Macroalgal Blooms in Waquoit Bay: The Relative Influence of Nutrient Supply, Grazing, and Predation

EPA Grant Number: FP916344
Title: Macroalgal Blooms in Waquoit Bay: The Relative Influence of Nutrient Supply, Grazing, and Predation
Investigators: Fox, Sophia E.
Institution: Boston University
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $97,476
RFA: STAR Graduate Fellowships (2004) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Oceanography and Coastal Processes , Aquatic Ecosystems


Top-down control of macroalgal blooms is well supported in the published literature. In spite of demonstrated control of macroalgal growth by grazers, blooms are widespread along the coasts of the world and are associated with anthropogenic inputs of nutrients to coastal waters. In places with high nitrogen loads, the effects of bottom-up forces related to increasing inputs of nitrogen may be large enough to overwhelm the influence of top-down control by consumers. The objective of this research is to examine the relative importance of these control mechanisms.


First, I will determine how increasing N loads and seasonality alter macroalgae and consumer assemblages. Second, I will assess whether the top-down controls might be paramount in environments subject to low nitrogen loads, but as nitrogen load increases, macroalgal growth rates may become larger than grazer consumption rates. Third, I will define how seasonal shifts between bottom-up (nitrogen supplies) and top-down controls (herbivory and predation) might alter trophic relationships during different times of year. I will assess these questions by defining the benthic macroalgae-based food web with a survey of producers and consumers and corroborating analyses of stable isotopic work. I also will examine the relative importance of nutrient supply, grazing, and predation by assessing the balance between the macroalgal growth rate stimulated by nitrogen supply in the ambient water and the rate of consumption of the produced biomass by grazers present with a series of field experiments. I will measure net growth of different species of macroalgae (growth minus consumption) under different nitrogen regimes (different estuaries) and grazing pressures (different species and abundance of grazers). To examine the relative “cascading” effects of predation on grazers from the top down and nitrogen supply from the bottom up, I will run an additional experiment in which I measure algal net growth and herbivore abundance under different nitrogen regimes (different estuaries) and predation pressures (predators excluded or present). The data from this work are siginificant because these organisms are a major bioassay that integrate the time course of eutrophication status of estuaries and are the best record of changes forced on the ecosystem by land use changes in the watershed.

Supplemental Keywords:

fellowship, eutrophication, top-down, bottom-up, macroalgae, benthic food web, nitrogen loading, grazing, predation,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Aquatic Ecosystem, Monitoring/Modeling, Water Quality Monitoring, algal blooms, Environmental Monitoring, Terrestrial Ecosystems, Watersheds, anthropogenic processes, anthropogenic stress, bioassessment, biodiversity, bloom dynamics, watershed management, ecosystem monitoring, predators, conservation, nutrient kinetics, biota diversity, diagnostic indicators, ecosystem indicators, redox chemistry, aquatic ecosystems, bioindicators, watershed sustainablility, dissolved organic nitrogen, biological indicators, macroalgal populations, ecosystem stress, grazing and window opportunities, watershed assessment, conservation planning, aquatic biota, nitrogen, oceanography, restoration planning, watershed restoration

Progress and Final Reports:

  • 2004
  • 2005
  • Final