From Bonaire, we here provide the first documented case of the green turtle feeding on the invasive seagrass, Halophila stipulacea, in the Caribbean. The seagrass is rapidly invading existing seagrass meadows and altering key foraging habitat of this endangered marine reptile throughout the eastern Caribbean. We expect that more records of green turtles feeding on this invasive species will gradually follow from throughout the region and that the green turtle might alter its foraging behavior in response to the changing species composition of its foraging habitat.
Many pelagic organisms, including sea turtles, host unique communities of epibionts on the surfaces of their bodies. Although sea turtle epibiota have been studied in other areas of the world, very little research has been conducted on the epibionts found on sea turtles inhabiting the water around Bonaire, Netherland Antilles. In this study, epibiont samples were obtained from 33 sea turtles found in Bonaire. Epibionts included green and red algae, polychaete worms, skin barnacles, and turtle barnacles. Barnacle abundance and epibiont biodiversity was determined for each size class (Small, Medium, Large juveniles) of the two most common species of sea turtles found on Bonaire (Eretmochelys imbricata and Chelonia mydas). There was no significant difference in number of barnacles between E. imbricata and C. mydas. However, there was a significant increase in the number of barnacles with increasing size class in both E. imbricata and C. mydas. Epibiont biodiversity was significantly higher on E. imbricata but did not increase with size class for either species. Such findings indicate that the distinct life histories of C. mydas and E. imbricata may lead to varying degrees of epibiont accumulation.
Invasive seagrass mega herbivore interactions
a study on the invasion of seagrass Halophila stipulacea in a Southern Caribbean lagoon affected by C. mydas grazing
In the Caribbean, the recent invasion of the seagrass species Halophila stipulacea has raised concerns regarding its impact on the invaded seagrass ecosystem and its associated flora and fauna. The main purpose of the experimental set-up was to understand the mechanisms and impacts of invasive species on a native seagrass in interaction with grazing impacts by the green sea turtle (C. mydas). The aims of the study were i.) to determine the colonization capacity of native seagrass species T. testudinum as affected by the presence of the invasive species (Halophila stipulacea) and vice-versa in a Caribbean lagoon (Lac Bay, Bonaire); ii.) To determine whether sexually and/or vegetatively colonization is affected by turtle grazing. and iii) to determine whether architectural properties of T.testudinum and H. stipulacea are affected by presence of other species and whether these are related to C. mydas grazing. For this study, four seagrass bed types were selected that naturally occur in the bay: (1) monoculture of T. testudinum, (2) monoculture of H. stipulacea , (3) mixed bed of H. stipulacea and T. testudinum and (4) mixed bed containing H. stipulacea, T. testudinum and S. filiforme. In each seagrass bed type, 12 experimental units were created divided over three experimental periods of six weeks. Within each unit, two patches of 150 x 150 mm were cleared of above and below ground biomass. Cages were placed over half of the cleared patches to prevent turtle grazing. After six weeks, recolonization of the patches by native species and invasive species were measured by resampling biomass. To assess whether turtle grazing changed architectural properties, measurements on length and width with and without grazing were taken. Lastly, lines around two T. testudinum turtle grazing plots were placed to measure the lateral expansion rate of the surrounding H. stipulacea patches.
Our results indicate that H. stipulacea is a ~11 times faster colonizer than T. testudinum. Effects of grazing on their colonization rate were different with T. testudinum colonization rate under C. mydas grazing being lower and H. stipulacea’s colonization rate being higher. These effects were not statistically proven, but strong trends were observed. The presence of other seagrass species did not seem to influence competitive abilities (colonization capacity and architectural properties). C. mydas grazing, on the other hand, clearly influenced T. testudinum’s architectural properties. Regarding T. testudinum’s grazing plots, an average lateral expansion of 0.35 cm day-1 by H. stipulacea was detected.
This study demonstrates that there is no direct competition between T. testudinum and H. stipulacea. It seems that H. stipulacea is colonizing areas unsuitable to T. testudinum. Sea turtle grazing creates less dense seagrass beds and therefore might further stimulate the expansion of H. stipulacea. The impact of the establishment of H. stipulacea on C. mydas is not yet clear: Even though it seems not to be the preferred seagrass species, C. mydas does graze on the invasive species in Lac Bay. It is, however, unknown how this new food resource will affect their fitness. Though the invasive may alter abiotic conditions in their habitat, the sea turtles may benefit from an extended cover of seagrass beds as the invasive seagrass is able to grow in places where native seagrass species currently cannot survive. It is recommended to keep monitoring changes and investigating the impact of H. stipulacea on the whole ecosystem.
Retreived from http://www.bonaireturtles.org on Aprile 13, 2015
Fibropapillomatosis is a disease that is affecting sea turtles all around the world. Turtles that are most at risk are those that live in near-shore waters and lagoons, especially areas next to large human populations with poor sewage treatment facilities. In this research project the main focus is fibropapillomatosis (FP) and green sea turtles captured by netting in Lac Bay, Bonaire. The research goal was to see how turtles living in Bonaire are affected by the disease. The two main research questions were: “What is the true rate of fibropapillomatosis affecting green sea turtles in Lac Bay?” and “What is the difference between healthy turtles and infected turtles that are caught by netting?”
To determine the true rate of FP, the percentage of diseased turtles is calculated as the percentage of captured turtles with FP compared to the whole amount captured during netting conducted from 2006 until 2014. In 2006 rates of FP were 20 percent, the infection rates then decreased dramatically, even reaching zero percent in 2010. FP rates started increasing again after 2012, and in 2014 the rates of FP now stand at 34 percent (n=89). It is still uncertain what causes FP to increase. To determine the difference between healthy turtles and diseased turtles, the length, weight, and overall growth rates have been assessed. Recapture rates were also assessed, to determine if diseased turtles were captured more, because of their limitations. There was a significant difference (p < 0.001) found between recapture rates of healthy and diseased turtles indicating that healthy turtles are recaptured more often than diseased turtles. Assessed length and weight of diseased turtles are not significantly different than from healthy turtles (p < 0.001). The growth rate in this research was not significantly different between healthy and diseased turtles. Overall there was no significant difference found between healthy turtles and diseased turtles living in Lac Bay, not in length, weight or in growth rates. The implications of this research suggest that the overall survival rate of turtles with FP on Bonaire is relatively high in comparison to other areas of the Caribbean. This could be due to the tumors not restricting the turtles to such a degree that they are unable to forage or flee.
Retrieved from http://www.bonaireturtles.org on April 13, 2015