Hidden sponges influence coral reef feeding cycles

Marine organisms hidden in caves, such as sponges, play an important role in the nutrient cycle of coral reefs. In his recent research findings, Dutch biologist Sander Scheffers contends that they may, in fact, play the most important role in sustaining and feeding coral reefs.

This could be valuable information for nature conservationists battling to preserve threatened reefs around the world...

Oceans cover more than 70% of the Earth's surface. This vastness gives a false sense of security that human activity could have little impact on the Big Blue. But evidence of dying coral reefs suggests otherwise. Coral reefs are extremely rich tropical marine habitats which are under threat worldwide. Experts estimate that up to 25% of them have been destroyed or badly degraded. Some scientists predict that, by 2020, up to 70% might be permanently lost.

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

To do this, he first had to build up a picture of the nature and overall importance of these organisms to coral. While working out of the Royal Netherlands Institute for Sea Research (NIOZ), Scheffers started examining the precise appearance and quantity of these virtually inaccessible caves and their living communities.

The location chosen for this was around the Caribbean island of Curaçao. Using a special underwater camera, his extensive filming revealed that sponges occupied the most space in these caves, followed by animals, such as tubeworms, tunicates and bivalves.

Together they fill more than 60% of the cavities – and these underwater caves were not small hidey-holes, either. As seen from above by divers, they were found to have surface areas significantly greater than the coral reefs they shared the ocean with.

According to Scheffers, who is now with the Faculty of Biology and Geography, Universität Duisburg-Essen, Germany, a larger living surface also means a larger filtering surface. Sponges filter the water. They take up planktonic particles, such as bacteria, and excrete inorganic nutrients. In turn, these nutrients can facilitate the growth of marine plants and other organisms.

Sponges filter at a phenomenal rate: if the seawater were to remain stationary, the sponges would have completely pumped it away within five minutes – removing all of the small plankton from it. Obviously this is not the case because there is a continuous supply of fresh water into the sea.

These hidden organisms play a key role in the marine nutrient cycle, notes Scheffers, due to their capacity to convert huge quantities of organic plankton into inorganic material. The results of his research, funded by The Netherlands Organisation for Scientific Research (NWO-WOTRO), have been made available to the personnel at the Marine Under Water Park of Curaçao and have been presented to the local government. Wider dissemination of the findings may also assist other reef regions of the world.

Experts have identified a number of coral reef ‘biodiversity hotspots’, regions that host a great diversity of endemic species which have been significantly affected and altered by human activities. In 2002, Conservation International, an environmental group, launched a strategy to focus conservation efforts on these hotspots. It targets conservation investment where it stands to have the biggest impact and names 25 such places on land and in the sea.

Marine research is also funded by the EU in the ‘Sustainable development, global change and ecosystems’ theme, under its current Framework Programme for research (FP6). Using the ‘Biodiversity and ecosystems’ budget, projects are funded which assess and forecast changes in biodiversity, structure and function, and which investigate the dynamics of ecosystems and their services, with an emphasis on how marine ecosystems function.

Source: www.divenews.com