ECOPHYSIOLOGICAL ADAPTATION STRATEGIES OF SOME INTERTIDAL MARINE MACROALGAE OF THE ISRAELI MEDITERRANEAN COAST

The dominant macroalgae growing at a rocky site on the Israeli coast were examined for ecophysiological responses to varying environmental parameters in an attempt to correlate such responses with their appearance at distinct vertical heights within the intertidal zone. These responses were measured as the photosynthetic performance during various conditions of Light, temperature, salinity, inorganic carbon and desiccation and were compared with algae cover during the year. While all algae apparently grew under light-saturating conditions, Enteromorpha compressa and Ulva lactuca, which occupy the uppermost level of the zone, were very tolerant to high and low temperatures as well as desiccation and varying salinity levels. They were also saturated both by HCO3- (while submerged) and atmospheric CO2 (during emergence). In contrast, 4 of the species dominating the middle and lower parts of the intertidal showed a narrower temperature response, could not tolerate exposure to high temperatures for prolonged time periods and were more sensitive to desiccation and salinity changes. In Acanthophora najadiformis and Hypnea musciformis, the sensitivity to desiccation in combination with the much higher rates of photosynthesis in air than in water might explain their growth in the mid intertidal, where, on one hand, waves would keep the thalli moist and, on the other hand, frequent exposure to air would ensure a high supply of atmospheric CO2. In all, these results show that the uppermost growing algae (Enteromorpha compressa and Ulva lactuca) are those that endure the most adverse atmospheric influences and thus can be assumed to lack competition from other species in the high intertidal. Even though they perform equally well under submerged conditions, it may be that biotic factors, such as grazing, limit them from growing lower down. In contrast, the other algae studied showed markedly adverse responses to atmospheric conditions, especially desiccation, and this may be what restricts them to the lower portion of the intertidal.