Slow-moving shallows put the heat on Bocas Coral

From STRI.org

Snorkel-perfect coral reefs in the calm, mangrove-fringed waters of the Bocas Del Toro Archipelago are expected to be among the hardest hit by warmer temperatures that lead to coral bleaching and mortality, a new study finds. These shallows in Panama’s Caribbean are characterized by low water flow, allowing water to reach precariously high sea surface temperature (SST) when compared to areas with greater water movement.

Angang Li and Matthew Reidenbach of the University of Virginia tapped into a wealth of long-term monitoring data collected by STRI scientists around the Bocas Del Toro Research Station, including coral bleaching records. Their models were published this May in the journal Coral Reefs.

“By 2084, almost all coral reefs are susceptible to bleaching-induced mortality, except for a region of relatively lower thermal stress along the outer boundary of the archipelago,” they write. “By 2084, only corals exposed to open ocean currents are predicted to survive.”

corals

 

There are some caveats. The key to heat-induced coral bleaching is not a single blast of hot water, rather long-term exposure to above-threshold temperatures. This is measured in degree heating weeks (DHW). By the end of the study period DHW >8 °C-weeks were modeled for the bay. The National Oceanic and Atmospheric Administration (NOAA) predicts widespread bleaching and significant mortality under these conditions. By comparison, DHW values during a 2010 Bocas bleaching event ranged between 2.3 °C-weeks and 9.5 °C-weeks.

Some coral species may adapt to higher temperatures. The study’s models predict that areas flushed by cooler water will have a higher chance at surviving well into the future.

Li and Reidenbach studied modern water-flow patterns, simulated heating scenarios for the 2020s, 2050s and 2080s, and quantified local thermal stress on coral reefs. While previous studies have looked at SST impact on corals at a large scale, the researchers focused on a much smaller spatial scale, which is less common. The fine scale of their work better lends itself to the creation of mitigation strategies for marine protected areas in Bocas.

“Our findings are also likely applicable to many coral reef regions worldwide, and in particular reefs that are found in shallow and partially enclosed coastal regions with long water retention times,” they conclude.

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