Behavior, physiology and the niche of depth-regulating phytoplankton

Abstract

To understand the population dynamics of phytoplankton species contributing to harmful algal blooms (HABs), we focus on physiological, biochemical, and behavioral features of phytoplankton that might influence ecological selection in different hydrographic regimes. Each species of phytoplankton has a different combination of adaptive characteristics that in many ways defines its niche, i.e., the suite of ecological factors that determines its distribution and activities. By understanding the adaptations of different phytoplankton species, it should be possible to describe patterns of species abundance as functions of hydrographic processes, nutrient distributions and the potential impact of herbivores. This understanding could be applied to determine the principal causes of HABs (e.g., eutrophication, upwelling, stratification, advection), to achieve better skill at forecasting their occurrence, and to predict the consequences for phytoplankton of environmental changes in coastal waters, such as might be associated with aquaculture, coastal engineering, or climate change. Because the ecological and commercial effects of algal blooms depend on the particular species involved, it is essential to focus on characteristics of phytoplankton that are likely to distinguish one species from another with respect to ecological selection during development and maintenance of a bloom. Recognizing that many harmful algae can move vertically, we discuss depth regulation in phytoplankton as an ecological strategy, emphasizing physiological and biochemical adaptations that can strongly influence the growth and survival of phytoplankton species in different hydrographic regimes. We identify adaptive features that can be quantified experimentally, so that species can be compared and predictive models can be developed. This discussion is focused on marine systems; a comprehensive presentation, including a thorough review of the extensive literature on freshwater cyanobacteria (Zevenboom 1986; Oliver 1994) is beyond the scope of this chapter.