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Helping Green Turtles Through Water Quality Assessment of Their Critical Habitat
Map of the Culebra Archigelago study Areas. Link to larger image.
Puerto del Manglar Bay and Culebrita (Tortuga Bay) sampling sites. Aerial photo courtesy of the NOAA Biogeography Program. Link to larger image.
Stormwater pipe empties in Mangrove-covered coastline
Water quality analysis is performed immediately after collection of samples
Green turtle (Chelonia mydas) populations have been steadily decreasing worldwide. One contributor to their declines is fibropapillomatosis (FP), a viral disease found in these turtles in many locations around the world. The disease causes warts and tumors that spread throughout the turtle’s body. These obstruct internal organs which can interfere with vital functions, or interfere with vision and mobility as large warts develop on the face and flippers. Most of the affected turtles die of starvation, because the tumors and warts impede swimming and foraging. Many turtles are also harmed by secondary bacterial infections that develop in dying tissues riddled with tumors.
In the summer of 2005, Dr. Marirosa Molina, from the United States Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, Ecosystems Research Division in Athens, Georgia, joined forces with researchers from the University of Georgia’s (UGA) School of Veterinary Medicine 
to investigate the spread of the disease in the green turtles of Puerto del Manglar Bay in the island of Culebra, Puerto Rico. The project is locally sponsored by the Puerto Rico Department of Natural Resources (PRDNR) and the U.S. Fish and Wildlife Service. While the UGA researchers study the pathology of the disease itself, Dr. Molina is evaluating the quality of the bay water, because water pollution might be promoting the spread of the disease in the turtles.
The EPA research is applying DNA-based markers of fecal contamination, and 15N isotopic analysis, to identify sources of contamination and assess the possible eutrophication of the bay. For the most part, Culebra uses septic tanks for wastewater disposal. Inadequate maintenance of septic systems, in combination with porous sandy soils, often leads to contamination of coastal areas with excess nutrients and possibly sewage.
Two bays, relatively close together, are being investigated. In Puerto del Manglar Bay, tumors are rapidly spreading through the green turtle population. In Tortuga Bay, only three miles away, the turtles are almost completely free of tumors. This striking situation, in which a healthy population of turtles is living close by a group that is falling prey to the disease, raises questions about changes in the quality of the environment that may be promoting the onset and spread of FP infections in the Puerto del Manglar turtles.
Preliminary bacteriological studies have detected a slight increase in enterococci numbers following a heavy rainfall. Two species of enterococci have been isolated from the bay: Enterococcus casseliflavus, and an unknown Enterococcus sp. Enterococcus faecalis and Enterococcus faecium have been isolated from turtle manure.
Because 15N enrichment due to wastewater can be distinguished from that due to fertilizers and natural atmospheric N
deposition, δ15N analysis has been applied to estuaries around the
world to assess human-induced nutrient loadings in coastal
ecosystems. EPA’s δ15N results show enrichment of 15N in the macrophytes (mostly
macroalgae) collected from Puerto del Manglar bay, which is above the 15N enrichment observed in macrophytes collected from
Future work will apply DNA-based markers to detect and confirm human fecal contamination. We will develop a clone library to make comparisons with other tropical coastal locations impacted by fecal contamination. Our assessments of macrophyte δ15N values at other locations around the Island (pristine vs. impacted locations) will build more robust baseline information for these subtropical ecosystems.
This study will help the PRDNR and the U.S. Fish and Wildlife Service formulate new coastal management plans that better protect Culebra’s critical green turtle habitat.
More Information
Green Turtle Research Study Slide Show. This slide show shows the process from leaving the dock for turtle and water sample collection to the sample analysis.