Graduate Thesis Or Dissertation
 

Production dynamics of sediment-associated algae in two Oregon estuaries

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  • Sediment-associated gross primary production, oxygen uptake, microalgal biomass expressed as chlorophyll a concentration, macroalgal biomass and total organic matter concentration expressed as ash-free dry weight were measured monthly at medium sand, fine sand and coarse silt sites between 0.5 m and 2.0 m above MLLW during an entire year at Netarts Bay, Oregon. Maximum biomass of microalgae occurred during the spring in medium and fine sand and during the fall and winter in coarse silt. Maximum biomass of macroalgae, primarily Enteromorpha and Ulva, was found during the summer in medium and fine sand. Factors controlling microalgal production dynamics were: daylength, temperature, water currents, sediment moisture and stability, animals and macrophyte cover. Apparently nutrients did not limit microalgal growth. Daylength and temperature appeared to control the initiation and cessation of macroalgal growth. Macroalgae were excluded from silt sites, probably because of relatively high turbidity which caused low available light intensity. In Netarts Bay estimated annual net primary production of microalgae was 13 g C·m⁻² in medium sand, 17 g C·m⁻² in fine sand and 5 g C·m⁻² in coarse silt; Enteromorpha contributed 2700 g C·m⁻² in medium and fine sand even though its growing season was only 60 days, during the summer. The concentration of organic matter and the rate of community oxygen uptake were maximum during the summer. Laboratory studies of intact sediment communities, isolated epipelic diatoms and macroalgae from Yaquina Bay, Oregon indicated that photosynthesis was light-saturated at 200 to 400 [mu]E·m⁻²·sec⁻¹. Gross primary production per unit chlorophyll a (mg C·mg chl a⁻¹·h⁻¹) was lowest for intact sediment communities (0.1 to 1.7), followed by isolated epipelic diatoms (2.3 to 6.9) and macroalgae (4.4 to 9.4). Mean algal respiration per hour for isolated epipelic diatoms and macroalgae was 34% and 15%, respectively, of hourly gross primary production. Microalgal biomass expressed as ash-free dry weight, was estimated from chlorophyll a concentration (mg chl a·m⁻²) with an expression determined in the laboratory using isolated epipelic diatoms (microalgal biomass = -167 x chlorophyll a concentration). Field and laboratory studies indicated that removal of infauna, primarily tanaids, allowed the increase of sediment-associated microalgal biomass and production. Grazing of microalgae appeared to be a mechanism for limitation of microalgal growth.
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