| Abstract: | Chl fluorescence during and immediately after low tide under four meteorological conditions was measured in embryos of three fucoid algae Ascophyllum nodosum (L.) Le Jol., Fucus vesiculosus L., and Fucus distichus subsp. edentatus Bach. (Pyl.) H. T. Powell] vertically distributed in the intertidal zone in Québec, Canada. Artificial substrata with attached embryos of each species were outplanted into each zone and into two different microhabitats: under and outside an adult canopy. Several fluorescence measurements were made using pulse‐amplitude‐modulated (PAM) fluorometry, from which maximum quantum yield (Fv/Fm), effective quantum yield (φPSII), relative electron transport rate (rETR), and nonphotochemical quenching (NPQ) were calculated. Fv/Fm, φPSII, and rETR decreased, and NPQ increased during low tide, most rapidly under the most desiccating meteorological conditions (i.e., sunny‐windy weather). The species occurring lowest in the vertical distribution, F. distichus subsp. edentatus, was the most affected, and the two highest species, A. nodosum and F. vesiculosus, only rarely differed. Tidal height itself also influenced the decline in fluorescence parameters, with more gradual declines in lower zones, except under the least desiccating conditions (i.e., cloudy‐calm weather). Recovery upon reimmersion was rapid in all circumstances. Under a canopy, decreases in maximum and effective quantum yields were more gradual than in exposed locations. Although the young stages of these species were affected by physical conditions experienced during low tide and their exact response depended on the precise meteorological conditions, differences in responses among species were surprisingly small. The abilities of young stages to withstand aerial conditions were, however, consistent with the zonation patterns of adults, and conditions under an adult canopy offered some protection. |
