Cell turnover in marine sponges: Insight into poriferan physiology and nutrient cycling in benthic ecosystems

The sponge loop is a major energy and nutrient recycling pathway that has recently been described in Caribbean coral reef ecosystems. The majority of food produced on coral reefs consists of dissolved organic matter (DOM), which is not readily available to heterotrophic multicellular reef inhabitants. Sponges enable the shunt of this energy source to heterotrophs through the conversion of DOM to particulate organic matter (POM), or detritus, which acts as a major food source for higher trophic levels. The main underlying mechanism behind the production of sponge-derived detritus is hypothesized to be a rapid turnover of sponge cells through fast cell proliferation balanced by cell shedding (De Goeij et al. 2013). This thesis aims to gain a deeper understanding of these cellular mechanisms and the effect that the physiological state of sponges has on cell proliferation, shedding, and detritus production.