Marine Protected Area monitoring in the nearshore waters of Grenada, Eastern Caribbean: benthic cover and fish populations

Annual monitoring of leatherback sea turtle (Dermochelys coriacea) nesting grounds in Grenada, West Indies has identified relatively low hatch rates compared to worldwide trends. This study investigated the impact of selected environmental variables on leatherback sea turtle embryonic development and hatching success rates on Levera Beach in Grenada between 2015–2019. The mean number of nests per year and eggs per nest were 667.6 ± 361.6 and 80.7 ± 23.0 sd, respectively. Within excavated nests, 35.6% ± 22.0 sd of eggs successfully developed embryos and 30.6% ± 22.6 sd of eggs successfully hatched. The number of eggs per nest, along with embryo and hatching success rates, differed by nesting year. Embryo development success rate was associated with nest location, and both embryo development and hatching success rates were positively associated with nest depth and negatively associated with the percentage of eggs exhibiting microbial growth and with the presence of inspissated yolk. There was no embryo development or hatchling success association with month of the nesting season, distance from the high-water mark, distance from vegetation, nor maternal carapace length. The mean nest temperature was 31.7 °C ± 1.64 sd and mean temperatures during the middle third of egg incubation suggest clutches are highly skewed towards a preponderance of female hatchlings. Histopathologic findings in hatchling mortalities included severe, acute, multifocal, heterophilic bronchopneumonia with intralesional bacteria in 4/50 (8%) hatchlings. Data from this study guide conservation strategies by identifying risk factors and further avenues of research needed to support reproductive success of leatherback sea turtles in Grenada and the greater Caribbean region.

Globally, the hatch success of leatherback sea turtles (Dermochelys coriacea) is much lower than any other sea turtle species. Causes of embryonic mortality, a contributing factor to the low hatch success of the species, are poorly understood. Muscle necrosis, renal mineralization, and bacterial pneumonia are prevalent among embryos and hatchlings in St. Kitts, where hatch success is much lower (<∼ 20%) than the global average (∼ 50%), yet the significance of these conditions in the wider region is unknown. The objective of this study was to describe the pathology of hatchlings and embryos in Grenada as a comparison population for St. Kitts. In 2017, 20 hatchlings, 6 pipped hatchlings, 35 late stage embryos, and 5 early stage embryos were sampled for comprehensive postmortem examination from 12 leatherback nests on Levera Beach, Grenada and 2 nests on St. Kitts. Pathology affected 71% of nests and 44% of individuals from Grenada and 100% of nests and 56% of individuals from St. Kitts. Lesions observed in both populations included skeletal muscle degeneration and necrosis (19%), bronchopneumonia (8%), and renal tubular degeneration (5%) while chorioallantoitis (17%) and mycotic dermatitis (5%) were only observed in Grenada. Gonads were histologically classified as female in all instances (n = 60), suggestive of high incubation temperatures in nests at both locations. Further study is needed to find interventions that reduce the prevalence of perinatal pathology and to identify the basis for the large proportion of eggs that fail to develop as well as embryos that die without significant pathology.

Annual benthic and fish population surveys were completed at five locations in the nearshore waters along Grenada´s southwest coast during 2008 - 2010. Two survey sites are located in a newly launched Marine Protected Area (MPA). Photo Quadrat (PQ) and Point Line Intercept (PLI) surveys were used to determine substrate cover. Algae was the primary live cover increasing significantly from 45.9% in 2008 to 52.7% in 2010 (PLI). Algae was also predominant (61.0% - 59.3%) in the PQ surveys although annual variation was not significant. Hard coral cover ranged from 16.5% to 15.4% (PLI) and 11.4% to12.0% (PQ) with no significant differences between years. Branching and encrusting corals occurred more frequently than massive corals. In the three annual surveys neither algal cover nor hard coral varied significantly between MPA and non-protected areas (PLI). Relative abundance of fishes along 30x2m belt transects did not vary significantly among years however density of fishes decreased significantly across years for most major groups. Chromis spp. dominated the survey sites at 65.2% in 2008 and 49.8% in 2010, followed by territorial damselfish,11.1% and 15.5%, wrasse increased from 7.3% to 15.5%. Both the substrate cover and fish survey data analyses indicated a stable but degraded community. Annual surveys are planned at these sites for the foreseeable future. Existing and future data from this project will be valuable in determining the efficacy of MPA management, guiding resource management decisions and monitoring the health status of Grenada’s valuable reef systems