"The continuing degradation of coral reefs may be soon beyond repair, if threats are not identified and rapidly controlled," said author Camilo Mora at Dalhousie University, Halifax. "In the Caribbean alone, these losses are endangering a large number of species, from corals to sharks, and jeopardizing over four billion dollars in services worth from fisheries, tourism and coastal protection."
Healthy corals near Puerto Rico (Photo courtesy CCRI)
"The future of coral reefs in the Caribbean and the services they provide to a growing human population depend on how soon countries in the region become seriously committed to regulating human threats," Mora said.
Published in the current issue of the "Proceedings of the Royal Society of London B," the study includes a comprehensive set of socioeconomic databases on human population density, coastal development, agricultural land use as well as environmental and ecological databases. The data cover temperature, hurricanes, productivity, coral diseases and richness of corals.
"It is well acknowledged that coral reefs are declining worldwide but the driving forces remain hotly debated," said Mora.
Through statistical analysis, his study shows that the number of people living near coral reefs is the main driver of the mortality of corals, loss of fish biomass and increases in macroalgae abundance.
Macroscopic algae, commonly referred to as macroalgae or seaweeds, are large plant like structures commonly found in coastal waters worldwide. An excess of macroalgae can decrease oxygen levels in the water when the algae die and decompose.
Camilo Mora (Photo courtesy Dalhousie University)
Mora's comparative analysis of different human impacts revealed that the area of cultivated land, with its discharges of agricultural chemicals to coral reefs, was the main driver of increases in macroalgae in the Caribbean.
He found that coastal development, which increases the amount of sewage and fishing pressure by facilitating the storage and export of fishing products, was mainly responsible for the mortality of corals and loss of fish biomass.
Coral mortality was accelerated even more by warmer temperatures, the study shows.
"The human expansion in coastal areas inevitably poses severe risks to the maintenance of complex ecosystems such as coral reefs," Mora said. "On one hand, coral reefs are maintained due to intricate ecological interactions among groups of organisms."
"Given the intensity of these interactions, the effects of a threat in any one group may escalate to the entire ecosystem," he said.
Mora advises that an ecosystem-based approach for conservation and an integrated control of multiple human stressors are needed if the health of Caribbean ecosystems is to be maintained.
Agricultural chemicals used on land, such as on these trees in the Dominican Republic, find their way to the sea. (Photo courtesy IICA)
The study also showed that the effective compliance with fishing regulations inside Marine Protected Areas has been successful in protecting fish populations.
But coral mortality and macroalgae abundance showed no response to the presence of Marine Protected Areas, MPAs, Mora found.
He says Marine Protected Areas in the Caribbean do not safeguard against threats such as land runoffs and ocean warming.
"Unfortunately, the degradation of the coral reef matrix inside MPAs may, in the long term, defeat their positive effect on fish populations," Mora said. "This further highlights the need for a holistic control of human stressors."
"Although coral reefs will experience benefits of controlling fishing, agricultural expansion, sewage or ocean warming, it is clear that underlying all these threats is the human population," Mora said.
"The expected increase of the world's human population from six billion today to nine billion for the year 2050 suggests that coral reefs are likely to witness a significant ecological crisis in the coming half century if effective conservation strategies, including policies on population planning, are not implemented soon."
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