Coastal bays and coral cays: Multi-element study of Chelonia mydas forage in the Great Barrier Reef (2015-2017)

Green Turtle (Chelonia mydas) Blood and Scute Trace Element Concentrations in the Northern Great Barrier Reef

Marine turtles face numerous anthropogenic threats, including that of chemical contaminant exposure. The ecotoxicological impact of toxic metals is a global issue facing Chelonia mydas in coastal sites. Local investigation of C. mydas short-term blood metal profiles is an emerging field, while little research has been conducted on scute metal loads as potential indicators of long-term exposure. The aim of the present study was to investigate and describe C. mydas blood and scute metal profiles in coastal and offshore populations of the Great Barrier Reef. This was achieved by analyzing blood and scute material sampled from local C. mydas populations in five field sites, for a suite of ecologically relevant metals. By applying principal component analysis and comparing coastal sample data with those of reference intervals derived from the control site, insight was gleaned on local metal profiles of each population. Blood metal concentrations in turtles from coastal sites were typically elevated when compared with levels recorded in the offshore control population (Howick Island Group). Scute metal profiles were similar in Cockle Bay, Upstart Bay, and Edgecumbe Bay, all of which were distinct from that of Toolakea. Some elements were reported at similar concentrations in blood and scutes, but most were higher in scute samples, indicative of temporal accumulation. Coastal C. mydas populations may be at risk of toxic effects from metals such as Co, which was consistently found to be at concentrations magnitudes above region-specific reference intervals. Environ Toxicol Chem 2023;42:2375-2388. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Transfer and accumulation of trace elements in seawater, sediments, green turtle forage, and eggshells in the Xisha Islands, South China Sea

Chemical pollutants present a substantial threat to the survival of the green turtle (Chelonia mydas). In this study, the concentrations of 12 trace elements (TEs) in seawater, sediments, and green turtle forage and eggshells from the Xisha Islands in the South China Sea, along with their patterns of transfer and accumulation, were identified. The results revealed that the median TE concentrations in seawater and sediments were lower than the first-grade limit values of the national standard in China, indicating a low ecological risk. The concentrations (μg·g-1) of TEs in forage ranged from 0.05-0.69, 3.43-14.4, 157-2391, 27.9-124, 2.05-9.39, 0.30-9.78, 2.01-80.50, 0.18-5.76, 0.06-0.98, 2.00-18.4, 0.02-0.24, and 0.01-0.09 for Cr, Mn, Sr, Fe, Ni, Cu, Zn, Se, Cd, As, Pb, and Hg, respectively. Seawater, sediments, turtle forage, and eggshells exhibited different TE profiles, which were driven by Hg, Sr, Cr, and Pb in seawater and sediments; Fe and Ni in sediments; Cd and As in forage; and Zn, Se, and Cu in eggshells. The contents of Cu, Zn, and Se increased slightly with trophic level, indicating that they were transferred through dietary pathways. Although Cd and As appeared to bioaccumulate in green turtle forage, it was not transferred to their eggshells, which may be related to the excretion and metabolism process in the mother's body. Thus, eggshells may be a poor bioindicator for the exposure of female green turtles to these toxic elements.

Trace element concentrations in forage seagrass species of Chelonia mydas along the Great Barrier Reef

Toxic metal exposure is a threat to green sea turtles (Chelonia mydas) inhabiting and foraging in coastal seagrass meadows and are of particular concern in local bays of the Great Barrier Reef (GBR), as numerous sources of metal contaminants are located within the region. Seagrass species tend to bioaccumulate metals at concentrations greater than that detected in the surrounding environment. Little is known regarding ecotoxicological impacts of environmental metal loads on seagrass or Chelonia mydas (C. mydas), and thus this study aimed to investigate and describe seagrass metal loads in three central GBR coastal sites and one offshore site located in the northern GBR. Primary seagrass forage of C. mydas was identified, and samples collected from foraging sites before and after the 2018/2019 wet season, and multivariate differences in metal profiles investigated between sites and sampling events. Most metals investigated were higher at one or more coastal sites, relative to data obtained from the offshore site, and cadmium (Cd), cobalt (Co), iron (Fe) and manganese (Mn) were found to be higher at all coastal sites. Principle Component Analysis (PCA) found that metal profiles in the coastal sites were similar, but all were distinctly different from that of the offshore data. Coastal foraging sites are influenced by land-based contaminants that can enter the coastal zone via river discharge during periods of heavy rainfall, and impact sites closest to sources. Bioavailability of metal elements are determined by complex interactions and processes that are largely unknown, but association between elevated metal loads and turtle disease warrants further investigation to better understand the impact of environmental contaminants on ecologically important seagrass and associated macrograzers.

Trace elements in green turtle eggshells and coral sand sediments from the Xisha Islands, South China Sea

This study investigated 12 trace elements in paired green turtle (Chelonia mydas) eggshell composites and coral sand samples to examine within-habitat heavy metal pollution from 40 nesting sites in the Xisha Islands. The concentrations of the elements (μg·g^-1) found in the eggshells ranged as follows: Sr (41.3) > Zn (20.3) > Cu (12.8) > Fe (4.92) > Al (4.37) > Se (2.44) > Mn (0.91) > Cr (0.81) > Ba (0.44) > Pb (0.14) > As (0.08) > Cd (0.02). Significant correlations were observed between the levels of Cd and Se and the levels of Zn, Cu, and Pb in eggshells. The concentrations of Mn, Zn, Se, As, Cd, and Pb in C. mydas eggshells were significantly correlated with those in coral sand sediments. Cu concentrations in the eggshells exceeded the toxic reference value for bird eggs and Se concentrations were between the worst- and best-case scenario hazard quotients.

Editorial - Virtual special issue (VSI) green turtles as silent sentinels of pollution in the Great Barrier Reef - Rivers to Reef to Turtles project

This special issue of STOTEN is dedicated to presenting the results of the WWF-Australia "Rivers to Reef to Turtles" project, which focused on investigating pollutants in the environment, food and bodies of green turtles (Chelonia mydas) on the Great Barrier Reef (GBR). The project brought together organic and inorganic trace chemical analysis, bioanalytical tools and individual health monitoring to investigate potential causes of an unusual mortality event in 2012. Together, the ten studies in this special issue highlight the shortcomings of current chemical monitoring and impact assessment programmes, which are focused on a limited number of prioritised chemicals and fail to account for the incredible diversity of toxicants released by human activities. It is essential that future management efforts consider the impact of these contaminants on the GBR, already under threat from global warming and sediment and nutrient runoff. Understanding the impact that chemical contaminants have on turtles not only informs green turtle conservation but can also, as they are sensitive and long-lived bioindicators of environmental health, guide efforts to protect, conserve and restore marine ecosystems such as the GBR.