Colin S. Reynolds

The ecology of phytoplankton

Communities of microscopic plant life, or phytoplankton, dominate the Earths aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

What factors influence the species composition of phytoplankton in lakes of different trophic status

The paper articulates some present concepts relating to the selection of phytoplankton along trophic gradients. Concerns over lake eutrophication have heightened the importance of nutrients but it is not obvious that interspecific differences in the nutrient requirements of algae genuinely segregate species except under chronic deficiencies. The selectivity supposedly generated by altered resource ratios is re-examined. It is argued that ratios explain very little of the distribution of species with respect to trophy. However, changing nutrient loading does have consequential impacts on the availability of other requirements including light and carbon dioxide. It is argued that the trophic spectrum is not a single dimension of a single factor but, rather, a template of factors covarying in consequence of the larger levels of biomass that are supported, and which weight in favour of the growth and survival prospects of particular kinds of planktonic algae. The trophic spectrum is a probabalistic outcome of several dimensions of variability.

Cyanobacterial dominance: The role of buoyancy regulation in dynamic lake environments

Abstract The interactions of size, shape, and density of cyanobacteria result in a 5‐order of magnitude difference in flotation or sinking rates which, in turn, influence the extent of their disper...

Cyanobacterial Water-Blooms

Publisher Summary Besides the many species representative of the major eukaryotic algal phyla, the freshwater phytoplankton comprises a number of cyanobacteria (or blue-green algae). These aggregations have earned recognition in their own collective term, “water blooms”. This chapter reviews the aspects of ecology of planktonic cyanobacreria in relation to the factors governing their buoyancy, population dynamics, and perennation in natural limnetic environments. The buoyant properties of cyanobacteria are assessed in relation to the Stokes equation, drawing distinctions between the differential contributions of size, density, and form resistance among individual genera. Density is altered through the erection or collapse of gas vesicles, their dilution by growth and through the maintenance of glycogen ballast. The outcome of buoyancy-controlled movements in natural fields of turbulent mixing is described in empirical terms. The chapter also reviews the growth requirements of cyanobacteria with respect to temperature, light, and nutrients together with their responses to deficiencies of supply. The outcome of interactions between buoyancy regulation and limiting resources are proposed in a series of hypothetical model environments. The circumstances under which excess buoyancy is acquired and expressed in surface bloom formation are re-examined. Adaptations for perennation and re-establishment of populations after bloom formation or other adverse conditions are reviewed. The evolutionary strategies of planktonic cyanobacteria are deduced.

Selection of phytoplankton associations in Lake Balaton, Hungary, in response to eutrophication and restoration measures, with special reference to the cyanoprokaryotes

Restoration of shallow lakes degraded by eutrophication has often been protracted as a consequence of the accumulation and subsequent releases of phosphorus in their sediments (internal load). Balaton, the largest shallow lake in Central Europe, underwent rapid eutrophication during the 1960s–1970s, during which a west-east gradient of trophic state developed. Measures to reverse the eutrophication and to restore the lake to its historic quality were initiated in the mid-1980s. The external phosphorus load has been decreased considerably but the responses of the phytoplankton have been slight and sometimes counterintuitive. At the level of total biomass, the erstwhile distinctiveness of the down-lake trophic gradient has weakened. The eukaryotic plankton flora has altered little but floristic changes in the dominant cyanoprokaryota are consistent with environmental changes attributable to the eutrophication and subsequent restoration. The dominant species are shown to have been consistently related to variables including sediment-water interactions, physical disturbances and the specific biotic adaptations of the organisms but the phytoplankton development in given years and in given parts of the lake has fluctuated with the stochasticity of the weather. In some years, hypertrophic conditions have continued to develop, marked by the development of prolific cyanoprokaryote blooms; in other years, phytoplankton biomass scarcely exceeded a mesotrophic level, with a species composition resembling that which obtained prior to the recent eutrophication. The species associations represented are believed to be consistent with the responses of groups of species observed elsewhere, suggesting that the patterns of community assembly in the phytoplankton are potentially predictable.

The long, the short and the stalled: on the attributes of phytoplankton selected by physical mixing in lakes and rivers

Paradoxically, although turbulence characterises the open water environments of planktonic organisms in lakes, rivers and seas, most species of phytoplankton are smaller than the size of the smallest eddies dissipating the energy and, so, must function in an immediate medium which is inherently viscous. Intensively mixed systems, such as wind-stirred shallow lakes, rivers and estuaries, however, constantly readjust the vertical position of suspended algae and, often, other non-living, light-absorbing particles with the effect that the light field to which the algae are subject is erratic and the received day-time light dose is aggregately depressed: cells need to photoadapt accordingly. In fluvial environments the additional constraint of rapid, horizontal, supposedly unidirectional, transport is applied, requiring the attribute of rapid processing of primary products and cell replication. Significant downstream recruitment, however, is benefitted by the presence of so-called ‘dead-zones’ which retain water (and suspended plankton) sufficiently to accommodate additional cell divisions.

