Sea turtles are ancient marine reptiles integral to the health of marine ecosystems. These migratory creatures inhabit diverse environments, from nesting beaches to open seas, maintaining seagrass beds and coral reefs. Today, sea turtles face numerous threats, with pollution emerging as a significant concern. Human-generated contaminants in marine environments pose serious risks to their survival, contributing to declining populations globally.
Major Pollutants Threatening Sea Turtles
Various types of pollution threaten sea turtles, originating from human activities and entering marine environments through diverse pathways. Plastic debris, a widespread contaminant, includes macroplastics like bags and bottles, often entering the ocean from land-based sources. Microplastics, tiny fragments from larger plastics, also permeate ocean waters.
Oil spills, from offshore exploration, shipping accidents, or land runoff, introduce petroleum products into marine habitats. These substances can spread widely, affecting both open ocean areas and coastal zones.
Chemical contaminants include pesticides and fertilizers from agricultural runoff, industrial discharges containing heavy metals and polychlorinated biphenyls (PCBs), and untreated waste. These chemicals often reach the ocean through rivers and atmospheric deposition.
Artificial light emissions from coastal development significantly alter the natural darkness of nesting beaches. This light pollution extends into the night sky, impacting areas even some distance from direct sources. Noise disturbances, generated by shipping, seismic surveys, and naval sonar, introduce disruptive sounds into the underwater environment. These human-made noises can travel long distances, permeating vast areas where sea turtles forage and migrate.
Direct Physical and Physiological Impacts
Pollution directly harms sea turtles, compromising their health and survival. Ingestion of plastic debris is a common threat, as turtles often mistake items like plastic bags for jellyfish. This leads to internal blockages, digestive system damage, and false satiation, causing starvation and malnutrition. Plastic and other debris have been found within the stomachs and intestines of deceased turtles.
Entanglement poses another physical danger, primarily from discarded fishing gear, or “ghost gear,” and other plastic refuse. Turtles can become ensnared in nets and lines, leading to drowning, limb loss, restricted movement, and chronic injuries. This can also hinder their ability to surface for air or feed effectively.
Exposure to oil and chemical contaminants results in toxicosis and organ damage. Oil can irritate sensitive mucus membranes in the eyes, mouth, and respiratory and digestive tracts. Toxic compounds in oil can be absorbed into vital organs like the lungs and liver, causing internal poisoning. Chemical pollutants, including heavy metals and PCBs, can accumulate in tissues, leading to liver and kidney damage, skin lesions, and immune system suppression.
Chemical pollutants can also impair reproduction by disrupting hormone systems, resulting in reduced fertility, abnormal eggs, or altered hatchling sex ratios. Pollutant exposure increases disease susceptibility by weakening the immune system. Fibropapillomatosis (FP), a tumor-forming disease linked to a herpes virus, is correlated with water pollution and prevalent in green sea turtles. Excess nitrogen from runoff, accumulating in algae consumed by turtles, has been linked to the virus’s growth.
Disruption of Sea Turtle Behavior and Ecosystems
Pollution disrupts sea turtle behavior, life cycles, and the ecosystems they depend on. Altered foraging habits occur when pollutants degrade food sources or render them toxic. Oil contamination, for instance, can kill seagrass beds, a primary food source for green sea turtles, forcing them to seek sustenance in less suitable areas or consume contaminated prey. This can lead to reduced food availability and poorer health.
Navigational disorientation is a significant behavioral impact, especially from light pollution. Artificial lights from coastal development disorient nesting females, causing them to abandon nesting attempts or crawl in circles. Hatchlings, naturally drawn to the ocean’s brightest horizon, are misled by artificial lights and crawl inland, increasing their vulnerability. Noise pollution from human activities like shipping and seismic surveys can interfere with sea turtles’ acoustic navigation and communication, potentially causing them to abandon important habitats. Intense underwater noise can lead to temporary hearing loss, impairing their ability to detect environmental cues.
The degradation of critical habitats is a widespread consequence of marine pollution. Oil and plastic debris can contaminate nesting beaches, making them unsuitable for egg-laying and hatchling emergence. Foraging grounds, such as coral reefs and seagrass beds, can be severely affected by chemical runoff and physical debris, diminishing their capacity to support sea turtle populations. This contamination extends to migratory pathways, forcing turtles to navigate through polluted waters.
Food web contamination results from the bioaccumulation and biomagnification of toxins. Pollutants like heavy metals, released into the marine environment, are absorbed by microscopic organisms at the base of the food web. As these contaminated organisms are consumed, toxins become more concentrated at each successive trophic level. Sea turtles, as consumers, can accumulate dangerous levels of pollutants, affecting their health and potentially impacting the entire ecosystem.