Lab-Raised, Algae-Eating Sea Urchins May Reverse Coral Reef Decline

This pioneering effort is the first phase of an innovative research effort on the part of scientists from two universities and a federal agency who will next attempt to re-seed the reef with lab-cultured coral larvae.

Coral reefs throughout the Caribbean and Florida have undergone major degradation over the past two decades. Among the causes of decline are the loss of a previously abundant, grazing sea urchin, Diadema antillarum, in 1983, followed a few years later by increasing losses of live coral cover due to elevated seawater temperatures that cause corals to turn stark white before dying. This phenomenon, known as coral bleaching, is thought by some to be one of the first early-warning signs of global warming.

The black long-spined sea urchin Diadema was almost wiped out over a one-year period starting in 1983 by an epidemic disease that killed 95 percent of the population throughout the entire region. Since then, as corals have died due to bleaching, storm damage, predation, ship groundings and diseases, they have left more reef substrate open for reef algae to grow on.

Without the large numbers of sea urchins to graze the algae down, the reef substrate has become progressively overgrown by fleshy seaweeds instead of the short turfs and crustose coralline algae that characterize healthy, heavily grazed coral reefs. The thick cover of seaweeds has prevented tiny coral larvae from recolonizing the reef substrate. Diadema has begun to recover in some locations in the Caribbean and these locations are beginning to show signs of reduced algal cover. It is hoped that coral recovery will soon follow. But so far Diadema shows little evidence of returning to the coral reefs of the Florida Keys, which have lost 50 percent or more of their coral cover over the last 10 years.

Scientists from the University of Miami, the University of North Carolina at Wilmington, and the National Oceanic and Atmospheric Administration (NOAA) Southeast Fisheries Science Center are working to reverse this dire situation. For corals to recolonize the reef, first the substrate must be appropriate for them to grow on, and this means helping Diadema make a comeback.

Tom Capo, director of the Experimental Fish Hatchery at the University of Miami's Rosenstiel School of Marine and Atmospheric Science, has worked out the life cycle of the sea urchin and is now working on mass-culturing them for restoration. The first batch of laboratory-raised juvenile sea urchins will be released to an experimental site on Little Grecian Reef offshore of Key Largo, FL later this week. Margaret Miller, from NOAA's Southeast Fisheries Science Center, will lead a group of students and technicians from the University of North Carolina at Wilmington (UNCW) and University of Miami to monitor the behavior and health of the newly released sea urchins.

A major concern is that fish and invertebrate predators will try to eat the spiny youngsters, and the scientists need to learn the best way to re-introduce them to ensure their survival. The project, funded by National Sea Grant, and supported by the National Center for Caribbean Coral Reef Research at UM, and the National Undersea Research Center at UNCW, and NOAA Fisheries is led by Alina Szmant from UNC Wilmington.

Szmant's research on the reproductive ecology of Caribbean reef corals will be applied to the second step in the restoration effort: that of raising millions of coral larvae from field-collected spawn, and then enticing the larvae to settle onto the reef areas where the Diadema were re-introduced. The reef-building corals targeted for restoration mass spawn during a few brief days each summer dictated by the lunar cycle. Szmant's years of work led her to learn how to predict the spawning dates, and now teams of divers can collect the spawn as they are released by the corals.

The team will be using large floating nursery chambers developed by colleagues working on the Great Barrier Reef to raise the coral larvae until they are mature enough to put down on the reef. Even if all goes as planned, it will take years before the scientists see the fruit of their labors. Reef-building corals grow only a centimeter or less per year. However, coral reefs took thousands of years to form to begin with, and recovery will likely take decades to centuries.

Szmant, Miller and Capo hope that their work will lead to new approaches to the ecological restoration of coral reefs, knowing that it will be future generations of humans who will reap the benefits of their efforts.