Linking Food Web Structure, Grazer Toxin Resistance and Ecological Stoichiometry in Understanding Harmful Algal Blooms

EPA Grant Number: R831706
Title: Linking Food Web Structure, Grazer Toxin Resistance and Ecological Stoichiometry in Understanding Harmful Algal Blooms
Investigators: Dam, Hans G. , Kremer, Patricia , McManus, George
Institution: University of Connecticut
EPA Project Officer: Hiscock, Michael
Project Period: January 1, 2005 through December 31, 2007 (Extended to December 31, 2008)
Project Amount: $408,315
RFA: Ecology and Oceanography of Harmful Algal Blooms (2004) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Ecosystems , Water , Ecology and Oceanography of Harmful Algal Blooms (ECOHAB)


The complex dynamics and feedbacks of planktonic food webs determine the formation and fate of harmful algal blooms (HAB), and the trophic transfer of toxins. In principle, both bottom-up forcing (nutrient availability), which constrains the upper limit of plant productivity, and top-down forcing (grazing pressure), which keeps this productivity from reaching its maximum, control HAB. In the simplest case, depletion of top predators and enhanced nutrient supply due to eutrophication can account for the increase of plant production (including HAB) in coastal regions. However such prediction is biased if it ignores three feedback factors seldom considered in tandem in HAB studies: (1) the toxicity of the algae; 2) toxin resistance of grazer populations; and 3) the elemental stoichiometric (C: N: P) imbalance between algae and grazers. Three hypotheses involving these feedbacks will be tested. The first two hypotheses apply to conditions in which the algae are nutrient rich. H1: Trophic cascades are stronger in the presence of toxic algae. H2: trophic cascades are weaker in the presence of toxin-resistant grazer populations. H3: The strength of trophic cascades depends on the interaction of the stoichiometric imbalance of the grazers, the toxicity of the algae and the complexity of the food web.


These three hypotheses will be tested in combination of controlled laboratory and mesocosm experiments. Rigorous experimental tests for toxic effect of prey on grazers will be run. Comparative and manipulative trophic cascade studies will also be run with simple food webs consisting of several trophic levels with mixtures of toxic and nontoxic foods, under nutrient replete and depleted conditions, and facing toxin resistant and nonresistant metazoan grazer populations.

Expected Results:

There is an immediate and urgent societal need to understand what factors govern HABs in order to develop effective HAB mitigation strategies. This work will provide some of the required tools to predict under what conditions HAB happen and to what extent the strength of trophic cascades involving toxic algae are modified by toxin-resistant grazers and the elemental composition of grazers and algae. This knowledge is essential for properly designing adequate mitigation plans for toxic algal blooms.

Publications and Presentations:

Publications have been submitted on this project: View all 28 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 4 journal articles for this project

Supplemental Keywords:

marine, health effects, ecological effects, dose-response, toxics, ecosystem, aquatic, habitat, public policy, ecology, genetics, oceanography, zoology, modeling, Northeast,, RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Oceanography, algal blooms, Ecological Risk Assessment, Ecology and Ecosystems, marine ecosystem, bloom dynamics, food web, nutrient kinetics, phytoplankton, algal bloom detection, grazing and window opportunities

Progress and Final Reports:

  • 2005 Progress Report
  • 2006 Progress Report
  • 2007 Progress Report
  • Final Report