Phytoplankton Communities in Green Bay, Lake Michigan after Invasion by Dreissenid Mussels: Increased Dominance by Cyanobacteria

Michael Schrimpf,Brendan Cornwell,Bart De Stasio

doi:10.3390/d6040681

Michael Schrimpf, Brendan Cornwell + Show 1 more

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https://doi.org/10.3390/d6040681

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Abstract

Biological invasions of aquatic systems disrupt ecological communities, and cause major changes in diversity and ecosystem function. The Laurentian Great Lakes of North America have been dramatically altered by such invasions, especially zebra (Dreissena polymorpha) and quagga (D. rostriformis bugensis) mussels. Responses to mussel invasions have included increased water clarity, and decreased chlorophyll and phytoplankton abundance. Although not all systems have responded similarly, in general, mussels have changed nutrient dynamics and physical habitat conditions. Therefore examination of different impacts can help us further understand mechanisms that underlie ecosystem responses to biological invasions. To aid our understanding of ecosystem impacts, we sampled established locations along a well-studied trophic gradient in Green Bay, Lake Michigan, after the 1993 zebra mussel invasion. A strong trophic gradient remained during the period sampled after the mussel invasion (2000–2012). However, mean summer chlorophyll increased and other measures of phytoplankton biomass (microscope and electronic cell counting) did not change significantly. Multivariate analyses of phytoplankton community structure demonstrate a significant community shift after the invasion. Cyanobacteria increased in dominance, with Microcystis becoming the major summer taxon in lower Green Bay. Diatom diversity and abundance also increased and Chlorophyta became rare. Phytoplankton responses along the trophic gradient of Green Bay to zebra mussel invasion highlight the importance of mussel effects on nutrient dynamics and phytoplankton diversity and function.

Highlights

Biological invasions of aquatic systems have increased in frequency over the past 50 years and have led to major disruptions of ecological communities, thereby causing major changes in biological diversity and ecosystem function [1,2]
We have shown elsewhere significant increases in chlorophyll at the GB6 site following the invasion, indicating that similar responses occurred at both ends of the trophic gradient [28]
Green Bay has responded to invasion by dreissenid mussels in a different way than many of the waters in the Laurentian Great Lakes, as well as in other inland bodies of water

Summary

Introduction

Biological invasions of aquatic systems have increased in frequency over the past 50 years and have led to major disruptions of ecological communities, thereby causing major changes in biological diversity and ecosystem function [1,2]. Dreissenid mussels quickly spread throughout the Great Lakes and nearby inland lakes in the 1980s, and dramatically changed most of the invaded systems e.g., [6]. Dreissenids typically achieved extremely high abundances and filtered large volumes of water [7,8]. This resulted in changes in water clarity and decreases in abundance of algae [9,10,11,12,13]. America has been a major disruption of the invaded ecosystems [5] and has led to changes in the mechanisms producing well known system-level relationships. Recent literature reviews of responses of TP-Chl relationships to dreissenid invasions show a similar range of effects [18,20,21]

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