IV. KEY QUESTIONS TO BE ADDRESSED IN UNDERSTANDING THE ECOLOGY AND OCEANOGRAPHY OF HABS IN STRATIFIED SYSTEMS
A number of outstanding scientific issues have been identified in this report. These have been synthesized below into a series of key generic questions, under which some relevant sub-questions are listed. In general these follow a similar subject order to that of the scientific section in the report.
1) What are the turbulence length scales relevant to harmful phytoplankton and the formation of thin layers? How do we measure turbulence at these scales?
2) What are the main processes controlling the population evolution of a given species, and how does their ranking vary over the time course of a bloom?
* Is high density (aggregation) a pre-requisite for sexual recombination?
* Do HAB species migrate? Do they vertically migrate all the time or only at certain stages of the population growth or under certain hydrographic patterns? What are the gains of vertical migration: acquisition of nutrients from deeper waters, phototactic responses, social behaviour to promote sexual encounters, aggregation around some unknown cue?
* Is the high cell density in the thin layer due to in situ division and passive accumulation in density discontinuities or does it result from aggregation?
3) How can we quantify modifications in turbulence by phytoplankton through changes in the viscosity of its physical environment?
* What are the effects of a more viscous and localized layer on the turbulent spectra?
* To what extent do such local changes contribute to the maintenance of a thin layer?
* Can the changes in vertical diffusivity be inferred?
4) What nutritional opportunities do thin layers provide to phytoplankton, especially to the species selected within thin layers?
* Is growth rate in the thin layer higher due to a local enhancement in resources?
* Do the accumulated breakdown products, resulting from the rain and decomposition of particles sinking from the overlying water column and captured in the thin layer, enhance or impede phytoplankton growth and do they select for the species present?
* What is the role of the microbial loop in thin layers?
5) Are allelopathy and “chemical warfare” at work in situ within thin layers?