Collaborative Research: Microbial influences on Alexandrium populations

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The harmful algal bloom (HAB) syndrome known as Paralytic Shellfish Poisoning (PSP) is a significant and growing problem worldwide, with negative and sometimes devastating economic and human health impacts. Dinoflagellates within the genus Alexandrium are responsible for many of these PSP outbreaks. In the northeastern US and Canada, Alexandrium blooms occur in two types of habitats -- one that is large and widespread, covering vast expanses of open coastal waters and another that is small and localized, such as within salt ponds or kettle holes on Cape Cod. Blooms in these latter systems exhibit strong "point source" characteristics in which localized cyst germination inoculates the overlying waters, leading to bloom development and eventual deposition of new cysts at that location, and thus to recurrent, self-seeding blooms. Due to their small geographic scale and limited connectivity with coastal populations, Cape Cod salt ponds represent a unique natural laboratory for the investigation of many important aspects of Alexandrium fundyense autoecology that are difficult to study in open coastal waters, larger estuarine systems, or even in mesocosms. In this project, researchers at the Woods Hole Oceanographic Institution and the Marine Biological Laboratory will conduct a coordinated field and laboratory study of population and genetic dynamics of A. fundyense in two Cape Cod salt ponds, coupled with an investigation of host-parasite interactions, grazing losses, and bacterial associated dynamics, examined within the context of local hydrodynamics. The project hypothesis is that abrupt, short-term changes in Alexandrium population dynamics and structure are associated with identifiable changes in abundance and community composition of bacteria, parasites, and/or grazers. A comparative approach will be used to reveal processes that are common to both sites, but that occur at different times. Specific objectives are to: 1) Characterize Alexandrium population abundance and structure in two isolated salt ponds, as well as the dynamics and impacts of losses due to parasitism and grazing; 2) Generate and analyze comparative high resolution microbial community structure data before, during, and after Alexandrium blooms; and 3) Obtain high-resolution hydrodynamic data within the study area and use that information to interpret microbial network data and Alexandrium population structure in an environmental context. Having worked together in the past as PIs in the Woods Hole Center for Ocean and Human Health (WHCOHH), the investigators will share and synthesize data to identify the major influences on A. fundyense populations, and use these insights to inform an existing physical/biological model of A. fundyense bloom dynamics within the NMS. These will also help us to refine our models of the offshore blooms for the Gulf of Maine, for which forcing functions and loss terms are difficult to isolate and quantify. Broader Impacts. The study site is a multi-user, high-value resource that includes parts of the Cape Cod National Seashore (CACO). PSP has become a major concern to residents and commercial shell fishermen due to the temporal and spatial increase in harvesting closures over the last two decades. The data and analyses produced will be of value in policy decisions about many issues in the system, including sewage treatment, groundwater quality, aquaculture, shellfish propagation, and harvesting closure policies. This project also lends itself to undergraduate, graduate, and postdoctoral training.