The world’s seven species of sea turtles are facing population declines due to human activity. Every species is classified as vulnerable, endangered, or critically endangered, reflecting the cumulative pressures they face across their vast migratory ranges. As long-lived reptiles inhabiting both coastal waters and the open ocean, sea turtles serve as important biological indicators of marine ecosystem health. The pervasive nature of human pollution, from microplastics to toxic chemicals accumulating in the food web, directly impacts their survival at every life stage.
The Threat of Plastic Ingestion and Microplastics
Sea turtles frequently consume plastic debris, often mistaking it for natural prey. Species that feed on gelatinous organisms, such as leatherbacks, are particularly susceptible to ingesting clear plastic bags, which resemble jellyfish floating in the water column. Large plastic pieces, or macroplastics, are dangerous because they cannot be digested or passed through the gut. The ingested plastic causes internal blockages, preventing nutrient absorption and leading to false satiety, meaning the turtle starves while feeling full. Sharp plastic fragments can also cause physical damage, leading to gut perforation and infection. Younger turtles are vulnerable because their smaller digestive tracts are easily obstructed by debris.
Microplastics
The problem extends to microscopic fragments known as microplastics, which are less than five millimeters in size. These particles are nearly ubiquitous in ocean waters, and studies show a high percentage of sea turtles have ingested them. Microplastics can carry adsorbed pollutants on their surface, introducing toxic chemicals into the turtle’s system upon ingestion. The concentration of microplastics is especially high in the pelagic zones where young turtles spend their early years.
Physical Entanglement and Ghost Gear
A significant physical threat to sea turtles is entanglement in discarded fishing equipment, often referred to as “ghost gear.” Ghost gear includes abandoned nets, lines, traps, and ropes made from durable synthetic materials that continue to catch marine life for years. Entanglement restricts the turtle’s movement, making it difficult to forage or escape predators.
For air-breathing reptiles, a major consequence is drowning, as the weight of the gear prevents them from reaching the surface to breathe. The materials wrap tightly around the flippers, neck, and carapace, causing deep lacerations and severe infections. These wounds often compromise blood flow, resulting in the eventual loss or amputation of a flipper.
Chemical Contamination and Bioaccumulation
Sea turtles are subjected to a wide array of chemical pollutants, including heavy metals, oil spills, and persistent organic pollutants (POPs). Heavy metals like mercury, lead, and cadmium are non-biodegradable and enter the marine food web from industrial sources. POPs, such as PCBs and DDT, are lipophilic, meaning they dissolve easily in fat.
Bioaccumulation and Endocrine Disruption
The long lifespan and migratory nature of sea turtles make them susceptible to bioaccumulation, where these fat-soluble toxins build up in the body’s fatty tissues over time. Studies indicate that mercury concentrations can be negatively correlated with immune function, suggesting immune system suppression. The liver and kidneys, organs responsible for detoxification, are highly affected by the accumulation of heavy metals.
Chemicals, particularly POPs and plastic-derived chemicals, can also act as endocrine disruptors. These substances interfere with the turtle’s hormonal system, potentially impacting growth, development, and reproductive success. The feminizing effect of some pollutants is a concern, as it can skew the ratio of male to female hatchlings.
Disruption of Nesting Habitats
Pollution affects sea turtles during their reproductive phase on land as well as in the ocean. Artificial light pollution, often from coastal development, is a major factor disrupting nesting. Female turtles emerging to lay eggs are often deterred by bright lights, causing them to abandon their nesting attempt, known as a false crawl.
Light Pollution and Hatchlings
The most significant impact of light pollution is on the hatchlings, who rely on natural light cues to orient themselves toward the ocean. Artificial lights from buildings and vehicles disorient the hatchlings, causing them to crawl inland instead of toward the sea. This misdirection increases their risk of dehydration, exhaustion, and predation, reducing their chances of survival.
Physical Debris on Beaches
Physical debris on nesting beaches also poses an obstacle to successful reproduction. Piles of trash and plastic waste can block the path of a nesting female, preventing her from finding a suitable spot to dig her nest. For emerging hatchlings, the debris creates a physical barrier, trapping them or slowing their journey from the nest to the ocean.