Award: OCE-1314642

Overall Program Intellectual Merit: The WHCOHH Program addressed fundamental issues of the dynamics of harmful algal blooms (HABs), biological events with significant human health consequences, in the temperate coastal ocean, including offshore, coastal and estuarine systems. The Center research employed focused and complementary biological, hydrographic, and modeling studies of key habitats and processes, and considered critical yet largely unaddressed toxicological mechanisms. The latter addressed consequences of sub-acute exposure, especially during development, with potentially pervasive and pernicious effects in exposed populations. Fundamentally new understanding of HAB populations and toxicity were obtained. Broader impacts: Each Project and the Administrative Core in the program conveyed research findings in primary publications and presentations at national and international meetings, as well as to the general public. The research in each Project contributed to the training and professional development of several students. Project 1 This research investigated mechanisms regulating Alexandrium catenella bloom initiation and termination. In 2018 and 2019, multiple sensors, including a submersible microscope (Imaging FlowCytobot, IFCB), were deployed in Nauset estuary. High-frequency observations provided estimates of cell division and toxin production rates in situ, both vital for bloom development and toxicity assessments. Results demonstrated that a network of instruments can provide high-frequency toxicity estimates to augment weekly shellfish flesh testing currently used for regulatory decisions. Dormant cysts that overwinter in bottom sediments are critical to A. catenella bloom dynamics. Experiments demonstrated that cold exposure (?chilling?) regulates the duration of dormancy and that cysts must surpass a quantifiable chilling requirement to break dormancy and germinate. Similarly, a thermal (warming) requirement is needed to re-enter dormancy. Model simulations using these mechanisms demonstrate the importance of temperature seasonality for synchronization of dormancy and germination. Alexandrium is more tolerant of warming in habitats with higher temperature seasonality. Therefore, as climate warming shifts species? ranges, cyst accumulation zones may persist longer in seasonally variable, shallow inshore habitats compared to deep offshore areas, leading to more localized and earlier blooms. Finally, a particle tracking model incorporating A. catenella life cycle processes was developed to simulate A. catenella blooms in Nauset. This model will facilitate studies of past and future blooms in a changing climate. Project 2 The toxic diatom genus Pseudo-nitzschia is a growing presence in the Gulf of Maine (GOM), where regionally unprecedented levels of domoic acid (DA) in 2016 led to the first Amnesic Shellfish Poisoning closures in the region. Sampling of Pseudo-nitzschia and associated oceanographic conditions in the GOM by WHCOHH investigators provided insight as to the underlying causes of the bloom. Pseudo-nitzschia biogeography was consistent in the years 2012, 2014, and 2015, with greater Pseudo-nitzschia cell abundance in low-salinity inshore samples, and lower Pseudo-nitzschia cell abundance in high salinity offshore samples. During the 2016 event, DA concentrations were an order of magnitude higher than in previous years, and inshore-offshore contrasts in biogeography were weak, with P. australis present in every sample. The greater DA in 2016 was caused by P. australis ? the observation of which is unprecedented in the region ? and may have been exacerbated by low residual silicic acid, a key limiting nutrient for diatoms. The novel presence of P. australis may be due to local growth conditions, the introduction of a population with an anomalous water mass, or both factors. A definitive cause of the 2016 bloom remains unknown, and continued DA monitoring in the GOM is warranted. Project 3 Intellectual merit: The major goal of this research was to elucidate the molecular mechanisms by which early life exposure to harmful algal bloom (HAB) toxins (saxitoxin, domoic acid) and marine toxicants (polychlorinated biphenyls) cause neurological abnormalities later in life. Using the zebrafish embryo as an experimental model, we found that early life exposure to low levels of domoic acid during specific developmental stages disrupted myelination and caused the loss of axons of neurons in the hindbrain, leading to behavioral changes. Exposure to saxitoxin caused changes in gene expression and cellular changes suggesting disruption of axonal growth of neurons. Embryonic exposure to 3,3?,4,4?,5-pentachlorobiphenyl (PCB126) reprogrammed gene expression and led to impaired short- and long-term habituation to a novel environment in adult zebrafish. Embryonic exposure to 2,2?,4,4?,5,5?-hexachlorobiphenyl (PCB153) caused changes in gene expression and altered circadian rhythms. Additional studies showed changes in DNA methylation and DNA methyltransferase enzymes after exposure to PCB126 or 2,3,7,8-tetrachlorodibenzo-p-dioxin in embryonic or adult zebrafish. Broader impacts: This research revealed novel mechanisms of developmental neurotoxicity caused by low-level exposure to marine toxins and toxicants. Last Modified: 06/15/2020 Submitted by: John J Stegeman