TEMPERATURE AND LIGHT EFFECTS ON THE SEASONAL SUCCESSION OF ALGAL COMMUNITIES IN SHALLOW COASTAL LAGOONS

The effects of temperature and light on the relative abundance of coas tal lagoon algae were quantified in 2-1 aquaria maintained in environm ental chambers. Three groups of algae, phytoplankton, green macrophyte s, and benthic mats of cyanobacteria, were grown together and biomass compared. Final biomass of phytoplankton and mats was highest at high temperature (25-degrees-C), while macroalgae had maximum biomass at 18 and 22-degrees-C. Reduced light and short days (150 muE.m-2.s-1, 9 h) favored the accumulation of phytoplankton and attached macroalgal bio mass, while high light (500 muE.m-2.s-1) and longer days (12-15 h) fav ored floating macroalgae and cyanobacterial mats. We hypothesize that differences between our results and those from similar experiments, in cluding only one group of algae, may be due to interactions between th e groups such as shading or competition for space. Our mixed community experiments helped to explain the seasonal sequence in southern Calif ornia coastal lagoons: attached macroalgae dominate in early spring, f loating macroalgae in summer, cyanobacterial mats in late summer and e arly fall, and phytoplankton in late fall.