As part of a CI-organized Rapid Assessment Program (RAP) off the northeastern coast of Madagascar, an international team of marine scientists is spending three weeks exploring ecosystems, documenting species – and reporting back to us about what they’ve found. Read all of the team’s posts from the field here.
Today was our second day surveying Loky Bay. We arrived after an overnight voyage from Ambodivahibe, steaming against a strong wind. The bay was refreshingly calm compared to the rough open seas, and our captain – warily scanning his digital charts – crept slowly into a sandy anchorage, just 200 meters from one of our survey sites.
Our days start early – or at least it feels early to my night owl self, because I keep staying up late looking over Keith’s photos from the day before. Either way, we’re up before seven, chatting over coffee and homemade pineapple preserves before preparing our equipment for our day’s work. By eight, we’re geared up and head off in the small boats to survey. We’ve been managing two dives each morning, spending the afternoons hiding from the beating, tropical sun while we process our samples and data.
So far on this expedition, I’ve spent about ten hours underwater, counted and sized over one thousand corals, and only barely begun to understand and appreciate this little-studied region. In the team’s paperwork, I’m officially referred to as the ‘coral resilience specialist’, which means I spend a lot of time thinking about what makes corals and the ecosystems they support capable of dealing with the inevitable perturbations that climate change and human exploitation are delivering.
We’ve just seen an example of one of these disturbances. Weeks before this expedition, this region experienced strong and prolonged “high sea surface temperature anomalies,” which roughly translates to hot water. More accurately, the event took water temperatures at least one degree Celsius above the temperatures usually seen in the hottest month of the year, and held them that high for about six weeks. These high temperatures receded just a week before we began our trip.
For humans, getting through hot days is a matter of cold beverages and some air conditioning, or at least finding a nice shady spot to curl up for a nap. For corals, even small heat waves can trigger the breakdown of the fundamental symbiosis that lies at the foundation of coral reefs – the connections between the coral animal and the single-celled algae that live inside them. This phenomenon, called coral bleaching, can be a minor event that passes during hot periods, like a seasonal flu does in human populations. Or, when heat stresses are severe and other factors line up to accentuate the stress, bleaching can lead to major die-offs of whole reef systems, more akin to a global flu pandemic. For example, reefs are still trying (and mostly failing) to recover from a single global bleaching event that affected a huge proportion the world’s reefs over ten years ago.
So when temperatures rise, coral biologists take it seriously. From here, so far the news is mostly good. We’ve seen some bleaching, especially in the very shallow reef flats, where the heat and light are most intense. But so far, it’s not widespread, it’s mostly restricted to the more sensitive species, and while we’ve seen bleached corals, signs of bleaching-induced death are very few. For those colonies damaged by this bleaching, most will likely recover, so long as another perturbation doesn’t hit them first. It’s early yet to make the call, but these reefs seem to have managed the temperature challenge without falling too far behind.
Tom Oliver is a specialist on coral genetics. He recently completed his PhD at Stanford University and is currently conducting research in Madagascar.