Carbon and nitrogen cycling by Red Sea coral reef sponges

Sponges are dominant components of coral reefs where they fulfil a number of structural and functional roles that make them key ecosystems engineers. In particular, their high filtering capacity and association with diverse microbial communities enables sponges to moderate flows of organic matter and inorganic nutrients, thereby influencing the biogeochemical cycling of carbon (C) and nitrogen (N) on coral reefs. This cycling of C and N is central to understanding how coral reefs, some of the most productive and diverse ecosystems on Earth, can thrive in such nutrient poor environments. Studying the fluxes of organic matter and nutrients mediated by sponges is therefore essential to understanding coral reef ecosystem functioning. However, many of these fluxes are poorly understood. By investigating the mechanisms and rates at which sponges retain, transform, and transfer organic matter and inorganic nutrients within coral reef ecosystems, this thesis provides new insights into roles that sponges play in the biogeochemical cycling of C and N on coral reefs.