Due to their longevity and extensive migration areas, marine turtles are able to accumulate diverse contaminants over many years and as a consequence they represent an interesting bioindicator species for marine ecosystem pollution. Metals provoke toxicological effects in many aquatic animal species, but marine turtles have been under-investigated in this area. Thus, we have determined the presence of certain inorganic elements (As, Cd, Cu, Ni, Pb, Se and Zn) in olive ridley turtles (Lepidochelys olivacea) and related them to metallothionein (MT), superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) transcription and/or enzymatic activities. Gene expression of sod, cat and gr was found to be higher in blood than liver or kidney but most of the significant relationships were found in liver, not only for gene expression but also for enzyme activities. This must be related to the role the liver has as the first filter organ. Several positive relationships of sod, cat and gr gene expression in the different tissues were found in this population, as well as very high Cd concentrations. This could mean that these turtles are adapting to the metals-production of ROS and damage through a high transcription of these antioxidants. Multiple positive relationships with GR seem to be part of its compensatory effect due to the decrease of SOD production against the high and chronic exposure to certain xenobiotics. CAT, on the other hand, seems not to be used much, and glutathione detoxification of H₂O₂ may be more important in this species. Finally, despite the very high Cd concentrations found in this population, no significant relationship was found in any tissue with metallothionein gene expression. These results, along with very high Cd concentrations and a negative relationship with Cu, lead us to consider some kind of disruption in mt gene expression in these turtles.

In this study, we have analyzed how geo-ecological cues for endangered Olive Ridley turtles’ mass nesting behavior got modified by impact of four severe cyclones during 2010-2019 that made landfall in the vicinity of Rushikulya estuary, which is one of the largest mass nesting congregation (arribada) sites in the world. Analyzing last 10 years of shoreline dynamics, we show that even the slightest modification in beach morphology influenced their nesting behavior in Rushikulya rookery. Shoreline change analysis showed periodic phases of high/low erosion and the northward longshore sediment movement, which becomes impeded by the southern spit, the length of which increased by about 1800 m. During the analyzed period, the nesting behavior of Olive Ridley turtle was greatly influenced by changes in land use and land cover pattern around the Rushikulya rookery. Such reductions in tree cover and marshy land areas were majorly driven by anthropogenic activities and extreme weather events, such as cyclones. We also report increased mortality of turtles, no or false mass nesting events due to significant loss and/or erosion of the nesting sites due to cyclones. The results indicate that conservation of Olive Ridley turtles should be more holistic, or ecosystem centric, rather than species centric. It is important to maintain the ecological integrity of their habitat for highly synchronized mass nesting event and eventually their survival.

Mercury concentrations were assessed in the sea turtle Lepidochelys olivacea from a nesting colony of Oaxaca, Mexico; 25 female turtles were sampled, a total of 250 eggs were collected during the season 2005–2006. Higher concentrations were found in yolk fraction, while in blood and albumen mean levels were below of 0.0010μgg⁻¹ dry wt. On the basis of one nesting season, the maternal transfer of Hg via eggs-laying was estimated in 2.0±1.1%. According to international norms, the health of this population and its habitats is acceptable for Hg and corresponds to baseline levels of a nearly pristine environment.

Estuaries receive the anthropogenic pollutants of their watershed area. Dhamra estuary, on the east coast of India, is such an estuary that receives a huge amount of pollutants, and it will eventually pose a threat to the ecological sensitive areas in its vicinity. Therefore, a study was carried out on physico-chemical parameters and chlorophyll-a to delineate the sources of variation during pre-monsoon and post-monsoon seasons. Surface water sampling was carried out from 12 stations in the estuarine and coastal area. Factor analysis and cluster analysis were applied to seasonal data to understand the sources of variation. From the study, it was observed that the chemical parameters are severely affected by anthropogenic influences such as sediment dredging, aquaculture effluent, and waste from industry and sewage from upstream. In the long run, this will affect the nearby nesting ground of vulnerable Olive Ridley turtles, high bio-diverse mangrove forests, and saltwater crocodile habitat.

For the first time, the qualitative and quantitative characteristics of marine debris ingested by six hawksbill (Eretmochelys imbricata) and seven olive ridley (Lepidochelys olivacea) sea turtles from the Gulf of Oman coast of the United Arab Emirates were investigated. The numeric and gravimetric proportions of ingested marine debris obtained from the esophagus, stomach and intestines were quantified following categories of presumed sources, Marine Strategy Framework Directive (MSFD), rigidity, color and plastic polymer types. Marine debris was observed in 28.6% of olive ridley (x̅: 2.00 items; 4.83 g) and 83.3% of hawksbill specimens (x̅: 6.00 ± 2.32 items; 0.32 ± 0.24 g). Overall, the results of this preliminary study suggest that hawksbill sea turtles were ingesting marine debris at higher frequencies and that plastics were observed to be the most predominant debris ingested. However, non-plastic rubbish, particularly metallic fishing gear (fish hooks and fish traps), were observed to present lethal hazards for both species.

