Abstract. Predicting the dynamics of ecosystems requires an understanding of how trophic interactions respond to environmental change. In Antarctic marine ecosystems, food web dynamics are inextricably linked to sea ice conditions that affect the nature and magnitude of primary food sources available to higher trophic levels. Recent attention on the changing sea ice conditions in polar seas highlights the need to better understand how marine food webs respond to changes in such broad-scale environmental drivers. This study investigated the importance of sea ice and advected primary food sources to the structure of benthic food webs in coastal Antarctica. We compared the isotopic composition of several seafloor taxa (including primary producers and invertebrates with a variety of feeding modes) that are widely distributed in the Antarctic. We assessed shifts in the trophic role of numerically dominant benthic omnivores at five coastal Ross Sea locations. These locations vary in primary productivity and food availability, due to their different levels of sea ice cover, and proximity to polynyas and advected primary production. The d 15 N signatures and isotope mixing model results for the bivalves Laternula elliptica and Adamussium colbecki and the urchin Sterechinus neumeyeri indicate a shift from consumption of a higher proportion of detritus at locations with more permanent sea ice in the south to more freshly produced algal material associated with proximity to ice-free water in the north and east. The detrital pathways utilized by many benthic species may act to dampen the impacts of large seasonal fluctuations in the availability of primary production. The limiting relationship between sea ice distribution and in situ primary productivity emphasizes the role of connectivity and spatial subsidies of organic matter in fueling the food web. Our results begin to provide a basis for predicting how benthic ecosystems will respond to changes in sea ice persistence and extent along environmental gradients in the high Antarctic.
We investigated the composition of benthic microbial mats in permanently ice‐covered Lake Hoare, Antarctica, and their irradiance vs. photosynthetic oxygen exchange relationships. Mats could be subdivided into three distinct depth zones: a seasonally ice‐free “moat” zone and two under‐ice zones. The upper under‐ice zone extended from below the 3.5 m thick ice to approximately 13 m and the lower from below 13 m to 22 m. Moat mats were acclimated to the high irradiance they experienced during summer. They contained photoprotective pigments, predominantly those characteristic of cyanobacteria, and had high compensation and saturating irradiances (Ec and Ek) of 75 and 130 μmol photons·m−2·s−1, respectively. The moat mats used light inefficiently. The upper under‐ice community contained both cyanobacteria and diatoms. Within this zone, biomass (as pigments) increased with increasing depth, reaching a maximum at 10 m. Phycoerythrin was abundant in this zone, with shade acclimation and efficiency of utilization of incident light increasing with depth to a maximum of 0.06 mol C fixed·mol−1 incident photons under light‐limiting conditions. Precipitation of inorganic carbon as calcite was associated with this community, representing up to 50% of the carbon sequestered into the sediment. The lower under‐ice zone was characterized by a decline in pigment concentrations with depth and an increasing prevalence of diatoms. Photosynthesis in this community was highly shade acclimated and efficient, with Ec and Ek below 0.5 μmol·m−2·s−1 and 2 μmol·m−2·s−1, respectively, and maximum yields of 0.04 mol C fixed·mol−1 incident quanta. Carbon uptake in situ by both under‐ice and moat mats was estimated at up to 100 and 140 mg·m−2·day−1, based on the photosynthesis–irradiance curves, incident irradiance, and light attenuation by ice and the water column.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.