ECOHAB 2017: Life and Death of a Karenia bloom
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Introduction: Harmful algal blooms (HABs) are increasing in frequency worldwide and pose a significant threat to human and environmental health. In the Gulf of Mexico (GoM), the most common HAB species is the toxic dinoflagellate Karenia brevis. Blooms of K. brevis occur nearly annually along the Florida coast, which has led to intense study of K. brevis HABs in the eastern GoM. In contrast, much less is known about K. brevis blooms that affect the western GoM, even though they appear to be occurring with increasing frequency along the lower Texas coast. As a result, almost all hypotheses regarding K. brevis bloom processes are derived from studies in the eastern GoM (or in the lab); their relevance to the western GoM remain untested. Rationale: Blooms in Texas and Florida appear to start from the same offshore source population and experience similar light, temperature, and salinity conditions. Historically, Texas blooms occurred less frequently, but are more common in recent years, implying that different processes drive K. brevis blooms in the western and eastern GoM. There is a management need for better forecasting of K. brevis blooms. While an existing physical model does well at predicting initiation, this work would further improve the model and develop indicators of bloom persistence and termination that would aid management. Hypotheses: The overall goal of this project is to determine the processes that drive K. brevis blooms in the western GoM. While physical processes are a primary determinant of bloom initiation in the western GoM, other factors may modify its effects or act at later stages of the bloom life cycle, e.g. termination. We hypothesize that: 1 – K. brevis is subject to lower grazing pressure than the community as a whole 2 – K. brevis blooms occur under low DIN:P conditions and an abundance of organic N 3 – Endogenous cell death contributes to bloom decline in K. brevis Proposed work: A combination of detection by an Imaging FlowCytobot and forecasting by physical models will be used to identify the earliest stages of a K. brevis bloom. Observations and experiments will commence at bloom initiation and continue through termination, including analysis of nutrients, microzooplankton grazing, cell death markers, and gene expression. The results will be used to modify the existing individual based model of K. brevis blooms, which will be validated against field observations. Expected Results: Project results will identify both the unique and shared drivers of K. brevis blooms across the GoM. Notable outputs include the first measurements of in situ grazing rates on K. brevis, quantification of the impact of endogenous cell death on K. brevis bloom decline, and an improved model of K. brevis blooms for the western GoM. The proposed work directly addresses both ECOHAB program priorities. Hypotheses 1 and 2 contribute to understanding community ecology and ecosystem dynamics, including top-down and bottom-up control of HABs while analysis of cell physiology (H3) and gene expression will increase understanding [of] the factors controlling HAB growth… by focusing on harmful algal genetics[and] physiology. All project PIs work closely with the state agencies regarding HAB monitoring, so the ultimate project outcome will be improved management knowledge and skill in terms of predicting and tracking K. brevis blooms.
