Environmental requirements and habitat preferences of phytoplankton: chance and certainty in species selection.

This paper is written in honour of the influential career of Professor T.J. Smayda. It celebrates the brief, but productive, period in which we collaborated on the formulation of the principles and mechanisms of community assembly in plankton. The topics considered then provide the structure of the present paper - the origin of communities (nascence), the common and differential requirements of phytoplankton species that might affect their selection, the general and specialist adaptive traits that differentiate their performances and their relative successes, and the sensitivity of performances to sub-ideal or hostile environmental conditions. In all these instances, it is the reactivity of the net dynamic responses of the species present to imposed environmental variations that shapes the structure of the assemblage and the composition of the community. These are the high-level properties that emerge from the behaviour of low-level components. The patterns that emerge at the community level - selection by performance or competition, dominance and temporal succession - are qualitatively predictable and, at the assemblage level, are amenable to quantitative modelling. In turn, it is theoretically possible to make deductions about the likelihood of biological events that involve species occurring in abundances sufficient to affect water quality and/or constitute risks to human health (harmful algal blooms). [ABSTRACT FROM AUTHOR]