While they may make great loofas, in the coral communities of the Caribbean reefs sponges are a greater threat than perhaps even humans. Aggressive competitors for resources and space, these nefarious neighbors have been known to use shading, smothering, snot and even toxins to kill their coral counterparts, literally living on what's left of their remains. And without many natural predators, these sponges continue to damage reef-building corals unless kept under control.
In a new study published this week in the journal PeerJ, researchers with the University of North Carolina Wilmington surveyed reefs amongst 12 Caribbean nations only to find that overfishing in this tropical paradise is having drastic ramifications for the coral reefs just below the surface. By removing the few natural predators of sponges, fishermen are actively increasing the threats against already diminishing coral populations.
"If the goal is to save the corals that build Caribbean reefs, we have to protect the angelfishes and parrotfishes that eat sponges" coauthor of the study, Tse-Lynn Loh says.
Though not all sponge species are consumed by predators on account of their toxic or even distasteful chemical defenses, angelfish and parrotfish do a great job at keeping the pesky invaders from taking over coral reefs in normal, undisturbed areas. But researchers found that on overfished sites, coral colonies had twice the incidence of sponge infestation that those that were not fished at all. And when it comes to coral conversations, this unique discovery may change how ecologists and Caribbean nations will address fishing policies on and near the reefs.
"Caribbean nations can now base their fishing policy decisions on the clear connection between overfishing and sponge-smothered corals" lead researcher for the study, Dr. Joseph Pawlik says. "Coral conservation requires a healthy population of reef fishes."
Why is it that Caribbean reefs have such a rough time?
While coral reefs around the world are seeing their local population sizes diminish, corals within the Caribbean reefs are particularly threatened because of far more factors than just human intervention. Warming seawaters, disease and storms have already crippled the slow-growing sea creatures, and for that reason many have been added as protected species to the world conservation list. But that doesn't mean that the fish that call it home are offered the same special treatment.
Though these fish may not be endangered, litigators may soon need to append existing laws to extend similar rights to these protectors of the coral reefs. And if they plan on protecting the species from invaders of the sponge variety, they had better do so soon, because with dwindling fish counts, surveys may say that the time for corals is up.
