Hurricanes & Coral Reefs
Hello!
My name is Adeline and I’m a third-year PhD Student (already!) at the NOC. I have been a MOOC facilitator for over a year now, and I’m learning lots of weird and wonderful things thanks to all your very thoughtful questions. If you’re curious about what I am doing (four words: Hydrothermal vents and mineral resources).
I invite you to read my three other articles about me and about my work
How did I become involved in marine science
What do the Oceans mean to me?
On board the James Cook, heading to some black smokers in the middle of the Atlantic
I was away for the 1st week of the course and unfortunately haven’t had the opportunity to meet all of you yet. My absence was due to holidays in Guadeloupe (Lesser Antilles Islands) to dive in the beautiful coral reefs there … To make amend of my absence, I would like to write about a very recent subject: Hurricanes Maria and Irma and their impact on the coral reefs.
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The end of summer signals the peak of hurricane season (Aug-Sept) for those bordering the western side of the Atlantic Ocean. For those living in the Caribbean, this year’s storms where to be the worst since records began. Two category 5 hurricanes (Irma and Maria) followed each other and hit the Caribbean Islands. Irma was the first category 5 hurricane to ever strike the Leeward Islands at the end of August. Which left a devastating effect, the islands of Barbuda and Saint-Martin have been reported as having 95% of all properties destroyed. Maria, two weeks later turned from tropical storm to category 5 hurricane in less than 24 hours and struck the islands of Puerto Rico and Dominica mainly.
The diver guide I had in Guadeloupe told me stories about when Maria passed over the island. Fortunately the eye of the storm was further out to sea and the damages were lower than predicted. What a relief when I read the updates that the diving sites, mostly corals reefs on the West coast of the Basse-Terre territory (west side of the island) hadn’t been damaged. However the impact of the hurricane could be seen, there was a slightly higher than normal amount of rubbish on the beach, it’s not unusual to find large items of pollution in this area – bikes and large metal sheets often get washed up! The biggest visible impact on the beach was the beach itself, it had gone from being a sandy beach right down to the shore, which continued to a couple of meters water depth. It was now a beach which was rimed with large rocks and pebbles. Which had been deposited on the beach by a powerful wave action. We also noticed more plant debris in the water. There were a lot of boats which had been washed up on the shore, when the boats are loose they pose a lot of danger. If they collide with the reef, the reefs will be damaged and if the boats are damaged the fuel may leak. Which will have a serious impact on the water quality.
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Now that I have seen the damaged caused by hurricanes with my own eyes, I wanted to search more about the real impact of hurricanes on coral reefs.
Hurricanes churn the water so much that the ferocity of the wave action can break the corals apart. The coral branches get snapped off and colonies are overturned. Imagine the reef suddenly being subjected to a washing machine cycle with great bit boulders and tree trunks swirling around. The biggest threat is that you get huge amount of pollutants and nutrients dumped onto the reef that upset the delicate balance between the corals (polyps) and the symbiotic algae living in them. Another aspect is the input of sediments over the coral reef. A thin layer depositing on the reef decreasing the precious visibility, i.e. the amount of sunlight penetrating the water column that the algae need for sustenance and growth. Therefore in both situations the algae leave the corals, and without the symbiosis, the polyps die and bleach.
But sometimes though, the influence can be also beneficial. This season, the surface temperature was higher than the rest of the year and the corals were under a thermal stress. To alleviate this stress, cyclones and hurricanes reduce the temperature by the transfer of latent heat, and inducing local deep (colder) water upwelling and shading at the ocean surface with primary productivity. It also scours dead organisms from the reef and enhances the bio-diversity by stimulating new colonies.
In the Caribbean, many dive centres and scientists have come to the same conclusions for this year’s season of hurricanes. They were expecting to see more damage, but in fact most of the reefs look spectacular again and although they did accumulate little garbage, thousands of passionate divers helped to clean it up. However, it seems that reef’s storm buffer capability (for the shorelines) have weakened in the recent years. This weakness comes from the increase of bleaching events and the warming waters. Resulting in a degraded coral reef with a relatively smooth surface, which reduces its natural protection against a strong storm surge. A healthy reef is more resilient and capable to recover after a hurricane.
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![](https://i1.wp.com/moocs.southampton.ac.uk/oceans/wp-content/uploads/sites/5/2017/11/AG-hurricane-Photo2.jpg?resize=640%2C360)
Article based on four newspaper posts:
- https://www.washingtonpost.com/news/energy-environment/wp/2017/09/12/how-floridas-damaged-coral-reef-makes-it-more-vulnerable-to-storms-like-irma/?utm_term=.33bcebad44d2
- https://www.coris.noaa.gov/activities/caribbean_rpt/SCRBH2005_03.pdf
- https://www.livescience.com/60452-how-caribbean-will-recover-from-hurricane-irma.html
- https://www.sanpedrosun.com/old/99-343.html
Further reading