DESICCATION PROTECTION AND DISRUPTION: A TRADE-OFF FOR AN INTERTIDAL MARINE ALGA(1).

For marine algae, the benefits of drying out are often overshadowed by the stresses involved. Here we used laboratory and field experiments to examine both the costs and benefits of desiccation in the intertidal turf alga Endocladia muricata (Endlichter) J. Agardh. Laboratory experiments showed that when Endocladia is dry, photosynthesis stops, but thermotolerance increases to the point that the alga is protected from heat-induced mortality. Drying rates measured in a wind tunnel, combined with tidal data and measured wave splash, indicate that a substantial fraction of the year is spent "drying out" (∼30% of the total time available for photosynthesis). During these periods, the rate of drying determines how much time is spent hydrated and potentially engaged in photosynthesis, but also vulnerable to high temperatures. Turf algae such as Endocladia dry from the edge of a clump inward. Consequently, the clump center remains hydrated longer than the clump edge. The resulting regionalization of a clump results in notable patterns of frond mortality ("fairy rings," and zoned patterns of frond bleaching) within the Endocladia zone.