Nearshore Drift-Cell Sediment Processes and Ecological Function for Forage Fish: Implications for Ecological Restoration of Impaired Pacific Northwest Marine Ecosystems

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Abstract

Sediment processes of erosion, transport, and deposition play an important role in nearshore ecosystem function, including forming suitable habitats for forage fish spawning. Disruption of sediment processes is often assumed to result in impaired nearshore ecological function but is seldom assessed in the field. In this study we observed the sediment characteristics of intertidal beaches of three coastal drift cells with impaired and intact sediment processes and compared the functional metrics of forage fish (surf smelt, Hypomesus pretiosus, and sand lance, Ammodytes hexapterus) spawning and abundance to define linkages, if any, between sediment processes and nearshore ecological function. Key findings include: (1) beach sediment characteristics of the northern Washington nearshore are complex, with strong seasonal variation in habitat form and function both within and across geomorphic habitat types; (2) loss of sediment supply to the nearshore due to in-river damming and shoreline alterations results in significantly larger and more variable beach sediment at the drift-cell scale; (3) these differences in intertidal beach sediment characteristics have implications for habitat function as indicated by less forage fish spawning habitat and lower ecological function than intact drift cells; (4) feeder bluffs are important nearshore sediment sources for forage fish spawning beaches. Forage fish may spawn at the base of feeder bluffs if appropriate sediment is available during the spawning season; and (5) seasonal rate, total volume, and grain size of sediment delivery are important for habitat suitability for fish use. Feeder bluffs therefore should be managed more conservatively and understanding and protecting their role in nearshore habitat restoration practices is a high priority.

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