Microplastic ingestion in invertebrates within rockpool communities

Abstract

Microplastics (<5 mm) are abundant across the world in the marine environment and so it is vital that we gain further understanding of their fate and their possible impacts on marine life. Due to their size, microplastics can interact with small marine organisms which are part of the lower trophic levels and the main interaction with these plastics is ingestion. Chemical characteristics and changes to the plastic properties, due to, for example, adsorbed chemicals and colonisation of biofilms, may affect how readily plastics are ingested. Research into the interactions of a range of organisms with microplastics enables for a better understanding of how they could be taken in, impact the organism as well as predict potential trophic transfer. This in turn could aid in predicting bigger impacts in the marine environment and on humans themselves. Rockpools are a key environment and nursery for many important marine and intertidal species, particularly those that we rely on commercially, such as crab species. This study exposed three key rockpool species of three feeding types - Beadlet anemone (Actinia equina), common prawn (Palaemon serratus), Thick top shell (Phorcus lineatus) to nylon fibres within ex-situ mesocosms. These species represent three feeding types found in a rockpool community – Suspension feeding, Filter feeding of the whole water column and deposit feeding. The organisms were exposed to either biofouled or non-biofouled, blue, black, red, or white in colour and 0.5 mm or 2 mm microfibres for six hours. This was undertaken when individuals were individually housed as single species, as well as a mixed community with a representative of all three species. Once biofouling was complete, dissection to observe the digestive tract was undertaken and then an alkaline digest was completed to obtain evidence of retention other than in the digestive tract. Beadlet anemones ingested the most microfibres and thick top shell the least. This study shows that overall, biofouled fibres are significantly more likely to be ingested than 6 that of non-biofouled (H(1)= 16.780 , p<0.001). Some ingestion and interaction colour patterns were found – black in anemones and shrimp ((H(1)= 6.224 , p=0.013 and (H(1)= 6.008 , p=0.014) and black (H(1)= 12.270 , p=0.007) and white in shrimp (H(1)= 8.143 , p=0.043). This could possibly be to do with the dye chemicals on the plastics rather than visual cues. The 0.5mm fibres were ingested and retained more than 2mm (H(1)= 20.924 , p<0.001). Thick top shells were the only organism with a difference between housing with more microfibres ingested/retained when housed individually than when housed in a mixed community. This study provides further evidence of the potential ingestion and retention of microplastics in a rockpool setting and therefore highlights the potential impact on these organisms and predator species. This may likely cause negative impacts within that rockpool as well as present a route for microfibres to expose other intertidal organisms to microfibres, particularly as the three study organisms are prey animals to many other species.