to similar experiments, low temperature supressed the rates of community respiration and macrofaunal C uptake. While benthic C fixation occurred, the biological processing of organic carbon was dominantly controlled by low temperature and high photic zone productivity.