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<p>The toxic marine dinoflagellate <i>Karenia brevis</i> causes near-annual red tide events along the Gulf of Mexico (GoM). Top-down control from microzooplankton grazers has been implicated in both bloom initiation and termination in many phytoplankton species; however, grazing pressure on <i>K. brevis</i> has not yet been quantified in the field. Understanding differential grazing on <i>K. brevis</i> specifically vs. community can provide insights into potential effects of top-down control on the progression of red tides. Quantification of <i>K. brevis</i> can be challenging given their morphological similarity with other <i>Karenia</i> species and low densities at the beginning and end of blooms. A new quantitative real-time polymerase chain reaction (qPCR) method targeting D1-D2 region of the 28S ribosomal RNA gene was developed for accurate quantification of <i>K. brevis</i> from environmental samples. The primer set exhibits strong specificity for detection of <i>K. brevis</i> cells from both laboratory and field environments. High amplification efficiency (&gt; 90%) was obtained with the presence of environmental DNA, revealing robust and precise amplification of this qPCR method. Its lower limit of detection is considered to reach 1 cell per sample, enabling early detection of red tides. Coupled with the dilution method in a field grazing experiment, microzooplankton grazing on <i>K. brevis</i> and the whole phytoplankton community in the bloom season were differentiated and quantified. This study provides a valuable proof-of-concept that integrated application of the grazing dilution method and the “absolute” qPCR quantification is suitable for measuring <i>in-situ</i> grazing pressure on marine harmful microalgae, especially for cryptic or morphologically indistinct species.</p>

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Development of a novel quantitative PCR assay for the toxic dinoflagellate Karenia brevis and its application for measuring in situ microzooplankton grazing impact

  • 期刊论文

  • 发表日期：

    2025年9月3日

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  • Yida Gao,
  • Deana Erdner

摘要

The toxic marine dinoflagellate Karenia brevis causes near-annual red tide events along the Gulf of Mexico (GoM). Top-down control from microzooplankton grazers has been implicated in both bloom initiation and termination in many phytoplankton species; however, grazing pressure on K. brevis has not yet been quantified in the field. Understanding differential grazing on K. brevis specifically vs. community can provide insights into potential effects of top-down control on the progression of red tides. Quantification of K. brevis can be challenging given their morphological similarity with other Karenia species and low densities at the beginning and end of blooms. A new quantitative real-time polymerase chain reaction (qPCR) method targeting D1-D2 region of the 28S ribosomal RNA gene was developed for accurate quantification of K. brevis from environmental samples. The primer set exhibits strong specificity for detection of K. brevis cells from both laboratory and field environments. High amplification efficiency (> 90%) was obtained with the presence of environmental DNA, revealing robust and precise amplification of this qPCR method. Its lower limit of detection is considered to reach 1 cell per sample, enabling early detection of red tides. Coupled with the dilution method in a field grazing experiment, microzooplankton grazing on K. brevis and the whole phytoplankton community in the bloom season were differentiated and quantified. This study provides a valuable proof-of-concept that integrated application of the grazing dilution method and the “absolute” qPCR quantification is suitable for measuring in-situ grazing pressure on marine harmful microalgae, especially for cryptic or morphologically indistinct species.