Embryo deformities and nesting trends in Kemp’s ridley sea turtles Lepidochelys kempii before and after the Deepwater Horizon oil spill

Kemp’s ridley sea turtles Lepidochelys kempii were disproportionately affected by the Deepwater Horizon (DWH) oil spill, which began on 20 April 2010. Embryo deformities were documented in inviable L. kempii eggs before (2008-2010) and after (2011-2013) the DWH spill in 2 Texas (USA) nesting areas (Upper Texas Coast and Padre Island National Seashore). Additional nesting trends, including clutch size and hatching success, were also investigated. Total and late-stage embryo deformity prevalence were 1.5 times greater after 2010 than before, but low in all nesting seasons (mean ± SD: 0.7 ± 8.5% total; 0.6 ± 8.0% late-stage) and did not differ between locations. Craniofacial and carapace deformities were the most frequently observed deformity types. Documented nests in both areas declined in 2010 relative to previous years, ending an exponential increase observed beginning in 1995. Clutch size remained consistent before and after the spill. Hatching success averaged 87.0 ± 33.3% in all years, but no effects from DWH were determined. Collectively, these data represent useful benchmarks against which to judge impacts of future crude oil spills and other catastrophic events.

Conservation and Enforcement Capacity index (CECi): Integrating human development, economy, and marine turtle status

Human societies are closely linked to their ecological environments. Natural ecosystems and wildlife populations are often in better condition in countries with healthy, educated and economically prosperous populations compared to countries with lower health and literacy conditions, and depressed economies. In the latter countries, these socio-economic factors can compromise government's capacity to manage their natural resources. Thus, the conservation capacity of a government is likely to play key role in the protection of threatened species, such as marine turtles. This paper aims: (1) to evaluate the conservation capacity and enforcement within the 58 Regional Management Units (RMUs) of the seven species of marine turtles throughout the world, and (2) to develop a proxy that predicts the conservation status of RMUs. We developed a Conservation and Enforcement Capacity index (CECi) by integrating the following indices: (a) the economic level and, (b) the Human Development Index (HDI) of each country, plus (c) the risks and threats in the RMUs. We used the conservation status of 15 RMUs recently assessed by the International Union for Conservation of Nature - IUCN to predict the conservation status of the 43 RMUs without updated IUCN categorisation. CECi values ranged from 0 to 1, where lower values represent a better capacity for implementation of conservation initiatives. We found that using our multi-index model, we predicted the status of 33 of 58 RMUs, 57% of which may be of threatened conservation status due to their high CECi values. This study highlighted how socio-economic aspects may impact conservation of endangered species.

Mitochondrial genomes and genetic structure of the Kemp's ridley sea turtle (Lepidochelys kempii)

The Kemp's ridley (Lepidochelys kempii) is the world's most endangered sea turtle species and is primarily distributed in the Gulf of Mexico. In the United States, South Padre Island, Texas serves as a key nesting ground for the species. Genetic studies of the Kemp's ridley have been used to aid in conservation and management practices, with the mitochondrial control region as the most commonly used marker due to its perceived hypervariability and ease of sequencing. However, with the advent of next generation sequencing technology, targeting complete mitochondrial genomes is now feasible. Here, we describe a more complete mitochondrial genome for the Kemp's ridley than has been previously published in literature and demonstrate a cost-effective and efficient method for obtaining complete mitochondrial genomes from sea turtles. We compare the genetic diversity and taxonomic resolution obtained from whole mitochondrial genomes to that obtained from the mitochondrial control region alone. We compare current genetic diversity with previous records. Furthermore, we evaluate the genetic structure between the breeding stock in South Padre Island and that of deceased Kemp's ridleys recovered on the Northern coast of the Gulf of Mexico after the 2010 BP Deepwater Horizon oil spill, and of Kemp's ridleys stranded on the East Coast of the United States. Our results show that complete mitochondrial genomes provide greater resolution than the control region alone. They also show that the genetic diversity of the Kemp's ridley has remained stable, despite large population declines, and that the genetic makeup of deceased turtles stranded after the Deepwater Horizon oil spill is indistinguishable from the breeding stock in South Padre Island, Texas.

OPEN DATA BADGE

This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://www.ncbi.nlm.nih.gov/genbank/.

Beyond trophic morphology: stable isotopes reveal ubiquitous versatility in marine turtle trophic ecology

The idea that interspecific variation in trophic morphology among closely related species effectively permits resource partitioning has driven research on ecological radiation since Darwin first described variation in beak morphology among Geospiza. Marine turtles comprise an ecological radiation in which interspecific differences in trophic morphology have similarly been implicated as a pathway to ecopartition the marine realm, in both extant and extinct species. Because marine turtles are charismatic flagship species of conservation concern, their trophic ecology has been studied intensively using stable isotope analyses to gain insights into habitat use and diet, principally to inform conservation management. This legion of studies provides an unparalleled opportunity to examine ecological partitioning across numerous hierarchical levels that heretofore has not been applied to any other ecological radiation. Our contribution aims to provide a quantitative analysis of interspecific variation and a comprehensive review of intraspecific variation in trophic ecology across different hierarchical levels marshalling insights about realised trophic ecology derived from stable isotopes. We reviewed 113 stable isotope studies, mostly involving single species, and conducted a meta-analysis of data from adults to elucidate differences in trophic ecology among species. Our study reveals a more intricate hierarchy of ecopartitioning by marine turtles than previously recognised based on trophic morphology and dietary analyses. We found strong statistical support for interspecific partitioning, as well as a continuum of intraspecific trophic sub-specialisation in most species across several hierarchical levels. This ubiquity of trophic specialisation across many hierarchical levels exposes a far more complex view of trophic ecology and resource-axis exploitation than suggested by species diversity alone. Not only do species segregate along many widely understood axes such as body size, macrohabitat, and trophic morphology but the general pattern revealed by isotopic studies is one of microhabitat segregation and variation in foraging behaviour within species, within populations, and among individuals. These findings are highly relevant to conservation management because they imply ecological non-exchangeability, which introduces a new dimension beyond that of genetic stocks which drives current conservation planning. Perhaps the most remarkable finding from our data synthesis is that four of six marine turtle species forage across several trophic levels. This pattern is unlike that seen in other large marine predators, which forage at a single trophic level according to stable isotopes. This finding affirms suggestions that marine turtles are robust sentinels of ocean health and likely stabilise marine food webs. This insight has broader significance for studies of marine food webs and trophic ecology of large marine predators. Beyond insights concerning marine turtle ecology and conservation, our findings also have broader implications for the study of ecological radiations. Particularly, the unrecognised complexity of ecopartitioning beyond that predicted by trophic morphology suggests that this dominant approach in adaptive radiation research likely underestimates the degree of resource overlap and that interspecific disparities in trophic morphology may often over-predict the degree of realised ecopartitioning. Hence, our findings suggest that stable isotopes can profitably be applied to study other ecological radiations and may reveal trophic variation beyond that reflected by trophic morphology.