Senior Research Scientist, U.S. Geological Survey
Phytoplankton: Large Cells Rule in Temperate Estuaries, and Why
Abstract: Phytoplankton biomass across much of the world oceans is dominated by small-celled picoplankton, while biomass produced in upwelling systems is dominated by large cells. What about coastal ecosystems influenced by nutrient runoff from land, such as estuaries? I explored a 20-year record of phytoplankton sampling in San Francisco Bay and found 3 patterns: (1) mean cell size increased with increasing biomass; (2) overall biomass was dominated by large (> 20 M) cells, because (3) blooms were events of selective growth of large cells, including taxa that form HABs such as Alexandrium spp., Karenia mikimotoi, and Dinophysis spp. From this data set I built a size structured NPZ (nitrogen, phytoplankton, zooplankton) model that described growth and grazing rates as functions of phytoplankton and zooplankton size. The model reproduced the 3 observed patterns, and provided insights into the processes that select for large cells in high-nutrient environments. Small cells grow faster than large cells, but they are also grazed at a faster rate so there is no difference in the net growth rates of small and large cells. Why, then, do large cells dominate blooms and overall biomass? The key is that large grazers, unlike small grazers, have lagged population responses to phytoplankton growth, providing windows of opportunity for large-cell biomass to accumulate until nutrients are depleted or large grazers catch up. Size-structured models provide a framework for understanding how different environments select for phytoplankton on the basis cell size. Simulations across a range of environmental conditions showed that large cells dominated only in high-nutrient, temperate estuaries like San Francisco Bay and Chesapeake Bay. Small cells (< 5 M) dominated in simulations representing low-nutrient or warmer (+ 5 °C) waters. Therefore, anthropogenic nutrient enrichment might favor development of large-cell HABs, but only in the temperate zone. And, progressive warming of enriched waters might lead to a growing probability of HABs by small-cell taxa.These hypotheses come from consideration of size as a fundamental trait that constrains rates of growth, resource acquisition, and metabolism. Deeper understanding of the HAB problem requires additional consideration of how bloom-forming taxa are selected on the basis of size plus other key traits such as motility, nutritional mode, and predator defenses.
Tuesday, November 14, 2017 8:30AM
Associate Professor, Aquatic Environmental Microbiology and Chemistry, University of Wisconsin Milwaukee, Zilber School of Public Health
Cyanotoxins in Lakes and Drinking Water: A tale of four cities
Wednesday, November 15, 2017 8:30 AM
Executive Director, Southern California Coastal Ocean Observing System
The struggle is real: regional challenges for predicting blooms of toxic Pseudo-nitzschia
Abstract: Determining when and how Pseudo-nitzschia blooms turn toxic has become one of the perennial struggles of harmful algal bloom science. Gaps in our knowledge of the biodiversity and ecophysiology of this complex genus are a significant part of the problem. Regional variation in the biophysical response of the organism to bloom and subsequently produce its neurotoxin, domoic acid, is an emerging topic of discussion in ‘Pseudo science.’ With the launch of quasi-operational models for toxic Pseudo-nitzschia blooms on the U.S. West Coast, there is interest in not only vetting the ability of the predictions to capture what we think is the true ecosystem-level variability in toxin production and fisheries exposure at the event scale, but also to extend these capabilities to both coasts of the U.S. where domoic acid events are an emerging concern. Useful predictions could be anything from seasonal to weather-scale forecasts depending on regional needs and modeling capabilities. This plenary talk will delve into the nature of these regional differences and the various approaches proposed to devise early warning systems from models (of varying complexity), satellite remote sensing, and cutting-edge monitoring tools.
Thursday, November 16, 8:30 AM
Senior Scientist, Wood Hole Oceanographic Institution
THE US NATIONAL HAB PROGRAM – A RETROSPECTIVE AND LOOK TO THE FUTURE
Abstract: The US national harmful algal bloom (HAB) program is considered by many to be an effective and well-organized program, but this was not always the case. Thirty years ago, work on HABs was limited to a few laboratories, each struggling to obtain funding in competition with many other scientific disciplines. The first national plan for HABs was formulated in 1993 to build a cohesive program and funding base, but it took several years, some good fortune, and some hard work for those recommendations to be refined and repackaged into ECOHAB (Ecology and Oceanography of HABs), a fundamental science program that continues to this day. Recognizing the diverse research and management challenges of HABs, more practical research agendas were formulated and political support sought, leading to the MERHAB (Monitoring and Event Response for HABs), PCMHAB (Prevention Control and Mitigation of HABs), and COHH (Centers for Ocean and Human Health). A major development was the initiation of a series of conferences focusing exclusively on US HAB science, starting with the 1st US HAB Symposium in Woods Hole in 2000. These biennial meetings have been an integral part of the success and cohesiveness of the US HAB community. This talk will provide a retrospective view of the US HAB program, highlighting the state of science at each of the US HAB symposia. A personal view will also be offered of the future of the national program and efforts needed to sustain this highly successful program in an increasingly challenging funding climate.
Friday, November 17, 8:30 AM