PREDICTING DESICCATION STRESS IN MICROSCOPIC ORGANISMS - THE USE OF AGAROSE BEADS TO DETERMINE EVAPORATION WITHIN AND BETWEEN INTERTIDAL MICROHABITATS

We describe an easy and inexpensive way to determine whether intertida l microhabitats remain wet during tidal emersion. This new technique u ses agarose beads (120 mum diameter when fully hydrated) that shrink i n a graded fashion as they dry. The agarose beads allow variability in surface wetness to be gauged over distances of less than 1 mm. Descri bing this parameter of microclimate is important in order to predict t he likelihood and spatial pattern of survival of settled larvae, repro ductive propagules, and other microscopic stages in the life histories of organisms growing in intertidal and other water-stressed environme nts. For the brown seaweed Pelvetia fastigiata (J. Ag.) DeToni (Fucale s, Phaeophyta), the use of agarose beads demonstrated that survival of zygotes during tidal emersion was highest at those sites that remain damp. Temperature alone was found to be an unreliable measure Of wetne ss within a single microhabitat (e.g. red algal turf).