The National Oceanic and Atmospheric Administration recently reported on an increase in the phenomenon of coral bleaching—the process of corals expelling the symbiotic algae living in their tissue, which causes the coral to lose color. “Without the algae,” NOAA reports, “the coral loses its major source of food and is susceptible to disease.”
Although corals can recover from mild bleaching, long-term or repeated bleaching kills the coral, and the reefs they’ve built begin to erode. In some cases coral reefs provide protection for vulnerable shorelines; in almost all cases the reefs provide habitat for shellfish. It can take decades for a colony to recover once a die-off occurs.
What does this have to do with stormwater? Several stressors are believed to be responsible for the bleaching. One is increased levels of nutrients in the surrounding water. In many places stormwater runoff into bays and estuaries increases nutrient levels, leading to eutrophication and dead zones in regions like the Gulf of Mexico. Rising water temperatures are also believed to cause coral bleaching.
Corals in the western Pacific began to experience severe bleaching in June, and it may be spreading. Last fall Hawaii experience widespread coral bleaching, and NOAA scientists are concerned that if the phenomenon recurs there it will further weaken or kill corals that have yet to completely recover.
NOAA is also tracking the phenomenon around the world, including the Solomon Islands, Papua New Guinea, American Samoa, and elsewhere in the South Pacific, and in parts of the Indian Ocean. The agency publishes a Coral Reef Watch.
Janice Kaspersen
Janice Kaspersen is the former editor of Erosion Control and Stormwater magazines.
