Ecological stoichiometry in six species of Antarctic marine benthos
Elemental (C, N, P) composition was examined in 6 benthic marine invertebrates from Antarctica: 2 suspension feeders (the holothurian Heterocucumis steineni and the polychaete Thelepus cincinnatus), 1 epifaunal grazer (the limpet Nacella concinna), 1 deposit feeder (the polychaete Flabelligera mundata), 1 predator (the nemertean Parborlasia corrugatus) and an omnivore (the asteroid Odontaster validus). Correction for inorganic carbon was necessary only for O. validus, where skeletal carbonate produces a high mineral ash content. Elemental composition of tissue was 49 to 60 % C, 10 to 14 % N and 0.7 to 1.3 % P (all on an organic mass basis); these are all within the normal range of values for aquatic invertebrates. The most variable component was P, though variability was much lower than in stream insects. Stoichiometric molar ratios (C:P, C:N, N:P) were all typical of consumers, with a strong inverse relationship across species between %C and %N in tissue. Stoichiometry varied strongly between phyla, with less variation between species within phyla. There were also indications of variations in elemental composition (C:N ratio and %P) with feeding mode, but the limited range of taxa studied constrains this conclusion. Despite differences in nutrient status, the elemental composition of marine and freshwater benthos were, with the exception of insects, closely similar. Despite the very slow growth rates that characterise polar marine benthos, P contents were relatively high, suggesting that the predictions of the growth rate hypothesis are not upheld at low temperatures.