Abstract
The red abalone Haliotis rufescens, a marine snail, supports two industries in California: an aquaculture industry that grows abalone as a food source and a $44 million per year recreational fishing industry. Both industries are negatively affected by El Niño events that bring abnormally warm ocean water to the California coast. For example, in 2015 there was an El Niño event that led to significant mortality on aquaculture farms; some farms in northern California have yet to fully recover from this event. In addition, in 2018 recreational fishing of wild red abalone was banned due to severe population declines. With the current predictions for climate change and more frequent warming events, thermal tolerance research on H. rufescens is needed to prevent further economic loss. Previous research has connected the residential microbial community to host thermal tolerance in organisms such as corals and oysters, but the microbial contribution to heat stress response has yet to be studied in H. rufescens. The objectives of this study are to identify 1) what gut microbes are present in juvenile H. rufescens before and after heat stress, and 2) what metabolic pathways these microbes are actively using. To accomplish these objectives, I obtained juvenile heat stress growth rate data as a proxy for thermal tolerance and full shotgun metagenomic sequencing data to examine the juvenile H. rufescens microbiome. Overall, 48 individuals from Monterey Abalone Company were exposed to a 24 day heat stress that mimics El Niño events. Individual fecal samples were collected from 6 different groups: 1) thermally tolerant pre heat stress, 2) thermally tolerant post heat stress, 3) thermally intolerant pre heat stress, 4) thermally intolerant post heat stress, 5) control pre benign temperature exposure, and 6) control post benign temperature exposure. Extracted DNA (n = 6 per treatment group x 6 treatment groups = 36 total) was sequenced using an Illumina NovaSeq PE250 approach. The sequencing data was analyzed using the bioinformatics pathways DIAMOND and MEGAN to identify bacterial taxa and associated metabolic functions. I compared the core microbiome of the six different groups to see the similarities and difference between thermally tolerant, thermally intolerant, and control individuals before and after a heat stress. I created a PCoA with unweighted Bray-Curtis distances for the pre and post heat stress samples which showed that the control, thermally tolerant and thermally intolerant were distinct groups before and after a heat stress. Bacterial taxa such as Vibrionaceae were more abundant in the thermally tolerant individuals post heat stress compared to the thermally intolerant and control pre and post groups. Using SEED analysis in MEGAN I compared the function of the microbiome among the groups and found that metabolic functions were more similar between the thermally tolerant and the thermally intolerant groups compared to the control. In addition, thermally tolerant individuals had a more stable functional microbiome compared to the thermally intolerant group that showed significant decreases in several metabolic functions post heat stress. Based on the current published literature, this research is the first to examine the gut microbiome of juvenile abalone. This work demonstrates that the microbiome should be considered when assessing the response of the economically important red abalone to climate change.