BERGER, M.S.; University of Oregon, OIMB: Juvenile performance of the barnacle Balanus glandula along an estuarine gradient

The acorn barnacle, Balanus glandula, has a wide intertidal distribution within the South Slough Estuary in Oregon that ranges from the oceanic mouth to approximately six kilometers upstream towards the riverine head of the estuary. Along this horizontal estuarine gradient, environmental conditions such as salinity and water temperature, along with food abundance, vary over seasonal and tidal cycles. In the Spring and Summer of 2002 and 2003, laboratory reared juveniles were outplanted for twenty days at three sites within the estuary to test the hypothesis that as stress increases up the estuarine gradient, survivorship and growth rates of recently settled juveniles will decrease. In addition, the effect of intertidal height on juvenile performance, over a range of 12.5 centimeter increments was examined at each site. Juvenile performance was affected by season and relative intertidal height. Results indicated that when a strong estuarine gradient was present in early May 2002 and 2003, juvenile performance was lowest at the riverine site. In contrast to the predicted outcome, juvenile performance was higher at the mid-estuarine site in comparison to the oceanic site. During late June 2002, when the marine influence extended further up the estuary, survivorship and growth rates were high at all sites. However, in late June 2003, when the salinity gradient was similar to the previous year, low survivorship was observed at the riverine end of the estuary. In addition, during late June 2003, fewer juveniles survived at the oceanic site when relative height in the intertidal was increased by a 12.5 centimeter increment. Throughout all seasons examined, growth rates were observed to increase as relative height in the intertidal decreased by 12.5 centimeter increments.