Macroalgal bloom dynamics in a highly
eutophic Southern California estuary
Karleen A. Boyle and Krista Kamer
University of California, Los Angeles
Friday, August 6, 1999
12:00 NoonPacific Forum
Anthropogenic eutrophication of estuaries in Southern California is common
due to increasing urbanization of local watersheds. Episodic nutrient inputs can fuel
blooms of opportunistic estuarine algae such as Enteromorpha intestinalis and Ulva
expansa. Upper Newport Bay (UNB), Orange County, California, is located in an urban
environment and large macroalgal blooms are common in the estuary. This study documents
algal community composition and water column, sediment, and algal tissue nutrients in UNB
over a 16-month period. This field monitoring was supplemented with a microcosm experiment
testing nutrient limitation of macroalgal biomass in UNB.
The abiotic parameters we measured indicate a highly eutrophic system. The freshwater
source for UNB was high in N (800m M) following the winter
rains. Sediment N levels peaked after this period, then declined throughout the summer and
fall, reaching their lowest point in early winter before the rainy season began again. We
hypothesized that this decline was due to utilization of sediment nutrients by the
substantial macroalgal blooms (max. of 1.11 kg wet weight m-2) that occurred
during the summer and fall. Our microcosm experiment supported this hypothesis and
demonstrated that macroalgae are capable of using sediment stores of nutrients to fuel
The algal community exhibited seasonal shifts in dominance. Large blooms of E.
intestinalis began in spring and continued through early summer. U. expansa
became dominant in late summer and significant amounts of Ceramium sp. were
measured in the fall. In the winter the system was dominated by benthic diatom mats.
Macroalgal tissue N exceeded 4 % dry weight indicating luxury uptake of N. Algal community
data also indicate a highly eutrophic system, and any further nutrient inputs will only
exacerbate the problem.
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Last updated: December 19, 2000