Spatial and Temporal Variation in the Diets of Pacific Staghorn Sculpins Related to Hydrological Factors in a Glacially Influenced Estuary

Abstract

In southeastern Alaska, a large volume of freshwater flows into estuaries from thinning and retreating glaciers and from high rainfall in the surrounding coastal temperate rainforest. Freshwater runoff to the coast affects the physical and chemical properties of estuarine habitats and, in turn, the structure and dynamics of biological communities. This study quantified temporal and spatial variation in the diets of Pacific Staghorn Sculpins Leptocottus armatus as an important step toward understanding how climate-driven changes in freshwater runoff may translate into shifts in the feeding ecology of a highly abundant consumer in estuaries along the west coast of North America. Stomach contents of Staghorn Sculpins were collected monthly (April–September 2014) from three intertidal sites at the mouths of rivers that differ in their headwater hydrology. Staghorn Sculpins (N = 402) consumed a variety of marine prey items including epibenthic invertebrates, juvenile fishes, and terrestrial and aquatic insects. Based on a multivariate analysis of similarity, diet composition showed weak to moderate differences across sampling months and sites. Diet differences reflected seasonal shifts in the contributions of freshwater-tolerant marine invertebrates and young of the year fishes. The greatest site differences were observed between the Cowee Creek estuary and Mendenhall River estuary, the watersheds with the lowest and highest glacial coverage, respectively. Overall, the generalist feeding behavior of Staghorn Sculpins and their consumption of prey items that are well adapted to brackish and freshwater conditions suggest that these fish are resilient to changes in estuarine conditions associated with increasing freshwater runoff.

Received January 31, 2017; accepted June 7, 2017 Published online September 22, 2017

ACKNOWLEDGMENTS

We thank the many field volunteers, including Asia Beder, Ragnhildur Fridriksdottir, and Melissa Rhodes-Reese, who assisted in fish sample collection, and Jason Fellman for providing river discharge data. We thank Carolyn Bergstrom for providing valuable feedback throughout the project. Thanks to Chris Sergeant and four anonymous reviewers for reviewing a draft of the manuscript. This project was funded by Alaska’s Experimental Program to Stimulate Competitive Research (EPSCoR NSF award OIA-1208927) and the University of Alaska Fairbanks.