Models of harmful algal blooms: conceptual, empirical, and numerical approaches.

Now is a historic time in the field of harmful algal bloom (HAB) science. HAB problems are growing worldwide, and society's need for understanding these phenomena is more pressing than ever. Technological advances have expanded our capabilities for observing the ocean, providing unprecedented opportunities not only for the detection of blooms, but also for the physical, chemical, and biological factors that trigger their initiation, development, and ultimate demise. However, despite these rapidly expanding observational capabilities, HAB processes will continue to be undersampled for the foreseeable future, owing to the wide range of space and time scales relevant to these oceanographic phenomena. As such, we must rely on models to help interpret our necessarily sparse observations. Such models can take many forms, ranging from conceptual models, to simple analytic formulae, to complex numerical models that assimilate data (Franks, 1997). Of course, the topic of HAB modeling is embedded within, and benefits from, the accomplishments of the broader field of physical– biological interactions generally (Franks, 1995; Hofmann and Friedrichs, 2002; Blackford et al., 2007; Lynch et al., 2009). In June 2009, a workshop was convened under the auspices of the Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) program to develop strategies for using observations and models to address the science questions articulated in the Open Science Meeting Reports for each of the GEOHAB Core Research Projects (Cembella et al., 2010; Gentien et al., 2008; Glibert, 2006; Pitcher et al., 2005). A total of 80 participants from 26 nations, including 20 students and postdocs met for one week at the National University of Ireland Galway (McGillicuddy et al., in preparation). This volume is comprised of a set of papers conceived at the Galway workshop. Collectively, these contributions illustrate the wide variety of approaches being brought to bear on harmful algal bloom phenomena, spanning conceptual, empirical, and numerical approaches. Conceptual models are not only useful in their own right, but also form the foundation of all other types of models. As such, conceptual models figure prominently into each of the papers contained herein. One paper in particular provides a pedagogical guide to conceptualization of phytoplankton life cycles in both Eulerian and Lagrangian frameworks (Hense, 2010-this issue). Because many HAB species have complex life cycles that can include resting stages, vegetative growth, and sexual reproduction, explicit representation of these biological aspects can be essential to accuratemodeling of their bloom dynamics. Empirically-based algorithms are playing an increasingly important role in HAB modeling, providing an important link between conceptual and dynamical modeling approaches. For example, Blauw et al. (2010-this issue) use fuzzy logic to relate nuisance foam events in Dutch coastal waters to Phaeocystis globosa blooms, quantifying their relationships with environmental parameters such