Marine Scientist Explores Ecosystem Balancing Act on Caribbean Coral Reefs
University of Maine marine scientist Bob Steneck participated in a study that indicates overfishing and climate change have collided to create a new dynamic on Caribbean coral reefs.
The study, led by University of Exeter geographer Chris Perry, was published in the journal Proceedings of the Royal Society B.
It highlights the delicate balance between bioerosion caused by feeding and excavating of bioeroders — sea urchins, sponges and parrotfish — with the natural production of carbonate that occurs on coral reefs.
On healthy coral reefs, bioerosion rates can be high, but more carbonate is typically produced than is lost to biological erosion, say the researchers.
But due to warming seas and ocean acidification, Steneck says rates of carbonate production have slowed on many Caribbean coral reefs and coral cover has declined dramatically since the early 1980s.
Still, he says, marked shifts to states of net coral reef erosion have not widely occurred because bioerosion rates experienced by corals have plummeted in recent years due to disease and overfishing of bioeroders that rasp away limestone.
The dynamics are opposite in Maine, Steneck says, because shell-crushing crabs (green, Jonah and rock crabs) have increased in recent decades.
“Marine ecosystems continue to surprise us both here in Maine and in the Caribbean because the cast of characters and the climate both keep changing,” he says.
The study, says Perry, shows the future health and growth potential of coral reefs is, in part, dependent on rates of coral carbonate production and the species that live in and on them and act to erode carbonate.
If historical levels of bioerosion were applied to today’s Caribbean reefs, researchers say there would be widespread destruction, threatening many of the benefits that reefs provide to society.
“If bioeroding species increase in number, and erosion rates increase relative to carbonate production, then this could spell trouble for many Caribbean coral reefs,” Perry says.
That trouble, says Steneck, would include if “bioeroded reefs lose their breakwater function to protect shorelines and they lose their habitat value for reef fish on which many people depend.”
Management efforts are directed at protecting one group of bioeroders — parrotfish. Although parrotfish erode reef substrate, researchers say an increase in the number of parrotfish will benefit reefs because the advantages they provide by removing fleshy macroalgal cover and promoting coral recruitment outweigh negative effects of substrate erosion.
“In essence, we need to work towards restoring the natural balance of ecological and geomorphic processes on coral reefs,” Perry says. “From a bioerosion perspective that may seem counterintuitive, but these species also play a critical role in maintaining reef health.”
In addition to the University of Exeter in England and the University of Maine, the University of Auckland in New Zealand, Memorial University in Canada, James Cook University in Australia and the University of Queensland in Australia took part in the collaborative study. A Leverhulme Trust International Research Network Grant funded the research.
To read the research paper titled “Changing dynamics of Caribbean reef carbonate budgets: emergence of reef bioeroders as critical controls on present and future reef growth potential” in Proceedings of the Royal Society B: rspb.royalsocietypublishing.org/content/281/1796/20142018.full.
To read the release published by University of Exeter, where Perry is a professor in physical geography and director of research for geography: exeter.ac.uk/news/featurednews/title_416424_en.html.
Contact: Beth Staples, 207.581.3777