Microplastics: effects on oyster physiology and reproduction

Plastics are persistent synthetic materials, which can accumulate in the marine environment. Although the consequences of macroplastic debris for wildlife are well documented, the impacts of microplastics on marine life are still largely unknown. Microplastics are defined as plastic particles smaller than 1 mm and may derive from many different sources. Filter feeders organisms are likely to be impacted by MP pollution as they filter large volumes of water and can ingest little particles while feeding. Occurrence and effects of MP filtration evidenced reduction of the feeding activity, inflammatory response and translocation of MP in the circulatory system. Longer term effects on growth, survival or reproduction are still unknown. As part of the MICRO EUInterreg project (MicroPlastics – Is it a threat for the 2 seas Area?), biological effects of MP were assessed through an integrative approach on the Pacific oyster Crassostrea
gigas during a gametogenesis period.
A chronic exposure of adult oysters to MP, during two months, was performed under controlled conditions using a mix of yellow-green fluorescent polystyrene MPs (2 and 6 μm). Appropriate experimental conditions were designed to induce gametogenesis. Physiological perturbations were assessed by measuring ecophysiological behaviour (ingestion rate, assimilation efficiency), condition index and reproductive effort. A preferential uptake of 6 μm particles was observed compared to 2 μm. Ingestion rate in MP exposed animals was significant higher, supposedly to compensate the lower energy intake. Reproductive effort tended to be reduced together with a significant decrease in the total number of produced oocytes (-40%). This could be caused by a disruption of the energetic metabolism and should be explored further. These measurements would help defining toxic endpoints and to guide future studies on the effects of MP on Pacific oyster physiology.