Climate change is leading to hurricanes that are increasing in intensity and duration, altering the flow of wind, waves, and currents in the ocean. As water flows shift, so does habitat connectivity for marine life.
Changes in connectivity brought on by hurricanes are likely to have lasting impacts, particularly in vulnerable ecosystems such as coral reefs. Although coral reefs only cover 0.2% of the ocean, they support approximately a quarter of marine life by providing shelter, food and breeding areas. Despite their importance, coral reef ecosystems have declined by 50% in live coral cover since the 1950s and remain under threat.
Dobbelaere, T., Dekens, A., Saint‐Amand, A., Alaerts, L., Holstein, D.M. and Hanert, E. 2024. Hurricanes enhance coral connectivity but also superspread coral diseases. Global Change Biology, 30(6): e17382.
Hurricanes have the potential to both negatively and positively impact coral reef ecosystems. On the plus side, hurricanes can enhance the dispersal of coral larvae through altered wave currents, promoting exchange of adaptive genes between otherwise isolated coral communities. In contrast, hurricanes might also accelerate the spread of diseases through coral reef ecosystems.
To disentangle the effects of hurricanes on coral reef ecosystems, a new study modeled the effects of Hurricane Irma on coral larval dispersal and the spread of a coral disease. Hurricane Irma, which struck Florida in September of 2017, was one of the most intense hurricanes to cross Florida’s Coral Reef. It also occurred during the spawning season of a few reef building coral species, and at a time when parts of the reef were infected with sonty coral tissue loss disease, which has decimated Florida reefs since 2014 and has high mortality.
Using a model of ocean waves and currents, coupled with models of larval movement for the coral species Montastrea cavernosa and disease agent movement, researchers compared coral larval dispersal and disease propagation during the hurricane to just after the hurricane.
The models showed that hurricanes can facilitate both coral dispersal and disease spread. Overall, the hurricane was associated with an 18% increase in coral larval dispersal distance, although this varied widely by location. The hurricane also impacted the proportion of larva that settled on a new reef, and the amount of new larva new reefs received. Both of these measures varied widely by location as well, meaning some reefs benefited from the hurricane much more than others.
Models also showed that the hurricane likely accelerated the spread of Stony Coral Tissue Loss disease: The impact of modeled disease spread by hurricane was equivalent to 25 days of disease spread under fair weather conditions. Relative to a simulation of fair weather conditions, modeled disease spread by the hurricane led to a 28.9% increase in the distance the disease was able to propagate and a 87% increase in the coral reef area that was infected. Overall, Hurricane Irma aided Stony Coral Tissue Loss disease in spreading further and infecting more reefs.
Climate change poses a major threat to coral reef ecosystems. Although hurricanes can be detrimental to reefs by causing structural damage and facilitating disease spread, hurricanes may also help coral reefs adapt to climate change by promoting coral larval dispersal. However, we should not rely only on hurricanes to enhance dispersal and gene exchange for corals. Given the ecological importance and the many threats faced by coral reefs, protecting marine dispersal corridors is an important strategy for conserving coral reefs and the biodiversity they support.
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