Killer Seaweed in Coral Reefs

Studies have shown that several species of seaweed common in both the Pacific and Caribbean Oceans can kill corals upon contact using chemical means.

The study used racks of transplanted coral placed next to different types of common seaweed as well as plastic plants to simulate the effects of shading and mechanical damage. For comparison, other coral racks had neither seaweed not plastic plants near them. In as little as two days the corals in direct contact with the some seaweeds bleached and died.

Chemicals were extracted from the seaweeds causing death. These chemicals were applied to the corals in a gel matrix. As a control, the gel without the chemicals was added to a different group of corals. The results confirmed that these chemicals were responsible for the death of corals in contact with the killer seaweeds.

Overfishing of herbivorous fishes has resulted in more seaweeds being present amongst corals, and some of these seaweeds are responsible for the death of coral. The less coral there is, the fewer fish will be recruited into the area to feed, so the number of seaweeds increase, more coral dies.

Reference:
Douglas B. Rasher, Mark E. Hay. Chemically rich seaweeds poison corals when not controlled by herbivores. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.0912095107