Why do marine organisms ingest plastic? Plastic is yummy!

Ever wondered what drives marine organisms to ingest plastics? Can it be that they find it tasty?

Many marine organisms rely on chemosensory systems enabling them to locate food. Such organisms include corals, sea anemones, marine snails, and crustaceans. Fish and sea turtles also use chemoreception to determine if potential prey items should be ingested or rejected.

So, what does this feeding strategy have to do with plastic?

Plastics have been found to release compounds known as phagostimulants, which act as chemical cues. When organisms that rely on chemosensory cues detect these phagostimulants, it triggers a feeding response, leading to the ingestion of plastic and microplastics.

Another factor influencing the palatability of plastics and microplastics is what lives on their surfaces. Epibionts and biofilms can mimic the characteristics of natural prey, causing organisms to mistake fully ingest these plastic particles.

Biofilm formation on the surfaces of plastic sheets (sourced by Lobelle and Cunliffe, 2011).

Certain sea anemones, like the sandy anemones (Bunodactis reynaudi) along the Muizenberg beach, in South Africa, actively ingest flexible HDPE (high-density polyethylene) bags and packets due to the presence of phagostimulants and epibionts.

Examples of plastic items ingested by sea anemones found along the coast of South Africa (sourced by The Beach co-op).

The adsorption of certain chemicals, like dimethyl sulfide, onto plastic, can further increase its palatability, increasing the ingestion by organisms that rely on chemical cues to detect food.

What happens once plastics and microplastics are ingested?

Some sea anemones have symbiotic algae, that provide the sea anemones of nutrients via photosynthesis for growth and health. However, the presence of microplastics impairs the establishment of this symbiotic relationship. Without the support of the algae, sea anemones can struggle to get food, which can lead to health issues and reduced resilience.

Removing compounds such as phagostimulants from plastic may help reduce plastic and microplastic ingestion by organisms that rely on chemoreception. Alternatively, adding compounds to plastics that deter ingestion could also reduce the likelihood of plastic consumption.

In conclusion, by understanding these small-scale interactions, we can better appreciate the urgency of addressing plastic pollution in our oceans. Exploring the palatability of microplastics to marine organisms reveals more than just their susceptibility to ingesting these particles—it provides insight of the ripple effects on marine food webs and ecosystem health.

By Cornel-Mari du Preez

MSc student

Unit for Environmental Science;

North-West University

Potchefstroom 

South Africa

cornelmarivdmerwe@gmail.com