86 Book reviews

References cited

Bullock, T.H. and Heiligenberg, W. (eds) (1986) Electroreception. New York: Wiley. Crawford, J.D. (1989) Acoustic and electric communication in mormyrid fishes. PhD dissertation,

Cornell University. UMI Diss. Inf. Serv. No.3058. Lissmann, H.W. (1958) On the function and evolution of electric organs in fish. J. exp. Biol. 35,

156-91.

Dynamics of Marine Ecosystems: Biological-Physical Interactions in the Ocean K.H. Mann and J.R.N. Lazier Blackwell, Boston MA, 1991 ISBN 0-86542-082-3, $44.95 Soft cover, pp. xi + 466, 14 tables, 160 figures (2 in colour)

Oceanic processes affect the lives of plants and animals in the sea profoundly and can now be described physically at all scales. Drs Mann and Lazier describe the dependence of biological processes upon the physics of the sea at three scales, < 1 km, 1-1000 km and > 1000 km. The biology and the physics are treated differently: the biology "emphasizes the recent developments of the field" but the physics is "fairly elementary and emphasizes the important physical processes". Some of the detailed physics is presented in boxes, to be ignored by the fearful but to be read avidly by the eager; in general, the arguments in the boxes are developed clearly.

Life at low Reynolds numbers, the vertical structure of the mixed layer and the effects of tides and freshwater runoff are presented in the first section on small-scale processes. An account is given of the cascade of turbulence to the smallest eddy and of the viscous boundary layer around the smaller organisms. Algal cells can sink or swim, they take up nutrients as they go, and the increment of nutrient flux with cell size appears to depend on the degree of shear and turbulence. An interesting point is that Smayda's dependence of sinking rate on phytoplankton cell size does not follow Stokes' Law, but the possible explanations are not pursued. The physical arguments lead to a discussion of the persistence of photosynthesis in the absence of nitrate in the oligotrophic ocean. The authors believe that production in the blue waters is indeed low, but I am not convinced.

There is a good account of the work of Strickler and his colleagues on the feeding mechanisms of copepods as revealed by high-speed cinematography. The animals do not filter their food because the water is too viscous; indeed, Strickler likened the feeding process to catching a grain of rice in honey with a pair of knife blades. The food particles are taken by a 'fling and clap' mechanism. One of the most important of Strickler's discoveries is that particles are detected at up to a range of four body lengths, but the consequences are not discussed. Perhaps the mortality of algal cells due to grazing has been under-estimated.

The development of the vertical structure of the ocean is well described and this leads to a discussion of the deep chlorophyll maximum in the ocean and how it might depend on the upward diffusion of nitrate through the pycnocline, but there may well be other mechanisms. A full account is given of the critical depth as developed by Sverdrup, but the authors have decided to call it the Gran effect, the mechanism of stabilization. I believe this to be a mistake because Sverdrup compared production and respiration integrated in depth which Gran did not do. There follow good accounts of the

Book reviews 87

Lagrangian models as developed by Woods and his colleagues. Coriolis' force is an 'imaginary' force which takes into account the rotation of the earth

as a current is observed and is described in terms of a ball (or shell) thrown (fired) towards the sun; when Big Bertha was fired at Paris at a range of 70 miles it was aimed off by a mile to counter the effects of the rotation of the earth during the three-minute flight of the shell. Motion in the sea cannot be described without an understanding of Coriolis' force. Then the physics of the various forms of estuaries is given together with the Simpson-Hunter calculation of the conditions for a tidal front, as illustrated on Georges Bank and in the waters around the British Isles.

The second section on intermediate scales is a long account of coastal upwelling, physically and biologically in the major upwelling systems (but not the Somali Current). The Ekman Spiral and the link between the width of coastal upwelling systems and the Rossby deformation scale are described well. In the last two decades much work has been done in the upweUing areas in many expeditions, but also including Lasker's on the survival of fish larvae. Satellite studies have revealed the complex structure of swirls, jets and divergences offshore of the strictly coastal upweUing. I would have liked to have seen a discussion of the part played by such structures seaward of the coastal upwellings.

There are various forms of front in the ocean - tidal, shelfbreak, upwelling, plume and estuarine. Production is high on the convergent edge of a tidal front, but the reason remains somewhat obscure; if stock accumulates there by convergence, even a moderate algal division rate will generate a relatively high production.

The physics of the wind-driven circulation in the ocean with surface and deep currents, meanders, cold and warm core rings are developed in relatively simple but clear terms. E1 Nifio/Southern Oscillation events in the Pacific, the time series in the California Current and those in the Alaska gyral follow. In the Atlantic an extensive account is given of the changes in the North Sea plankton, the Russell cycle and other changes. Then follows a summary of global warming and the climatic changes back to the Ice Ages.

The book is written for biological oceanographers, marine and fisheries biologists as an account of present biological problems within a physical context. It is successful and many young biologists, now mathematically competent, will learn the physics and start to read the original papers. Then we shall approach the ideal where physicists and biologists work together, instead of alongside each other.

The figures are self explanatory and clear. The boxes are well designed and easy to follow, if lacking derivation in one or two places. The text is well written and has the virtue of leading the reader on to the conclusion or the next question. I have enjoyed reading and reviewing it.

D.H. CUSHING

Lowestoft, UK