Investigating the relationship between the comb jellyfish, <i>Mnemiopsis leidyi</i> , and the abundance of pathogenic <i>Vibrio</i> spp. and harmful algae species in the Maryland Coastal Bays

Ctenophores (<i>Mnemiopsis leidyi</i>) release large amounts of nutrients and organic matter that stimulate microbial growth and alter planktonic community composition. We investigated the distribution and abundance of <i>M. leidyi</i> and its association with pathogenic <i>Vibrio</i> and harmful algal bloom (HAB) species at seven sites in the Maryland Coastal Bays (MCBs) between April 2021 and June 2022. Water and <i>M. leidyi</i> samples were collected concurrently with temperature, salinity, dissolved oxygen, nutrient, and turbidity data. <i>M. leidyi</i> was present in both years at all sites but was most abundant in areas with high turbidity (Isle of Wight and Newport Bays). Both <i>V. parahaemolyticus</i> and <i>V. vulnificus</i> were present in <i>M. leidyi</i> tissue and water samples and had a moderate positive association with turbidity. HAB species composition varied significantly between sites, with distinct populations of the dinoflagellate <i>Karlodinium veneficum</i> (Chincoteague Bay) and picoplankton taxa (Newport Bay) noted. A generalized linear model (GLM) revealed that temperature was best at predicting total (<i>vvhA⁺</i>) <i>V. vulnificus</i> in <i>M. leidyi</i> tissues and total dissolved nitrogen (TDN) was best at predicting total (<i>trh</i>⁺) <i>V. parahaemolyticus</i> in water. There was no strong association between <i>M. leidyi</i> abundance and HABs. However, we observed weakly positive associations between <i>V. vulnificus</i> in <i>M. leidyi</i> tissues and total dinoflagellate biomass, between <i>M. leidyi</i> abundance and dinoflagellate biomass, and between <i>V. parahaemolyticus</i> in <i>M. leidyi</i> tissues and picocyanobacteria biomass. This study provides information on associations between <i>M. leidyi</i>, <i>Vibrio</i> spp., and HAB species that could aid the development of a <i>Vibrio</i> predictive model for the MCBs.IMPORTANCE<i>Vibrio</i> and algal bloom species naturally occur in marine ecosystems; however, some species of <i>Vibrio</i> and algae can be harmful to humans, causing gastroenteritis. <i>Vibrio</i>-associated illnesses have been expanding globally in marine environments, and many studies have linked this expansion to increases in water temperatures, nutrients, and plankton blooms. We observed seasonal interactions between <i>Vibrio</i> spp., <i>Mnemiopsis leidyi</i>, and HABS and found that temperature was the best predictor of total (<i>vvhA⁺</i>) <i>V. vulnificus</i>, while TDN was the best predictor of total (<i>trh</i>⁺) <i>V. parahaemolyticus</i>. These findings provide biotic and abiotic factors that managers, researchers, and stakeholders can use in the development of HAB and <i>Vibrio</i> spp. mitigation strategies and predictive models for the MCBs.