Seasonal stresses shift optimal intertidal algal habitats
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ORIGINAL PAPER
Seasonal stresses shift optimal intertidal algal habitats Megan N. Dethier · Susan L. Williams
Received: 15 April 2008 / Accepted: 1 December 2008 / Published online: 20 December 2008 © Springer-Verlag 2008
Abstract We studied how the growth, reproduction, and survival of a common intertidal rockweed (Fucus distichus) varied across its tidal elevation at 14 sites around San Juan Island, Washington, USA in spring–summer and fall-winter seasons. We also measured a suite of environmental factors including temperature, light, emersion time, slope, fetch, and herbivory. To interpret the response of Fucus we included measurements of phlorotannins and carbon storage compounds (mannitol, laminarin). Growth and reproduction exhibited parallel patterns across tidal zones and sites. Tidal zone was a signiWcant source of variation for many Fucus response variables, whereas variation between sites was high but not generally a signiWcant factor explaining Fucus growth and physiology. Unexpectedly, the tidal zone in which Fucus achieved its highest growth and reproduction switched between seasons. High zone thalli grew and reproduced better than Mid zone thalli in fall but not in spring. This result can be explained by diVerent combinations of factors inXuencing Fucus in each season. In spring, longer emersion times due to daytime low tides resulted in lower growth rates higher on the shore, likely due to carbon limitation. In fall during nighttime low tides, emersion and carbon limitation stresses were minimal. Overall, fall growth was lower than spring growth, but low fall light was
Communicated by P. Kraufvelin. M. N. Dethier (&) Department of Biology and Friday Harbor Labs, University of Washington, 620 University Road, Friday Harbor, WA 98250, USA e-mail: [email protected] S. L. Williams Bodega Marine Laboratory, University of California at Davis, P.O. Box 247, Bodega Bay, CA 94923-0247, USA
not responsible. Instead, warmer average fall temperatures in the High zone apparently favored growth and reproduction relative to the Mid zone. In contrast, Mid zone thalli were subjected to more intense herbivory and hydrodynamic stress associated with wave exposure and steep substrata during the fall. At least for some seaweeds, living in the presumably more stressful high zone can actually confer higher integrated performance.
Introduction Marine benthic algae are responsible for a signiWcant fraction of the productivity of the world’s oceans (Valiela 1984), supplying organic carbon to both nearshore and oVshore food webs (Mann 1982; Duggins et al. 1989). Even the narrow, environmentally variable rocky intertidal zone is highly productive (Leigh et al. 1987). Seaweed growth and hence productivity are potentially limited in the Weld by physiological stress caused by various abiotic factors that exceed some threshold for optimal organismal function. Herbivory can also limit macroalgal biomass, and both stress and herbivory are known to inXuence algal distribution, abundance, chemistry, and morphology (e.g., C
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