Date of Award

4-23-2008

Document Type

Thesis open access

Abstract

The factors contributing to the success of the bioluminescent dinoflagellate, Pyrodinium bahamense var. bahamense in the bays of Vieques, Puerto Rico, are not fully understood, although the dinoflagellate’s success is closely tied to its environment and the nutrients within that environment. Exploring the present and past nutrient concentrations and sources of organic material within the bioluminescent bays of Vieques assists in determining the status of and potential threat to the population of Pyrodinium bahamense var. bahamense. Modern carbon, nitrogen, and phosphorus nutrient concentrations were measured, primarily in the seagrass Thalassia testudinum, to evaluate the distribution and potential limitation of those nutrients. As a primary producer, the seagrass is the first biota to reflect any changes in the nutrient availability

of the ecosystem. All seagrass samples were within healthy C:N:P ranges as defined for

the species, but trends in relative limitation were established. Puerto Ferro had lower nitrogen availability relative to Puerto Mosquito, while Puerto Mosquito had lower phosphorus availability. Relative phosphorus and nitrogen availability also exhibited trends related to distance from shore; phosphorus availability increased with greater distance from shore while nitrogen availability decreased by the same measure. The hydrodynamics in the bays, especially Puerto Mosquito, could be the cause of the spatial trends in nutrient availability as well as the higher nutrient content of the bays relative to

larger bodies of water with more interaction with the open ocean. The relative isolation of Puerto Mosquito is a potential factor limiting nutrient flushing, allowing the nutrient content that supports the present dinoflagellate population to thrive.

In addition, δ13C values were measured in numerous samples of seagrass and mangrove, two primary sources of organic material, in order to establish their isotopic vi compositions. With these isotopic and nutrient data, in addition to isotopic data from the third primary source of organic matter, suspended particulate matter (SPM), three end member N:C and δ13C values were established. δ13C isotopic analysis of sediment cores revealed overall temporal shifts in organic matter source from mangrove in the past to seagrass and suspended particulate matter in the recent to present-day environment.

The evaluation of the past and present habitat of the bioluminescent bays suggests that the bays experienced a sea level transgression approximately 3000 years B.P. and that the dinoflagellate did not thrive until recently. The relatively recent success suggests that human involvement might not be the only source dictating the future success or failure of the species in the bays of Vieques. Future development within the watersheds of the bays, as well as natural habitat change, could force changes to established nutrient cycles, organic matter sources, and therefore, the success of the dinoflagellate. The protected nature of the bays, from natural and commercial change is a primary reason the dinoflagellate demonstrates its present success. In the future, this isolation could have hazardous implication for dinoflagellate populations, as isolated habitats can have difficulty adapting to change.

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