Meeting Abstract
P2.148 Saturday, Jan. 5 The ups and downs of life in a halocline: The behavior of P. ochraceus larvae after prior exposure to low salinity BASHEVKIN, S*; GEORGE, S; Tufts University, Medford, Massachusetts; Georgia Southern University, Statesboro, Georgia georges@georgiasouthern.edu
The vertical distribution of planktonic larvae in the water column determines their horizontal displacement by currents. In recent years, the salinity in the Salish Sea has periodically dropped during summer months due to increased freshwater input from the Fraser River. Larvae of the sea star Pisaster ochraceus, a keystone predator of the intertidal zone, are especially vulnerable to these changes since they lack the ability to ion- or osmo-regulate. We examined the impact of prior exposure to low salinity on the behavior of P. ochraceus larvae in a halocline. We reared larvae in 20-22 (low salinity) or 30-32ppt (control) filtered seawater. At the bipinnaria stage, we introduced them into the top or bottom of haloclines comprised of 20ppt at the top and 30ppt at the bottom. Very few bipinnariae introduced either above or below the halocline were able to pass through to the other side, indicating that the halocline posed a major barrier to larval movement. In addition, low salinity larvae introduced above the halocline were trapped in the upper region of the column. Low salinity larvae changed their distribution in the water column at a much slower rate than control larvae, possibly indicating impaired swimming abilities. Reduced salinity in the Salish Sea could result in larvae arriving in unsuitable habitats since larvae developing in surface waters with lower salinity would be distributed differently in the water column and therefore carried elsewhere by currents. Due to impaired swimming abilities, they may be unable to pass through the halocline in search of food or to evade predators. Smaller P. ochraceus populations in the rocky intertidal could result in drastic changes to the ecosystem including a reduction in species diversity.
