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JPR Advance Access published online on February 6, 2004
Journal of Plankton Research, doi:10.1093/plankt/fbh035
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Received July 24, 2003;
accepted December 22, 2003

Article

Phytoplankton community growth-rate-response to nutrient pulses in a shallow turbid estuary, Galveston Bay, Texas

Erla Björk Örnólfsdóttir 1*, S. Elizabeth Lumsden 2, and James L. Pinckney 2

1

Estuarine Ecology Laboratory, 3146 TAMU, Department of Oceanography, Texas A&M University, College Station, TX, 77843-3146, U.S.A.

Current address: Center for Coastal Fisheries and Habitat Research, National Ocean Service, NOAA, 101 Pivers Island Road, Beaufort, NC 29516.

Phone: 252 728 8792

Fax: 252 728 8784


2 Estuarine Ecology Laboratory, 3146 TAMU, Department of Oceanography, Texas A&M University, College Station, TX, 77843-3146, U.S.A.

* To whom correspondence should be addressed. E-mail: Eroa.Ornolfsdottir{at}noaa.gov.


  Abstract

Phytoplankton growth is a physiological process often limited by temperature, nutrients or light while biomass accumulation is a function of growth rates, grazing, and deposition. Although primary productivity measurements are usually used to assess responses to limiting factors, the rates are proportional to biomass and inversely related to grazing pressure during experimental incubations. Alternatively, carbon-specific growth rate determinations provide insights into physiological responses without the confounding effects of biomass and grazing. The objective of this study was to quantify the growth rate responses of phytoplankton to enhanced nutrient availability (nitrate and phosphate) over a range of in-situ irradiances. Growth rates were determined based on chl a-specific 14C uptake rates by phytoplankton. Phytoplankton demonstrated high (24h) growth rates when exposed to increased concentrations of limiting nutrients independent of the surface irradiances (12 - 41%). Growth rate responses were also compared with the biomass (chl a) responses and community composition. Observed and estimated phytoplankton biomass changes during the incubations differed, emphasizing the structural role of grazers on the phytoplankton community. The phytoplankton community in Galveston Bay has the potential to instantaneously respond to nutrient pulses, facilitating diatom biomass accumulation in spring and summer and small flagellated species and cyanobacteria during periods of low nutrient inputs. Thus Galveston Bay phytoplankton biomass and community composition reflect a dynamic balance between the frequency of nutrient pulsing and grazing intensity.


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