New research shows the devastating effects sponges can have on reef-building corals.
These sponge bullies smother and kill nearby coral colonies and take up residence on the skeletons of their victims, PeerJ reported. Humans are also playing a role in the mass coral massacre; overfishing is removing predators of sea sponges, accelerating their rate of destruction among coral communities.
To make their findings, a team of researchers surveyed reefs from 12 Caribbean countries and compared 44 sites with abundant fish populations to 25 sites where these predators which much more scarce. They found over 25 percent of coral colonies at the overfished sites were in contact with sponges, which is more than double the contact seen in the protected sites. On the less-fished reefs, fast-growing sponge species were usually consumed by angelfish and parrotfish, protecting the majority of local coral.
"If the goal is to save the corals that build Caribbean reefs, we have to protect the angelfishes and parrotfishes that eat sponges" said Tse-Lynn Loh, now a Postdoctoral Research Associate at the Haerther Center for Conservation and Research at Chicago's Shedd Aquarium and lead author on the study published today in the open access journal PeerJ.
Corals are not just threatened by sponges, but also seaweeds and diseases. Seaweeds are considered to be one of the biggest threats to coral reefs, and were found to cover almost twice as much of the reef surface as corals and sponges. The recent analysis made the shocking discovery that these seaweeds were more abundant in regions where fish were also more plentiful. The findings contradicts the idea that fish eat and control seaweed, which has often been a factor in decision making on how to protect certain regions of the ocean. Despite these findings, the researchers concluded protecting fish populations is critical to survival of coral reefs.
"Caribbean nations can now base their fishing policy decisions on the clear connection between overfishing and sponge-smothered corals," said study leaderJoseph Pawlik, of UNC Wilmington. "Coral conservation requires a healthy population of reef fishes."