Sea Turtles: Pollution's Impact On Their Habitat

Sea turtles are affected by water pollution in several ways, including through the ingestion of plastic waste, entanglement in abandoned fishing nets, and oil spills. They are vulnerable to pollution at all stages of their life and face threats from both marine and coastal pollution. Water pollution can cause immediate harm to sea turtles or build up in their tissues over time, leading to immunosuppression and disease. Pollutants may also accumulate in the food chain, increasing the concentration levels of chemicals and pollutants that sea turtles ingest.

Oil spills and urban runoff

Sea turtles are highly migratory and occupy different habitats throughout their lives, making them vulnerable to oil spills at all life stages. From eggs on beaches to adults migrating between nesting and foraging grounds, oil spills can have devastating consequences. Oil that washes up on beaches can contaminate nests and impact nesting females and hatchlings. Oil spills far offshore concentrate in convergence zones, which are crucial for young turtle development, and can have long-lasting effects on their growth and survival.

Urban runoff, including chemicals and fertilizers, also contributes significantly to water pollution. Fertilizers from farms and lawns cause eutrophication, leading to algal blooms that deplete oxygen and suffocate marine life, creating dead zones like those in the Gulf of Mexico. Improper sewage disposal further exacerbates this issue. These pollutants accumulate in the food chain, increasing concentration levels in the bodies of small animals that sea turtles consume, leading to health issues and reproductive problems in sea turtles.

The impact of oil spills and urban runoff on sea turtles is far-reaching and detrimental. It disrupts their habitats, affects their health and development, and threatens their survival. These issues highlight the importance of addressing water pollution and its sources to protect sea turtles and the marine ecosystems they depend on.

To address these issues, education and public awareness are crucial. People can reduce oil consumption, support renewable energy initiatives, follow local codes for fertilizer use, and advocate for better waste disposal practices to minimise the negative impacts of oil spills and urban runoff on sea turtle populations and their habitats.

Fertilizer and eutrophication

Eutrophication is an ecological phenomenon caused by a large influx of nutrients into an aquatic system. Nitrates and phosphates are key limiting nutrients that are scarce in the ocean and restrict algal and plant growth. Fertilizer runoff from farms, lawns, and sewage carries high concentrations of these nutrients and is carried to the ocean by rivers and streams.

Once the runoff reaches the ocean, the high availability of nutrients allows photosynthesis to flourish and algae to bloom. This process, known as algal bloom, is a rapid increase in algal populations in a marine system. This high density of photosynthesizing biota drastically affects the local water chemistry, clouding up the water and reducing light availability for marine plants. When this mass of algae dies, bacteria take over and decompose this organic matter, consuming much of the available dissolved oxygen in a process called aerobic decomposition.

The depletion of dissolved oxygen can lead to hypoxia or anoxia, causing mobile animal populations to flee the area, while less mobile populations may perish. This has severe ecological and economical impacts on the region. Sea turtles, in particular, are vulnerable to eutrophication at all stages of their lives. They may not only face immediate harm through direct contact with pollutants but also suffer from the accumulation of toxins in their tissues over time, leading to immunosuppression and various health issues.

Fertilizers are a significant contributor to eutrophication and marine pollution. In the Indian River Lagoon, for example, fertilizers are the largest source of nitrogen, a pollutant that also fuels eutrophication and algal blooms. To combat this issue, most municipalities in Florida have implemented a fertilizer ban during the rainy season to reduce the amount of fertilizer entering the lagoon through stormwater runoff.

Plastic ingestion and entanglement

Sea turtles are vulnerable to plastic ingestion and entanglement at all stages of their life. A recent survey found evidence of sea turtle entanglement and ingestion of marine debris in over 43 countries. Sea turtles have been recorded to be entangled in anything from lost fishing nets, plastic twine and nylon fishing line, six-pack rings from canned drinks, plastic packaging straps, plastic balloon string, kite string, plastic packaging and discarded anchor line and seismic cables.

