Sediments as Toxin Reservoirs and Benthic Habitats for Harmful Algae

EPA Grant Number: F5E70932
Title: Sediments as Toxin Reservoirs and Benthic Habitats for Harmful Algae
Investigators: Sosa, Tania
Institution: University of California - Santa Cruz
EPA Project Officer: Zambrana, Jose
Project Period: June 1, 2005 through August 1, 2006
Project Amount: $107,252
RFA: GRO Fellowships for Graduate Environmental Study (2005) RFA Text |  Recipients Lists
Research Category: Academic Fellowships


Domoic acid (DA), a harmful algal bloom (HAB) toxin, is an amino acid-like water-soluble compound produced by several species within the diatom genus Pseudo-nitzschia. Although high levels of this toxin are generally present in marine animals only during an algal bloom, several species of benthic invertebrates in Elkhorn Slough, California contain high concentrations at times well beyond the duration of a bloom. This suggests that either these invertebrates have a mechanism for retaining toxin beyond the usually short depuration rates, or they have access to an alternative source of DA. This project addresses the latter suggestion: that sediments may extend the residence time of domoic acid available to benthic communities.

The primary goal of this project is to understand the persistence of domoic acid in benthic communities in Elkhorn Slough and to determine the role of sediments in extending the residence time of this toxin beyond the ephemeral duration of an algal bloom. Specific aims are:

  • Do sediments represent a reservoir of toxin capable of contaminating benthic animals?
  • Do different types of marine sediments have different potentials to retain toxin?
  • Is there a benthic life stage for these plankton when there are undetectable in the water?
  • How general are the interactions of algal toxins with sediments?


The presence and concentration of DA in sediments will be determined using liquid chromatography/mass spectrometry (LC-MS) analysis of sediment samples subjected to a variety of extraction schemes. Results will be validated against a positive control sample spiked with a standard of DA. To identify the potential for different types of marine sediments to retain DA, various sediment samples from Elkhorn Slough and Monterey Bay will be analyzed after exposure to controlled concentrations of toxin. The abundance of live toxic cells in sediments will be determined under the light microscope and identified to species by SEM. To determine if the interactions of algal toxins with sediments may be a general phenomenon, a parallel study will be conducted with samples from Midway Atoll using the lipid soluble Ciguatoxins as a contrasting system.

This project tests the potential for sediments to be reservoirs capable of contaminating benthic communities with high levels of the natural algal toxins domoic acid and ciguatoxin. This will be the first intensive analysis of algal toxins in sediments. Measuring toxin concentrations in field samples and assessing their association with marine sediments will offer new insights on the fate of algal toxins, enhance understanding of sources of natural toxin in marine food webs and increase awareness of threats to wildlife, fisheries and public health.

Expected Results:

The structural similarity of domoic acid to amino acid glutamic acid, which like other amino acids accumulates in sediments, suggests that DA is likely to have a similar association with sediments. Fine sediments (with their higher surface area to volume ratio) should accumulate more toxin than coarse sediments. If there are live Pseudo-nitzschia in sediments, higher abundances are expected where high levels of toxin are found. As Ciguatoxins are lipid soluble they may demonstrate enhanced associations with organic matter in sediments relative to DA.

Supplemental Keywords:

fellowship, domoic acid, ciguatoxin, natural toxin, sediments, benthic contamination, Pseudo-nitzschia,, RFA, Scientific Discipline, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems, algal blooms, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, marine ecosystem, marine food web, estuaries, Pseudo-nitzschia, phytoplankton, trophic transfer of phycotoxins, algal bloom detection, algal toxins, trophic interactions, benthic algae, domoic acid producing diatoms, marine toxins

Progress and Final Reports:

  • 2005
  • Final