PHYSIOLOGICAL COMPARISON OF THE ISOMORPHIC LIFE-HISTORY PHASES OF THEHIGH INTERTIDAL ALGA ENDOCLADIA-MURICATA (RHODOPHYTA)

The isomorphic phases of Endocladia muricata (Post. & Rupr.) J. Ag. we re compared for photosynthetic and respiratory differences in response to a variety of environmental manipulations. Photosynthetic light res ponse during submergence at 15-degrees-C and the pattern of respirator y recovery following prolonged emergence (3 h) at either 15-degrees or 30-degrees-C were similar between gametophytes and tetrasporophytes. The phases showed the same ability to photosynthesize and respire duri ng emergence at each temperature tested (15-degrees 25-degrees, and 35 -degrees-C fully hydrated thalli) and at various desiccation states (m easured at 25-degrees-C only). Submerged rates of photosynthesis follo wing prolonged emergence at 15-degrees and 30-degrees-C were, however, slightly greater (17%) for tetrasporophytes as compared to gametophyt es. Regardless of the life history phase, plants incubated at 15-degre es-C during emergence recovered more completely than plants incubated at 30-degrees-C. Photosynthetic recovery after 1 h in plants incubated at 15-degrees-C often ''spiked'' and yielded rates as great as 185% o f pretreatment rates. Increased photosynthetic rates during recovery w ere absent from the 30-degrees-C incubations. The initial photosynthet ic recovery of plants collected from the upper limits of distribution was greater than that of plants collected from the lower limits. Recov ered rates of respiration were highly variable over time. Respiration often exceeded pretreatment values more than threefold, and the elevat ed rates were sustained for 12 h. Photosynthesis and respiration in ai r were comparable to rates in seawater and varied slightly with increa sing temperature. Photosynthetic and respiratory rates also decreased with increasing tissue water loss. Thus, only slight differences in ph ysiological performance were observed between phases and individuals c ollected from different vertical positions. Metabolic differences were transient and apparent only under experimental conditions that modele d extreme environmental conditions.