Journal of Plankton Research Vol.22 no.10 pp.1841-1853, 2000
© Oxford University Press 2000
Advantages from diel vertical migration can explain the dominance of Gonyostomum semen (Raphidophyceae) in a small, steeply-stratified humic lake
Department of Biological and Environmental Sciences, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland and 1 University of Helsinki, Lammi Biological Station, FIN-16900 Lammi, Finland
In late summer, a large flagellated alga, Gonyostomum semen (Raphidophyceae), constituted most of the phytoplankton biomass in a small steeply-stratified humic lake. Its diel vertical migration (DVM) was very distinct and extended at night into the anoxic hypolimnion. After midsummer, the depletion of hypolimnetic oxygen led to a gradual release of soluble reactive phosphorus (SRP) from the sediment, but one month later, irrespective of continuing stratification, the concentrations again returned to undetectable levels down to the bottom. As this coincided with the rapid increase in G.semen population, the latter was probably responsible for the depletion of SRP. The flux of SRP from the sediment to the epilimnion was virtually interrupted, making non-migrating phytoplankton dependent only on regenerated and inflowing inorganic phosphorus. Besides nutrient availability, DVM also benefited G.semen in the reduction of metabolic and grazing losses. In this lake, the remarkable multiple advantages of DVM probably explain the dominance of the large G.semen in the late summer phytoplankton biomass over much smaller algae.