Posted on June 26, 2012
To pick up where I left off, after the Great Vermetid Surveys of 2012 (see previous posts), for the past few weeks I have been focusing my efforts on deploying several field experiments out here on the island of Moorea in French Polynesia. These experiments are part of my dissertation research, and this summer in particular, I am looking at the effects of coral reef habitat loss and isolation as well as nutrient pollution on herbivory. Herbivory is essential on coral reefs, because it helps to control the abundance algae, which can outcompete coral and take over reefs, with drastic ecological consequences (simply put, from teeming coral reefs to slime).
One of our first focuses is to look at the relationship between distance from the reef and herbivory. The assumption is that herbivorous fish are scared to travel across open sand flat to find food, because they don’t want to get gobbled up by a predator or speared by a fisherman. This ‘fear effect’ could have very important implications for reef habitat loss and fragmentation that result from natural and human-driven processes. So, for one of our experiments, we have created an “algae hors d’oeuvre platter” (i.e., a cinder block with a variety of algae tied to it), which we place at 5 different distances from the reef and video tape what happens. This approach allows us not only to get a sense of how herbivory may change with distance but also tells us who is doing the eating—what species, what size, how much eating etc. After a few weeks of running these trials, we are starting to get some interesting results and also some surprises. The best so far happened two days ago, when we returned to our cameras after leaving them for 4 hours. This time, we noticed that one of the far cameras (30 meters from the reef) was now facing the sky instead of the algae hors d’oeuvre platter. This was upsetting, because it meant that we did not get the full 4 hour observation period for that unit, but we were happy that the camera was still there. We assumed that the current, which had picked up that afternoon, could have been the culprit, but fortunately the camera was still recording when we arrived, so we knew that whatever caused the camera to move was caught on video. So, we took the camera back to the lab to analyze the video. This is what we saw (turn up your volume if you can when you watch this for the full effect):
SPOILER ALERT BELOW.
The hungry animal featured in the video is called a triggerfish, a Yellowmargin triggerfish to be exact, and it primarily eats sea urchins and shellfish (hence the impressive/grotesque teeth). As evidenced by the video, these guys can be quite aggressive and bitey—lucky for me, the GoPro camera housing stood up to the challenge, except for a bit of chipped plastic. On a side note, a close but much, much larger relative of the Yellowmargin triggerfish, the aptly named Titan triggerfish (measuring nearly 3 ft long), attacked me during a dive in January.
Fortunately, the biting was restricted to my fins, but the encounter was a stressful one to say the least.
The next day (yesterday), we deployed the video cameras again, only this time to capture a different experiment. In this experiment, we are looking at the effects of sedimentation and vermetid snails on coral growth. Sedimentation is a big problem for coral reefs around the world, because sediment can smother corals, and increased coastal development tends to lead to increased runoff and sedimentation of nearshore marine ecosystems (like coral reefs, seagrass meadows, and kelp forests). We also know that vermetid snails that use mucus nets to feed can also be quite detrimental to corals (see previous posts for more info). So, we wanted to see how these two stressors together may affect corals—for example, maybe sediment is actually pulled off of the coral by the vermetid mucus net, or, alternatively, maybe the mucus net, being sticky as it is, allows sediment to better adhere to the coral surface, causing more damage. These are the hypotheses we are testing, and to help us understand what exactly is going on, we have been shooting photos of each coral at 10-second intervals throughout the day. Yesterday was one of these days, so we again left our GoPro cameras out in the field for several hours. Upon our return to retrieve the cameras just before dusk, my assistant Julie noticed that one of the cameras was missing from the 5 lb dive weight to which we’d had it cable tied. The cable tie was mangled. She also noticed a very large octopus atop the reef next to where the camera was. When she called me over, I approached the octopus. Yes…he stole our GoPro:
Fortunately, we got the camera back in one piece, and even more fortunately, the camera was snapping photos throughout the ordeal! So we got some pretty interesting shots:
The first is the standard, (now considered boring) shot of our experiment coral:
But then, our Hero is kidnapped!
And plunged into darkness…
And finally rescued. Woohoo!
What a wild couple of days it has been. I can’t wait to see what else these cameras capture over the next two months…
Thanks for reading/watching! More soon.
Posted on June 13, 2012
Our third and final island to survey for vermetids (snails that are linked to coral die off in French Polynesia—read more in my previous post) was our home island: Moorea (pictured above). We surveyed each shoreline—north, east and west, over three days. To give you a better idea of what our surveys are like, I’ve uploaded a video clip of one of our dives off the west coast (This time we were diving in Haapiti, another famous surf spot, as evidenced by the surge in the video. BUT, It did not compare to the big wave in my previous post…) :
As seen in the video, we place quadrats (square metal frames) on top of the reef at different locations and count up the number and species of vermetids as well as branching corals that fall within the square. By doing this many, many times in many locations (and across islands), we are able to get a better sense of vermetid distribution patterns and how these patterns may be linked to potential drivers, such as human development.
Fortunately, the weather cooperated nicely throughout all our inter-island surveys, aside from a little rain. But who cares about rain when you’re submerged all day anyway?
In the end, we completed all of the work we set out to accomplish and got to experience some epic scenery while island hopping. The video below features our triumphant boat ride home along the north shore of Moorea after completing our final site survey–kite surfing, trans-Pacific yachts and a lush-green mountainous backdrop are all regular sights on the way to/from work out here:
The inter-island vermetid survey is now complete for this summer. We had a great time and a great team, and I look forward to what these data can tell us about vermetids and how we might better understand their role on the reef. Now, and for the rest of the summer, I will be conducting experiments for my dissertation (read more about the topic here). Stay tuned for more South Pacific island adventures for science!