Whilst aboard the MV Emperor Voyager in the Maldives, the Catlin Seaview Survey team assessed the condition of coral reefs across human impact gradients. There are many different threats to coral reefs ranging from global-scale overarching threats like climate change to localized impacts such as pollution and Crown-of-Thorns Seastars (COTS) outbreaks. Many of these threats may not cause outright mortality like a mass-bleaching event, but can greatly decrease the health of coral reefs. Corals are animals and, like people, have immune systems and fight off infections on a regular basis. Just like a population living in a city with low air quality might have higher incidences of asthma, corals living in degraded environments can also be more susceptible to infections.
Here in the Maldives, we have been seeing a lot of pink, pimpley bumps on smooth massive corals like Porites. From the literature, these could either be ‘coral zits’ caused by a trematode, worm-like parasite or swollen tissues surrounding tiny coral barnacles. These cases typically do not kill the coral, but can cause decreased growth or reproductive output. In combination with other threats such as warming oceans and decreased herbivory, it can contribute to the overall decline of the corals ecosystems.
Another interesting localized impact we saw was a COTS outbreak on Reethi Rah reef. COTS have lived and evolved on coral reefs for millions of years and are a part of a healthy reef ecosystem. However, COTS populations can boom for unknown reasons and turn destructive. There were over a hundred COTS on our Reethi Rah transect and it was dotted with gleaming-white coral skeletons that had been cleaned of their tissue and fuzzy yellow-green remains that had become overgrown with algae. Fortunately, this seemed to be a localized event with only one site where we encountered large numbers of COTS.
Here in the Maldives, the Catlin Seaview Survey shallow reef team has been working hard to gather data that will enable us to tease apart some of the questions concerning localized impacts on coral reefs. All in all, both the global and localized threats to coral reefs need to be addressed if we are to ensure our coral reefs stay healthy and survive for posterity.