PREDICTING DESICCATION STRESS IN MICROSCOPIC ORGANISMS THE USE OF AGAROSE BEADS TO DETERMINE EVAPORATION WITHIN AND BETWEEN INTERTIDAL MICROHABITATS 1

We describe an easy and inexpensive way to determine whether intertidal microhabitats remain wet during tidal emersion. This new technique uses agarose beads (120 üm diameter when fully hydrated) that shrink in a graded fashion as they dry. The agarose beads allow variability in surface wetness to be gauged over distances of less than 1 mm. Describe this parameter of microclimate is important in order to predict the likelihood and spatial pattern of survival of settled larvae, reproductive propagules, and other microscopic stages in the life histories of organisms growing in intertidal and other water‐stressed environments. For the brown seaweed Pelvetia fastigiata (J. Ag.) DeToni (Fucales, Phaeophyta), the use of agarose beads demonstrated that survival of zygotes during tidal emersion was highes at those sites that remain damp. Temperature alone was found to be an unreliable measure of wetness within a single microhabitat (e.g. red algal turf).