The Intertidal and Shallow Subtidal Food Web at Marion Island

Abstract

The diets of the seven main predators of intertidal and subtidal organisms at Marion Island are described, based on the food and feeding habits of the Kelp Gull, Larus dominicanus, Lesser.Sheathbill, Chionis minor, Imperial Cormorant, Phalacrocorax atriceps, nototheniid fish, Notothenia coriiceps, and N. magellanica, Plunder Fish, Harpagifer georgianus, and the starfish, Anasterias rupicola. The biomass and standing crop energy values of the main prey species, and the energy requirements and biomass of the predators, were determined, to yield data for a quantitative account of major patterns of energy flow in the food web of the marine coastal ecosystem. The limpet, Nacella delesserti, has the highest biomass of all the prey species and is also the major food of Larus dominicanus, Notothenia coriiceps, and Anasterias rupicola which tend to exploit limpets of different sizes and from different habitats. Nacella delesserti maintains extremely high population densities despite the intense depredation. Connectivity in the food web is relatively weak, and there is little evidence for interspecific competition for common food resources. However, there are indications that intraspecific competition for grazing occurs in the N. delesserti population. The system, as a whole, is generally composed of opportunistic generalists which may be regarded as constituting a set of loosely interacting colonizers of a relatively young and isolated Sub-Antarctic island.