This is the third book I have written on the subject of phytoplankton ecology. When I finished the first, The Ecology of Freshwater Phytoplankton (Reynolds, 1984a), I vowed that it would also be my last. I felt better about it once it was published but, as I recognised that science was moving on, I became increasingly frustrated about the growing datedness of its information. When an opportunity was presented to me, in the form of the 1994 Ecology Institute Prize, to write my second book on the ecology of plankton, Vegetation Processes in the Pelagic (Reynolds, 1997a), I was able to draw on the enormous strides that were being made towards understanding the part played by the biochemistry, physiology and population dynamics of plankton in the overall functioning of the great aquatic ecosystems. Any feeling of satisfaction that that exercise brought to me has also been overtaken by events of the last decade, which have seen new tools deployed to the greater amplification of knowledge and new facts uncovered to be threaded into the web of understanding of how the world works.

Of course, this is the way of science. There is no scientific text that can be closed with a sigh, 'So that's it, then'. There are always more questions. I actually have rather more now than I had at the same stage of finishing the 1984 volume. No, the best that can be expected, or even hoped for, is a periodic stocktake: 'This is what we have learned, this is how we think we can explain things and this is where it fits into what we thought we knew already; this will stand until we learn something else.' This is truly the way of science. Taking observations, verifying them by experimentation, moving from hypothesis to fact, we are able to formulate progressively closer approximations to the truth.

In fact, the second violation of my 1984 vow has a more powerful and less high-principled driver. It is just that the progress in plankton ecology since 1984 has been astounding, turning almost each one of the first book's basic assumptions on its head. Besides widening the scope of the present volume to address more overtly the marine phytoplankton, I have set out to construct a new perspective on the expanded knowledge base. I have to say at once that the omission of 'freshwater' from the new title does not imply that the book covers the ecology of marine plankton in equivalent detail. It does, however, signify a genuine attempt to bridge the deep but wholly artificial chasm that exists between marine and freshwater science, which political organisation and science funding have perpetuated.

At a personal level, this wider view is a satisfying thing to develop, being almost a plea for absolution - 'I am sorry for getting it wrong before, this is what I should have said!' At a wider level, I am conscious that many people still use and frequently cite my 1984 book; I would like them to know that I no longer believe everything, or even very much, of what I wrote then. As if to emphasise this, I have adopted a very similar approach to the subject, again using eight chapters (albeit with altered titles). These are developed according to a similar sequence of topics, through morphology, suspension, ecophysiology and dynamics to the structuring of communities and their functions within ecosystems. This arrangement allows me to contrast directly the new knowledge and the understanding it has rendered redundant.

So just what are these mould-breaking findings? In truth, they impinge upon the subject matter in each of the chapters. Advances in microscopy have allowed ultrastructural details of planktic organisms to be revealed for the first time. The advances in molecular biology, in particular the introduction of techniques for isolating chromosomes and ribosomes, fragmenting them by restriction enzymes and reading genetic sequences, have totally altered perceptions about phyletic relationships among planktic taxa and suppositions about their evolution. The classification of organisms is undergoing change of revolutionary proportions, while morphological variation among (supposedly) homogeneous genotypes questions the very concept of putting names to individual organisms. At the scale of cells, the whole concept of how they are moved in the water has been addressed mathematically. It is now appreciated that planktic cells experience critical physical forces that are very different from those affecting (say) fish: viscosity and small-scale turbulence determine the immediate environment of microorganisms; surface tension is a lethal and inescapable spectre; while shear forces dominate dispersion and the spatial distributions of populations. These discoveries flow from the giant leaps in quantification and measurements made by physical limnologists and oceanographers since the early 1980s. These have also impinged on the revision of how sinking and settlement of phytoplankton are viewed and they have helped to consolidate a robust theory of filter-feeding by zooplankton.

The way in which nutrients are sequestered from dilute and dispersed sources in the water and then deployed in the assembly and replication of new generations of phytoplankton has been intensively investigated by physiologists. Recent findings have greatly modified perceptions about what is meant by 'limiting nutrients' and what happens when one or other is in short supply. As Sommer (1996) commented, past suppositions about the repercussions on community structure have had to be revised, both through the direct implications for interspecific competition for resources and, indirectly, through the effects of variable nutritional value of potential foods to the web of dependent consumers.

Arguably, the greatest shift in understanding concerns the way in which the pelagic ecosystem works. Although the abundance of plank-tic bacteria and the relatively vast reserve of dissolved organic carbon (DOC) had long been recognised, the microorganismic turnover of carbon has only been investigated intensively during the last two decades. It was soon recognised that the metazoan food web of the open oceans is linked to the producer network via the turnover of the microbes and that this statement applies to many larger freshwater systems as well. The metabolism of the variety of substances embraced by 'DOC'varies with source and chain length but a labile fraction originates from phytoplankton photosynthesis that is leaked or actively discharged into the water. Far from holding to the traditional view of the pelagic food chain - algae, zooplankton, fish - plankton ecol-ogists now have to acknowledge that marine food webs are regulated 'by a sea of microbes' (Karl, 1999), through the muliple interactions of organic and inorganic resources and by the lock of protistan predators and acellular pathogens (Smetacek, 2002). Even in lakes, where the case for the top-down control of phytoplankton by herbivorous grazers is championed, the otherwise dominant microbially mediated supply of resources to higher trophic levels is demonstra-bly subsidised by components from the littoral (Schindler et al, 1996; Vadeboncoeur et al., 2002).

