Grantee Research Project Results
2007 Progress Report: Quantifying Grazing on Harmful Algae with a Novel, qPCR-based Technique
EPA Grant Number: R833222Title: 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: Packard, Benjamin H
Project Period: March 15, 2007 through March 14, 2010
Project Period Covered by this Report: March 15, 2007 through March 14,2008
Project Amount: $409,856
RFA: Ecology and Oceanography of Harmful Algal Blooms (2006) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Water
Objective:
The overall objective of this project is to develop a quantitative PCR-based method to assay zooplankton grazing rates on harmful algae. The specific objectives are to: 1) optimize the qPCR assay for quantitative detection of ingested Alexandrium, 2) calibrate and test the qPCR-based measure of grazing rate in laboratory experiments, and 3) apply the qPCR-based grazing technique to quantify grazing by copepods on an in-situ Alexandrium bloom.
Progress Summary:
Harmful algal blooms (HABs) cause serious threats to coastal ecosystems and human health on a global scale. Grazing is one of the most important loss rates for phytoplankton populations, including potentially harmful species. High grazing rates could therefore prevent a HAB from developing, limit cell concentration in the bloom, or terminate a bloom. Conversely, low grazing has been implicated as a necessary condition, or even a trigger, for some HABs. Quantifying and understanding variability in grazing rates is important to predicting when and where HABs occur. For this work, we applied polymerase chain reaction (PCR) and quantitative PCR (qPCR) to measure grazing specifically on harmful algal species, even when they are at low abundance. To date, we have tested the amplification and signal recovery from cells ingested by several different zooplankton predators, including the copepods Acartia hudsonica, and Calanus finmarchicus, Nassarius veliger larvae, and the ciliates Strombidinopsis sp., Favella sp. and Eutintinnis sp. Amplifiable DNA was recovered by PCR from all of the different predators tested that had fed on Alexandrium. No Alexandrium DNA was recovered from predators that did not ingest the dinoflagellate. In A. hudsonica, the Alexandrium signal was qualitatively detectable for approximately 2-6 h after ingestion stopped.
The quantitative effectiveness of qPCR for measuring zooplankton grazing rates was tested in laboratory experiments using A. hudsonica, fed a sole diet of Alexandrium (0 cells mL-1; low prey (100 mL-1); high prey (600 cells mL-1)). The ingestion rates determined by qPCR of gut content were much lower (~0.01 cells copepod-1) than the rates calculated by cell counts and did not increase with prey concentration. Extensive testing ruled out PCR inhibition and other potential problems that might have contributed to the low qPCR signal in copepods. By contrast, in similar experiments with a different zooplankton predator, Nassarius veliger larvae, qPCR recovered approximately 20%-40% of the ingested Alexandrium DNA from the predator’s gut contents. Moreover, the Alexandrium signal in veligers increased with prey concentration and was quantitatively related to ingestion rate. It is hypothesized that the difference in recoverable Alexandrium DNA between these two grazers was a result of their feeding strategies. Veliger larvae ingest prey cells whole, and digestion is relatively slow. However, copepods tend to macerate prey, and prey DNA may be lost through sloppy feeding and more rapid digestion. The hypothesis is supported by additional grazing experiments using the tintinnid ciliate, Favella sp., which also ingest dinoflagellate cells whole. As in the veliger experiments, the Favella experiments yielded a quantitative relationship between gut content and ingestion rate. Together, these results suggest that feeding strategy and digestion play a significant role in the recovery of detectable prey DNA. Work is ongoing to test additional grazers.
To apply PCR-based detection methods to an in-situ Alexandrium bloom, field samples (dominated by the copepod Calanus finmarchicus) were obtained from the Gulf of Maine. Qualitative PCR was used to detect ingestion of Alexandrium cells. Of the 16 stations from which samples were collected, 12 had detectable free-living Alexandrium cells present. From the stations with free-living Alexandrium, 10 stations were found to have cell ingestion by Calanus. The 4 stations with no Alexandrium present yielded no detectable DNA signal by PCR.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 7 publications | 3 publications in selected types | All 3 journal articles |
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Haley ST, Dyhrman ST. The Artistic Oceanographer Program: encouraging ocean science literacy through multidisciplinary learning. Science and Children 2009;46(8):31-35. |
R833222 (2007) R833222 (2008) R833222 (Final) |
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Supplemental Keywords:
aquaculture, aquatic, biology, ecological effects, estuary, human health, marine, Northeast, Northwest, RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Oceanography, algal blooms, Ecological Risk Assessment, marine ecosystem, bloom dynamics, HAB ecology, water qualityRelevant Websites:
http://www.ldeo.columbia.edu/~andyjuhl/index.html Exit
http://www.whoi.edu/sites/dyhrman Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.