Beach wrack is an organic subsidy that supports high intertidal and supralittoral invertebrate communities in many coastal systems. Beaches fringed with riparian vegetation accumulate wrack from both terrestrial leaf litter and marine algae/seagrasses, forming a reciprocal connection. Previous research has shown that shoreline armoring disrupts this marine-terrestrial connection and alters the amount and composition of beach wrack. We sampled invertebrates associated with beach wrack at 29 paired armored and unarmored beaches in Puget Sound, WA and conducted wrack decomposition experiments. Armored beaches had significantly fewer invertebrates as well as different assemblages. Unarmored assemblages were characterized by talitrid amphipods and dipteran and coleopteran insects (flies and beetles), and were correlated with the amount of beach wrack and logs, the proportion of terrestrial material in the wrack, and the maximum elevation of the beach. Experiments showed that talitrid amphipods and oligochaete worms were positively correlated with wrack decomposition rates. The substantial reduction in high-shore invertebrates at armored beaches represents a decrease in subsidies to secondary consumers in both adjacent terrestrial and nearshore ecosystems. These armoring effects may thus cascade, via altered food webs, to organisms in other environments. Our sampling of multiple armored-unarmored beach pairs allowed us to control for variability of many environmental parameters, improving our ability to identify armoring-related differences, and greatly expanding the scale of inference of previous studies showing the negative effects of armoring on beach fauna.
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This research project required many hours of field and laboratory work and would not have been possible without the assistance of Helen Berry, Jeff Gaeckle, Erin Morgan, Katie Dowell, Claire Levy, the UW Wetland Ecosystem Team, and the UW Sediment Dynamics Group. We thank the property owners who allowed us access to their properties on the shores of Puget Sound. This work was part of the doctoral dissertation of the corresponding author, who would like to thank Charles Simenstad for providing academic and scientific mentorship. 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/ES-57. 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 Alf Norkko
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Heerhartz, S.M., Toft, J.D., Cordell, J.R. et al. Shoreline Armoring in an Estuary Constrains Wrack-Associated Invertebrate Communities. Estuaries and Coasts 39, 171–188 (2016). https://doi.org/10.1007/s12237-015-9983-x
- Beach wrack
- Shoreline armoring
- Spatial subsidy