One of the transect photos used to identify the percent cover of different bottom types.
During the 1980’s-90’s there was a dramatic increase of macroalgal cover on Caribbean reefs, specifically Discovery Bay, Jamaica. This shift from coral to algal cover has been attributed to top-down control due to the reduction of herbivory by both the continuous overfishing of grazers (Acanthurids and Scarids) and the mass die off of Diadema antillarum in 1983-84. Since the return of D. antillarum in the late 1990s, a trend of reduced macroalgae began. Our study looks at the current phase state of the Discovery Bay reefs by measuring percent cover of coral, macroalgae, turf algae and coralline algae. Three sites were selected in Discovery Bay where 20 meter transects were run multiple times per site at depths of both 9 m and 18 m to assess benthic cover and potential variation with depth. Video transects were taken along each transect as well as counts of D. antillarum within one meter of the transect line to determine the presence or absence of herbivores in each transect. Data analysis supports a continued dominance of an algal phase state. Percent coral cover was 3-6 % compared to algal cover of 46.6 – 57.7 %. The reduced presence of D. antillarum in the study sites below 9 m may support the idea that decreased herbivory results in higher algal percent coverage and therefore lower coral coverage.
Tripneustes ventricosus covering itself in natural and bendable materials.
Tripneustes ventricosus and Lytechinus variegatus have been known to cover themselves for a few reasons; avoidance of predation and protection from UV rays. It is thought that there may be a correlation between the use of materials that conform to the urchins’ body and its preferences for that material. For this paper, it was hypothesized that urchins are more likely to use a bendable natural material over materials that are not able to conform to their body shape. Samples of both these species were collected from two sites, mangroves and turtle grass, in Discovery Bay. Of these samples two were large for both species and two were smaller in size for each species collected. A total of 16 individuals were used to conduct this experiment. There were seven different conditions they were tested under; the use of natural bendable material, natural unbendable, unnatural bendable, unnatural unbendable, unnatural and natural bendable, unnatural and natural unbendable, and bendable and unbendable materials. Although the majority of the data was not statistically significant, there were some noted correlations. On average the larger sized urchins, of both species, used more material to cover themselves than the smaller sized urchins. T. ventricosus covered itself more than L. variegates, with a statistically significant difference when using unnatural, bendable materials (p=0.0095). The urchins collected from the mangroves used more materials for coverage than those from the turtle grass; statistically significant difference when using natural, bendable materials (p=0.008176). Although there is no statistical significance natural, bendable materials were used the most, while unnatural, unbendable materials were used to least.
A brittle star at the start of one of the time trials.
Two species of brittle stars that are abundant in the reef flat of Discovery Bay are Opidoderma appressum and Ophiocoma enchinata, commonly known as the Banded-Arm brittle star and the Blunt-Spined brittle star respectively. When threatened, these organisms use their long arms to quickly find cover. If they are caught they have the ability to detach their arms in order to escape. We hypothesized that Ophiocoma enchinata would have a faster escape rate because they tend to be larger than Opidoderma appressum. Our hypothesis was not correct. Our data showed that larger brittle stars were not necessarily faster than the smaller ones and there was no difference in velocity between the two species. However, we did find that there was a significant difference in velocity among the different color variants of Opidoderma appressum, which led us to believe that surface color may have an effect on the velocity. We hypothesized that the color variants would move faster on a lighter surface when compared to a darker surface. We found that the average velocity significantly increased when the brittle star was placed on a light surface compared to a dark surface. As a result, we hypothesized that Opidoderma appressum may have a color preference. We found no statistical significance that would support our hypothesis but our data for this experiment was skewed due to a lack of specimens.
A tile baited with a brittle star and a crab.
Predation is an important interaction within communities that keeps some species from overpopulating and causing shifts in habitats from overgrazing, or resource depletion. We measured the rates of predation in 3 habitats to see how it changes from habitat to habitat within the fringing reef ecosystem in Discovery Bay. These habitats are the mangroves, the turtlegrass beds, and the sand flats. We took two prey species, the reticulated Brittle Star (Opheonereis reticulata) and the Green Clinging Crab (Mithrax sculptus), and used them as bait that was attached to a hook, and approximately 2 feet of 8 or 25 pound test line that was secured to a tile on the bottom. On each tile were 2 lines, one with Mithrax s. and the other with Opheonereis r. to see if there was a preference among the two species. For each habitat we placed five of these tiles approximately 3 meters apart, leaving ten lines per zone. We also measured the night vs. day predation in these zones as well to compare that data to the total predation rates among the habitats. The only significant data we found was that in the mangroves the predation dramatically increased for nocturnal predators, though we could not catch any of them, the mean number of missing prey items was much higher during night trials there.
Setting out the turtle grass tethers (in low visibility conditions).
Due to the fresh groundwater infiltrating into the lagoon of Discovery Bay, the Thalassia Testudinum in the area is naturally enriched with nitrogen. In our study, we collected samples of grass from both nitrogen enriched areas and from areas of normal conditions. We enriched some of the blades with phosphorus to determine a preference from marine life grazers. This was accomplished by securing the blades of grass to tethers using clothes pins, and by fastening those tethers to tiles with zip-ties. To get a complete understanding of the herbivory in the area, we sampled the grass from both the lagoon and bay to determine the bites on each blade. Many blades of grass appeared scared by what seems to be urchins. These blades were discarded, since we are counting only clear bites in the grass. Although the data did not show significant differences between the phosphorus enriched blades and naturally occurring blades of grass, there was a slight preference shown toward the phosphorus enriched grass. The toughness of the grass was also tested in each area by using a tensometer, and no significant difference was found.
