Global coastal change

Eutrophication and habitat loss lead the list of most important agents of global coastal change in Ivan Valiela’s most recent book, closely followed by the harvest of finand shellfish. At middle ranks in intensity and scale are global warming and sea level rise, the alteration of sediment and freshwater transport along with invasions of introduced exotic species. Impacts of petroleum, chlorinated hydrocarbons, metals, UV radation and litter are ranked lower as they have less intense effects, or recovery from them is more likely than in the case of higher ranked impacts. All these and more agents of change are treated one after another in 12 chapters, extensively cross-referenced to highlight interactions. Each chapter opens with an extreme case. Beginners may choose to read all of these first. In the entire book, the disastrous state of the Black Sea ecosystem serves as a worst case scenario for the future if environmental policies are not improved. The case of the Black Sea also points to a lack of crucial data and controversial interpretations that arise in such situations. Sea level rise is exemplified by the drowning city of Venice, reduced freshwater discharge from the fading Aral Sea, and loss of coastal habitats by shrinkage of salt marshes and mangroves. Case histories are provided for the Exxon Valdez oil spill, PCBs in New Bedford Harbor, mercury contamination in Minamata Bay and fisheries on the shallow banks off North America. These case studies at the beginning of each chapter are followed by detailed reviews of the scientific evidence for change caused by specific human activities, and by comments on mitigation and restoration. The particular strength of the book is the critical evaluation of available evidence, and the attempts to explore the global dimension of the effects of the respective agents of coastal change. The abundant footnotes should not be skipped as they make the text even more interesting to read. Chapters finish with comprehensive references to the primary literature. The text is highly readable with plenty of graphs and illustrative photographs. As human populations have increased and concentrated along coasts our activities have thoroughly, and widely, altered or destroyed coastal organisms and environments (p. 349). Throughout his book, Valiela keeps to the published evidence, refrains from using merely plausible inferences and speculations, and avoids value judgements. The focus is on environmental aspects, leaving out human health, economics and political issues or concepts such as ‘Integrated coastal zone management’. Further, sheltered coasts of developed countries in temperate regions dominate in the book, simply because that is where most of the anthropogenic changes have been recorded. The book is remarkably free of typographic and other errors. I may mention that on p. 231 the introduced bivalves Corbicula fluminea and Potamocorbula amurensis are apparently mixed up under the name ‘Asiatic clam’, and in fig. 10.5 trans-Suez canal and other exotic macroalgal species numbers in the Mediterranean Sea are reversed. Some topics I missed or would have expected to see better covered, i.e., intensive hunting of marine mammals and coastal birds prior to the 20th century and their partial recovery in more recent times; collapse of oyster fisheries followed by oyster cultivation; bottom-up and top-down anthropogenic effects in kelp forests; habitat change in coastal dunes; UV radiation effects on vertical ranges of macroalgae. On the whole, however, the wide and heterogeneous spectrum of coastal changes is amazingly well covered and written with an outstanding expertise that may not be equalled by any other author on this subject. Valiela’s conclusion for technogenic toxic substances is that, in spite of clear effects on the individual organism, impacts at the population or ecosystem level are scarcely documented for marine coastal environments. He stresses that bottom-up effects via nutrient supply interact with human altered top-down effects in most circumstances. His statement ‘‘w.x it seems safe to conclude that most coastal waters are exposed to some degree of eutrophication, and that in most cases conditions are worsening’’ (p. 311) sounds quite pessimistic. Yet his examples of efforts to manage eutrophication along American coasts and improving trends in Europe give cause for more optimism. The author conveys coastal studies into the arena of global environmental subjects, where they clearly belong. The inherent heterogeneity of coasts and the multitude of agents transforming them required a scientist of exceptionally wide experience and knowledge to show how local effects coalesce into global change. I believe Ivan Valiela has written a great book. His ranking of the agents of global coastal change certainly constitutes a challenge for future research and at the same time offers a common framework for coastal science.