TEMPORAL PATTERNS OF RAIN-FOREST STREAM EPILITHIC ALGAE IN RELATION TO FLOUR-RELATED DISTURBANCE

Physical disturbance owing to spates can have a significant influence on the structure and dynamics of periphyton assemblages in streams. Th e effects of flooding on epilithic algae in two subtropical rainforest streams was investigated. Periphyton chlorophyll a and biomass (mainl y of diatom origin) were monitored over three and a half years in rela tion to rainfall and stream discharge. High discharge events had a red ucing effect on periphyton chlorophyll a and biomass in both streams. However, these values recovered quickly (within a period of approximat ely 10-30 days post-spate) in the absence of any further disturbance. After approximately 60 days, however, levels declined in the absence o f subsequent disturbances. Differences in the epilithon between the tw o streams could be related to the geomorphology and the pattern of dis turbance. Cobbles in the steeper-gradient stream-reach supported more chlorophyll a containing material of algal origin and less non-algal b iomass than those in the low-gradient stream-reach. Overall, changes i n the standing crop of epilithic algae could be attributed directly to the effects of spates. However, some major variations in chlorophyll a and biomass occurred in the absence of high discharge events, sugges ting that other factors, such as extreme low flows, could also be sign ificant agents of disturbance. (C) 1997 Elsevier Science B.V.