Scleractinian corals incorporate microplastic particles: identification from a laboratory study

Abstract

Microplastics have been detected on beaches and in the ocean from surface habitats to the deep-sea. Microplastics can be mistaken for food items by marine organisms, posing a potential risk for bioaccumulation and biomagnification in the food chain. Our understanding of microplastic pollution effects on ecosystem and physiological processes of coral reefs is still limited. This study contributes to the understanding of effects of microplastic pollution on skeletal precipitation of hermatypic corals. In a five month aquarium-based experiment, specimens of four tropical species were temporarily exposed to high concentrations (ca. 0.5 g L-1) of polyethylene terephthalate (PET) microplastic particles (< 500 μm). The coral specimens all survived this treatment and show skeletal growth. The skeletal material produced during the experiment, however, incorporated plastic particles and plastic fibres in the aragonitic structure. Long-term consequences of such inclusions on skeletal properties such as stability are yet unknown.

Reef‐building corals act as long‐term sink for microplastic

“…Ingested particles occasionally get stuck in gastrovascular cavities (Allen et al, 2017) and can be translocated from tissue to the skeleton during growth. Translocation of microplastic to the skeleton has been recently proven through thin section analyses and likely occurs during the formation of a new basal plate, which is periodically built on top of the old one and leads to the formation of chambers within the skeleton (Hierl et al, 2021). Another mechanism of plastic uptake is the overgrowth and encrustation of particles stuck to a surface (Hierl et al, 2021;Reichert et al, 2018).…”

“…Translocation of microplastic to the skeleton has been recently proven through thin section analyses and likely occurs during the formation of a new basal plate, which is periodically built on top of the old one and leads to the formation of chambers within the skeleton (Hierl et al, 2021). Another mechanism of plastic uptake is the overgrowth and encrustation of particles stuck to a surface (Hierl et al, 2021;Reichert et al, 2018). Particle density, in contrast, was stronger determined by colony shape parameters.…”

“…First observations of microplastic particles in the skeleton of tropical coral species (Ding et al, 2019;Hierl et al, 2021;Krishnakumar et al, 2021) and the tissue of the temperate coral Astrangia poculata (Rotjan et al, 2019) suggest that reef-building corals may act as longterm sink for microplastic (Soares et al, 2020). However, it remains unclear what quantity of particles is deposited, and which processes determine the permanent deposition in coral colonies.…”

Microplastics alter feeding strategies of a coral reef organism

“…However, coral reefs are generally located in areas that accumulate large amounts of plastic waste because of a combination of high population densities, lack of developed waste management (Morrison and Munro 1999;GESAMP 2015), and ocean currents (Berloff et al 2002;Connors 2017). The responses of reef-building scleractinian corals to microplastic exposure include microplastic ingestion (Hall et al 2015;Hankins et al 2018), changes in feeding behavior (Allen et al 2017;Rotjan et al 2019;Savinelli et al 2020), and incorporation of microplastic into the skeleton (Hierl et al 2021). Furthermore, visible stress reactions (e.g., polyp retraction and increased mucus production), which potentially deplete energy reserves of the coral, and increased disease likelihood have been documented when corals are in contact with plastics (Lamb et al 2018;Reichert et al 2018).…”

Microplastics: impacts on corals and other reef organisms

“…Plastic particles have been found embedded within the skeletal matrix of both experimental and colonies collected from the wild [79,[88][89][90][91][92]. Two mechanisms by which the particles become trapped within the skeleton have been suggested.…”