Seasonal changes of diel vertical migrations of crustacean plankton in lake constance
Archiv fur Hydrobiologie, Supplementband 83(3): 355-406
ISSN/ISBN: 0365-284X Accession: 007772594
From April to November 1977 and in January and March 1978, the vertical distributions of crustaceans were monitored in monthly 24-hour investigations along with phytoplankton biomass, temperature stratification, oxygen saturation and secchi transparency. Vertical migrations with seasonal changing amplitudes were observed from June until November. Migrations affected ambient water temperature of the crustacean populations; the extent was mainly influenced by vertical distribution and migration of crustaceans, which differed interspecifically. Available food concentrations (POC .ltoreq. 30 .mu.m) were only moderately in during daytime. Dawn and seasonal variations in day length. The remaining sampling times were adjusted to obtain equal time intervals approximately symmetric around noon and midnight respectively. During this "migration" nighttime-sampling light was reduced period, non-migrating and migrating species co-occurred. In April and May 1977, January and March 1978 no distinct vertical migrations were observed. Animals were dispersed throughout the investigated water column. During the spring algal bloom in May, however, distributions of all crustaceans were restricted to the upper 15 m to 20 m of depth. During this "non-migration" period, no interspecific differences in the vertical distributions of crustaceans were observed. Results support the interpretation of vertical migration as a predator avoidance mechanism. Onset of migration coincided with the hatching of fish larvae. The predacious impact of young fish is temporally limited to spring and early summer, but the predation pressure of older fish which also increases in spring continues throughout summer.