A MODEL FOR GAMETE RELEASE IN ASCOPHYLLUM-NODOSUM (PHAEOPHYTA)

The question of what controls gamete release in Ascophyllum nodosum (L.) Le Jolis was studied at six sites along the central coast of Maine. Percent release was assessed weekly along randomly marked transect lines in the mid-intertidal zone. Six independent variables-water temperature at high tide, air temperature at low tide, nitrogen (ammonia, nitrite, and nitrate), and salinity-were measured concurrently. Stepwise multiple regression analysis on the percentage of plants having released gametes revealed that water temperature at high tide accounted for most of the among-site variation (R2 = 0.77) in the timing of release. The addition of Julian day increased the R2 to 0.82; no other variables were significant. Probit analysis, based on water temperature at high tide, generated an environmentally realistic model for predicting gamete release. The model predicts the onset, midpoint, and termination of gamete release at 6, 10, and 15-degrees-C, respectively, and the midpoint at a cumulative water temperature of 358-degrees-C. This model has value for developmental studies and, potentially, for reseeding A. nodosum populations. Probits may be useful for characterizing phenological events in other fucoids and algal species.