The harmful algae, and , elicit stronger transcriptomic and mortality response in larval bivalves () than climate change stressors.

Global ocean change threatens marine life, yet a mechanistic understanding of how organisms are affected by specific stressors is poorly understood. Here, we identify and compare the unique and common transcriptomic responses of an organism experiencing widespread fisheries declines, (bay scallop) exposed to multiple stressors including high CO, elevated temperature, and two species of harmful algae, (aka ) and using high-throughput sequencing (RNA-seq). After 48 hr of exposure, scallop transcriptomes revealed distinct expression profiles with larvae exposed to harmful algae ( and ) displaying broader responses in terms of significantly and differentially expressed (DE) transcripts (44,922 and 4,973; respectively) than larvae exposed to low pH or elevated temperature (559 and 467; respectively). Patterns of expression between larvae exposed to each harmful algal treatment were, however, strikingly different with larvae exposed to displaying large, significant declines in the expression of transcripts (3,615; 87% of DE transcripts) whereas exposure to increased the abundance of transcripts, more than all other treatments combined (43,668; 97% of DE transcripts). Larvae exposed to each stressor up-regulated a common set of 21 genes associated with protein synthesis, cellular metabolism, shell growth, and membrane transport. Larvae exposed to displayed large increases in antioxidant-associated transcripts, whereas acidification-exposed larvae increased abundance of transcripts associated with shell formation. After 10 days of exposure, each harmful algae caused declines in survival that were significantly greater than all other treatments. Collectively, this study reveals the common and unique transcriptional responses of bivalve larvae to stressors that promote population declines within coastal zones, providing insight into the means by which they promote mortality as well as traits possessed by bay scallops that enable potential resistance.