Models of harmful algal blooms

Abstract

Models used to study harmful algal blooms are a subset of those used to examine more general planktonic processes. Most models have been heuristic, examining the likelihood of certain processes generating a harmful algal bloom. Several models have been more closely coupled to field data and have been used to gain insights into the dynamics underlying the observations. As better physical and biological models are developed, models may play an increasingly important role in harmful algal bloom research. Techniyucs such as data assimilation may increase the predictive power of models, suggest stratcgics for improving field sampling, and better constrain poorly known parameters and proccsscs.Beginning with Kierstead and Slobodkin's (1953) model of the opposing effects of growth and diffusion in the formation of a bloom, models have served useful purposes in the study of bloom dynamics. These range from the testing of theoretical hypotheses to the identification and quantification of processes contributing to bloom formation, More recent advances in modeling techniques may allow models to play an increasingly important role in understanding and predicting blooms.Models of harmful algal blooms (HABs) are a small subset of models used in biological oceanography or plankton ecology in general. However, HABs present a particular set of problems that makes them interesting, socially relevant, and possibly excellent models for more general plankton dynamics. The most obvious aspect of HABs is that they often consist of a single species that grows toxic or unusually dense. To describe the dynamics of this species we must be able to adequately describe the dynamics of the ecosystem in which the species is embedded.In the sections below, I present many of the models used to explore HABs (Table 1). I have arranged the models by degree of complexity, beginning with highly aggregated biological models with no physical dynamics. These models segue into biological models with more resolution of taxa or species -less aggregation, more complexity, and more unknown parameters and processes. I then explore coupled physical-biological models used to study HABs, beginning with those using only simple physics (e.g. diffusion or swimming) and then examining those with more detailed physical dynamics. Throughout the presentation of these models, I emphasize the similarities of model structure, the way in which the models have been used, and the aspects of the models that might help us understand the dynamics underlying harmful algal blooms. Finally, I discuss some of the directions that I feel might be most fruitful for models of HABs, including a closer coupling with field programs and the use of data assimilation to better dissect the dynamics of the blooms. AcknowledgmentsI thank Sharon Franks for constructive comments on this manuscript.

Influence of environmental nutrient conditions on Gymnodinium breve (Dinophyceae) population dynamics: a numerical study

“…More complete observations on the external nutrient condition and its relationship with the population distribution are needed for further simulation and understanding of Gymnodinium breve bloom dynamics. Red tide concentrations of Gymnodinium breve may result when dinoflagellates accumulate phototactically during the day through diel vertical migration along downward moving convergences (frontal systems) produced by wind, tide, or current interactions (Donaghay & Osborne 1997, Franks 1997. These vertical lenses may contain between 10 and 100 times their mean concentrations in the water mass in which they are growing (e.g., Seliger et al 1979).…”

Vertical distribution of division rates in coastal dinoflagellate Dinophysis spp. populations: implications for modelling

“…population dynamics in the Rías Baixas can be analyzed with the use of a simplified biological model. Although these models are generally unable to represent all the variability of an ecosystem, they can provide the necessary framework for exploring different aspects of harmful algae outbreaks (Franks 1997).…”

“…population dynamics in the Rías Baixas can be analyzed with the use of a simplified biological model. Although these models are generally unable to represent all the variability of an ecosystem, they can provide the necessary framework for exploring different aspects of harmful algae outbreaks (Franks 1997).In the present study, we compare values of μ estimated from integrated water-column samples (hereafter referred to as 'integrated samples') (μ int ) with values based on samples collected at specific depths (μ z ), especially those collected at the depth where the maximum concentration of Dinophysis spp., P max , was detected (μ Pmax ). The importance of vertical heterogeneities in division rates of populations and their implications for population dynamic models are discussed.…”

Phytoplankton potential growth rate versus increase in cell numbers: estimation of cell lysis

“…When testing a model against field data, the latter has many limitations, such as lack of spatial and temporal resolution and inappropriate criteria for the selection of the variables to measure (Franks 1997). Few studies report in situ specific growth rates during major events such as dinoflagellate proliferation (Chang & Carpenter 1985, Reguera et al 1996, since spatial and temporal monitoring of such events is extremely difficult.…”