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Communities of microscopic plant life, or phytoplankton, dominate the Earth's 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.

1.A logical way of distinguishing functional groups of phytoplankton is to cluster species according to their functional traits, such as growth rate and nutrient assimilation constants. However, data for such an approach are lacking for the vast majority of the species. 2. In this study, we show that a classification based on simple morphological traits may capture much of the variability in functional properties among the phytoplankton. We used information on more than 700 freshwater species, from more than 200 lakes situated in climate zones ranging from subpolar to tropical. 3. Morphological characteristics correlated well with functional properties, such as growth rate and sinking rate, and also with the population size and biomass attained in the field. This suggests that morphology is a good predictor of the functional characteristics of species. 4. Cluster analysis was used to define seven species groups based on morphology. Although some of the clusters are taxonomically homogeneous, others include species of several separate divisions. Functional traits (not used for the classification) differed significantly among the clusters, suggesting that the clusters may indeed represent meaningful functional groups. 5. Advantages of our morphological approach to classification include its objectivity, its independence from taxonomic affiliations, and the relative ease of its application to the majority of species for which physiological traits are unknown and are not readily determined.

Summary 1. Peculiarities in the ecology of planktonic blue‐green algae are reviewed in relation to recent advances in understanding their physiological characteristics. 2. Dense water‐blooms are always the result of buoyant migration of existing populations to the lake surface under calm weather conditions. The size of the population is the direct result of photoautotrophic growth, and is dependent upon light and the availability of inorganic nutrients; it is apparently enhanced by moderately high water temperatures, high pH, low oxygen tensions and possibly, the presence of organic solutes. The relative effectiveness of these factors is untested. 3. Buoyancy is imparted by gas vacuoles whose principal function is to regulate the position of the alga in the water column. Control is effected by two mechanisms: (i) ‘dilution’ of newly produced vacuoles during active cell division; (ii) changes in cell turgor‐pressure acting on the gas‐vacuole structure. Gas‐vacuole production is greatest at low light intensities and the alga becomes more buoyant; at higher light intensities, increased turgor‐pressure collapses the weaker vacuoles causing the alga to lose buoyancy. 4. Potentially, algae are able to poise themselves at an optimum point in the light gradient, usually towards the bottom of the euphotic zone, where the algae are likely to encounter the conditions most favouring their growth. 5. Different species of blue‐green algae differ in the typical sizes of their colonies and, hence, in their rates of controlled movement. These differences are interpreted as hydrodynamic adaptations to the variations in turbulent water movements to which the algae are subject. 6. Populations of single‐filamentous Oscillatoria agardhii and O. rubescens come to occupy the stable metalimnia of stratified lakes, provided that they are located within the euphotic zone. 7. The large stream‐lined colonial forms occur mainly in polymictic lakes and in the unstable epilimnia of stratified lakes where light penetration is restricted to the superficial layers. These algae are adapted to sink or float rapidly to the optimum depth when turbulence subsides. Because of their potentially high rates of movement, it is the large colonial forms that commonly form blooms. 8. Bloom formation can occur when most of the algae possess excess buoyancy. Excess buoyancy is acquired when the photosynthetic rate is insufficient to develop the necessary turgor‐pressure to cause collapse of the vacuoles. Photosynthesis may be sufficiently impaired under four circumstances: (i) during turbulent circulation of the population over a depth that significantly exceeds the euphotic depth; (ii) in the absence of light (e.g. at night): (iii) at limiting concentrations of carbon dioxide: and (iv) when the algal population is senescent. 9. Because bloom‐formation depends upon the coincidence of persistent algal overbuoyancy with calm weather, its occurrence is incidental, and serves no vital function in the biology of blue‐green algae. 10. Some possible causes for the occu...