Hurricane Impacts On Coral Reefs: Executioner, Savior, Or None Of The Above?

With Flossie bearing down on Hawaii, I've been asked by more than a few people today what impacts, if any, hurricanes can have on coral reefs. Since coral reefs are the bedrock of Hawaii's tourism, the fear that severe hurricanes can have a catastrophic effect on the state's economy is very real. So what do we know?

Much of what we know about hurricane impacts to reefs comes from studies in the Caribbean where severe storms have been slamming well monitored reef communities for decades. Studies show that the base coral frame is fairly resistant and immovable. But strong storm surge and wave energy can certainly damage or destroy branching corals or even smaller boulder coral colonies. Reef life such as soft corals, sponges, and any other encrusting organisms that live attached to the base coral frame can break away and be pulverized in the churning wave surge. Some of the fragmented life (sponges and corals) might survive, reattach, and continue growing in a new location if it is not buried or transported to a location where living conditions are inhospitable.

Another threat to reefs from hurricanes can be smothering from sediment suspended in wave surge or, more commonly, muddy runoff from land as a result of torrential storm downpour. Along Australia's Great Barrier Reef, sediment laden flood waters can completely block sunlight to some shallow reefs allowing only 1% of light to reach corals at depths of 10 m. Large scale flooding can carry land-based pollutants such as insecticides, fertilizers, and herbicides out to the reef. Fresh water can kill corals at shallow depths where mixing is low.

Despite these seemingly formidable assaults from hurricanes, coral reef ecosystems have recovered from severe storms for millions of years. Coral reefs are characterized as disturbance communities. While subject to frequent changes, disturbance communities tend to promote biodiversity by either selecting for species that can capitalize on rapid fluctuations or by promoting competition (and speciation) through specialization to exploit microhabitats and niches.

While hurricanes can be catastrophic for reefs, recent studies also show that hurricanes may actually have beneficial outcomes in some scenarios. Evidence is building that the cooling effect hurricanes have on sea temperatures may actually help corals recover from the bleaching caused by warming oceans. It is a controversial debate at the moment, but if the frequency of hurricanes increases with global warming, then the negative effects that are expected for coral bleaching [due to ocean warming] could be mitigated by the cooling that the hurricanes bring about.

But keep in mind that such a hypothesis only considers relief from reef threats caused by elevated sea surface temperatures. Hurricanes offer no quick fix to threats coming from unsustainable uses of coral reefs (coastal development, commercial or destructive fishing, coral mining, etc.) So while a storm-prone world might help mix (and cool) a warming sea, a slew of other stressors are waiting in the wings to further punish already over-stressed and sensitive coral reef systems.