Sea-urchin for the answers

Completely fascinating and unlike life on land, the underwater world is an oasis waiting to be discovered. Throughout our time in the Bocas del Toro Archipelago we had the incredible opportunity to figuratively and literally immerse ourselves in an ecosystem many of us had previously not known much about. During our incredible three days there, we snorkeled around reefs, mangroves and seagrass, discovered million-year-old fossils and admired the world around us.

To get a better understanding of the ecosystem dynamics, we completed two short projects, one on predation intensity in three costal habitats and my group’s project on intra- and interspecies differences in thermos-tolerance limits of sea urchins. We subjected six different species of urchins to five different temperatures (30, 32, 34, 35, and 36 degrees) to see what kind of effect an increasing temperature will have on the different species and on same species from different locations and different sizes.


In the Caribbean Sea, the yearly temperature fluctuations are small and water is fairly warm, so most organisms live close to their thermal maximum. In addition, different habitat types also have an effect on the temperature species experience. The idea behind the project was to get a better understanding of how tropical sea urchins will respond to warmer oceans with global temperature changes. In order to understand how the biodiversity of oceans would change with climate change, it is important to evaluate the ability of different species to cope with increased temperatures.

I think it’s safe to say that diving for the urchins was the most enjoyable part of the whole experience. For several hours we snorkelled around two locations, collecting urchins of various sizes off the bottom of the ocean floor. The small urchins like the Echinometra lucunter and Echinometra viridis were easily collected by hand, while the larger, pricklier Diadema antillarum had to be picked up with tweezers to avoid having your fingers pierced by their long, sharp spines. Although long and laborious, the experiments were very fun (minus the sand flies) and the results a little surprising. Most species seemed to adapt very well to the increasing temperatures, with very low levels of death, even at the highest temperatures. The most important determinants of survival seemed to be location and species.

However, I think the most defining moment of our trip was on our dive with Aaron O’dea, when we went to see what he had referred to as ‘one of the best reefs in Bocas’. We arrived and jumped in the water, full of excitement, only to find a barren ocean floor full of dead, bleached corals. The look on Aaron’s face said it all. A reef that was beaming with life only 6 months ago, was now completely devastated by death.

Healthy corals have symbiotic algae living on their surface, which undergo photosynthesis and supply the corals with the nutrients it needs to survive. These algae are what gives the corals their vibrant colours. With increasing water temperature and pH, these algae get stripped off the coral, leaving it with a bleached appearance. Although corals do not necessarily die without their algae, they are under a lot of stress which can cause mortality. Coral systems support a very large diversity of animal life, from multitudes of fish to mollusks, crustaceans and echinoderms. As corals die off, these organisms must either move to a new location or they too risk death. It was very sad to see the lack of colourful fish, especially in contrast with some of the other reefs we got to see.


Healthy coral full of fish

I’d be lying if I didn’t acknowledge that I definitely re-considered my choice of study system, but I think I will stick to life on land for now. Although I do miss the warm waters and beautiful corals of the Caribbean, I am definitely happy to be far away from all the sandflies and mosquitoes to whom I unwillingly donated so much of my blood.


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