THE ROLE OF WATER MOTION IN

Environmental conditions, such as water motion, can influence fertilization success and spore dispersal in marine algae. Previous studies on fucoid algae showed that gamete release is restricted to, or enhanced by, periods of low water motion. Few other algal taxa have been investigated, however, including species with an alternation of generations. I investigated gamete and spore release in the macroalgae Alaria esculenta and Ulva lactuca, as well as in the diatom Pseudo-nitachia multiseries to determine if water motion is inhibitory or stimulates propagule production and release. I used orbital shakers to simulate water motion; these were interspersed with stationary platforms within a walk-in culture chamber. Gamete and zoospore release (A. esculenta and U. Itrctuca) or gamete and zygote production (P. multiseries) were determined daily for several days. Alaria esculenta released a significantly higher number of zoospores under turbulent conditions (P = 0.0001, 2-way ANOVA) and a higher number of sperm under calm conditions (P = 0.0052, 2-way ANOVA). Juvenile A. esculenta sporophytes were present in significantly higher numbers in calm treatments (P = 0.001 2-way ANOVA; contact time, male + female gametophytes = 150 min). Turbulent conditions resulted in