Quantifying Grazing on Harmful Algae with a Novel, qPCR-based TechniqueEPA Grant Number: R833222
Title: Quantifying Grazing on Harmful Algae with a Novel, qPCR-based Technique
Investigators: Juhl, Andrew , Dyhrman, Sonya
Institution: Lamont Doherty Earth Observatory of Columbia University , Woods Hole Oceanographic Institution
EPA Project Officer: Hiscock, Michael
Project Period: March 15, 2007 through March 14, 2010
Project Amount: $409,856
RFA: Ecology and Oceanography of Harmful Algal Blooms (2006) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecosystems , Water
The proposed, targeted study will develop and apply a novel approach for measuring grazing on harmful algae. Grazing is an important, but poorly constrained, factor in the dynamics of harmful algal blooms (HABs). The new method measures the number of ingested algal cells within grazer gut contents by quantitative polymerase chain reaction (qPCR). Initial development will study grazing by the common copepod, Acartia hudsonica, on the toxic, dinoflagellate, Alexandrium fundyense.
The project has three research objectives. 1) Optimize the qPCR assay for quantitative detection of Alexandrium ingested by Acartia. 2) Calibrate and test the qPCR-based measure of grazing rate in laboratory experiments. 3) Use the qPCR-based grazing technique to quantify Acartia grazing rates and their impact on a coastal Alexandrium bloom.
Preliminary observations show that Alexandrium DNA can be recovered from copepods that have fed on Alexandrium cells. Using similar information as the widely-used gut pigment technique for measuring copepod grazing, the qPCR-based measure of ingested cells will be converted to a specific ingestion rate of A. hudsonica on A. fundyense. Development will begin with laboratory experiments using cultured A. hudsonica and A. fundyense. Degradation of ingested Alexandrium DNA will be determined and ingestion rates of the copepod on Alexandrium will be measured in single- and multi-species prey fields. Once verified in the lab, the qPCR-based method will be used to study the impact of A. hudsonica grazing on an Alexandrium bloom in a coastal bay. During both lab and field work, results of the qPCR-based approach will be compared to copepod ingestion rates determined using the best currently-available method.
The primary advantages of the qPCR-based method over other currently available grazing measures include: in-situ assessment of grazing without incubations, increased sampling resolution, and high sensitivity. Initial application of this new, innovative method will improve understanding of how grazing influences the dynamics of Alexandrium blooms in coastal bays. Increased understanding and quantification of grazing and toxin transfer are important HAB research goals. Ultimately, wide use of the new method could provide high resolution grazing data for improving Alexandrium bloom models. By improving models, the new method will aid forecasting and mitigation of Alexandrium blooms by coastal managers. Once developed, the general method could be used to quantify grazing by many types of zooplankton on many types of phytoplankton. The approach may develop into a tool with widespread application and utility to HAB researchers, monitoring programs, and general oceanographic research.