Assessing the effects of ocean acidification on larval Mediterranean mussels (Mytilus galloprovincialis) and California mussels (Mytilus californianus): growth, survival, and microbiome community composition

Ocean acidification (OA) affects marine calcifying organisms in a variety of ways, including: growth, survival, disease resistance, microbial communities, and physiological functions. With oceanic pH projected to drop to 7.7 or lower by the year 2100, it is important to the aquaculture industry to characterize the affects of these environmental conditions on species of economic and ecological importance. Associated microbiota can have a strong impact on organismal health, however, the microbiomes of many aquaculture species are only beginning to be thoroughly investigated within the context of climate change. This study assessed the growth, survival, and microbial communities of two mussel species, the Mediterranean mussel Mytilus galloprovincialis and the California mussel Mytilus californianus in response to experimental low-pH exposure across larval development (2–21 days post-fertilization). We found that experimental exposure resulted in significant decreases in growth rates for both species, but did not strongly affect larval survival probability. Sequencing of the V3-V4 region of the 16S ribosomal subunit demonstrated that although microbial membership and relative abundance were similar between the two mussel species, diversity measures were significantly different. Following exposure, we found that reduced-pH during the larval stage resulted carry-over effects into adulthood of wet weight and total length in M. galloprovincialis mussels. The results suggest that OA exposure during the larval stage may exert stronger effects in M. galloprovincialis than in M. californianus and provide insights into the response of mussel microbial communities to future ocean conditions.