Hidden Sponges Determine Coral Reef's Nutrient Cycle

In orderto protect coral reefs it is important to understand how both the reefsand their environment function. Researchers often concentrate onsubjects such as physical damage to reefs, the bleaching of coral andcoral diseases. Sander Scheffers investigated a lesser-studied subject:the nutrient cycle on the coral reef and the role that organisms livingin cavities, such as sponges, play in this.

Underwater camera

To determine the nature and size of this role, Scheffers first ofall examined the precise appearance and quantity of these virtuallyinaccessible caves and their living communities. He did that on theCaribbean island of Curaçao using a special underwater camera. Thefilms shot revealed that sponges were the most important inhabitants,followed by animals such as tube worms, tunicates and bivalves.Together they fill more than 60 percent of the cavities. Further thecavities were found to have a surface area eight times greater thanthat of the coral reef, as seen from above by divers.

Filterers

And according to Scheffers a larger living surface also means alarger filtering surface. Sponges filter the water. They take upplanktonic particles such as bacteria and excrete inorganic nutrients.In turn, these nutrients can facilitate the growth of marine plants andother organisms.

Sponges filter at a phenomenal rate: if theseawater were to remain stationary, the sponges would have completelypumped it away within five minutes, i.e. they would have removed all ofthe small plankton from it. This is of course not the case, as there isa continuous supply of fresh water into the sea. According toScheffers, these hidden organisms play a key role in the marinenutrient cycle due to their incredible capacity to convert enormousquantities of organic plankton into inorganic material.

Theresults from Scheffers' research have been made available to thepersonnel from the Marine under water park of Curaçao and have beenpresented to the local government.