IMPACTS OF SALINITY ON SETTLEMENT, SURVIVAL, AND ACCLIMATION IN THE COMMENSAL BARNACLE <i>Chelonibia testudinaria</i>
Reilly, Meghan Emily
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Planktonic larval stages are important in the life cycle of most sessile marine organisms because they allow colonization of new territory to maintain populations and reduce competition between generations. However, transport in the plankton also exposes larvae to the risk of being dispersed into unsuitable habitats and to challenges such as maintaining vertical position, avoiding predators, and coping with fluctuating food availability. As larvae disperse from the parent, they may confront variable environmental conditions, including changes in salinity. Salinity varies on both spatial and temporal scales and when larvae experience changes in external salinity it can affect both their survival and settlement. Epibiotic sessile species, like barnacles, have the additional complication of needing to settle on a host organism that may be mobile. Mobile hosts can move between water masses of varying salinities which may influence where they encounter the larvae of their epibionts. For the present study, the balanomorph barnacle <i>Chelonibia testudinaria</i> was selected to examine the impact of salinity on the larval stages of this epibiotic species to infer its planktonic distribution relative to salinity. I performed laboratory experiments to determine mortality and settlement for the cyprid larval stage of this species across a range of salinities as well as tested cyprid behavioral responses to haloclines and acclimation ability. Mortality was lowest and settlement highest between salinities of 20-30 ppt. In stratified water columns, swimming cyprids avoided low salinity waters, particularly salinities below 20 ppt. Rearing salinity had a significant impact on settlement and on cyprid behavior in the water column. Overall, I demonstrated that salinity does have an impact on larval biology and behavior in the barnacle <i>Chelonibia testudinaria</i>, indicating that salinity regimes inhabited by the host may influence the presence or absence of this epibiont.