There have been many other revolutions. One more to mention here is the progress in ecosystem ecology, or more particularly, the bridge between the organismic and population ecology and the behaviour of entire systems. How ecosystems behave, how their structure is maintained and what is critical to that maintenance, what the biogeochemical consequences might be and how they respond to human exploitation and management, have all become quantifiable. The linking threads are based upon thermodynamic rules of energy capture, exergy storage and structural emergence, applied through to the systems level (Link, 2002; Odum, 2002).

In the later chapters in this volume, I attempt to apply these concepts to phytoplankton-based systems, where the opportunity is again taken to emphasise the value to the science of ecology of studying the dynamics of microorganisms in the pursuit of high-order pattern and assembly rules (Reynolds, 1997, 2002b). The dual challenge remains, to convince students of forests and other terrestrial ecosystems that microbial systems do conform to analogous rules, albeit at very truncated real-time scales, and to persuade microbiologists to look up from the microscope for long enough to see how their knowledge might be applied to ecological issues.

I am proud to acknowledge the many people who have influenced or contributed to the subject matter of this book. I thank Charles Sinker for inspiring a deep appreciation of ecology and its mechanisms. I am grateful to John Lund, CBE,

FRS for the opportunity to work on phytoplank-ton as a postgraduate and for the constant inspiration and access to his knowledge that he has given me. Of the many practising theoretical ecol-ogists whose works I have read, I have felt the greatest affinity to the ideas and logic of Ramon Margalef; I greatly enjoyed the opportunities to discuss these with him and regret that there will be no more of them.

I gratefully acknowledge the various scientists whose work has profoundly influenced particular parts of this book and my thinking generally. They include (in alphabetical order) Sal-lie Chisholm, Paul Falkowski, Maciej Gliwicz, Phil Grime, Alan Hildrew, G. E. Hutchinson, Jorg Imberger, Petur Jonasson, Sven-Erik Jorgensen, Dave Karl, Winfried Lampert, John Lawton, John Raven, Marten Scheffer, Ted Smayda, Milan straskraba, Reinhold Tuxen, Anthony Walsby and Thomas Weisse. I have also been most fortunate in having been able, at various times, to work with and discuss many ideas with colleagues who include Keith Beven, Sylvia Bonilla, Odécio Caceres, Paul Carling, Jean-Pierre Descy, Monica Diaz, Graham Harris, Vera Huszar, Dieter Imboden, Kana Ishikawa, Medina Kadiri, Susan Kilham, Michio Kumagai, Bill Li, Vivian Monte-cino, Mohi Munawar, Masami Nakanishi, Shin-Ichi Nakano, Luigi Naselli-Flores, Pat Neale, Soren Nielsen, Judit Padisaok, Fernando Pedrozo, Victor Smetacek, Ulrich Sommer, José Tundisi and Peter Tyler. I am especially grateful to Catherine Legrand who generously allowed me to use and interpret her experimental data on Alexan-drium. Nearer to home, I have similarly benefited from long and helpful discussions with such erstwhile Windermere colleagues as Hilda Canter-Lund, Bill Davison, Malcolm Elliott, Bland Finlay, Glen George, Ivan Heaney, Stephen Maberly, Jack Talling and Ed Tipping.

During my years at The Ferry House, I was ably and closely supported by several co-workers, among whom special thanks are due to Tony Irish, Sheila Wiseman, George Jaworski and Brian Godfrey. Peter Allen, Christine Butterwick, Julie Corry (later Parker), Mitzi De Ville, Joy Elsworth, Alastair Ferguson, Mark Glaister, David Gouldney, Matthew Rogers, Stephen Thackeray and Julie Thompson also worked with me at particular times. Throughout this period, I was privileged to work in a 'well-found' laboratory with abundant technical and practical support. I freely acknowledge use of the world's finest collection of the freshwater literature and the assistance provided at various times by John Horne, Ian Pettman, Ian McCullough, Olive Jolly and Marilyn Moore. Secretarial assistance has come from Margaret Thompson, Elisabeth Evans and Joyce Hawksworth. Trevor Furnass has provided abundant reprographic assistance over many years. I am forever in the debt of Hilda Canter-Lund, FRPS for the use of her internationally renowned photomicrographs.

A special word is due to the doctoral students whom I have supervised. The thirst for knowledge and understanding of a good pupil generally provide a foil and focus in the other direction. I owe much to the diligent curiosity of Chris van Vlymen, Helena Cmiech, Karen Saxby (now Rouen), Sian Davies, Alex Elliott, Carla Kruk and Phil Davis.

My final word of appreciation is reserved for acknowledgement of the tolerance and forbearance of my wife and family. I cheered through many juvenile football matches and dutifully attended a host of ballet and choir performances and, yes, it was quite fun to relive three more school curricula. Nevertheless, my children had less of my time than they were entitled to expect. Jean has generously shared with my science the full focus of my attention. Yet, in 35 years of marriage, she has never once complained, nor done less than encourage the pursuit of my work. I am proud to dedicate this book to her.

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