Benthic communities

The sea bottom is often the final recipient of solid waste, and has indeed been used as a dumping ground for such waste, and even for toxic and nuclear waste. Sediments and toxic sludges build up here, particularly close to coastlines. In areas of high nutrients, the high productivity on the ocean surface can lead to deposition of organic detritus and bacteria, and in extreme cases this can lead to anoxia. The majority of the ocean bottom is made up of soft sediments which support a diverse fauna, dominated by burrowing animals, but also surface dwelling organisms. Physical smothering and toxic pollution are clear problems for some of these.

In the shallower waters of the continental shelf, high levels of suspended sediments or algae can reduce light levels at the seabed, affecting rates of photosynthesis of benthic algae, and seagrasses.

Coral reefs appear to be particularly susceptible to a broad range of land-based waste issues. Sediments block light that is critical for coral growth, while they can also stress or kill corals through direct physical smothering. Nutrient build-ups have been shown to threaten coral reefs by encouraging the rapid growth of macroalgae which is able to outgrow corals and gradually replace them. Coral reefs also appear to be one of the most sensitive ecosystems to climate change. Under high temperatures corals exhibit a stress response known as coral bleaching ? they loose the symbiotic algae which normally lives within their tissues. Without this they go a pale or white colour and, in extreme cases, may die.