A comprehensive review of North America’s most imperiled faunal group: setting the framework for new hypotheses

As more ecological work is being conducted on freshwater mussels, we are coming to appreciate the importance of this secretive fauna to ecosystem function and structure. Yet we still lack an understanding of the factors that control the distributions of this group, their reproductive strategies, the fish hosts they use, and the factors causing their decline. This book provides a thorough literature review of the available information, and a detailed analysis and synthesis of this information. Haag does a magnificent job at compiling this information, summarizing it, and attempts to make some important inferences based on the available data. Whether or not one is a freshwater mussel enthusiast, this book provides a comprehensive review of the literature on these inconspicuous animals that will be useful for both novices and experts alike. Wendell Haag, a USDA ecologist, has done an excellent job pulling together the beginnings of the study of freshwater mussels and the current status of our understanding. Haag’s poignant review and respect for these creatures is made apparent in the preface of the book and is a common theme throughout. This nicely laid-out book spotlights the amazing diversity of mussels, their life history strategies, their importance in the ecosystem, and the unfortunate loss and continued loss of many mussel species. Yet this book does not only serve as a resource for pulling pertinent literature together, it synthesizes this information and serves as a meta-analysis of much of this work to invigorate new research in the field. The book is split into 11 chapters, with each giving an overview of some component of the history of the study of unionids, mussel life history, mussel ecology, and the past and current stressors that have led to their decline. The book will be pleasing to read for both scientists and history buffs alike. Not only does this book focus on the study of these organisms, but also the early fascination of native peoples with mussels and the pearl and button industries of the late 19th and early 20th centuries. Figures such as the one showing mussel harvesting camps are fascinating and illustrate the over harvest of mussels during the early 1900s for the button industry. The first three chapters serve as an introduction to mussels, the history of their study, and the global distributions of these animals. Chapters 4–7 focus on the habitats required by mussels, reproductive strategies, life history, and population biology. Through these chapters, the author develops a framework for classifying mussel species based on their life history traits and then develops a conceptual framework to determine assemblage structure. Chapter 8 tries to combine all this information to understand assemblage patterns and niche partitioning in mussel communities. The final chapters discuss human exploitation, declines of mussels, and conservation challenges for mussels in the future. The book is well organized throughout and includes 21 color plates that illustrate shell and nacre color variation, sexual dimorphism, and astounding mantle lures. Additionally, the pictures and figures that accompany each chapter are well done and illustrate points made throughout. I think the most important contribution of this book is the conceptual framework Haag terms the host-habitat continuum. To outline this conceptual framework, Haag lays the groundwork by categorizing various mussel species into three strategy categories (opportunistic, periodic, and equilibrium) based on many of their life history characteristics presented in Chapter 7. This framework is useful for researchers to build upon and to make predictions regarding population dynamics and recruitment following disturbance. He uses these life history traits along with various means of niche partitioning, including competition for fish hosts, food, and habitat, to help determine assemblage structure. The all-encompassing literature review that makes up a large proportion of this book culminates with the role life history and host strategy play in determining mussel assemblage structure and outlines how these three strategies may be distributed across the river continuum. This summation stimulates the reader to think about the traits that lead to the patterns we see in assemblage structure and how these vary with habitat types due to niche partitioning. With the concept of the host-habitat continuum, Haag provides testable hypotheses to guide future research in mussel ecology. Overall, the book is a fantastic contribution to the ecological literature and a very nicely produced book. However, some of the analyses that Haag presents are inadequately described and some additional detail would have aided an interested reader. Furthermore, while some of Haag’s conclusions are supported by multiple studies, other inferences made within the book are not fully supported by current data. Although some portions of the book contain some speculative claims made regarding certain patterns, this speculation is included to provide a framework for future inquiry and study. While the book is unfortunately very much North American-centric, this slant occurs because the diversity of freshwater mussels as well as the study of this faunal group is centered primarily in the United States. The book does a great job of clearing up some common misperceptions of unionid freshwater mussels—even for those that work in the field of mussel biology (e.g., the issue of longevity). As more work is being done across the globe on these animals, I think we are going to discover a large variety of traits and hosts associated with mussels that will take our understanding further. In the final chapter Haag states, ‘‘The value of any wild creature is inseparable from its context within the ecosystem of which it is an integral component.’’ Given the highly imperiled status of freshwater mussels, this idea is essential if we wish to protect this fauna and to articulate their importance within the ecosystem. This book is an important contribution to our understanding of diversity within the natural world because it shows that within this faunal group of seemingly similar species there is a great variety in life history traits, strategies, and