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 occurrence and severity of Harmful Algal Blooms (HABs) produced by dinoflagellates such as members of the genus Alexandrium (also known as "Red Tide") are increasing in frequency and severity worldwide. HABs not only present a threat to human health via consumption of contaminated shellfish and Paralytic Shellfish Poisoning (PSP) outbreaks but can also have devastating economic impacts on the local shellfish industry. We have been studying the Nauset Marsh System on Cape Cod, Massachusetts, U.S.A. that experiences annual blooms of Alexandrium fundyense associated with PSP outbreaks that have increased in intensity over the last 20 years. Mill and Salt Ponds are two kettle holes or salt ponds within the Nauset Marsh System that we have been using as "natural laboratory" for studying the diversity and dynamics of A. fundyense blooms. Many biological and environmental drivers of these blooms remain unknown and in particular, little is known about the relationship between the Nauset Marsh System bloom dynamics and the microbial communities associated with A. fundyense. In this study we tested to what extent A. fundyense blooms are associated with specific types of bacteria across samples and ponds and contain indicator species that may help forecast the bloom onset or decline. We hypothesized that abrupt, short-term changes in A. fundyense population dynamics and structure are associated with identifiable changes in abundance and community composition of bacteria. To test this hypothesis, we carried out intensive manual and automated sampling (every other day at both high tides) before, during, and after A. fundyense blooms and analyzed the data using Illumina next-generation DNA sequencing of ribosomal RNA marker genes to generate bacterial community profiles. Our data show compelling linkages between bacterial community structure and HAB bloom stage. Peak- and post-bloom populations in Mill Pond were similar to those in Salt Pond despite the one-month difference in bloom onset and there was a clear succession of bacterial communities associated with the pre-, peak- and post-bloom stages. In particular, we noted certain bacterial species increasing in abundance as HAB numbers decreased. Many of these bacteria are capable of producing algicides that can kill algae including HABs. We hypothesize that some of these bacteria may help contribute to bloom termination. Additional research will be required to test this hypothesis generated from our findings. The broader impacts of this work include the application and refinement of automated water sampling equipment that continues to be used for HAB sampling in the Nauset Marsh System and other locations around the world. The results from this work have been presented at national and international meetings and published in one manuscript with another in preparation. This research also contributed to the training and education of two postdoctoral students, one graduate student, and one undergraduate.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Donald L. Rice
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Marine Biological Laboratory
Woods Hole
United States
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