Water movement and seasonal algal growth in Hawaii

The biomass distribution of frondose algae on a Hawaiian reef varied from a period of minimum biomass (635 g wet weight m^-2) during July–September to a period of maximum biomass (1,554 g m^-2) during February–May. The pattern of variation had no significant correlation with any of the 4 environmental parameters measured (light intensity, temperature, water movement and salinity), although the decrease in wet biomass in winter was observed at the time of maximum water movement. When the biomass distribution of individual species was correlated with environmental parameters, 4 groups of ecological species emerged. One group had positive correlations with light intensity and negative correlations with water movement, while a second group of species had the opposite trend. Species in a third group had an irregular pattern of distribution throughout the year. Those in the fourth group had a regular annual cycle which did not correlate with any physical parameters, but did correlate negatively with the biomass distribution of another species of the same genus. The horizontal distribution of all species studied changed throughout the year, expanding or retracting across the reef in a manner correlating with the horizontal changes of water movement in many cases.