Investigation of Toxic Raphidophyte Population Dynamics Using Molecular and Physiological Tools

EPA Grant Number: R831041
Title: Investigation of Toxic Raphidophyte Population Dynamics Using Molecular and Physiological Tools
Investigators: Hutchins, David A. , Cary, S. Craig , Coyne, Kathryn J. , Doblin, Martina
Institution: University of Delaware , Old Dominion University
EPA Project Officer: Hiscock, Michael
Project Period: September 1, 2003 through August 31, 2006
Project Amount: $567,331
RFA: Ecology and Oceanography of Harmful Algal Blooms (2002) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Water Quality , Ecosystems , Water


In 2000, an abrupt and unprecedented bloom of the toxic Raphidophyte Chattonella verruculosa reached densities as high as 107 cells/L in the Delaware Inland Bays (DIB), causing massive mortality of marine life. Extensive monitoring revealed the presence of Raphidophytes throughout the bays and blooms have occurred several times since their discovery. Initially thought to consist of unialgal blooms of Chattonella, it has since become clear that Raphidophyte blooms in the bays are instead made up of a consortium of four Raphidophyte species. The abundance of each species in the blooms varies, suggesting that there are species-specific responses to the environment and that inter-specific interactions between Raphidophytes have variable outcomes, or both. The effects of environmental and physical factors, as well as biotic interactions, on the dominance and succession of mixed Raphidophyte blooms are currently unknown.


The goals of this project are: (1) to gain a better understanding of the effects of environmental perturbations and grazing pressure on Raphidophyte community dynamics; (2) to identify environmental factors that stimulate the growth of Raphidophytes relative to other algal taxa; and (3) to investigate the potential of Raphidophyte cyst distributions as an indicator of seasonal bloom “hot spots”. We will investigate the following hypotheses: H1: the relative abundance of species within Raphidophyte assemblages is controlled by physical and chemical conditions, such as light, nutrient concentrations and nutrient ratios; H2: the relative abundance of species within Raphidophyte assemblages is controlled by inter-specific interactions, such as differential grazing rates; H3: the abundance of Raphidophytes as a group relative to other algal taxa is affected by bottom-up controls, especially Penrichment; H4: local strains of Raphidophyte species are grazed at similar rates as other community members; and H5: resident populations of Raphidophyte cysts in Delaware Inland Bays sediments can be used as a predictive determinant for seasonal blooms.


Sensitive molecular techniques, HPLC pigment analysis, and microscopic methods will be used to assess the relative abundance of the four Raphidophyte species vs. other major algal taxa in the DIB. Raphidophyte assemblages at several key sites in the DIB will be routinely monitored along with environmental parameters such as nutrients, light, temperature and salinity. Sediment samples will also be collected periodically throughout the course of the investigation to determine the distribution and relative abundance of Raphidophyte cyst populations. Laboratory investigations will evaluate the effect of bottom-up (nutrients and light) and top-down (grazing) controls on the four Raphidophyte species individually, in mixed assemblages and in natural populations.

Expected Results:

The proposed investigation addresses fundamental questions of Raphidophyte physiology and population dynamics. We will (1) determine physiological requirements and tolerances to nutrients and light for the four Raphidophyte species in culture, (2) evaluate the effect of grazing on Raphidophyte species and assemblages, (3) evaluate the effect of environmental factors on Raphidophyte population dynamics in natural assemblages, and (4) identify resident Raphidophyte cyst populations in natural sediments and correlate the distribution and relative abundance of Raphidophyte cysts to seasonal blooms.

Publications and Presentations:

Publications have been submitted on this project: View all 32 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 13 journal articles for this project

Supplemental Keywords:

marine science, estuary, ecology, monitoring, Mid-Atlantic, RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Oceanography, Monitoring/Modeling, algal blooms, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, marine ecosystem, aquatic ecosystem, bloom dynamics, pigment analysis, algal growth, nutrient kinetics, aquatic toxins, marine biogeochemistry, Raphidophyte blooms, algal pigments, Delaware, Chattonella

Progress and Final Reports:

  • 2004 Progress Report
  • 2005 Progress Report
  • Final Report