MEPS 320:109-120 (2006)  -  doi:10.3354/meps320109

Variability in phytoplankton pigment biomass and taxonomic composition over tidal cycles in a salt marsh estuary

Michael S. Wetz1,6,*, Kenneth C. Hayes2, Alan J. Lewitus2,3, Jennifer L. Wolny4, David L. White5

1College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Administration Building, Corvallis, Oregon 97331, USA
2Belle W. Baruch Institute for Marine and Coastal Sciences, University of South Carolina, PO Box 1630, Georgetown, South Carolina 29442, USA
3South Carolina Department of Natural Resources, Marine Resources Research Institute, Hollings Marine Laboratory, 331 Fort Johnson Road, Charleston, South Carolina 29412, USA
4Florida Institute of Oceanography, Fish and Wildlife Research Institute, 100 Eighth Avenue SE, St. Petersburg, Florida 33701, USA
5NOAA, Hollings Marine Laboratory, 331 Fort Johnson Road, Charleston, South Carolina 29412, USA
6Present address: Institute of Marine Sciences, The University of North Carolina-Chapel Hill, 3431 Arendell Street, Morehead City, North Carolina 28557, USA

ABSTRACT: Tidal flow causes high temporal variability in environmental properties that impact ecosystem dynamics. Microbes such as phytoplankton are especially susceptible to tidal advection and mixing, and understanding their role in estuarine food webs and biogeochemical cycles requires information on their biomass and taxonomic composition over short time scales (e.g. tidal cycles). We conducted a survey of phytoplankton pigment biomass and taxonomic composition over complete tidal cycles in 2 salt marsh creeks on 5 sampling occasions from July to September 2000, and assessed environmental factors regulating phytoplankton properties. Tidal input of low chl a water combined with phytoplankton losses (microzooplankton grazing, oyster grazing, settling) caused large decreases in phytoplankton biomass (by 47 to 51% on average) on the flood tide, and also influenced the taxonomic composition. Depending on sampling date, pennate diatoms or flagellates were primarily reduced on the flood tide. One sampling date followed a heavy rain event, and was marked by substantial increases in tidal creek nutrient concentrations and reduced microzooplankton grazing rates, emphasizing the need to consider the combined influences of nutrients and grazing in explaining bloom formation following rain events. The high tidal variability in phytoplankton properties suggests that strict attention to tidal phase is needed in determining long-term trends or inter-estuary comparisons in phytoplankton biomass, and primary production in tidally-driven estuaries.

KEY WORDS: Phytoplankton · Estuaries · Tidal cycles · Grazing · Diatoms · Storms

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