On the high Antarctic shelf, as well as in other marine coastal regions, fish play a central role in the food web as they provide a major trophic link between small sized low trophic level organisms and large vertebrate predators. Marine living communities in the Antarctic are increasingly threatened by alterations of the abiotic and biotic environment due to climate change. The impact of environmental changes on fish not only operates directly, but also indirectly through the food chain. The vulnerability of a particular fish species to such indirect effects and its risk to get lost due to alterations in food web structure are mainly determined by (i) the species plasticity to respond to resource fluctuations, and (ii) predator induced mortality. Species vulnerability decreases with increasing prey diversity (generalist vs. specialist consumers) and decreasing predator diversity. Whether or to which degree fish species loss indirectly affects overall food web structure and ecosystem functioning, depend on the communities or populations capacity for functional compensability (species redundancy), i.e. the degree to which coexisting species can compensate for one another within the food web. Based on data on fish species composition and a large dataset on who eats whom we evaluate the functional role of fish species in the food web of the high Antarctic Weddell Sea shelf, the vulnerability of particular species to food web alterations, and the potential for functional compensability in case of species loss. Fish fauna on the shelf is composed of 50 different fish species, with one plankton feeding species, Pleuragramma antarcticum, distinctly dominating the fish community. Most other fish species inhabiting the Weddell Sea shelf are feeding on benthos or a mixture of benthos and plankton. Vulnerability of species is positively related to the amount of planktonic prey items in the diet, as plankton consumers are mostly specialized on few prey items and are additionally preyed upon by a multitude of higher trophic level predators in the water column. Benthos feeders, in contrast, are generalist consumers with a low number of predators. Vulnerability is consequently low in these species and functional redundancy buffers the effect of eventual species loss. Plankton consumers, mainly represented by P. antarcticum, are highly sensitive to alterations in trophic structure. Due to the lack of functional redundancy within this trophic group, extinction of P. antarcticum might have severe consequences for overall food web structure and ecosystem functioning. On the high Antarctic shelf, P. antarcticum represents a wasp-waist, and thus plays a similar role as sardines and anchovies in tropical upwelling systems.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL4-Response of higher marine life to change