Posted on November 22, 2009
Guest Blog by Marah J. Hardt
There’s something not quite right about the coral reefs in Jamaica. Alan notices it straight away, following our first dive: “its just so quiet down there.” Coral reefs are naturally noisy places: the sound of waves crashing over the reef crest, the snapping of snapping shrimp, grunting of grunts, and the incessant oscillating scrape, crunch, chomp, scrape, crunch, chomp, chomp of parrotfish as they cruise the reefs, scraping seaweed off the bottom. Just as the jungle has its background hoots and trills, so too does a coral reef come with its own musical melodies…at least, they used to.
So where did all the fish go? To quote a famous fisheries biologist, Daniel Pauly, “we ate them.” Jamaica’s reefs are some of the most overfished reefs in the world, with a history of decline dating back several centuries. It started with sea turtles as early as the 17th C. and from there, fishermen worked there way through the food web, virtually eliminating whole groups of fishes from the reef. Groupers and large parrotfish (and by large, I mean adult-sized fish greater than about 1 ft) are missing entirely, and it’s uncommon to see snapper, jacks, or even grunts.
The result: a silent reef, slowly eroding under a carpet of algae (aka, seaweed).
Corals build reefs, but they are in constant competition with seaweed for space and light. Slower growth rates mean corals cannot outcompete seaweeds, unless something keeps the seaweed in check. Enter fish and sea urchins. These are the grazers of the reef. And in Jamaica, they are too few and far between to keep seaweeds from taking over.
And even though there are so few fish left, the fishermen keep on fishing— their traps are literally lined up along the reef slopes, catching any and everything that wanders in. And that’s the problem. Too many fishermen fishing too many fish.
All hope is not lost, however. Nowhere are corals yet extinct, so the potential for recovery exists if we can alleviate some of the pressures placed upon them.
Creating marine protected areas and reducing CO2 emissions would go a long way towards helping to restore the reefs. Nature remains full of resilience and surprises: although seriously degraded, Jamaica’s reefs are one of the few places where scientists think there may be some recovery of the endangered staghorn coral; and, where sea urchins occur in higher numbers, we see less algae and more corals.
The reefs here in Jamaica are in trouble, from local threats such as overfishing, to global threats, such as climate change. And with fewer corals, it may just be that sponges become even more important—offering three-dimensional structure to replace the habitat that corals once provided. Which takes us back to why we are here—to see how sponges will do under a changing climate. Click here for a pdf summarizing the basics of our study or here for an intro to climate change. To learn more about how climate change affects ocean ecosystems in general, check out the climate change section of staff publications at Blue Ocean, and especially this article Carl and I published last year. Stay tuned for an addition post about climate change and coral reefs…
Here off the north coast of Jamaica, the silence is an eerie reminder that things are out of balance. One of the biggest signals of disturbance, and source of the silence, is an extreme lack of fish: look out into the water column above the reef and all you see is empty blue.