Esther van der Ent

You can already see by eye the high productivity on coral reefs, reflected by the colorful corals, busy fish and noisy shrimps. Most of this productivity however, is invisible. Sponges are continuously pumping vast amounts of water through their body; filtering, assimilating and transforming the nutrients in the water. This way, nutrients become available for organisms higher up in the food chain. Inside these sponges, symbiotic microbes are thought to play an important role in the cycling of nutrients, especially nitrogen. On healthy coral reefs, nitrogen is a limiting nutrient. However, eutrophication is threatening coral reefs everywhere. How will this environmental change influence sponges, their symbionts and the important functions they carry out on coral reefs?