ECOLOGY OF YELLOWSTONE THERMAL EFFLUENT SYSTEMS: NET PRIMARY PRODUCTION AND SPECIES DIVERSITY OF A SUCCESSIONAL BLUE‐GREEN ALGAL MAT1

Abstract

Net primary production and species diversity were studied during the successional development of a thermal blue‐green algal community on a linear series of wooden troughs. The source spring was high in dissolved silica and CO2. During July–August 1968 net primary production (minus grazing and export) was 25 kcal m‒2 days‒1 on board 1 and decreased downstream to 17 kcalm‒2 days‒1 on board 4. Linear increases in standing crop were observed during the first month of succession. An identical pattern of productivity and mat increase was observed during August–September 1969. Measurements of particulate export in the second year indicated that as much as 22% of total net production (minus grazing and dissolved organic export) may be lost via this pathway. Efficiencies of conversion of solar energy ranged from 1.0–1.6%. The chlorophyll content per gram organic matter increased and the ratio of OD 480:665 nm decreased with successional age of the mat. Species diversity (H̄) peaked after 2 weeks and increased with distance from the source. Although ten species of blue‐green algae were recognized, three made up most of the volume. Phormidium was dominant during the first few days but declined in importance as Mastigocladus increased. After 3 weeks a species of Oscillatoria increased; its volume varying directly with distance from the source. A hypothesis naming free CO2 as an important nutrient limiting the growth rate of the mat is developed.