Low functional redundancy in sponges as a result of differential picoplankton use

Understanding the way that closely related co-existing species utilize resources is important for explaining biodiversity patterns and understanding how organisms contribute to ecosystem functioning. Here we investigated the utilization of food resources by sponges to determine if different sponge species from the same habitat utilize different fractions of their picoplanktonic food resources, and examined the validity of treating sponges as a single trophic group in functional diversity assessments. Using flow cytometry, we demonstrated that different groups of sponge species have different retention efficiencies for different types of picoplankton, providing evidence for differential use of food resources among different sponge species living in the same habitat. Although the mechanisms to explain these differences remain undetermined, we propose that this differential food use means that the feeding activities of sponges should not be considered as a single functional role.