Crabs In Crisis: Plastic Pollution's Impact

Crabs are among the many marine species affected by plastic pollution. Plastic pollution has been found to cause harm to crabs in various ways, from entanglement and ingestion to toxic contamination. Crabs can become trapped in plastic containers, unable to escape and eventually dying of starvation. Additionally, crabs may ingest microplastics, which can have negative consequences for their health. Studies have also shown that crabs are attracted to certain chemicals in plastics, such as oleamide, which can have toxic effects and even lead to cancer. With plastic pollution reaching even the most remote corners of the world, the impact on crab populations and the wider ecosystem is a growing concern.

Crabs are attracted to plastic

Research has found that hermit crabs exposed to low concentrations of oleamide show a behavioural attraction comparable to their response to a feeding stimulant. This is likely because oleamide resembles oleic acid, a chemical released by arthropods during decomposition. As scavengers, hermit crabs may mistake oleamide for a food source, creating a trap.

In addition to the chemical attraction, plastic pollution also creates physical barriers and deadly traps for crabs. Crabs can become trapped inside plastic containers and are unable to escape, eventually dying. This is especially true for hermit crabs, which require shells for shelter and protection. When a hermit crab dies, it emits a chemical signal that attracts other crabs, who may then fall into the same trap. This creates a gruesome chain reaction, leading to the deaths of many crabs.

The impact of plastic pollution on crab populations can be significant, with studies finding hundreds of thousands of crabs killed by plastic debris on remote islands. Given the amount of plastic dumped into our oceans each year, this problem is only expected to worsen.

Crabs get trapped in plastic containers

Crabs, particularly hermit crabs, are highly susceptible to becoming trapped in plastic containers. This is due to their natural behaviour of seeking out shells, which are essential for their survival and protection. When a crab dies, it emits a chemical signal, indicating the availability of a shell. This scent attracts other crabs, who are then lured into the deadly trap.

The design of plastic containers further exacerbates the problem. The openings of these containers often face upward, allowing crabs to crawl in but making it difficult for them to crawl out due to the smooth and slippery sides. Once trapped, the crabs eventually die from dehydration and sun exposure.

The issue of crabs being trapped in plastic containers is not an isolated incident. Researchers studying the impact of plastic pollution on crab populations have found shocking results. On average, each plastic bottle trapped about nine crabs, with one container holding the shells of 526 crabs. This was discovered on remote islands in the Indian Ocean and the Pacific, far from highly populated areas, yet inundated with plastic waste.

The problem is likely to be widespread, affecting hermit crab populations on islands worldwide. With the constant influx of plastic pollution, the piles of debris on beaches create physical barriers and deadly traps for crabs, leading to a gruesome chain reaction of entrapment and death. The very mechanism that ensures their survival—the search for shells—has become a lethal lure due to human-made plastic waste.

The impact of these losses on ecosystems cannot be overstated. Hermit crabs play a crucial role in their environments, including aerating and fertilising soil, dispersing seeds, and maintaining the nutrient cycle. Their absence would have far-reaching consequences for the delicate balance of nature. It is imperative that we address our actions, especially regarding the use of single-use plastic products, to prevent further harm to these vulnerable creatures and the ecosystems they inhabit.

Crabs ingest microplastics

A study by the University of Exeter used fluorescently labelled polystyrene microspheres to show how ingested microplastics were retained within the body tissues of the common shore crab, Carcinus maenas. Multiphoton imaging suggested that most microspheres were retained in the crab's foregut after sticking to hair-like 'setae' structures within them. The study also found that when microplastics are drawn in through gills, they take over six times longer to leave the body compared to standard digestion.

The impact of microplastics on crab populations is not yet fully understood, but it is known that they can cause toxic contamination. Microplastics can adsorb toxins, which can then be transferred to the fatty tissues of the crabs that ingest them. This can have detrimental effects on the overall population of crabs and the ecosystem as a whole.

Additionally, a chemical called oleamide, which is released from plastics dumped in the ocean, has been found to increase the respiration rates of hermit crabs, causing hyperactivity. Crabs are attracted to this chemical due to its similarity to oleic acid, a naturally occurring chemical released by their food sources. This attraction could waste the crabs' energy and potentially lead to negative health consequences if ingested.

Crabs are affected by plastic additives

The impact of plastic additives on crab behaviour has been observed in studies conducted by the University of Hull off the Yorkshire coast, specifically in Robin Hood's Bay. These studies revealed that crabs exhibited a behavioural attraction to oleamide, mistaking it for a feeding stimulant. This attraction may be due to the presence of oleamide in the sex pheromone of cleaner shrimp, a distant relative of the hermit crab, indicating a potential broader role in chemical signalling across species.

Additionally, plastic pollution, in combination with rising sea temperatures, can disrupt the breeding cycles of marine invertebrates such as blue mussels. Research has shown that male blue mussels are affected by increased temperatures, while females are more sensitive to a toxic chemical found in plastics known as DEHP. As a result, the reproduction rates of these species may be negatively impacted.

The presence of plastic additives in the ocean can also impair the sense of smell of hermit crabs and other marine creatures. Lower environmental pH caused by ocean acidification can alter the chemical properties of odour molecules, affecting the ability of crabs to detect and interpret smell-related information accurately. This disruption in communication can have further detrimental effects on the behaviour and survival strategies of crab populations.

Overall, the impact of plastic additives on crabs is complex and multifaceted, influencing their behaviour, reproduction, and survival in both direct and indirect ways. Further research and understanding of these impacts are crucial to address the growing issue of plastic pollution in marine ecosystems and mitigate its effects on crab populations and other marine life.

Crabs are at risk of starvation due to plastic pollution

The ingestion of plastic has been found to have dire effects on the crab population. A study by the University of Exeter found that microplastics ingested by common shore crabs were retained in the foregut, sticking to hair-like structures within the crabs' bodies. This blockage in their digestive system leads to reduced food intake, resulting in starvation and potentially death.

The problem is exacerbated by the fact that plastic pollution acts as a trap for crabs, creating physical barriers that hinder their movement and ability to find food. Piles of plastic on beaches and in coastal areas create deadly traps, with crabs crawling into containers and becoming trapped, unable to escape. This was evident in a study that found 526 hermit crabs trapped and killed in a single container.

The impact of plastic pollution on crab populations is not limited to starvation but also extends to toxicity and hyperactivity. The chemicals in plastic, such as oleamide, can be toxic to crabs, leading to negative health effects, including cancer. The increased respiration rates caused by oleamide exposure can waste the crabs' energy, further contributing to their risk of starvation.

Additionally, the presence of plastic can disrupt the natural cycle of renewal in ecosystems. Crabs play a vital role in fertilizing and aerating soil, dispersing seeds, and maintaining healthy coral reefs. When plastic debris smothers and breaks coral reefs, it hinders the ability of crabs to carry out these essential ecological functions, impacting the availability of food sources for themselves and other species.

Frequently asked questions