Algal Growth and Primary Productivity in a Thermal Stream

Abstract

Estimates of primary production and respiration of cyanophycean algal species growing in the run-off stream of a hot spring (37 C) were obtained throughout 1966 using the diurnal oxygen curve technique. Rates of gross primary production were slightly higher than published values from other aquatic ecosystems, but were less than recent estimates from hot springs in Yellowstone and Mount Lassen National Parks using the C14 uptake method. Production/respiration ratios were calculated and ranged from 1.1 to 5.0. The effect of photosynthesis on the ionic concentration of influent and effluent water was noted, together with morphological changes in the algal mat as the growing season progressed. Changes in algal standing stock were studied in 1964 and 1965, together with growth rates from denuded areas by two methods of harvest. In both years the most rapid growth was recorded in May and June, whereas during the winter months growth was negligible. Maximum values of primary production in May and June 1966 coincided with these maximum growth periods. Significant differences in growth rates between years were thought to be due to several factors; most notably, harvest methods and auto-inhibitory toxins produced by layers of senescent cells composing the "mature" algal mat. Energy losses due to algal export and grazing are discussed in relation to the dynamics of the mat, and an annual energy budget is derived from estimates obtained in 1966.