Allometry and stoichiometry of unicellular, colonial and multicellular phytoplankton

ntroduction 296 Unicellular, pseudocolonial, colonial and multicellular phytoplankton: definitions, taxonomy and morphology 296 Symbioses 298 Physical constraints on size, morphology and motility 298 Elemental stoichiometry 302 Allometry of specific growth rates and specific metabolic rates 302 Trophic interactions 303 Global significance of large unicells, colonies and multicellular organisms 303 Significance of colonies and multicellular organisms relative to large unicells in the phytoplankton 304 Acknowledgements 306 References 306.Phytoplankton life forms, including unicells, colonies, pseudocolonies, and multicellular organisms, span a huge size range. The smallest unicells are less than 1 mu m(3) (e.g. cyanobacteria), while large unicellular diatoms may attain 10(9) mu m(3), being visible to the naked eye. Phytoplankton includes chemo-organotrophic unicells, colonies and multicellular organisms that depend on symbionts or kleptoplastids for their capacity to photosynthesize. Analyses of physical (transport within cells, diffusion boundary layers, package effect, turgor, and vertical movements) and biotic (grazing, viruses and other parasitoids) factors indicate potential ecological constraints and opportunities that differ among the life forms. There are also variations among life forms in elemental stoichiometry and in allometric relations between biovolume and specific growth. While many of these factors probably have ecological and evolutionary significance, work is needed to establish those that are most important, warranting explicit description in models. Other factors setting limitations on growth rate (selecting slow-growing species) await elucidation. New Phytologist (2009) 181: 295-309doi: 10.1111/j.1469-8137.2008.02660.x.