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A bloom of the macroalga Cladophora prolifera (Chlorophyta, Cladophorales) has recently been reported in Bermuda. The present study summarizes results of experiments conducted in June, 1977, designed to measure rates of primary production and to determine biological, physical and chemical factors controlling the rapid spread of the plant. Productivity was measured using three different methods: 14 C uptake, growth and biomass accumulation. Production values for the alga as estimated by these three methods were 3.1, 2.7 and 0,7 gC/m 2 /day, respectively. Production in June, 1977 was identical to that in December, 1976. Growth of the alga appears to be controlled largely by light intensity and nutrient availability. It is also likely that C prolifera is responding to elevated levels of nutrients in Bermudas' inshore waters. The possible roles of nutrient availability, algal morphology and natural selection in structuring marine benthic macroalgal communities are discussed,

Long-term sampling of intertidal macroalgae along permanently marked transects within San 'Francisco Bay has shown a marked decline in overall species number along the estuarine gradient from the ocean to the river, presumably as a result of decreasing salinity and a progressive lack of hard substrata in the upstream direction. Green algae penetrated further landward than either brown or red species. Seasonally, macroalgal species diversity is lowest during the winter-spring months when salinity, temperature, and irradiance are at yearly minima. Macroalgal abundance as measured by percent cover was maximum during the late spring near the mouth of the estuary and during late summer towards the head. The seasonal increase in algal abundance is related to increasing salinity, temperature, and light availability to the bottom. The summer increase in irradiance is due to the longer photoperiod, increased frequency of day-time low tides, and reduced levels of suspended sediments. The aperiodic occurrence of algal blooms in San Pablo Bay may be caused by a combination of physical factors which are ultimately associated with the river inflow. A hypothesis based on interannual differences in river inflow and the contribution of phytoplankton to nutrient cycles in the benthos is presented to explain the occurrence of nuisance algal blooms. Hydrobiologia 129, 139-152 (1985). 0 Dr W. Junk Publishers, Dordrecht. Printed in the Netherlands.

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