Assessing the restoring landscape within the Nisqually River Delta for invertebrate prey production

Abstract

At the Nisqually River Delta, almost 900 acres have been reconnected to Puget Sound waters, representing the largest estuary restoration project in the Pacific Northwest. The restoring landscape mosaic represents one of the most significant advances towards the recovery of Puget Sound. The ultimate goal of the restoration is to increase the capacity of the estuary to support a diversity of wildlife, waterbirds, and native fish such as the Nisqually Fall Chinook (Oncorhynchus tshawytscha), a threatened population and a vital cultural resource. Here we compare invertebrate prey production and foodwebs throughout the Nisqually River Delta habitat types: Forested, Transition, Tidal marsh, Mudflat, and Eelgrass. We sampled terrestrial, aquatic, benthic and epifaunal (eelgrass only) invertebrates through the chinook outmigration season (Mar-Jul) in 2014 and 2015. These habitat types had distinct invertebrate assemblages and temporal patterns. For example, we detected two pulses of polychaete abundances in the Tidal Marsh in March and June, compared to the epifaunal invertebrates in Eelgrass beds that increased over time and peaked in July. We also used a stable isotope approach to identify and compare the carbon sources that support fish foodwebs within the landscape mosaic. Primary producers (above ground vegetation, macroalgae, particulate organic matter) showed distinct isotopic signatures (d13C and d15N) by habitat type. Tidal Marsh showed the broadest d13C values, while Forested and Freshwater habitats had somewhat overlapping values. Understanding the variation in the abundance and timing of invertebrate assemblages between habitat types can help us determine the restoration capacity for foodweb support and identify areas of high foraging value