¹Florida Institute of Oceanography, University of South Florida & Fish & Wildlife Research Institute, Florida Fish & Wildlife Commission, St. Petersburg, FL 33701 USA
²Great Lakes Environmental Research Laboratory–Lake Michigan Field Station, National Oceanic & Atmospheric Administration, 1431 Beach Street, Muskegon, MI 49441 USA
³Great Lakes Environmental Research Laboratory, National Oceanic & Atmospheric Administration, Ann Arbor, MI 48105 USA
⁴Annis Water Resources Institute, Grand Valley State University, Muskegon, MI 49441 USA
⁵Old Woman Creek National Estuarine Research Reserve, Division of Wildlife, Ohio Department of Natural Resources, Huron, OH 44839 USA
⁶Center for Coastal Fisheries & Habitat Research, National Oceanic & Atmospheric Administration, Beaufort, NC 28516 USA

*Corresponding author: david.millie@myfwc.com

Abstract

   The relationships among environmental conditions and phytoplankton assemblages were characterized during late summer (2003-2005) in Saginaw Bay, Lake Huron. Differences among sampling stations, arising primarily from spatial disparities in water-column optical properties and nutrient availability, were evident. Cyanobacteria and diatoms dominated phytoplankton assemblages, with the greatest total chlorophyll a concentrations occurring at the innermost portions of the Bay. Microcystis abundance was greatest in the Bay’s upper reaches and decreased with increasing distance from the mouth of the Saginaw River. A suite of variables, indicative of annually-distinct meteorological and hydrological conditions and phosphorus-laden inflows, were identified to (collectively) best ‘group’ stations in a manner consistent with that of phylogenetic-group chlorophyll a concentrations and cyanobacterial biovolumes. However, a great deal of variability between abiotic and biotic patterns remained unexplained and several abiotic variables singularly corresponded with Microcystis abundance. Taken together, it appears that multiple environmental conditions (including annual/episodic meteorological patterns, seasonal/intermittent riverine inflows, annual phosphorus loading, etc.) interact with taxon-specific physiological traits to holistically influence late-summer phytoplankton abundance throughout inner Saginaw Bay.