Meeting Abstract

24.5  Monday, Jan. 4  Emersion limits short term growth rates in intertidal Nucella lamellosa PRICE, RM*; ELAHI, R; Univ. of Washington, Bothell; Univ. of Washington, Seattle becca.price@uwb.edu

Many environmental factors affect the growth of marine invertebrates, but the way these factors interact remains poorly understood. For example, tidal emersion may limit the size of intertidal invertebrates directly by interfering with the physiological mechanisms of growth, indirectly by limiting foraging time, or through a combination of both factors. We used mesocosm experiments to isolate the effects that foraging and exposure have on the growth rates of the whelk Nucella lamellosa collected from intertidal, wave-protected locations. Two treatments exposed snails to air for two hours and for five hours each day. In two other treatments, snails remained underwater but were deprived of their food source for two hours and five hours each day. Snails in a control group were kept submerged and fed ad libitum. We measured the change in tissue weight, shell weight, height and the total degrees of new growth after 24 days. Snails in control mesocosms grew faster than snails from all four treatments, and the snails from the five hour exposure treatment grew most slowly. There was no significant difference in growth among snails from the two hour exposure treatment and either of the food removal treatments, suggesting that the decrease in growth rate from two hours of emersion is consistent with the indirect effect of restricting diet. Growth in the food removal treatments did not differ, so the act of interrupting foraging may be more influential than the duration of foraging. The slow rate of growth in the five hour exposure treatment suggests that exposing N. lamellosa to air retards soft and hard tissue growth directly by interfering with shell deposition and indirectly by limiting food intake. The direct and indirect consequences of emersion could explain the observation that some intertidal marine invertebrates with calcium carbonate shells are smaller than subtidal conspecifics.