How Tropical Corals Are Succumbing To Sugars
Chris - Thank you for joining us. Tell us about your work and what you're looking at in relation to coral.
David - I work at the Smithsonian Tropical Research Institute in Panama and I've been studying how tropical reefs have been declining. Throughout the world, reefs are declining at a scary rate. It's estimated that 20% of the world's reefs have already been effectively destroyed. A provisional 50% are under long term threat of collapse and the situation is even worse in the Caribbean. I've been looking at how all the different types of pollution we throw into the ocean change the relationship between the corals and their symbionts. Besides the algal symbionts, I'm also looking at bacteria that live in the coral tissue and how the pollutants affect these bacteria and potentially lead to diseases and mortality in the coral.
Chris - So are those bacteria bad for the coral?
David - Actually just like the algae, when they live in the corals at controlled levels they're actually quite good for coral. Corals are dependent on them. These bacteria could protect the corals from harmful bacteria, they can provide them with vitamins and other limited nutrients that they wouldn't be able to obtain otherwise. So in normal conditions, these bacteria are actually quite important for the health of the corals.
Chris - So when you chuck in a nice healthy dose of pollution, what's the impact on the coral then?
David - The main components of pollution that people monitor on reefs are nitrates and phosphates. These don't affect the bacteria on the corals directly. But what is affecting the bacteria are simple sugars. There are high levels of simple sugars associated with sewage and also with run-off from agriculture. These sugars are the perfect food for these bacteria. The bacteria can then grow so fast that they overwhelm the coral causing disease and mortality.
Chris - There must be knock-on effects. Jason was talking about how his reefs were home to a huge variety of fish. That must also be true in the shallows.
David - Yes that's very true. The coral reefs in the tropics are a nursery for many of the commercial fish species that we eat and they are the home of many invertebrates that we eat such as lobster and conch. When those corals start to die you lose the biodiversity and that includes these fish and animals that we eat.
Chris - The key question that will be going through a lot of people's minds now must be is it too late, or can we still remedy this?
David - I'm more on the optimistic side because I think that there are a lot of things we can do. There are sewage treatments that could definitely be improved. In the Caribbean less than 10% of the sewage is treated before being released onto the reefs, so sewage treatment is a big thing we can do. Marine reserves are being set up that can help bring back the fish and reducing fishing pressures. It's been shown that marine reserves can have really big impacts in improving the health of reefs. We can also try to reduce carbon dioxide emissions by using fuel efficient cars and try to drive less. With carbon dioxide emissions you get global warming, and with global warming as the oceans heat up it can disrupt a lot of these symbiotic relationships leading to the bleaching effects that we've been seeing all around the world.