Open Access
Lieb, David Andrew
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
September 07, 2011
Committee Members:
  • Dr Robert F Carline, Dissertation Advisor
  • Robert F Carline, Committee Chair
  • Eric S Post, Committee Chair
  • Hunter J Carrick, Committee Member
  • James Landis Rosenberger, Committee Member
  • Katriona Shea, Committee Member
  • Pennsylvania
  • management
  • conservation
  • distribution
  • ecology
  • crayfish
Although crayfish have long been the object of scientific inquiry and where studied appear to be functionally (ecologically) important, much remains to be learned about their ecology, distribution, and conservation. Even the most basic information (presence/absence data) is lacking for the majority of species. The absence of adequate crayfish data is a major problem, because many species are thought to be imperiled across all or parts of their range and even species that were once widely distributed are rapidly disappearing. Anthropogenic disturbances, especially crayfish introductions, appear to be responsible for many of these losses. The replacement of native crayfish by introduced (exotic) crayfish represents a significant threat to aquatic communities because introduced crayfish often become extremely abundant and can destroy aquatic macrophyte beds, suppress benthic invertebrate communities, reduce fish abundance and biomass, and negatively affect amphibian populations. At the turn of the 20th century, Arnold E. Ortmann published a monograph describing the crayfish fauna of Pennsylvania. Since then, very few crayfish studies have been published from the state. The need to re-examine Pennsylvania’s crayfish fauna and the opportunity to revisit previously sampled areas to assess changes in the state’s crayfish fauna over the past century motivated much of this work. The need for basic ecological and conservation information regarding Pennsylvania’s crayfish fauna, as well as specific strategies for managing the state’s native species, provided further motivation. To fulfill these needs, I conducted a series of crayfish studies in Pennsylvania. The findings of these studies and others were then utilized to address a broader ecological question: what determines surface-dwelling crayfish community structure? I first found that a previously unstudied, widely distributed assemblage of crayfishes (Cambarus bartonii bartonii and Orconectes obscurus) inhabiting Spruce Creek in central Pennsylvania had strong top-down effects on other invertebrates and reduced total invertebrate density by 70%. Crayfish were in turn readily consumed by brown trout (Salmo trutta), especially large trout (> 275 mm total length). Next, I surveyed Valley Creek in southeastern Pennsylvania for crayfishes and discovered a rare species of crayfish [Cambarus (Puncticambarus) sp., an undescribed member of the Cambarus acuminatus complex] that had not previously been reported from the state. The basic life history characteristics, reproductive status, and habitat preferences of C. (P.) sp. are described herein. Additional surveys in southeastern Pennsylvania and comparisons of these results to historical data indicated that exotic crayfishes have invaded many parts of the region, much of which no longer supports native crayfishes. In addition, populations of C. (P.) sp. were discovered from three more streams and are now known from a total of four streams in Pennsylvania, all of which are threatened by urbanization and exotic crayfishes. This information, in combination with other historical and contemporary data from Pennsylvania and nearby states collected for this study and other studies, indicate that C. (P.) sp. is critically imperiled in Pennsylvania and possibly across its range and that the range of another native Pennsylvania crayfish, Orconectes limosus, has declined (retreated eastward) by > 200 km in Pennsylvania and northern Maryland, likely as a result of exotic crayfishes. Although C. b. bartonii was found with exotic crayfishes in a number of water bodies in Pennsylvania, it was typically a minor component of the crayfish community and may not be able to persist in those systems indefinitely. An examination of potential determinants of surface-dwelling crayfish community structure suggests that a combination of local, regional, and historical processes operating across a variety of temporal and spatial scales shape these communities. More specifically, the interplay of competition with environmental conditions appears to limit the number of species that can occur in local communities, whereas regional, historical, and more recently human influences likely determine potential component species. In light of these findings, the role of barriers (e.g., dams), environmental protection, educational programs, and regulations in preventing crayfish invasions and conserving native crayfishes is discussed and management initiatives centered on those factors are presented. The need for methods to eliminate exotics and monitor natives is highlighted. Although tailored to a specific regional fauna, the ideas presented in this dissertation have broad applicability and would likely benefit many of North America’s crayfishes and the ecosystems in which they reside.