Studies of persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), organochlorinated pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs), in sea turtles are reported, but there are still spatial data gaps worldwide. POP contamination of live female blood plasma from Caretta caretta (n = 28), Chelonia mydas (n = 31) and Lepidochelys olivacea (n = 19), which nest in Brazil and feed along the South Atlantic Ocean, was investigated. Carbon and nitrogen stable isotopes from red blood cells (RBC) were also evaluated to obtain information about trophic ecology. C. caretta had the highest POP concentrations, followed by L. olivacea and C. mydas. PCBs predominated in all species, and the major OCPs were the DDTs (dichlorodiphenyltrichloroethane and derivatives) and Lindane. POPs and stable isotopes revealed intra- and interspecific variations, which reflect the high plasticity in the use of habitat and food resources, making individuals within the same population susceptible to different exposures to pollutants.

The Olive Ridley marine turtle (Lepidochelys olivacea) is characterized by individual morphological variability in the number and shape of scutes. The influence of pollutants on developmental instability and one of its consequences, the asymmetry of individuals, has been demonstrated in several species, especially invertebrates and some birds. However, the use of this asymmetry as a biomarker of contamination in adult individuals has never been explored. We developed an index to quantify developmental instability (DIx) based on the number and relative size of costal carapace scutes. The link between DIx and inorganic elements concentrations was explored in various tissues of stranded turtles from the Southern Mexican Pacific. The relationships between adult contamination and DIx could directly or indirectly reflect (i) the disruption of metal elimination in the adult stage dependent on embryonic perturbation and thus determining DIx, (ii) the difference in metal absorption dependent on DIx status, or (iii) DIx linked to other unknown factors.

Ingestion of marine debris is an established threat to sea turtles. The amount, type, color and location of ingested plastics in the gastrointestinal tracts of 55 sea turtles from Pacific longline fisheries from 2012 to 2016 were quantified, and compared across species, turtle length, body condition, sex, capture location, season and year. Six approaches for quantifying amounts of ingested plastic strongly correlated with one another and included: number of pieces, mass, volume and surface area of plastics, ratio of plastic mass to body mass, and percentage of the mass of gut contents consisting of plastic. All olive ridley (n=37), 90% of green (n=10), 80% of loggerhead (n=5) and 0% of leatherback (n=3) turtles had ingested plastic; green turtles ingested significantly more than olive ridleys. Most debris was in the large intestines. No adverse health impacts (intestinal lesions, blockage, or poor body condition) due directly to plastic ingestion were noted.

Concentrations of eight metals and metalloids (Pb, Cd, Cu, Zn, Mn, Se, Ni and As) were evaluated from 41 nesting females (blood) and 13 dead (tissues) Olive Ridley turtles (Lepidochelys olivacea), a species classified as vulnerable and also listed in Appendix I of the Convention of International Trade in Endangered Species (CITES). The mean blood, liver and kidney lead concentration were 0.02±0.01, 0.11±0.08 and 0.06±0.03μgg−1 ww respectively, values lower than other turtle species and locations, which it could be due to the gradual disuse of leaded gasoline in Mexico and Central America since the 1990s. Mean concentration of cadmium was 0.17±0.08 (blood), 82.88±36.65 (liver) and 150.88±110.99μgg−1 (kidney). To our knowledge, the mean renal cadmium levels found is the highest ever reported worldwide for any sea turtle species, while other six elements showed a concentration similar to other studies in sea turtles.

The ingestion of plastic marine litter (PML) by sea turtles is widespread and concerning, and the five species that occur in the southwestern Atlantic – green, loggerhead, olive ridley, leatherback and hawksbill – are vulnerable to this pollution. Here, we quantified and characterized PML ingested by these species in southern Brazil, and observed PML ingestion in 49 of 86 sampled individuals (~57.0%). Green turtles presented the highest rates and variety of ingested plastics, and such ingestion has been high at least since 1997. Omnivorous turtles presented higher PML ingestion than carnivorous ones. Loggerheads displayed a negative correlation between body size and number of ingested items. Green turtles ingested mostly flexible transparent and flexible/hard white plastics; loggerheads ate mainly flexible, hard and foam fragments, in white and black/brown colors. These results help us better understand PML ingestion by sea turtles, highlighting the seriousness of this threat and providing information for prevention and mitigation strategies.