Combined effects of short term exposure to seawater acidification and microplastics on the early development of the oyster Crassostrea rivularis

Ocean acidification and microplastics pollution are two consequences of anthropogenic activities. In regions such as estuarine areas, ocean acidification (OA) and microplastics (MPs) pollution are occurring simultaneously. The present study tested the combined effects of OA and MPs on the embryonic development and physiological response of the larval oyster Crassostrea rivularis in a short exposure duration. The fertilization process was exposed to six combinations of three MPs levels (0, 10 and 1000 items L-1) x two pH levels (7.3, 8.1) for 9 d after hatching. As a result, the hatching rate was not affected by either pH reduction or MPs exposure, while the deformation rate increased under low pH, MPs exposure and their combination. Larval shell length was reduced under low pH, MPs exposure and the combined exposure of the two factors. Furthermore, swimming speed decreased under low pH throughout the experiment but the MPs' effect was limited. Predictably, MPs in the body increased with the increase of MPs concentration. Compared to low pH, the oyster ingested more MPs under normal pH. But combined OA and MPs didn't affect the MPs intake. Moreover, no significant effects of OA and MPs on total antioxidant capacity and malondialdehyde were observed. However, alkaline phosphatase was significantly affected by low pH and MPs exposure independently. PCA showed that development of C. rivularis larvae changed over time and MPs concentration increase augmented intake of MPs by oysters. Consequently, we speculate that OA and MPs exposure may harm oyster C. rivularis embryonic and larval development, but not induce their antioxidant response in a short duration. Long term study about combined effects of OA and MPs on C. rivularis development is needed in the future.