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.

Project Report

The goal of this project was to investigate the influence of the microbial community on the population dynamics and structure of Alexandrium fundyense, the toxic microalgae species responsible for the harmful algal bloom (HAB) syndrome known as paralytic shellfish poisoning (PSP). This comparative study examined several key factors that can regulate A. fundyense population development and growth in two salt ponds in the Nauset Marsh System (NMS), Cape Cod, MA, including parasitism by Amoebophrya dinoflagellates, environmental and hydrodynamic factors, losses from zooplankton and other grazers, and the association with specific bacterial communities. Understanding host-parasite interactions and grazing impacts are high priority research topics, with implications for HAB control and prevention. Results from these studies provide direct, empirical evidence that Amoebophrya parasites specifically infect A. fundyense in the NMS, suggesting that parasitism may control A. fundyense populations in this system. This project also helped to characterize the role of biological factors such as parasitism and grazing in the induction of sexuality, as sexual processes and life cycle shifts have been identified as strategies that a host may use to avoid parasite and viral infections. Dinoflagellates have been shown to stop dividing in laboratory culture once infected by Amoebophrya spp., a result that is consistent with our observations in the NMS, as no parasite infections were found inside of asexually dividing A. fundyense pairs. However, we did observe sexual reproduction of infected A. fundyense cells in the field, suggesting that Amoebophrya spp. infections do not prevent sexual processes in their host populations. While most of the observed life-history shifts in dinoflagellate populations have been related to chemical factors, biological factors may also play an important role. The results of these studies have fostered new hypotheses regarding the potential role of parasite-induced stress signals (chemical cues) in HAB life-cycle strategies. In addition, the modeling work carried out by this project assessed the environmental and hydrodynamic factors controlling the development of annual A. fundyense blooms in the NMS. We found that water temperature was an important controlling variable for the bloom timing, and developed a relatively simple approach to modeling cell concentrations that consisted of monitoring temperature and calculating degree-day patterns. This approach could provide an effective means of providing early warning for shellfish monitoring programs in coastal systems like Nauset that have regularly occurring HABs. Finally, this project advanced laboratory technologies and techniques through the development of genetic markers for analyzing the population structure of Alexandrium blooms in the northwestern Atlantic, and the refinement of laboratory techniques for the detection and enumeration of Amoebophrya parasites, all of which will be of use to the scientific community. In terms of broader impacts, the results of this work were disseminated extensively through presentations at scientific conferences, workshops, and invited seminars, and resulted in ten publications (several more are currently in preparation) and one Ph.D. thesis (currently in progress). This project also provided laboratory and field training, education, and experience to two post-doctoral researchers, one Ph.D. student, and five undergraduate students.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Donald L. Rice
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Woods Hole Oceanographic Institution
Woods Hole
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