The ecology of freshwater wrack along natural and engineered Hudson River shorelines
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Organic matter that is washed onto shore, or “wrack,” is an important component of shoreline ecosystems, providing habitat for macroinvertebrates and organic matter and nutrients to both the upland terrestrial communities and aquatic ecosystems. While marine wrack has been studied extensively, wrack along freshwater shorelines has received less attention. In this article, we report on the standing stocks, mobility, decomposition rates, and macroinvertebrate communities of wrack on different types of Hudson River shorelines (natural: sand, rock, bedrock; and engineered: riprap, cribbing, and bulkhead). Standing stocks of wrack sometimes exceeded 1 kg dry mass/m2, and were the highest on shorelines having flat slopes. Artificial wrack (hay) placed below the high tide mark was rarely retained for more than a few tidal cycles, particularly on highly exposed shores. Wrack on cribbing shorelines decayed significantly faster than on other shoreline types. Macroinvertebrate abundance and diversity were significantly different among shoreline types, with the lowest abundance found on cribbing, along with significantly lower diversity. Consequently, if managers use structures such as cribbing and bulkheads to rebuild or reinforce shorelines, then certain ecological functions may be lost.
KeywordsFreshwater Wrack Engineered Decomposition Macroinvertebrate diversity Macroinvertebrate density
The authors thank Fanny Chauvière, Heather Malcom, David Fischer, Gary Kleppel, and Zara Dowling for their technical help and advice. Financial support was provided by the Hudson River Foundation, its Polgar Fellowship program, and through a grant from the Cooperative Institute of Coastal and Estuarine Environmental Technology.
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