Raiders of the Reef – No one likes a party crasher. The same holds true in the underwater world of coral reefs. Invading or disrupting the natural balance of the reef can have some serious implications, from the loss of a species to the collapse of an entire system. There are some species that are invading the Caribbean and their presence, so far, has had only a minor impact. However, a few species are on their way to raiding and completely taking over the reef.
Aside from the invasion of coral diseases, one of the most threatening species to raid the Caribbean is the venomous Indo-Pacific lionfish (Pterois volitans). Genetic testing of lionfish in the Atlantic has revealed ancestors coming from a population of only six fish, making it most likely they were introduced into the Atlantic as an unwanted fish from an aquarium. While they are quite striking fish to look at, lionfish by no means belong in the Caribbean. A new study from the University of Oregon found that it took only five weeks for lionfish to destroy 79 per cent of a population of juvenile fish. Currently there are no predators to naturally keep the numbers of these fish to a minimum so their populations have virtually exploded. (Lionfish are venomous and produce a painful sting—probably why they don’t have any predators). While the BVI doesn’t have any known established populations, it will only be a matter of time until they start invading our waters, especially since there is already a population off the eastern coast of Puerto Rico.
Another invader of the reef includes the orange cup coral (Tubastraea coccinea). Although this is an example of an invasive coral whose “threat” is considered negligible, the orange cup coral does often compete with native corals and sponges for space. It was first seen in Puerto Rico and Curacao in the early 1940s and has since been spotted throughout the Caribbean, particularly on artificial structures. If you have been diving on the RMS Rhone, you’ve probably seen this coral!
Not only does the introduction of an alien species have the potential to cause mass destruction, there are a few species that just want to take over the reef. An overgrowing mat tunicate (Trididemum solidum) and a destructive coral encrusting sponge (Cliona sp.) like to invade corals by smothering them. (Tunicates are often mistaken for sponges but are the one species that most resembles humans, as in their early stages of development they possess a central nerve cord). Possible reasons for its overgrowth are the slowly declining populations of parrotfish and angelfish that usually eat these species, an effect of overfishing.
The worst species of all in terms of invading the reefs are humans. While for the most part we don’t intentionally want to destroy these ecosystems, especially because so many people depend on them, around the world reefs are in severe decline and it is mainly our fault. From excessive carbon emissions that alter the chemical balance in ocean waters to physically beating up the reef and polluting the waters with toxic chemicals, we are probably the biggest raiders of the reef. And then there are the coral diseases… but that will be in next month’s issue.
The International Year of the Reef 2008 is a worldwide campaign to raise awareness about the value and importance of coral reefs and threats to their sustainability, and to motivate people to take action to protect them. To that end, over the next year, articles about coral reefs will be a regular feature in this magazine.
