The long-term dynamics and drivers of coral and algal cover on a coral reef of the tropical eastern Pacific

Jun 26 2019 03:00 PM - Jun 26 2019 04:00 PM

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Abstract: Coral reefs are highly dynamic ecosystems often affected by diverse natural disturbances. However, dramatic declines in coral cover during recent decades raise the question of whether such declines are due to increasing anthropogenic impacts. The dynamics of coral and algal cover have been studied since 1998 at two depths in two sites of La Azufrada reef, a coral reef free of local human impacts, located at Gorgona Island, in the Colombian Pacific Ocean. While overall coral and algal cover have fluctuated significantly exhibiting opposite patterns, temporal variation has been remarkably different between depths with shallow areas exhibiting major declines in coral cover, but also significant recovery. In contrast, coral cover in deep areas have declined only slightly. Even though El Niño warming events caused a dramatic decline in 1982-83, the global bleaching event of 1997-98 caused only minor mortality, and more recent events have not caused any coral bleaching. However, prolonged subaerial exposure of corals during extreme low tides appears to drive a cycle of coral disturbance and recovery. Coral growth makes the reef flat prone to subaerial exposure, after which corals bleach, die and are colonized by filamentous turf and fleshy algae. Sea urchins and herbivorous fishes increase their abundance in response to increased algal cover and control algal growth, leaving the substrate covered by crustose coralline algae and making it suitable for settlement by sexually-produced coral larvae. Fragmentation by both physical and biological agents (such as corallivores) enhances coral recruitment and the reef enters a coral recovery phase. Although this reef seems to be resilient to subaerial exposure because it is protected from anthropogenic perturbations, increasing threats from global climate change may still compromise its future resilience.