DIURNAL RECRUITMENT PATTERNS IN ALGAE: EFFECTS OF LIGHT CYCLES AND STRATIFIED CONDITIONS1

The diel pattern in algal habitat shift between sediment and water was recorded above (shallow site) and below (deep site) the thermocline in a stratified, unproductive forest lake. Migrating algae were caught in funnel traps, and the net transport was calculated. Diel recruitment patterns varied temporally within site and spatially between sites. For most species, recruitment and sinking was low at the deep site during stratification. When stratification began to break down in August, the migratory activity increased at the deep site, suggesting that the stratified conditions affected algal migratory behavior. Although light obviously affected algal migration, recruitment often deviated from consistent diel patterns, indicating that simple light-dark cycles are not sufficient to explain algal migratory patterns. Instead, the study suggests that some algal species have receptors able to detect several environmental variables, including light and variables associated with stratified conditions. Hence, some algal species, but not others, may be able to optimize resource needs by properly adjusting the timing for recruitment from the sediment surface in relation to the risk of being trapped below the euphotic zone by a thermocline not possible to penetrate .