All seven sea turtle species have been shown to ingest plastic. Plastic pollution poses a threat of entanglement, habitat degradation and ingestion. Microplastics occupy similar size ranges as some planktonic organisms and are consumed by pelagic and benthic marine organisms including planktivores, detritivores, and suspension feeders.

A study of 42 post-hatchling loggerhead sea turtles in Florida found plastic fragments in the gastrointestinal tracts of 39 of the 42 animals (92.86%). The plastic fragments ranged from 0.36 to 12.39 mm in length, with up to 287 fragments with a mass of up to 0.33 g per turtle. Hard fragments and sheet plastic were the most common type, while the dominant colour of the fragments was white.

Another study of oceanic-stage loggerhead turtles in the Azores region found that 83% of the turtles had ingested plastic. The average number of plastic items was 15.83 per individual, corresponding to a mean dry mass of 1.07 g.

The ingestion of plastic can cause intestinal blockage, malnutrition, reduced growth rates and even death. It can also cause physical discomfort that could affect feeding behaviour and buoyancy and swimming performance.

Light and noise pollution

Sea turtles are extremely sensitive to both light and noise. Light and noise pollution can therefore drive turtles away from critical foraging and nesting habitats.

Light Pollution

Unfiltered lights in coastal areas can disorient hatchlings and deter adult turtles from nesting. Coastal developments, such as condominiums, houses, and hotels, often discourage female turtles from nesting. If a female fails to nest after multiple attempts, she will resort to suboptimal nesting spots or deposit her eggs in the ocean, reducing the survival rate of hatchlings.

Artificial lights can cause two types of disturbances in hatchlings: misorientation, where hatchlings move in a circular motion or remain motionless without a clear direction; and disorientation, where hatchings crawl in the opposite direction of the ocean and move towards the artificial lights.

The intensity and wavelength of artificial light play a crucial role in hatchling behaviour. Studies have shown that green turtle hatchlings are highly attracted to wavelengths of light in the 350 to 450 nm range. White light has a stronger impact on hatchling behaviour than yellow light.

Noise Pollution

Persistent and abrupt low-frequency noise, such as seismic tests for energy exploration, can disturb turtles and may even cause hearing damage.

A study by the Woods Hole Oceanographic Institution found that turtles can experience temporary hearing loss from an excess of underwater noise. This high volume of sound, referred to as underwater noise pollution, can be caused by passing ships and offshore construction. The absence of studies on underwater noise and turtles has led to a data gap for endangered sea turtles.

The impact of light and noise pollution on sea turtles underscores the need for further research and the implementation of measures to reduce these types of pollution in critical habitats.

Chemical and effluent pollution

Sea turtles are vulnerable to chemical and effluent pollution at all stages of their life. Effluent, or wastewater, is discharged from a variety of sources, including manufacturers, oil refineries, wastewater treatment facilities, septic systems, and agricultural runoff. These sources can contain a range of harmful chemicals, heavy metals, and other toxins that contaminate water bodies and pose risks to sea turtles.

Agricultural runoff is a significant contributor to chemical and effluent pollution, as fertilizers, pesticides, and animal waste wash into waterways during rainfall. This leads to nutrient pollution, causing algal blooms that deplete oxygen levels and create "dead zones" where aquatic life cannot survive. Sea turtles' habitats overlap with areas affected by offshore oil exploration and production, making them particularly vulnerable to petroleum pollution from intentional discharges, vessel groundings, spills, and runoff from land-based sources.

Additionally, untreated wastewater in cities is a major concern, as it is often discharged directly into nearby water bodies without proper treatment. This type of effluent pollution contains household chemicals, human waste, toxic chemicals, and medical waste, which contaminate the environment and pose risks to both human and sea turtle health.

The impact of chemical and effluent pollution on sea turtles is a critical area of research in conservation efforts. By understanding the effects of these pollutants on sea turtle development, health, reproduction, and habitat condition, scientists can better address the threats posed by this type of pollution and work towards mitigating its impact on sea turtle populations.

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