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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