Starfish – Biology and Ecology of the Asteroidea

Starfish are icons of the seashore. The book edited by J. M. Lawrence offers a comprehensive review of their biology and ecology. It perfectly integrates the research conducted during the past decades, updating the still-quoted synthesis of Hyman (1955), and complimenting the serial ‘Echinoderm Studies’ that was last published in 2001. Any reader of the book would realize how starfishes are an exotic and fascinating group of organisms for study, and not only souvenirs to the kids and tourists. ‘Starfish – Biology and Ecology of the Asteroidea’ is designed to summarize the current knowledge of the group. It will be interesting to the widest audience, and is definitively an invitation to a compelling reading.

The first part of the book, entitled ‘comparative biology and ecology’, is organized into nine chapters that cover a wide spectrum of topics: anatomy, phylogeny, reproduction, development, ecology, and biochemistry.

The phylogeny of starfishes is a highly debated topic. Some key issues are central to the debate, including the monophyly of traditional orders and families as well as the relationships among the major clades. In particular, the position of the order Paxillosida, either derived or basal, remains an unresolved question. Morphology-based and molecular approaches of phylogeny tend to converge, and future studies should help to calm the debate. The author favours his own position in the book, but does not omit the major points of discussion.

The reproduction and development of echinoderms in general, and starfishes in particular, is among the most varied and original among marine organisms. They usually reproduce sexually, with a release of gametes into the seawater, followed by a planktonic, feeding larval stage before settlement on the sea floor. Depending on taxa, the larval stage can be shortened to direct development with either free-living or brooded larvae. Environmental conditions affect the development and some forms can delay the settlement of larvae, or reproduce by budding of larvae. Reproduction through scissiparity of the adult occurs in a few taxa. The analyses of developmental patterns are nowadays a fruitful field of research, perfectly summarized in the book.

Ecological roles of the starfishes in marine ecosystems are addressed at varied levels. The most prominent and best known impact of starfishes is due to the common predatory species in coastal areas. The population dynamics of prey strongly depends on predation pressure (e.g. the relationship between asteriids and mussel populations). The ups and downs of the starfish populations mostly rely on the recruitment of juveniles. Very few larvae usually reach the metamorphosis to benthic juveniles. The fluctuation in settlement success depends on the abundance and health of the planktonic larvae, and therefore on the phytoplankton productivity. Starfishes are high producers of secondary metabolites, especially of steroids and fatty acids, including distinctive and uncommon groups of molecules in the marine environments. Some of these molecules have antifoulant and antifeed properties and are involved in taxon interactions.

In a second part entitled ‘Integrative biology’, each of the 11 chapters synthesizes the current knowledge on a key taxon. The examples are selected according to the impact of the species on local benthic ecosystems and their potential consequences in conservation biology or in fisheries economy.

The crown-of-thorns starfish Acanthaster planci (Linnaeus, 1758) is renowned as a predator of corals, frightening by its ability to rapidly destroy reefs and consequently to reduce the richness of ecosystems where it settles. Major impact on coral reefs is sustained when massive recruitment of larvae occurs and leads to outbreaks of adults. The population dynamics of such a species, with highly volatile numbers of individuals, has long been difficult to understand. Any factor that could promote the survival of planktonic larvae and their settlement is likely to favour pullulating of adults later on. Terrestrial runoff is potentially one of a chain of causes.

Oreaster reticulatus (Linnaeus, 1758) is a typical species of the sandy substrates in the tropical Atlantic. Because they are pretty objects, easy to collect and to dry out, they have been subject to harvesting solely for sale as souvenirs. Omnivorous, the species feeds predominantly through microphagous grazing and deposit feeding, so that removal of the populations from natural environments modifies the composition of local benthic ecosystems. Other taxa suffer from human activity (e.g. Archaster, Linckia, Protoreaster, Pisaster).

The order Forcipulatida includes numerous specialized predators that can be keystone species in coastal benthic ecosystems. Some are potential pests and have an economic impact on the productivity of mollusc fisheries and farms. The book analyses the ecological significance of several species sampled from varied oceans and climates: Heliaster helianthus (Lamarck, 1816), Pisaster ochraceus (Brandt, 1835), Asterias amurensis Lütken, 1871, Leptasterias polaris (Müller & Troschel, 1842), Coscinasterias spp. Among the described cases, that of A. amurensis illustrates an example of an invasive species with a strong impact on the composition of benthic ecosystems that potentially can threaten a species of handfish, endemic to Australia.

The other four taxa are: the Antarctic species Odontaster validus Koehler, 1906, the widespread Echinaster, and the cosmopolitan Astropecten and Luidia that are major predators on sandy substrates and contribute to the regulation of mollusc populations.

The content of the chapters, all written by leading experts in their field, ensures the book is of a high scientific quality. It is richly illustrated with numerous black and white figures, and a central inset of eight colour plates. The reference list occupies 45 printed pages, which is definitively useful for a comprehensive synthesis. This kind of book is so rare that specialists would expect an exhaustive coverage of the science conducted on starfishes. The content is marked by strong editorial choices. It is definitively frustrating not to find at least two additional chapters: one on biodiversity patterns and a second on the deep sea forms. The spatial distribution of starfish species is strongly shaped by historical and ecological constraint. The investigation of phylogeographical and biodiversity gradients has already produced valuable results. Echinoderms are key taxa of the bathyal and abyssal environments, both in terms of biomass and diversity. Several groups of starfishes live preferentially in the deep sea, where they are key ecological taxa and develop outstanding adaptations. One can only regret that brisingids, porcelanasterids, pterasterids or goniasterids are only marginally mentioned in the book.

Loïc Villier

Professor

Centre de recherche sur la paléobiodiversité et les paléoenvironnements, Paris, France

Email: [email protected]

© 2014 Loïc Villier