Evidence for Host Selectivity and Specialization by Epizoic Chelonibia Barnacles Between Hawksbill and Green Sea Turtles

Epibionts are organisms that utilize the exterior of other organisms as a living substratum. Many affiliate opportunistically with hosts of different species, but others specialize on particular hosts as obligate associates. We investigated a case of apparent host specificity between two barnacles that are epizoites of sea turtles and illuminate some ecological considerations that may shape their host relationships. The barnacles Chelonibia testudinaria and Chelonibia caretta, though roughly similar in appearance, are separable by distinctions in morphology, genotype, and lifestyle. However, though each is known to colonize both green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) sea turtles, C. testudinaria is >5 times more common on greens, while C. caretta is >300 times more common on hawksbills. Two competing explanations for this asymmetry in barnacle incidence are either that the species’ larvae are spatially segregated in mutually exclusive host-encounter zones or their distributions overlap and the larvae behaviorally select their hosts from a common pool. We indirectly tested the latter by documenting the occurrence of adults of both barnacle species in two locations (SE Florida and Nose Be, Madagascar) where both turtle species co-mingle. For green and hawksbill turtles in both locations (Florida: n = 32 and n = 275, respectively; Madagascar: n = 32 and n = 125, respectively), we found that C. testudinaria occurred on green turtles only (percent occurrence – FL: 38.1%; MD: 6.3%), whereas the barnacle C. caretta was exclusively found on hawksbill turtles (FL: 82.2%; MD: 27.5%). These results support the hypothesis that the larvae of these barnacles differentially select host species from a shared supply. Physio-biochemical differences in host shell material, conspecific chemical cues, external microbial biofilms, and other surface signals may be salient factors in larval selectivity. Alternatively, barnacle presence may vary by host micro-environment. Dissimilarities in scute structure and shell growth between hawksbill and green turtles may promote critical differences in attachment modes observed between these barnacles. In understanding the co-evolution of barnacles and hosts it is key to consider the ecologies of both hosts and epibionts in interpreting associations of chance, choice, and dependence. Further studies are necessary to investigate the population status and settlement spectrum of barnacles inhabiting sea turtles.

Multi-Injection Pharmacokinetics of Meloxicam in Kemp’s Ridley (Lepidochelys kempii) and Green (Chelonia mydas) Sea Turtles after Subcutaneous Administration

The objective of this study was to determine the pharmacokinetics and safety of multiple injections of meloxicam (MLX) administered subcutaneously (SQ) in Kemp’s ridley (Lepidochelys kempii) and green (Chelonia mydas) sea turtles. Based on results from a previously published single-injection study, a multiple-injection regimen was derived for the Kemp’s ridleys, which consisted of administering MLX at a dose of 1 mg/kg SQ every 12 h for 5 days, and for green turtles at a dose of 1 mg/kg SQ every 48 h for three treatments. Six turtles of each species were used for the study, and blood samples were taken at multiple time intervals. The terminal half-life after the last dose for the Kemp’s ridley sea turtles was calculated at 7.18 h, and for the green sea turtles at 23.71 h. Throughout the multiple injections, MLX concentrations remained above 0.57 µg/mL, a concentration targeted in humans for the analgesic and anti-inflammatory effects. No negative side effects or changes to blood parameters evaluated were observed during the study in either species. The results of this study suggest MLX should be administered SQ to Kemp’s ridley sea turtles at a dosage of 1 mg/kg every 12 h and in green sea turtles at a dose of 1 mg/kg every 48 h. The novelty of this work is that it is a multiple-injection study. Multiple injections were administered and produced concentrations that were considered therapeutic in humans, and the turtles did not have any adverse side effects. Furthermore, there were large differences in the pharmacokinetic values between green and Kemp’s ridley sea turtles.

Association of ocean macroplastic debris with stranded sea turtles in the Central Gulf of Thailand

The impact of macroplastic debris (> 5 mm in size) on marine life is a global concern but is rarely investigated in Thailand. Our objective was to investigate the relationship between stranded sea turtles and macroplastics found in the Central Gulf of Thailand. The turtle (n = 388) stranding record between 2017-2020 was analysed retrospectively to determine their size, species, and interaction with macroplastics. Thereafter, between 2019-2020, macroplastics were collected, from the gastrointestinal (GI) tract of dead turtles and from the beaches where stranded turtles were found. A stereomicroscope was used to visually categorise the macroplastics, and the plastic composition was analysed using a Fourier-transform infrared (FTIR) spectrometer. Green sea turtles (Chelonia mydas) were found to account for the majority of stranded turtles (74%, n = 251), and macroplastics were discovered in 74% of cases of entanglement and ingestion. At the juvenile stage, the stranded turtle was strongly related to macroplastics. Immature turtles were more likely to become entangled than adult turtles. Entangled turtles had a greater survival rate than turtles that had consumed plastic. The plastic fibres were the majority of macroplastics found in the GI tracts (62%, n = 152/244) and on the beach (64%, n = 74/115). Most fibres from GI tracts (83%, n = 126/152) and the beaches (93%, n = 68/74) were identified as the fishing net comprised of polyethylene or polypropylene. We concluded that fishing nets made of polyethylene or polypropylene might be one of the significant causes of sea turtle stranding in the Central Gulf of Thailand, and this issue requires immediate resolution.

Genotype data not consistent with clonal transmission of sea turtle fibropapillomatosis or goldfish schwannoma

Recent discoveries of transmissible cancers in multiple bivalve species suggest that direct transmission of cancer cells within species may be more common than previously thought, particularly in aquatic environments. Fibropapillomatosis occurs with high prevalence in green sea turtles (Chelonia mydas) and the geographic range of disease has increased since fibropapillomatosis was first reported in this species. Widespread incidence of schwannomas, benign tumours of Schwann cell origin, reported in aquarium-bred goldfish (Carassius auratus), suggest an infectious aetiology. We investigated the hypothesis that cancers in these species arise by clonal transmission of cancer cells. Through analysis of polymorphic microsatellite alleles, we demonstrate concordance of host and tumour genotypes in diseased animals. These results imply that the tumours examined arose from independent oncogenic transformation of host tissue and were not clonally transmitted. Further, failure to experimentally transmit goldfish schwannoma via water exposure or inoculation suggest that this disease is unlikely to have an infectious aetiology.

Finding of a two-headed green turtle embryo during nest monitoring in Baa Atoll, Maldives

Green sea turtles are one of the two species of marine turtles known to nest in the Maldives. The prevalent time of nesting seems to be inconsistent throughout the island nation. In this study, sea turtle nesting activity was monitored on the island of Coco Palm Dhuni Kolhu in Baa Atoll over a period of 12 months. A total of 13 nests were confirmed with a median hatching success rate of 89.58% as ascertained by nest excavation. In one of the nests, a severely deformed hatchling with polycephaly, an opening in the neck area and a lordotic spine was found, and we investigated in detail with radiographic images and a necropsy. Our findings support the importance of consistent nesting activity and nest monitoring efforts in the country as a basis for conservation efforts.