PARENT SESSION
Oral Session #57: Aquatic Ecology: Wetlands, Estuaries, Marine. Presiding: T. Klinger.
Wednesday, August 8, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.

Effects of winter light limitation and herbivory on a high intertidal community.

Harley, Christopher¹, ¹

ABSTRACT- Light availability and consumer pressure are fundamental factors that structure aquatic communities, but their integrated effects are rarely studied in marine benthic systems. Using a factorial experiment, I investigated the effects of winter light availability and grazing by the limpet Lottia digitalis to determine the relative influence of each on the growth and abundance of producers and consumers in a rocky intertidal community. Light reduction resulted in lower filamentous algal cover and decreased abundance of the herbivorous snail Littorina sitkana. Light reduction also reduced Lottia growth, but only in low limpet treatments. Experimentally increased densities of Lottia resulted in reductions in filamentous algae, Porphyra, and diatom mats. Higher limpet densities also suppressed limpet growth via intraspecific competition, and adult (but not juvenile) Littorina spp. abundance via interspecific competition. Variation in bottom-up and top-down forces are important determinants of abundance at both trophic levels, but the effects are complex and taxon-specific. Because the study species accomplish most of their growth and reproduction during the winter, the interplay of winter light availability and herbivory will likely influence long-term community dynamics.

KEY WORDS: bottom-up, top-down, irradiance, herbivory