It's hard to see, but a Mithrax crab is hidden behind the anemone tentacles.
In Discovery Bay, there are an abundance of anemones, which provide shelter for different marine species. The ability for those species to seek shelter under anemones when a predator is present is critical for their survival. Mithrax sculptus crabs are the most common species found in anemones. For our experimentation on Mithrax sculptus, we wanted to test how important anemones are for their survival. We hypothesized that crabs in relatively smaller tanks will be able to seek shelter under anemones, with or without the presence of a predator, more easily than in a larger tanks. We also hypothesized that the smaller crabs will have an advantage of seeking shelter due to their sheer ability to hide undetected underneath anemones. In a survey of 650 anemones, it was concluded that the Condylactis gigantea was the dominant anemone, predominantly housing Mithrax sculptus. As predicted the smaller tanks showed a significantly lower amount of deaths due to predation. We also observed that there was not any significance of crab size to predation.
The Upside down jellyfish (Cassiopea frondosa) live in the mangroves and sandy areas here at Discovery bay. Like many corals they have a symbiotic and mutual relationship with the dinoflagellates zooxanthallae. Zooxanthallae grows on the down side of the jellyfish and photosynthesize to provide the jellyfish with nutrients and oxygen while jellyfish in turn provides the zooxanthallae with a home near the photic zone, carbon dioxide, and protection. Corals have an obligative mutualistic relationship with their zooxanthallae ; if jellyfish have such a relationship with their zooxanthallae, the current environmental changes may be detrimental to them as well and may cause jellyfish bleaching. Thus we wanted to see what conditions may cause the Cassiopea frondosa to expel their zooxanthallae. We completed two different experiments: the effects of darkness and different salinities on the jellyfish. For the Light/Dark experiment we collected jellyfish and exposed half of them to constant darkness and the other half to ambient light. For the salinities experiment we divided the jellyfish into three different settings, one with high, one with low, and one with ambient salinity. We then counted average cell densities of all the jellyfish every 24 hours for the light/dark experiment and every few hours for the salinity experiment. We concluded that under the time constraints and the particular conditions we chose the jellyfish did not show significant expulsion of their zooxanthalle. This means that the jellyfish may not expel their zooxanthallae like the corals or the conditions they we subjected to were not extreme enough.
Measuring how many tiles it takes to crush Eucidaris tribuloides.
The optimal foraging theory states that organisms forage for food in such a manner that will maximize their net intake of energy, resulting in organisms obtaining food that is most available to them. Occasionally, this can lead to organisms rejecting larger or more nutritious food sources for food that will require less energy to consume. Diodon holocanthus, commonly known as balloon fish, live in tropical marine habitats and feed on local Eucidaris tribuloides sea urchin (slate pencil urchin). For our project, we observed the eating habits of D. holocanthus to see if it was consistent to the optimal foraging theory. We determined the amount of weight needed to crush the shell of sea urchins of various sizes and found that smaller urchins were easier to break open than larger sea urchins. We also found that D. holocanthus tended to choose smaller urchins as opposed to larger urchins, however more data is needed to confirm this finding. For the final part of our project, we began looking into the effect of spine length and D. holocanthus preference. Our results indicated that urchins with smaller spines were not only easier to crush but appeared to be preferred by D. holocanthus.
We arrived back to NY last night and I'm sure everybody is getting over the shock of waking up this morning. It's a bit disconcerting to go from tropical breezes, clear aquamarine water, waves breaking over the reef, and fresh papaya, pineapple, and chocolate chip muffins at breakfast to several inches of snow and the thought that I need to find my snow shovel!
Speaking for Prof. Peterson and myself (and our TAs John and Amber), we really enjoyed working with the students over the past several weeks. They'll still be working on their research projects over the next few weeks as they write their final project papers, but we're posting all of their project abstracts here right now so folks can see what some of their results are.
Well, it’s our final few hours here in Discovery Bay, and although it’s sad to leave the beautiful, tropical weather we’ve enjoyed for the past 16 days and head back to NY (which is expecting 2-4 in of snow tonight and tomorrow), it will be good to go home and have a bit of a break. This trip has been a flurry of classes, research and data processing/analyzing. But it’s all been worth it, and let’s be honest, it’s really hard to complain about your ‘job’ when working involves diving every morning!
As John mentioned in his blog post, I have been doing research here for the past 3 years and this Jamaica trip marked the end of an ongoing 3-year study I have been conducting looking at the effects of beach erosion from large hotels on the adjacent reef (particularly on the sponge community). Although, I am extremely relieved to have managed to get a solid 3 years of data without having hurricanes or anything else ruin my project, it is bittersweet to see it coming to an end. I have been coming to Discovery Bay Marine Lab every 6 months since January 2008, and it’s sad to know that I won’t be returning until next January. Over the years, I have grown close to the staff at DBML and it’s always hard to say goodbye to such a great group of people who have always worked really hard to make sure my time in Jamaica goes as smoothly as possible.
But all good things must come to an end, and I think everyone today is feeling a bit sentimental about the time they have spent in Jamaica, whether it was the last 2 weeks or several years worth of visits. But I am sure that if everyone feels the way I do about this place, it won’t be the last time we spend time on this sunny, laid back island. Jamaica has a way of getting under your skin, and once you’ve experienced all it has to offer, it’s hard to stay away for too long. After all- we are Jamericans now.
Amber and a stalactite during the cave tour. [Ed: Amber didn't give me a photo for her blog so I tried to find one where she wasn't underwater as that's how she spends most of her time in Jamaica.]
– Amber (graduate student and course TA)