>When nutrients are added to a lake, river, estuary, lagoon or ocean, they invariably enhance the growth of some life forms (usually algae and sponges) at the expense of others; this is eutrophication. Eutrophication is the leading example of human activity degrading marine habitat in coastal waters, and it is always traceable to agricultural runoff, sewage (treated or otherwise) or both. Today the term is most frequently used to describe the effects on coral reefs from two groups of nutrients: phosphorus and nitrogen compounds.
>Some problems reefs face, such as storm damage, are the result of natural causes. Others are the result of human activity; overfishing, sedimentation from runoff and acidification are prime examples. When these stress factors are present, even a modest increase in phosphorus and nitrogen can spell the end of a coral ecosystem. Eutrophication is usually the final step in a shift from complex reef communities — desirable for so many human endeavors and economies — to simple, much less diverse communities. Simply put, a predominantly coral community becomes a predominantly algae community.
>Natural stressors such as coral bleaching and storms can be thought of as the forest fires of the reef. As bad as it looks right after the fire, the bleaching or the storm, the environment eventually benefits. Nature tends to periodically thin out areas choked with undergrowth, which stimulates resilience and new growth. Even coral reefs recover after a few years, possibly developing to even higher levels of complexity and community than before — provided the environment is fundamentally healthy.
>Klaus Ruetzler, a research biologist at the Smithsonian Institution, confirms that in many coastal waters of the world sponges of the Cliona genus are destroying coral reefs at an unprecedented rate. The rate of reef destruction due to Cliona is directly related to eutrophication. After determining the percentage of reef covered by Cliona and other eutrophic organisms increases with proximity to sewage outfalls, some scientists have proposed using Cliona levels as a pollution index.
>Biologists tell us sponges have played an important role in reef systems throughout time, especially in providing critical support to reef health during times of biological stress. Perhaps sponges are more resistant to eutrophication and other hazards like rising sea temperatures and ocean acidification than corals are. If so, we could once again see sponges become the dominant animals on Earth's reefs instead of corals. It's already happening.
>There are practices individuals can adopt to help reduce eutrophication: eating locally produced food, using biodegradable detergents without phosphates, reducing meat consumption and not dumping waste (even treated waste) into bodies of water. However, the problem exists primarily at the industrial and governmental levels. Governments of Baltic and some Caribbean nations, where eutrophication is most severe, are beginning to take steps to address it. Best-management practices for reducing phosphates and nitrates that enter the seas have been devised. As sources of agricultural phosphates grow scarcer, market forces are providing incentive to recover them before they enter coastal waters. As awareness of eutrophication grows, the hope is citizens will elect officials with the political will to implement phosphate and nitrogen remediation on a large scale.
>© Alert Diver — Spring 2012