# Coastal Wetlands Drive Isotopic Niche Plasticity of Top Predator Fish Communities in Green Bay, Lake Michigan (USA)

## TL;DR

This study explores how top predator fish in Green Bay adapt their diets and feeding strategies based on different wetland habitats.

## Contribution

The study introduces the use of stable isotope metrics and Bayesian models to analyze isotopic niche plasticity in top predator fish communities.

## Key findings

- Top predators showed high isotopic niche overlap among different feeding guilds.
- Invertivorous fish act as a critical link between top-level and lower trophic levels.
- Fish diversified diets in lacustrine wetlands but showed habitat preferences in riverine wetlands.

## Abstract

Green Bay, the largest freshwater embayment in Lake Michigan, is a unique environment consisting of a trophic gradient along its north‐to‐south axis that shapes the heterogeneous and dynamic habitat, driving diverse fish behavior among the remnant coastal wetlands of Green Bay. Although previous studies of aquatic food webs in Green Bay have focused on lower trophic levels to estimate trophic shift responses, we examined trophic relationships among fish communities in five coastal wetland areas of Green Bay, emphasizing top predator species of recreational and commercial importance in Lake Michigan. We used stable isotope‐based community metrics and Bayesian mixing models to describe food web structure and patterns in trophic position, isotopic niche, and diet contributions of top predators, including bowfin
Amia calva
, largemouth bass
Micropterus salmoides
, northern pike
Esox lucius
, smallmouth bass
Micropterus dolomieu
, walleye
Sander vitreus
, and yellow perch
Perca flavescens
. We found high probability (> 70%) of overlap among the isotopic niches of piscivorous, invertivorous, and benthivorous fish, reflecting the capacity of different feeding guilds to exploit isotopically similar sources. In addition, we found that invertivorous fish represented a critical trophic link between the top‐level fish populations and lower levels, such as aquatic invertebrates. Lastly, we found that top predators diversified their diet in lacustrine wetlands but had a distinct foraging habitat preference in riverine wetlands, emphasizing the importance of habitat type and structure in feeding diversity. Top predators in Green Bay displayed a high degree of isotopic niche plasticity, as evidenced by differences in trophic positions and foraging strategies at each site. Flexibility in fish feeding ecology, such as variations in dietary overlap and niche space, along with the hydrogeomorphic setting, underpins the ability of fish communities of Green Bay to thrive under different stressors.

Green Bay, the largest freshwater embayment in Lake Michigan, is a unique environment that drives diverse fish behavior among their remnant coastal wetlands. We used Bayesian models to describe the food web structure of top predators in Green Bay. Our findings suggested significant isotopic niche overlap among piscivorous fish and other feeding guilds, along with diet diversification between aquatic invertebrates and forage fish in lacustrine and riverine wetlands.