Tropical Marine Ecology 2013

Tiffany Hamm, Susan Le, and Peter Miller

The Effects that Surrounding Hard Structures have on Biodiversity and Abundance Found in Turtlegrass (Thalassium testudinum) Patches

Hamm, T., Le.S, and Miller, P.

Abstract

For our project, we decided to see how structures may influence the communities in the surrounding turtlegrass (Thalassia testudinum) meadows. This was done by comparing two turtlegrass patches; one relativately close to significant structures, and one approximately 50 meters away. Structures include, mangroves (Rhizophora mangle), and dead coral reefs. Over the course of five days, five samples of turtle grass was taken daily at each site. We also sampled the populations of epibenthic invertebrates and fish using five meter transects, twenty-five meters per site per day. The seagrass samples were analyzed to determine the number of leaves, number of bite marks, and epiphytic algal coverage per square meter and meter of seagrass surface area. The density of bite marks and epiphytic algal coverage was used as a proxy for (determining a level) of herbivory at each site. Average abundances of individual species were compared between the two sites, as well as the Shannon-Wiener index, the Simpson index, and a dominance curve, in order to compare the diversity and abundance of species at each site.

Peter diving to conduct a bottom survey.

Tracey Vlasak and Meaghan Coyne

The Correlation Between Herbivory and Algae Distribution in Different Areas of Discovery Bay

Algae can be found in all parts of Discovery Bay, from the mangroves to the fore reef. Our study aims to look at the correlation between herbivory and distribution of red, green and brown algae in the mangroves and the back reef. In the first part of the study a 63 cm by 63 cm PVC quadrat was used to observe the algal distribution in different parts of the mangroves and the back reef. We went to the mangroves and the back reef every day for a week and took pictures of the quadrats in five areas of each site. Through the pictures and samples that were collected, the algae and other species in each quadrat were identified. The distribution of the algae was recorded using the Braun-Blanquet scale. This uses a scale number to represent a percent coverage within the quadrat. We recorded the percent cover of no algae, turf algae, and encrusting algae along with red, green and brown. For the second part of our study two looked at herbivory on the algae. We weighed and attached red, green, and brown algae to tethers put them out at the back reef and the mangroves. These were out for two 24 hours periods and then reweighed. The results were recorded and analyzed using a two tailed t-value test.   

Quadrat sampling of bottom cover.

Nick Russell and Mike Maracic

Variegated Sea Urchin Cover Variability and Predation

Throughout Discovery Bay, it can be noticed that in different regions of the bay, Variegated Sea Urchin populations will vary, and they will also cover themselves with different materials found in their near-by environment. The bay was divided into three different regions: A, B, and C (Just outside the Mangroves, at the reef crest, and along the jetty) in order to study these changes. In each area, Variegated Sea Urchins were collected, as long as all the material that they were covering themselves with. The mass and area that this material was covered in was then recorded to see that the Urchins population was the smallest in region C, but Urchins in this region were found to have the highest mass and surface area of covering material on them. The most predation was also found to occur in region C, while the most variability in predation occurred at the Reef Crest in region B. It was believed that Turtle Grass would account for the highest percentage of area covered on each Urchin, however, Coral Debris was found to account for the highest numbers.  

Urchin collection.

Lindsay Stemke and Kyle Chadderton

Grouping Behavior in Rock-Boring Sea Urchins (Echinometra lucunter)

Abstract:

Echinometra lucunter, or Rock-Boring Sea Urchins, are a species of tropical echinoderm which are found in abundance in the Atlantic Ocean throughout the West Indies (Plazas, 2012). Common within rocky intertidal regions (McPherson, 1969), the urchins burrow into rocks to create their own shelters, which are continually enlarged as the urchins grow (McLean, 1967), supported largely by a diet of various algal species including Sargassum (Plazas, 2012). While swimming in Discovery Bay, Jamaica, we noticed that these urchins apparently cluster on rocks, with some areas covered with urchins and others containing few or no urchins, leading us to ask the following questions: 1. Do E. lucunter exhibit grouping behavior? 2. If so, do factors such as abundance of food and habitat size and availability influence grouping behavior? We hypothesized that the urchins do exhibit grouping behavior, and that if faced with the choice, they will cluster around larger habitats rather than food or smaller habitats. In order to test these hypotheses, we monitored changes in the spatial distribution of ten E. lucunter individuals, which we placed in an aquarium with a roughly uniform distribution pattern and then photographed over a specified number of time intervals under three experimental conditions: no food or shelter, shelter with no food, and food with no shelter. We then further tested the urchins' preferences for food vs. shelter and for small vs. large shelters, in order to determine potential drivers behind the suggested grouping behavior. We then measured distances between each urchin and its nearest neighbor, and will analyze this data by applying the Nearest Neighbor Analysis ("Nearest neighbor analysis") to determine if the urchins are exhibiting random, uniform, or clustered distributions. From a preliminary examination of histograms of our results, it appears possible that Echinometra lucunter individuals do exhibit grouping behavior, but there is no discernible preference for food vs. habitat or for smaller vs. larger habitats. Statistical analysis is required to determine whether or not these apparent trends are significant.

The initial setup for our first experiment, testing the distribution of Echinometra lucunter in an environment with no food or shelter.