A preliminary study of microplankton biothermodynamics in Sevastopol Bay showed an endothermic effect at the end of the first day of measuring the heat production. Measuring the heat dissipation of dark reactions in metabolism of some seaweeds, using a microcalorimeter, determined the analogous endothermic effect approximately within the same time period of measurements. One can observe that energy of consumption of O-2 exceeds that of heat-production energy in oxidative respiratory organisms and explain it on the ground that heat dissipation is the total index not only for biologic reactions in metabolism but also for physico-chemical reactions of hydration and dissolving metabolites for the cell-water phase. Thus, some substances (hydrocarbonates) reduce the solution temperature on dissolving and, consequently, reduce the total heat production. Experiments have shown that, when changing the oxygen respiration phase by an anoxidative one, the heat production can decrease temperature up to the conventional zero (20 degrees C-experiment temperature) and even to a negative value. We think it can be due to sodium hydrocarbonate transportation as a final product of aerobic respiration out of membranes of intracellular organelles into the cell-water phase. By glycolysis, HCO3 ion is not generated, and the heat production returns to its initial level in 2-3 h, but its nature changes. The obtained data show that W-s exceeds by several times the total energy of O-2 absorption and CO2 (HCO3) release. Rather intensive absorption of O-2, for the first hours of dark period, must be connected with the consequence of photorespiration, not with the aerobic (oxygenic) phase of respiration. As it has been shown in experiments, respiration energy of marine algae is contributed mainly by anoxic processes (glycolysis) even under sufficient (a few mg/l) O-2-supply. In the Black Sea macrophytes, photosynthesis is not followed by oxygen production in water photolysis. OH-ions do not convert to O-2, but are transported to habitat that may result from primary (ancient) mechanisms of water photolysis (photolytic anoxic photosynthesis) preserved in the studied organisms.