Scientists use underwater lab to study seaweed-eating fish

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A team of scientists have just completed a ten-day stint underwater in order to better understand how the diversity of seaweed-eating fish affects endangered coral reefs.

The mission, which started on September 13, took place in the NOAA Aquarius underwater ocean laboratory; a bus sized research station located 60' underwater in Key Largo in the Florida Keys.

It is hoped that the research may provide new information to help scientists protect and even restore damaged coral reefs in the Caribbean.

The team of four scientists, led by Professor Mark Hay of Georgia Tech’s School of Biology, have been studying how the interaction of seaweed and fish affects the health of coral reefs in the Pacific Ocean and Caribbean Sea. They have shown that the natural chemical defences of seaweed can harm the coral, and that herbivorous fish can control the growth of this seaweed. The new studies will build on that knowledge and provide new information on the complex factors affecting reef ecosystems.

Professor Hay said: "Consumption of seaweed plays a critical role in structuring coral reefs and in selecting for algal traits that deter herbivorous fish. Recent studies have noted dramatic variance among species in the susceptibility of herbivorous fish to seaweed chemical and structural defences. These differences can translate into dramatic direct effects of herbivore diversity on seaweed."

Ten months prior to the mission, the team built a series of large cages which they filled with either one species or a mix of different species of fish and sea urchins. The aim was to discover whether specific communities of fish had more of an impact on seaweed and the overall health and growth of the coral.   

Although only one of a number of factors affecting coral, in areas where overfishing has reduced the numbers of herbivorous fish, seaweeds can begin to over-populate coral reefs. Previous studies by the group have found that specific mixes of fish can not only decrease the amount of seaweed on coral by 76% but also increase coral growth by 22%. It is hoped that this will help in future plans to restore corals.

Hay added: "The particular biodiversity of herbivores may be as important as the density, or mass, of herbivores in determining reef communities. We know too little of the species-specific effects of reef herbivores…or which particular mix of herbivores is critical for suppressing aggressive seaweed to maintain reef function."

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