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.

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The paper investigates tolerance to UV radiation (UVR) in 3 amphipod species from the Arctic Kongsfjord, Spitsbergen: the herbivore Gammarellus homari (0-to 5-m water depth), the strictly carnivore scavenger Anonyx nugax (2-to 5-m water depth) and the detritivore/carnivore Onisimus edwardsi (2-to 5-m water depth). In previous radiation exposure experiments, both carnivore species displayed elevated mortality rates already at moderate UVR levels. Therefore, the concentrations of sunscreening compounds (mycosporine-like amino acids, MAAs, and carotenoids) and two antioxidant enzymes (superoxide dismutase, catalase) were studied in the animals under control conditions and following moderate as well as high UVR exposure.In both carnivore amphipods elevated sensitivity to experimental UVR exposure went along with a degradation of the tissue carotenoid and MAAs and a decrease of the enzymatic antioxidant defence, which resulted in increased lipid peroxidation in exposed animals. In contrast, the herbivore G. homari seems well protected by high concentrations of MAAs absorbed from its algal diet, and no oxidative stress occurred under experimental UVR. The species-specific degree of UV tolerance correlates well with the animals' typical vertical distribution in the water column. D

We investigated the shielding against solar ultraviolet radiation and inducible damage, as well as the short-term response of whole animal metabolic rate in two Antarctic shallow water amphipod species. Light absorbance by the carapace of Gondogeneia antarctica and Djerboa furcipes was higher in the UVR (UVB + UVA) range (42.1% and 54.5% on average respectively) compared to the PAR (photosynthetically active radiation) range (38.1% and 50.1% respectively) of the solar spectrum. Bands of higher absorbance correlated with maximal absorbance ranges of sunscreening compounds indicating mycosporine-like amino acids (MAAs) and carotenoids to be innate compounds of the exoskeleton of these species. Though the antioxidant enzyme catalase was photoinhibited, protein damage products did not accumulate under experimental exposure to a daily dose of 6.84 kJ m À2 d À1 UVB, 66.24 kJ m À2 d À1 UVA and 103.14 kJ m À2 d À1 PAR. Animal oxygen consumption during UV-exposure was measured as an indicator of immediate behavioural and physiological stress response. UVB as well as UVA induced a response with altered and highly variable respiratory intensity. Our findings indicate that sub-lethal UVR exposure causes increased oxygen consumption in polar amphipods due to radiation avoidance, shelter seeking behaviour, and presumably also from cellular repair processes.

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