For the inhabitants of many of the world’s major cities and towns, estuaries provide their nearest glimpse of a natural habitat; a habitat which, despite the attempts of man to pollute it or reclaim it, has remained a fascinating insight into a natural world where energy is transformed from sunlight into plant material, and then through the steps of a food chain is converted into a rich food supply for birds and fish. The biologist has become interested in estuaries as areas in which to study the responses of animals and plants to severe environmental gradients. Gradients of salinity for example, and the problems of living in turbid water or a muddy substrate, prevent most animal species from the adjacent sea or rivers from entering estuaries. In spite of these problems, life in estuaries can be very abundant because estuarine mud is a rich food supply, which can support a large number of animals with a large total weight and a high annual production. Indeed estuaries have been claimed to be among the most productive natural habitats in the world.
When the previous editions of this book appeared, biologists were beginning to realise that the estuarine ecosystem was an ideal habitat in which to observe the processes controlling biological productivity. In the interven¬ing period, several more estuaries and their inhabitants have been studied intensively, and it is now possible to answer many of the questions posed by the earlier edition, and to pursue further the explanation of high productivity in estuaries and of energy utilisation at different trophic levels within the estuarine food web.
Users of the previous editions were kind enough to welcome the framework of the book, which first outlined the estuarine environment and the physical and biological factors which are important within it. We then examine the responses of the animals and plants to these factors, consider the problems of life in estuaries and why so few species have adapted to estuaries, and then propose a food web for an estuary. Thereafter we shall examine each trophic level in the food web in turn, first the primary producers (plants and detritus), then the primary consumers (herbivores and detritivores) and finally the secondary consumers (carnivores). These chapters have been fully revised in this third edition, to reflect our latest knowledge in these topics.
In the period since the publication of the previous editions of this book, a vast amount of new information on pollution in estuaries has accumulated. It has been widely recognised that although the world’s seas are huge and may appear capable of receiving unlimited quantities of man’s waste, such waste is often discharged first into the confined waters of estuaries. Many international experts have stated that, whilst the open oceans may not be generally polluted, the coastal waters of the sea and especially the waters of estuaries are widely polluted. Thus in practice, marine pollution is often essentially estuarine pollution. To reflect this large impact of mankind on estuaries, and to consider how mankind may either destroy or enrich the estuarine ecosystem, new chapters have been prepared in this edition. These consider pollution in estuaries, and the diverse uses and abuses of the estuarine habitat by man, as well as the methods used to study human induced changes in estuaries and the ways in which estuarine management can either monitor, control or prevent pollution or destruction of the estuarine ecosystem.
This latest edition therefore retains the concept of the study of the ecosystem as the basis for our understanding of the natural world, and shows that estuaries are ideal habitats for such studies. The new content and chapters reflect our attempts to recognise both the problems of pollution in estuaries and the solutions which estuarine management can offer, as estuarine ecosystems come under increasing pressure from a wide range of demands made by an increasing world population. The topic of estuarine pollution, estuarine uses and abuses and their management has moved on considerably in the past decade. As many of the problems of “point” source pollution have been attended to, different problems of “diffuse” pollution have become apparent. In addition, while some pollution problems are seen as capable of being solved, habitat loss and degradation is more of a threat. Hence the third edition concentrates on these as well as including sections on the effects of fisheries, dredging, structures, aquaculture, etc. on estuarine ecosystems. The third edition seeks to include considerably more applied material and present case studies of estuarine change.
Estuaries can be perceived as either the originators of pollutants, or more often as the recipients of pollution that originate on land, freshwater, or from the sea. The problems of estuarine pollution and management are those dealing with a sheltered environment that acts as a trap for sediment and contaminants, and as areas subject to intense pressure from mankind’s activities such as land-claim (or reclamation).
Estuaries are the most protected habitat in the UK and elsewhere (measured as the percentage of the total habitat that is subject to protection orders), and for most students on aquatic biology are their most accessible marine habitat. Whilst few UK, European or American Universities have ships for access to the sea, many are located on the shores of estuaries. Thus for many University courses, their local estuary is the marine habitat which can be studied, whilst the open seas have to be studied only in films or video. Throughout the book examples are drawn from Britain, Europe and America, as well as other areas which have been well studied such as South Africa and Australia.