The biology of coral reefs

Charles R. C. Sheppard, Simon K. Davy &Graham M. Pilling

Oxford, Oxford University Press, 2009

352 pp, 130 b/w illus, 8 page colour plate section, ISBN 13: 978-0-19-856636-6 (paperback), £29.95, $49.95

This book is the most recent volume in Oxford University Press's Biology of Habitats Series. The text is suitable as an introduction to coral reefs, aimed mainly at students as well as professionals. The book is also suitable as basic reading material for undergraduate courses on tropical marine biology or as preparation for graduate students intending to start coral reef research. Since there are not many study books devoted to coral reefs, it is highly recommended. For students who want to learn more about tropical marine ecosystems in general, it can be used along with another book in the same series, Hogarth's (2007) The biology of mangroves and seagrasses.

Professor Charles Sheppard is a well-known author of numerous scientific and popular publications on coral reefs, including several books. He has been the editor of Marine Pollution Bulletin for many years. Therefore, Oxford University Press may consider itself fortunate to have him as leading author of this book. Dr Simon Davy has published on coral–algal symbiosis and coral disease. Dr Graham Piling is a specialist in the practical assessment and management of coral reef fisheries, whereas his recent work is focused on consequences of climate change for coral reefs.

While coral reefs are critically endangered, coral reef research appears to be blooming. A number of scientific publications of various scientific disciplines deals with coral reefs. Hence, the publication of this book is timely. Since so many new papers are being published on the biology of coral reefs, it is likely that a revised edition will be needed a few years from now. The production of a book like this usually takes a considerable amount of time, which makes it difficult for the authors to continuously include new information. Nevertheless, they have managed well to give a good overview on coral reef biology, including major new developments in the field.

The biology of coral reefs offers easy access to its readers. It consists of 10 chapters, each divided into paragraphs and subparagraphs. Within the chapters there are 19 ‘boxes’, each 1–4 pages long, dealing with a featured item written by an expert. The chapters are preceded by a convenient list of abbreviations and a list of the ‘boxes’. The bibliography is extensive and includes many recent works. The text on the back cover explains why coral reefs are so special as an ecosystem, referring to their spectacular appearance, their species richness, and their importance as a natural resource for people living in the tropical coastal zone. Furthermore, it mentions that the book deals with several biological aspects of coral reef organisms, but also with their present threats and conservation.

The first chapter serves as an introduction, dealing briefly with the geological history and geographical distribution of tropical coral reefs around the globe. There is a map indicating the global distribution of reef-building corals by species richness patterns (however, without sources), and there is a table, listing areas of coral reefs (in km²) in various parts of the world. The chapter includes a discussion on the centre of maximum marine species diversity, which is here referred to as the Indo-Australian Archipelago (IAA), and the possible processes that explain its origin. Furthermore, it mentions the major reef types and the predominant reef zonation found on most reefs, from the shallow reef flat to the deepest slopes. Since the map does not show the actual position of the reefs, readers who want to learn more about the distribution of tropical reefs should consult an atlas on this topic (e.g. Spalding et al. 2001). Anyone who is looking for information regarding the so-called deeper coldwater reefs should also look for other sources (e.g. Roberts et al. 2009).

Chapter 2 concerns types of corals, especially the main reef-building species, and other major reef dwellers, such as sponges and soft corals. All these organisms play important roles on the reef; they depend on each other for the ecosystem to function, but they also share the need for substrates to settle on. Some species have developed strategies to quickly occupy empty substrates, whereas others show aggressive behaviour towards other species in the competition for space. Free-living animals that dwell on reefs are also briefly discussed, such as molluscs, crustaceans and echinoderms. In contrast, there are also organisms that live hidden inside the corals, the so-called bioeroders. These are important for the local production of sediment, which may serve as habitat for burrowing organisms. Plants that are clearly present on reefs, such as algae, seagrasses and mangroves are discussed, but not all species depend on their proximity to reefs, although particular calcareous algae appear to be more closely associated with reefs. Seagrasses and mangroves that occur on or near reefs have an important functional role, since they provide shelter to juvenile fish that migrate to the deeper reef zones where they grow larger.

The third chapter deals with abiotic factors that limit the distribution of tropical reefs, such as light, temperature, salinity, sediment, and nutrients. This information is also relevant for chapter 4, in which biotic components are explained that are important for reef growth and depend on abiotic factors, such as the symbiosis with unicellular algae, the zooxanthellae. As a consequence of this symbiosis, reef corals depend on sunlight and sufficiently high water temperatures. Nevertheless, coral–microbial associations are discussed as is the role of sponges as hosts for algae and bacteria. Surprisingly little attention is given to the symbioses that involve all kinds of fish, shrimps and other colourful animals. This is not an important deficiency, since these animals are usually well represented in other popular coffee table books and field guides by underwater photographers.

Chapter 5 presents a close-up view of the ecological roles of microbes in the water column, such as bacteria, fungi, protozoans, microalgae, and viruses. Some animals and plants are planktonic for the whole of their life history, whereas others are large as adults and have a planktonic phase that enables them to disperse with the currents. All these aspects do not seem to be specifically reef-related, but it is important that attention is given to the role of microscopic organisms in relation to the functioning of a reef as an ecosystem and to the connectivity of reefs. When it comes to reef connectivity, other pelagic organisms, such as fish, also play a role. Fish are the major subject of the sixth chapter, by way of the various essential roles they play in reef communities.

Chapters 7 and 8 indicate the economic importance of coral reefs and the unsustainable use of reef resources. The management and control of reef fisheries are discussed, as well as aquaculture on reefs as an alternative source of income for fishermen that depend on reefs for their livelihood. Major harmful impacts on reefs are visible when dredging and reclamation activities take place in the proximity of or even on top of reefs. Pollution and eutrophication are other examples of anthropogenic damage to reefs, which may cause side effects by outbreaks of diseases and particular pest organisms. Such consequences are usually not well understood, but may be very destructive. Coral bleaching may have large-scale effects on corals by causing mass mortality and it can be even more disastrous since many other organisms depend on corals for their survival. There is a clear connection between coral bleaching and elevated seawater temperatures, an important aspect of global change. Likewise seawater acidification resulting from rising CO₂ concentrations is also a major concern, because it is expected to slow down reef calcification.

In chapter 9, examples of ecological consequences of environmental stress for reef communities are given. Coral-dominated reefs can be replaced by algae-dominated reefs when major grazers disappear. Caribbean reefs that were characterized by fields of large staghorn corals, Acropora cervicornis (Lamarck, 1816), and elkhorn corals, A. palmata (Lamarck, 1816), have completely lost their original appearance when these species almost completely disappeared. This had major consequences for animals depending on these large branching corals for food and shelter. Fortunately, these iconic species show some recovery, but their large-scale disappearance has been succeeded by that of boulder-shaped Montastrea species. In the Indo-Pacific such massive declines in species abundance have not yet been reported. Nevertheless, outbreaks of the coral predator Acanthaster planci (Linnaeus, 1758), the crown-of-thorns starfish, are notorious because they result in the mass mortalities of complete coral assemblages. The disappearance of reef corals has a direct economic effect where they protect the shoreline.

Chapter 10, finally, describes future perspectives and conservation attempts to limit total coral reef degradation.

In conclusion, The biology of coral reefs is a must for coral reef biologists and therefore it is a pity that it is also somewhat expensive.

Bert W. Hoeksema

Department of Marine Zoology

Netherlands Centre for Biodiversity Naturalis

Leiden, The Netherlands

E-mail: [email protected]

©2010 Bert W. Hoeksema