Friday, Feb 8, 2013
National Park Service divers recently killed almost 90 crown-of-thorn starfish (Acanthaster planci, or alamea in Samoan) offshore of Malia Mai in an effort to protect the reef from these voracious predators.
Alamea are a type of starfish with up to 21 arms and covered with poisonous spines. They prey upon coral tissue and can cause significant damage to reefs. While normally rare, alamea occasionally have population outbreaks where millions of individuals suddenly appear on the reefs. Over the last 30 years the Great Barrier Reef has lost over 50% of its coral due largely to an increase in alamea outbreaks, and is now threatened with being taken off of the list of World Heritage Sites.
Alamea have the ability to push their stomachs out through their mouths, covering a coral and using digestive enzymes to break down the coral animal. After consuming the coral tissue, they move on, leaving behind the white skeleton of the dead coral reef. A single alamea can consume up to 107 square feet of living coral in a year and will eat almost every coral species on the reef. The last time there was an alamea outbreak in American Samoa was 1977, when hungry alamea devoured over 80% of the territories coral reefs.
The reason for alamea outbreaks appears to be related to increased nutrients due to human development around high islands. Humans are now using more fertilizer and releasing more waste into the environment, and large storms with heavy rains wash these nutrients into the ocean. This process in turn fuels a bloom of phytoplankton, a marine plant which alamea feed on as larvae. Since it takes three years for alamea to mature, outbreaks typically occur three years after heavy rain or storm events.
Alamea populations are usually small, with adults rarely sighted, but during outbreak years they can carpet the reefs. Alamea release tens of millions of eggs during the spawning season, but most of these starve because they can’t find enough phytoplankton (a marine plant) on which to feed. The nutrient-fueled phytoplankton blooms after heavy rains provide an abundance of food for the alamea larvae, and many more survive than would otherwise be the case.
Although it’s not know for certain what is causing the current outbreak in American Samoa, it is notable that there was a large tsunami just three years ago that would have re-suspended nutrients that had settled on the bottom.
While alamea outbreaks have occurred in the past in American Samoa, they are quite rare. Elderly fishermen interviewed by Dr. Chuck Birkeland in the 1970s recalled outbreaks in 1916 and 1932. No outbreak was recorded between 1932 and 1977, and divers reported that they would occasionally see one or two individuals on a reef. However, in late 1977 divers observed an estimated 83,000 individuals on Taema Banks. A removal program was started to try to protect the reefs, and by the end of 1978 over 480,000 individuals had been collected along the coastline. Despite these efforts, the alamea outbreak continued until 1980, when most of the coral reefs were gone and the starfish finally starved to death.
The National Park Service is collaborating with the Department of Marine and Wildlife Resources, the National Marine Sanctuary, and the governor’s Coral Reef Advisory Group to combat the recent alamea outbreak. A joint meeting was held recently to discuss methods to monitor and eradicate alamea before their population reaches levels similar to the 1977 outbreak. While surveys to date have shown alamea to be abundant between Pago Pago Harbor and Vaitogi, additional effort will be made over the next two weeks to survey the entire island for alamea. Alamea will also be either removed from the reefs by divers or injected with a poison that is specific to the alamea but not harmful to other marine life or humans.