Ocean warming and acidification alter calcification and innate immune system gene expression in juvenile American lobsters, Homarus americanus.

The Gulf of Maine, home to American lobster, Homarus americanus, is experiencing rapid ocean warming (OW) and acidification (OA) due to climate change. While some studies have investigated the effects of either ocean acidification (OA) or warming (OW) on lobsters, few explore the interaction of these stressors, particularly on gene expression. We evaluated the effects of OA and OW on early benthic juvenile lobster transcriptomics using RNA sequencing and RT-qPCR through two distinct aquarium experiments. Lobsters were reared under OW/OA conditions aligned with values predicted for 2100: decrease in pH by 0.3-0.4 units; mean sea surface warming of 2.89 °C. RNA was isolated from carapace hypodermal tissue in both experiments. The multi-stressor treatment in the RNAseq experiment had the greatest differential expression. Genes of interest pertaining to calcification and cuticle development were primarily downregulated under high temperature but upregulated under acidified and multi-stressor conditions. In the RT-qPCR experiment, crustin alone was significantly downregulated and only under the most extreme multi-stressor treatment. This gene along with the prophenoloxidase activating enzyme had expression that trended toward downregulation across all treatments, suggesting a possible correlation to immune suppression. Expression profiles for crustin and the calcification gene, carbonic anhydrase differed across treatments based on molt cycle timing, indicating that stressor impacts may vary depending on the molt cycle phase. Elevated temperature had a greater effect on the expression of calcification and cuticle development genes, though the direction of expression reversed with multiple stressors. These results indicate the impacts of OW and OA on early benthic juvenile lobsters are complex, possibly synergistic, vary with molt cycle, and potentially interfere with normal cuticle development, which may increase susceptibility to injury or disease.