Community assembly in marine phytoplankton: Application of recent models to harmful dinoflagellate blooms

Abstract

The habitat preferences of dinoflagellate bloom species along an onshore-offshore, mixing-nutrient gradient, their associated life-form (morphotype) characteristics and adaptive strategies were evaluated from the perspective of Margalef's Mandala and Reynolds Intaglio. Nine different mixing-nutrient habitats and associated dinoflagellate life-form types having distinctive morphotype features and habitat preferences are distinguishable. Reynolds Intaglio provided greater fidelity to actual in situ dinoflagellate community assembly than the Mandala. We suggest that the correlation between degree of mixing and nutrient levels presumed in the Mandala is not the essential interaction in the selection of life forms and their succession. A more significant aspect of the turbulence axis is the degree of vertical, micro-habitat structural differentiation that it permits. Three primary adaptive strategies consistent with C-S-R strategies recognized among freshwater phytoplankton species characterize the component dinoflagellate species: invasive, small- to intermediate-sized colonist species (C) which often predominate in chemically-disturbed water bodies; acquisitive, larger-celled, nutrient stress-tolerant species (S); and disturbance-tolerant ruderal species (R) tolerant of shear/stress forces in physically-disturbed water masses (fronts, upwelling relaxations, current entrainment), It is suggested that harmful algal bloom community assembly and dynamics reflect two basic selection features-life-form and species-specific selection, that commonly held life-form properties override phylogenetic properties in bloom-species selection, and that the latter is often stochastic, rather than singular. The high degree of unpredictability of individual species blooms is consistent with stochastic selection, e.g. bloom species are often selected as a result of being in the right place at the right time at suitable inoculum levels. A focus on the life-form properties, habitat preference and stochastic selection of bloom species would appear to be more viable and realistic than current ecological investigative approaches.