Development of a Species Distribution Model for the East Pacific Green Sea Turtle using Ecological Geoprocessing Tools
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East Pacific green sea turtles, Chelonia mydas, play ecologically important roles in marine habitats which range from grazing (and thus regularly "mowing") algae and seagrass beds to cycling nutrients between the ocean and land. However, these important grazers have been hunted to ecological extinction in some places for their eggs, meat, and skin. The conservation initiative for the survival of sea turtles requires the protection of their primary habitats in conjunction with a decrease in their interaction with humans. One way these objectives can be met is through the creation of species distribution maps (SDMs). For this thesis, a SDM was created from a generalized additive model used to identify major feeding areas for East Pacific green turtles residing in the Galapagos Islands. The input for the model was green turtle sighting locations during a June 2010 marine life observation survey and remotely sensed values of four oceanographic parameters obtained from satellite sensors (Bathymetry, Sea Surface Temperature, Chlorophyll a, and Current Speed). Line transects of intertidal and subtidal shoreline regions of the islands of Isabela, San Cristobal, and Floreana were also completed, to describe similarities and differences in macroalgal abundance between the locations. A generalized additive model (GAM) explained 56% of the data's null deviance and had a true positive rate of 0.83. The corresponding species distribution map indicated that East Pacific green sea turtles prefer to forage in warm, low chlorophyll a, slow moving waters at depths mostly less than 250m throughout the archipelago. ANOVA analyses showed that macroalgal abundance was statistically different (p-value < 0.01) between the islands of San Cristobal and Isabela. The line transects analysis also documented that red algae was the most prominent phyla at the sites and that the macroalgal abundance did not vary much between months June 2010 and April/May 2011. With these results, potential foraging areas for East Pacific green turtles can be identified and protected. Future studies will be focused on the collection of macroalgae from coastal areas outlined in the SDM and the interactions between green turtles and their competitors and/or predators. This information can be used to validate the areas delineated by the model and to further the understanding of the spatial-temporal effects on macroalgal abundance.