Coral reefs suffer when the lands above them are disturbed, finds new research by scientists from Hawaii to Australia.
Clearcut logging, farming and development lead to erosion and runoff that kills corals, making it just as important to manage the land above reefs as it is to protect them from overfishing, the scientists confirmed.
Over six years, the researchers studied the connection between watersheds and adjacent coral reefs on three Micronesian islands – Palau, Guam and Pohnpei. The “Watersheds and Coral Reefs” study published in the current issue of “BioScience” magazine describes how multiple threats to reefs combine with lethal results.
“It is clear that sustaining our coral reefs depends on how well we manage human impacts from the mountains to the sea,” said Willy Kostka, a co-author of the study and director of the Micronesia Conservation Trust.
“The centuries-old way of managing reefs in Pacific islands recognizes that it is not the coral reefs and watersheds that can be managed, but rather the human activities affecting these ecosystems,” said Kostka. “If we provide care and respect to our reefs, they will provide for us.”
Sedimentation and runoff from activities on land are among the biggest threats to nearby reefs and are interfering with other marine conservation efforts, such as no fishing zones.
River runoff sends mud into the ocean, where it is compacted around reefs. Algae can outgrow corals to form a mat that traps the mud and prevents coral recruitment. When overfishing occurs, removal of plant-eating fish means algae growth can no longer be controlled, and the reefs are suffocated.
Actions taken by the three Pacific island communities to restore reef health focused on managing entire ecosystems from hilltop to sea floor.
Communities relocated crops from upland rainforests to lowland areas, restored vegetation in watershed areas to control erosion, halted the clearing of mangroves, and established a continuous protected area from the top of the watershed to the reef.
One community is also considering a temporary ban on catches of plant-eating fish.
Fouha Bay, the study site in Guam, is surrounded by steep hills that deer and pig hunters often burn to clear vegetation, which accelerates erosion rates. The bay has high levels of sedimentation that are suffocating the reefs.
Data taken along the southern side of the bay in 1978 and again in 2003 showed a clear loss of coral species and coral cover over time that appears to be due to watershed discharges.
The study’s conclusion that coral reefs and other coastal marine ecosystems extend into adjacent watersheds leads the authors to the recommendation that they should be managed as an integrated unit.
“Marine protected areas often will miss their targets of resource protection unless terrestrial protected areas are established and enforced,” they write.
Traditional ways of managing human interactions with the reef are still effective in modern times, says the study, citing Palau’s Marine Protection Act of 1994 as an example of new legislation for no-take areas based on traditional knowledge of spawning sites.