The North Atlantic turbine: Views of production processes from a mainly North Atlantic perspective

13 páginasA brief account is given of the ‘agricultural hypothesis’, the key studies which led to its replacement by the ‘grazing hypothesis’, and early models of the classical planktonic food chain. The budgetary problems posed by these views led to interest in the roles of dissolved and particulate components of planktonic ecosystems, and to discovery of the ‘microbial loop’. The balance between these alternative pathways is seen to reflect processes at the interface between hydrodynamics and ecologyPeer reviewe

Picophytoplankton in freshwater ecosystems: the importance of small-sized phototrophs

About 40 years have passed since the discovery of picophytoplankton; the present knowledge of the taxonomy, physiology and ecology of these tiny photoautotrophic cells offers new perspectives on the importance of the microbial contribution to global biogeochemical cycles and food webs. This review focuses on the relationships among the components of picophytoplankton (picocyanobacteria and the picoplanktic eukaryotes) and biotic and abiotic environmental factors. The dynamics of picophytoplankton in aquatic ecosystems are strictly dependent upon basin size and trophy, temperature, and nutrient and light limitation, but they are also regulated by grazing and viral-induced lysis. The review considers: the pros and cons of the molecular approach to the study of the taxonomy of freshwater Synechococcus spp.; the importance of ecological aspects in understanding the puzzle of picophytoplankton phylogeny (genotype vs ecotype); and the role of biotic vs abiotic interactions in controlling picophytoplankton dynamics. Biotic, top-down control mechanisms are reviewed as well as knowledge of other biological interactions