The ecological significance of algal and seagrass wrack subsidies has been well-documented for exposed-coast sandy beaches but is relatively unstudied in lower-energy and mixed-sediment beaches. In marine nearshore environments where beaches are fringed with riparian vegetation, the potential for reciprocal subsidies between marine and terrestrial ecosystems exists. Within the marine-terrestrial ecotone, upper intertidal “wrack zones” accumulate organic debris from algae, seagrass, and terrestrial plant sources and provide food and shelter for many organisms. Human modification also occurs within this ecotone, particularly in the form of armoring structures for bank stabilization that physically disrupt the connectivity between ecosystems. We conducted detailed wrack and log surveys in spring and fall over 3 years at 29 armored–unarmored beach pairs in Puget Sound, WA, USA. Armoring lowered the elevation of the interface between marine and terrestrial ecosystems and narrowed the width of the intertidal transition zone. Armored beaches had substantially less wrack overall and a lower proportion of terrestrial plant material, while marine riparian zones (especially trees overhanging the beach) were an important source of wrack to unarmored beaches. Armored beaches also had far fewer logs in this transition zone. Thus, they lacked biogenic habitat provided by logs and riparian wrack as well as the organic input used by wrack consumers. Results such as these that demonstrate armoring-associated loss of connectivity across the marine-terrestrial ecotone may be useful in informing conservation, restoration, and management actions.
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We thank Helen Berry, Jeff Gaeckle, Erin Morgan, Katie Dowell, Mary Ramirez, the Wetland Ecosystem Team, and the Marine Geology Group for their assistance with field and lab work. We thank the property owners who allowed us access to their properties on the shores of Puget Sound. This research was funded in part by a grant from the Washington Sea Grant Program, University of Washington, pursuant to National Oceanic and Atmospheric Administration Award No. R/OCEH-2. The views expressed herein are those of the author(s) and do not necessarily reflect the views of NOAA or any of its sub-agencies. Additional support came from the University of Washington School of Aquatic and Fishery Sciences. Matching funds were generously provided by the Washington Dept. of Natural Resources.
Communicated by Dennis Swaney
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Heerhartz, S.M., Dethier, M.N., Toft, J.D. et al. Effects of Shoreline Armoring on Beach Wrack Subsidies to the Nearshore Ecotone in an Estuarine Fjord. Estuaries and Coasts 37, 1256–1268 (2014). https://doi.org/10.1007/s12237-013-9754-5
- Beach wrack
- Shoreline armoring
- Marine riparian