Thursday, April 20, 2017

Coral Reef Project in Bocas del Toro

The trip from La Selva to Bocas del Toro is was long and culminated in a bumpy yet fun boat ride to Colón Island where the ITEC field station we stayed at is located. Upon arrival, it looked like we were about to run into the island, which is surrounded for the most part by mangrove forests, when all of a sudden the boat slowed down and entered a small hole in the mangroves that led us to the stations’ dock. After getting off the boat we lugged our packs through pastureland up to the station. The rustic wood station had a deck outside the rooms with a hammock and a view that included birds and a sliver of the ocean. Not a bad place to learn about biology for a week. 
Our focus for this trip was coral reef ecology which is something that I was personally excited about. We spent the first day taking our swim test and getting used to our snorkeling gear. I had previously taken a course on invertebrate animal diversity and it was exciting to recognize some of the organisms I had learned about in that class while we snorkeled. From tube worms that shrunk into their tube when you went near them to brittle stars and a variety of sponges and corals the reef was a new and complex ecosystem to observe. The following two days we completed a faculty lead project that looked at the abundance of macroalgae in comparison to where the abundance and size of sea urchins were. In addition we looked at rugosity which is a measurement of how complex the reef is. Rugosity is measured by placing a metal chain of known length along the ocean floor, next to a measuring tape, and recording how far it goes. If the area the chain is placed on has lots of corals and other structures or organisms that bend the chain then the length measured will be shorter than the actual chain length. If the ground is completely flat it would measure to be about the same length as the chain. In our project we laid out a transect using a 30 meter measuring tape and measured the rugosity, the number of small sea urchins, and the number of large sea urchins for a meter by meter square every other meter along the transect. Alain Duran, our guest faculty, then took pictures at each plot along our transects that we later looked at on the computer to estimate total cover of coral, sea grass, macroalgae, and sponges. It was a very different experience from doing terrestrial fieldwork but it was a fun challenge to work underwater. One of the most difficult parts was avoiding the sea urchins and fire corals that could sting you if you touched them. The idea behind this project is that macroalgae which can be thought of as marine plants are the main competitors for space and sunlight with corals. Corals don’t photosynthesize themselves but have a symbiotic relationship with zooxanthellae (single celled dinoflagellates) which photosynthesis and provide about 95% of the energy corals need to survive. Changes in environmental conditions mostly caused by climate change have caused the zooxanthellae to leave, ultimately killing the coral. Looking at the competitors of corals (macroalgae) is helpful for understanding the best methods for coral reef conservation. We looked at sea urchin abundance because they feed on macroalgae and so we hypothesized that areas with more sea urchins would have less macroalgae. Fish also feed on macroalgae although we did not test for fish abundance.  This ended up playing an important role in what we found from our data. We found that areas with a higher abundance of small sea urchins had less macroalgae whereas areas with a higher abundance of large sea urchins had lower amounts of macroalgae. In addition, plots with higher rugosity, or a more complex reef, had lower abundances of macroalgae. We believe that this is probably due to more herbivorous fish being present in higher rugosity areas because they have more crevices and corals that provide protection from predators. With the differences in sea urchin size we discussed how small sea urchins are more abundant compared to the large sea urchins and can therefore consume more macroalgae. From my personal observation it seemed like areas with higher rugosity and more corals also had more small sea urchins whereas flatter regions had more large sea urchins. Through this project I learned how difficult ecological research is underwater but I was also excited by the complexity and fascinating organisms we found around the reefs. On our last day we snorkeled for fun and found groups of squid that had beautiful fluorescent dots of color along with a couple of large stingrays. Needless to say I think snorkeling and marine biology may be in my future after this week.

Hayley Stutzman
Macalester College

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