Diet Composition of Two Temperate Calcareous Sponges: Leucosolenia echinata and Leucetta sp. from the Wellington South Coast, New Zealand

Sponges are an important component of benthic ecosystems in New Zealand, and as suspension feeders they can process large volumes of water meaning that their interaction with the water column is likely to be of great importance. Our research focuses on the functional role of sponges as suspension feeders in temperate rocky subtidal ecosystems on the Wellington South Coast, New Zealand. We investigated the diet composition of two common species of calcareous sponges (Leucosolenia echinata and Leucetta sp.) by identifying and quantifying food particles from water samples using flow cytometry, and estimating the removal efficiency for these species. The natural diet of both species included heterotrophic bacteria, Prochlorococcus sp. and Synechococcus sp., similar to that previously reported for demosponges. We found significant differences in the number of picoplanktonic organisms present between ambient and exhalent water for both study species. Prochlorococcus and Synechococcus were removed with the highest efficiency irrespective of sponge species (52-57%). Both species had similar overall removal efficiencies, but we detected significant differences in the removal rates of the three types of bacteria in each species. Our study is the first to investigate the natural diet of calcareous sponges in temperate rocky subtidal reefs using flow cytometry and we provide evidence for differences in the diets of calcareous sponges and demosponges.