Seasonal physiology and ecology of Antarctic marine benthic predators and scavengers

Pronounced seasonality in photoperiod and phytoplankton availability drives key physiological processes in many Antarctic primary consumers. To test the hypothesis that carnivores would be less markedly affected by environmental seasonality than benthic 'herbivores', we measured faecal egestion, oxygen consumption and nitrogen excretion every 2 to 3 mo for 18 mo in 5 benthic predators and scavengers common around Adelaide Island (West Antarctic Peninsula): the fish Harpagifer antarcticus, the brittle star Ophionotus victoriae, the nemertean Parborlasia corrugatus, the amphipod Paraceradocus miersii and the nudibranch Doris kerguelenensis. The degree of seasonality varied between species and was not consistent across the physiological parameters measured. Faecal egestion varied strongly between species and individuals. All species except Paraceradocus miersii ceased feeding for several months. No consistent seasonality in metabolic activity (oxygen consumption and nitrogen excretion) was observed, and seasonal factorial changes in oxygen consumption were less than in primary consumers. Use of metabolic substrates changed between seasons, particularly in H. antarcticus, which switched from a balanced diet to mainly protein utilisation at the start of winter. O. victoriae had the highest O:N ratio (232) and Parborlasia corrugatus the lowest (9), suggesting the latter species is the most exclusive carnivore. We conclude that food availability and quality is also variable for Antarctic secondary consumers but that this variation is not as tightly coupled to the environmental seasonality as in primary consumers. Other factors, such as reproductive activity, that are indirectly coupled to seasonal signals may have also been causing this variability.