(featured image: credits to Tara Simmons)
It’s incredible how much we’ve learned about reefs in just a couple of days.
On to the next location of Dartmouth’s Biology foreign study program. Coral reefs were a system that I was fairly unfamiliar with when I arrived to Cayman, as I didn’t have much background in reef ecology. But through the handful of lectures we’ve had so far, the reading I’ve done in field guides, past Dartmouth foreign study books, and online, and through my personal observations, I feel I have a much better understanding of coral reefs and associated ecosystems.
Each student conducted 3 group research projects while on Little Cayman– the first faculty-initiated, and the other two requiring independent project design. The first, for which all 11 students collaborated together, was on studying the population dynamics of the queen conch. It’s endangered throughout the Caribbean, namely because of overharvest as a delicacy. Though the population around Little Cayman, however, is stable enough so that there is a few sustainable harvest zones around the island. Our study investigated the differences in conch populations in a protected zone versus a harvest zone. How many conch are found in each area? Are conch individuals older in one zone than another, or do they grow larger? As it turns out, conch were more abundant– and older– in the protected zone than in the harvest zone. This is what we expected, but not what we hoped for: if conch were the same age in each zone, it may suggest that conch were growing to an old age in the harvest zone, rather than every conch eventually meeting its doom there.
The process of designing/executing projects was pretty much the same as it was in our six weeks in Costa Rica — each students thinks up research questions, we all vote on which ones we like the most, and then spend 2-3 days collecting data before a presentation and writing up a paper. But a lot of aspects of reef ecology are a little more difficult than terrestrial ecology. An obvious obstacle is that one is attempting to collect data while in the water…which means that remaining stationary– and breathing– do not come easily. Furthermore, many organisms are toxic, protected, or otherwise off-limits, which of course makes measuring, manipulating, or even finding study organisms pretty difficult. Finally, you can’t quite bring a field notebook, or even talk to your colleagues that much. We would bring clipboards with waterproof pencils to record data, but even with these tools one frequently ends up with a game of charades to communicate to your fieldmates.
The second project I worked on was another that had been inspired by one of my personal observations in the field: I noted that flamingo tongues, a snail that feeds on the polyps of soft corals, were found in clusters on certain coral colonies, but other colonies of the same coral species held no snails at all. Was this some type of aggregation? For a particular reason?
With a brief literature review, I found that these snails were likely toxic, and sequestered their toxins from the soft coral hosts they fed upon. With this in mind, I predicted the following:
Hypothesis 1: Flamingo Tongues would be more likely found on more toxic corals.
Hypothesis 2: Flamingo Tongues would be more likely found on larger corals.
Hypothesis 3: Flamingo Tongues on more toxic corals would be larger than those found on less toxic corals.
Jalen, Aldo, Robbie, and I were the ones involved. We snorkeled at Mary’s Bay on the north side of Little Cayman to collect data, counting how many flamingo tongues we found on various coral species. But we didn’t settle for just an observational study in the field when an experiment was possible as well. So we filed for a permit with the DOE (Department of Environment), and collected flamingo tongues, as well as pieces of live coral that had broken off the reef. In this experiment, we set up aquaria, each with two species of coral and flowing seawater, and let loose a single snail per tank to determine if it had a preference. We also set up tanks in which a first snail would be given two samples from the same coral colony, and once the snail chose one, we’d take it out and put another snail in. Now, the two choices of coral would be identical, except one piece would have a trail of snail mucus leading to it. Would the second snail follow these breadcrumbs to the same coral?
Unfortunately, the experimentation was inconclusive: snails did not prefer any species of coral other others, and there was no obvious “follow-the-leader” effect. With our limited time and resources, conditions were tough to perform a refined experiment. However, our observational study had some interesting results: we found significantly more snails on the black sea rod, which had the highest concentrations of type of toxins known to be sequestered by the snail of any of the corals identified as snail hosts. Additionally, snails on this coral species were on average larger than snails on any other coral. And the most interesting part: flamingo tongues aggregated on this coral, but not on any other coral. A reason for this aggregation? Well, the bright colors on the snail’s mantle may be aposematic– the term for natural warning signals, typically to ward off predators from toxins or a painful sting. According to previous studies, aposematic signals are stronger in groups; the more bright colors and patterns there are, the more obvious the signal is. So, the snails may benefit from feeding in groups. Pretty sweet, right?
The last project I worked on was a study of echinoderms: a class of invertebrates that includes brittle stars, urchins, and other marine creatures. Robbie, Tara and I looked at the distribution of echinoderms under rocks of various size, and on different substrates. It was a project that was not too dissimilar from several of my past projects (namely flamingo tongues and harvestmen), but the field work was pretty fun. Beth came to help us out, so we had some fun collecting data together.If you’re ever out snorkeling or diving, flip some rocks to see what’s underneath. You’ll probably find some fascinating critters hiding there.
It is surreal talking about our last projects on tropical adventures this term. I really feel the end is nearly upon us. Every day is just a little closer to our last here in paradise. I really hope that I’m doing all I can to make this the best it can be. So I’ll make this last week here just about the best one.