Researchers scramble to assess short- and long-term impacts of Hurricane Irma on Florida corals

Written by Brooke Benson

Just moments before 9:00 am on September 10th, Hurricane Irma had nearly completed its traverse of the Caribbean. Standing between the storm and its imminent landfall in the United States was the third largest barrier reef system in the world—the Florida Keys Reef Tract. Researchers have long recognized the dampening effect that reef crests have on the momentum of a storm. Yet at this moment, the reefs of the Florida Keys are facing an onslaught of challenges not seen in their 10,000-year existence. Much remains to be elucidated about how these multiple stressors may limit future reef growth and reduce this dampening effect.

Fig. 1 Sand fills sponge cavities at Carysfort Reef, FL. Sediment smothering poses a threat to many sessile reef organisms.

In 2016, extensive bleaching and recurrent disease outbreaks battered the reefs. With little respite from the cacophony of stressors, many corals were expected to succumb to the hurricane’s wave action. Those that survived the initial storm surge were subject to the rapid influx of freshwater, nutrients, and sediment. Understanding community-level resilience of these reefs in response to Irma became a key priority for the scientific community, and coral researchers from across the globe rushed to assess the damage.


Fig. 2 Boston University graduate student Nicola Kriefall samples tissue from a symmetrical brain coral.

In late September, principal investigators Dr. Karl Castillo of the University of North Carolina and Dr. Sarah Davies of Boston University were awarded a Rapid Response Research grant from the National Science Foundation. This grant enabled them to examine 80 colonies of reef-building corals for changes invoked by Irma in survival, growth, and symbiotic relationships. The colonies—spanning 8 sites, two reef zones, and two species—were sampled for tissue to characterize differences in the microbial communities and the symbiont populations they host, which often shift in response to stress.

Fig 3. UNC-Chapel Hill graduate student JP Rippe samples a massive starlet coral exhibiting high levels of tissue mortality.

Several months out from Irma’s landfall, many people have returned to their homes in the Keys as the majority of cleanup efforts come to a close. The fate of the corals is less certain. In April, the joint Castillo-Davies team will return to Florida for a second round of samples. The April sampling period will help the researchers understand whether or not any shifts they saw in October are long-lasting. If they are, it isn’t inherently good or bad news for the reefs. Community shifts can help corals fare better in tougher conditions, as the less fit microbes and symbiont groups fall to background levels. What remains to be seen is whether or not these changes, if they are occurring, will be enough to ensure the persistence of survivors that are ready to face the next onslaught.

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