Cytometric diversity in marine ultraphytoplankton

The concept and methods of ecological diversity in communities were applied to phytoplankton categorized by flow cytometric measurements related to size and chlorophyll content. Each cytometric signature was condensed to single numerical values indicative of diversity and evenness. Measurements pooled from studies disparate in temporal and spatial scales indicated greater chlorophyll biomass and primary production with greater cytometric diversity and evenness. Future development of these ideas may help link biological oceanographic processes with patterns established through ecological processes at the community level. The concept of biotic diversity is a central theme in community ecology, both in general (Pielou 1975; Magurran 1988) and in particular for marine communities (Frontier 1985; McGowan and Walker 1993). Diversity embodies two notions: richness, which indicates the number of different kinds of organisms; and evenness, which indicates the relative “importance” (e.g. abundance) of the different kinds of organisms. Thus, a community with say 100 species is more diverse (rich) than a community with 10 species. Further, a community with 5 species each of which has 10 individuals is more diverse (even) than a community with the same 5 species, one of which has 46 individuals and the other 4 species having only 1 individual each. Diversity is an expression of the organization or structure of a community; it is a collective property revealed at a high level of organization (the community) but not at lower hierarchical levels (populations and individuals). Usually, the purpose of measuring diversity is to judge its relationship to other community properties (e.g. productivity) or to the prevailing environmental conditions (Pielou 1975). Generally, but with important exceptions, high diversities are related to high environmental stability, high environmental predictability, and high productivity. Recent discussions (Kareiva 1996; Moffat 1996) on new experiments in grassland ecosystems (Tilman 1996; Tilman et al. 1996) have brought into sharp focus the earlier ideas of Charles Darwin, Charles Elton, and Robert May on the relation between diversity and productivity. These new discussions have not included phytoplankton. In phytoplankton ecology, the singular efforts of Margalef (1960, 1967, 1968) have led to a widespread study of diversity indices (Hulburt et al. 1960; Patten 1962; Travers 1971). In most cases, these indices refer to phytoplankton Acknowledgments This work is a contribution to the Canadian JGOFS program and was supported by the following Canadian government organizations: Department of Fisheries and Oceans, Department of National Defense, Canadian Panel on Energy R&D (PERD), and the interdepartmental “Green Plan.” Other support was provided by the Joint Research Centre, Commission of the European Communities. I am grateful to Paul Dickie, Brian Irwin, Edward Horne, and Richard Geider for procuring samples. 1 am indebted to Glen Harrison and Brian Irwin for primary production data and to Edward Home for CTD data. identified by species and whose importance is rated by abundance (cells m--l). In other words, the classifications are based on conventional binomial taxonomic nomenclature. However, as noted by Margalef (1968), “the notion of diversity can be applied to anything that can be distributed into categories.” Furthermore, importance can be rated by measures other than a count of individuals. It is therefore feasible to speak of diversity when the organisms are categorized by photosynthetic pigments (Margalef 1967, 1968), cell size (Parsons 1969; Ruiz 1994), biomass (Lurie and Wagensberg 1983), or when the “importance” of the organisms is expressed as ash-free weight (Wilhm 1968) or as biovolume (Parsons 1969). In fact, if the emphasis of the research goal so requires, importance could presumably be expressed as energy flow, productivity, calorific values, respiratory gas exchange rate, and other measures of resource utilization (Tokeshi 1993). In this paper, I explore the application of ecological diversity indices for phytoplankton that are classified in a novel way: namely by their bio-optical properties measured on an individual cell basis by flow cytometry. The purpose of this study in cytometric diversity is to discern whether this collective property of the phytoplankton community, which can be the same for greatly different collections of individuals, bears any relationship to the biomass and productivity