Are phytoplankton dynamics in rivers so different from those in shallow lakes

This paper introduces a series of contributions to the ninth meeting of the International Association of Phytoplankton Taxonomy and Ecology, held in Belgium during July, 1993. It draws from the original papers a synthesis which supports the view that the successful species in rivers and turbid shallow lakes are selected primarily on their ability to survive high-frequency irradiance fluctuations as they are circulated through steep light gradients. The selective distinction is less than that which discriminates between plankton of deep lakes and shallow lakes or even between clear and turbid shallow ones. River plankton is, however, dependent on fast growth rates but its survival in rivers is aided by a suite of water-retentive mechanisms. The ecology of turbid systems is dominated by physical interactions, those biotic interactions traditionally believed to regulate limnetic communities being suppressed and rarely well-expressed.

Scales of disturbance and their role in plankton ecology

The role of hydraulic and hydrographic disturbances in delaying, arresting or diverting successional sequences from achieving stable, climactic equilibria is discussed by reference to case studies. The critical time scale is expressed in terms of planktonic reproductive generation times. Environmental constancy persisting over some 12–16 generations may permit a climactic condition to be achieved. An Intermediate Disturbance, if sustained, can establish a new successional sequence or, if not, can lead to a reversion to a sequence similar to the predisturbance succession. At intervals of ∼ 1 generation time, species are selected according to their ability to accommodate disturbances at the physiological level. Highly disturbed environments are considered to be likely to maintain ‘plagioclimactic’ associations.

Physical Determinants of Phytoplankton Succession

Just as the composition of phytoplankton assemblages depends upon the presence and relative abundances of populations of individual species, so temporal changes in their composition are brought about by differences in the relative rates of augmentation and attrition of each population. These rates respond to a complex of interactions among various physical, chemical, and biotic environmental factors, operating at a variety of intensities and frequencies. This chapter addresses the impact of essentially physical variables on the population dynamics of individual species and it seeks to establish the particular properties of the organisms for which each selects. Factual information relating the performances of algae to quantifiable aspects of the physical environment is drawn largely from observations made in controlled laboratory experiments. Realistic potential combinations of the relevant physical factors are suggested in order to simulate the likely responses of specific populations in natural waters. The outcomes of such simulations are then compared with the PEG-model of phytoplankton succession (see Section 1.2) propounded by Sommer et al. (1986), which was originally elaborated to explain the pattern of seasonal change in species dominance, as regularly observed in Lake Constance (the Bodensee). A concluding section assesses the role of physical factors in regulating seasonal succession of phytoplankton generally. At the end of the chapter, beginning on page 52, there are three appendices. The first one, Appendix 2.1, defines the units used in this chapter. The second, Appendix 2.2, identifies the symbols used, and Appendix 2.3 explains the abbreviations used for algal names.

Strategies of marine dinoflagellate survival and some rules of assembly

Dinoflagellate ecology is based on multiple adaptive strategies and species having diverse habitat preferences. Nine types of mixing-irradiance-nutrient habitats selecting for specific marine dinoflagellate life-form types are recognised, with five rules of assembly proposed to govern bloom-species selection and community organisation within these habitats. Assembly is moulded around an abiotic template of light energy, nutrient supply and physical mixing in permutative combinations. Species selected will have one of three basic (C-, S-, R-) strategies: colonist species (C-) which predominate in chemically disturbed habitats; nutrient stress tolerant species (S-), and species (R-) tolerant of shear/stress forces in physically disturbed water masses. This organisational plan of three major habitat variables and three major adaptive strategies is termed the 3-3 plan. The bloom behaviour and habitat specialisation of dinoflagellates and diatoms are compared. Dinoflagellates behave as annual species, bloom soloists, are ecophysiologically diverse, and habitat specialists whose blooms tend to be monospecific. Diatoms behave as perennial species, guild members, are habitat cosmopolites, have a relatively uniform bloom strategy based on species-rich pools and exhibit limited habitat specialisation. Dinoflagellate bloom-species selection follows a taxonomic hierarchical pathway which progresses from phylogenetic to generic to species selection, and in that sequence. Each hierarchical taxonomic level has its own adaptive requirements subject to rules of assembly. Dinoflagellates would appear to be well suited to exploit marine habitats and to be competitive with other phylogenetic groups, yet fail to do so.