Reduced seasonality in elemental CHN composition of Antarctic marine benthic predators and scavengers

At all but the lowest latitudes, photoperiod varies through the year, resulting in seasonal variation in coastal primary productivity. This leads to a pronounced seasonality in the physiology of most primary consumers, particularly in the seas around Antarctica, which are amongst the most seasonal on the planet. However, higher trophic levels have a more constant food supply and a recent study showed that a range of Antarctic benthic predators and scavengers had very little seasonal variation in physiology. This study investigated the seasonal signal in tissue elemental composition of these same five common benthic predators and scavengers: the gammarid amphipod Paraceradocus miersii; brittle star Ophionotus victoriae; nemertean Parborlasia corrugatus; nudibranch Doris kerguelenensis and tissues of the notothenioid fish Harpagifer antarcticus. Carbon (C), hydrogen (H) and nitrogen (N) contents and C:N ratios were determined for five to seven time points during one year at Adelaide Island, Antarctic Peninsula. Whilst there were significant differences between species, only P. miersii exhibited seasonal differences, with significantly higher CHN content and C:N ratio in summer than in winter. In the other four species, elemental composition and C:N ratio were very stable throughout the year, supporting the assumption of homeostasis in ecological stoichiometry of benthic consumers and adding to the previously measured lack of seasonal physiological patterns. Recent disruption of the annual patterns of primary productivity, due to reduced occurrence of winter sea ice, may, therefore, not have an immediate impact on higher trophic levels.

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