L. David Smith

The ecological consequences of limb damage and loss in decapod crustaceans: a review and prospectus

Abstract Autotomy, the reflex severance of an appendage, is considered an adaptation to avoid predators and limit wounds. While an autotomy response may provide immediate survival benefits, the loss of one or more appendages can result in long-term functional and energetic costs. In this paper, we present an overview of the incidence of limb damage and loss in decapod crustaceans; review the literature on the ecological consequences of such injury; and suggest areas for future research. A survey of limb damage and loss in field populations showed consistently high incidences of injury in 14 reviewed species. Typically, chelipeds were the limb type lost most often and injuries were distributed symmetrically. No consistent correlation existed between injury frequency and body size among species. In general, the frequency of injury was independent of sex and moult stage. Fishery practices were responsible for substantial limb loss in some commercial species. In terms of energetic costs, experiments demonstrated that limb injury could reduce growth increment and affect intermoult duration. Functionally, limb damage was capable of reducing foraging efficiency and mating success, and increasing vulnerability to intra- and interspecific attack. The magnitude of these effects depended on the type and number of limbs lost. Given the prevalence of injury in decapod crustacean populations, the costs involved, and the ecological importance of many crustacean species, nonlethal injury has the potential to affect population dynamics and community processes. Convincing evidence of autotomys effects beyond the level of the individual, however, is, at present, lacking. Future work should redress this shortcoming. In addition, comparative studies are needed on decapod species from different habitats and with different lifestyles before generalizations can be made about the costs and benefits of autotomy.

Invasion pressure to a ballast-flooded estuary and an assessment of inoculant survival

The relationships between invasion pressure, post-transport inoculant survival, and regional susceptibility to invasion are poorly understood. In marine ecosystems, the movement and release of ballast water from ocean-going ships provides a model system by which to examine the interplay among these factors. One of the largest estuaries in North America, the Chesapeake Bay, receives tremendous amounts of foreign ballast water annually and thus should be at high invasion risk. To date, however, few introductions in Chesapeake Bay have been attributed to ballast release. To understand better the dynamics of this invasion process, we (1) characterized and quantified the biota arriving to Chesapeake Bay in foreign ballast water, (2) compared temperatures and salinities of ballast water and harbor water in upper Chesapeake Bay, and (3) tested experimentally survival of organisms collected from ballast water in temperatures and salinities characteristic of the region. From 1993 to 1994, we sampled planktonic and benthic organisms from 60 foreign vessels arriving to Chesapeake Bay. Our data show that the estuary is being inoculated by a diverse assemblage of aquatic organisms from around the world. Furthermore, the short transit time (≤15 d) for most vessels ensured that substantial numbers of larval and post-larval organisms were being deballasted alive. Most of the ballast water discharged into the upper Chesapeake Bay, however, was significantly higher in salinity (>20‰) than that of the receiving harbor. In laboratory tolerance experiments, ballast water organisms perished under such conditions. Thus, a mismatch in physical conditions between donor and receiver regions may explain the dearth of invasions in the upper Bay. It is likely that the lower Chesapeake Bay, which is more saline, remains at higher risk to ballast water invasion. Recognition of such intraregional differences should allow more focused predictions for monitoring and management.

The effect of cheliped loss on blue crab Callinectes sapidus Rathbun foraging rate on soft-shell clams Mya arenaria L.

Abstract Loss of single chelipeds was common (4–17%) in populations of blue crab Callinectes sapidus Rathbun surveyed in Chesapeake Bay and along the southeastern Atlantic coast and Gulf of Mexico. In contrast, blue crabs missing both chelipeds were relatively rare (0–5%). Laboratory experiments were conducted to determine the effects of cheliped autotomy on blue crab foraging rate on soft-shell clams Mya arenaria L. In replicated aquarium experiments, clams (44–72 mm shell length) were allowed 48 h to burrow in sandy substratum before an intact male crab or one missing one or both chelipeds was introduced. After 48 h, clams were checked for evidence of siphon injury or mortality. Foraging rate (clams consumed/48 h) of crabs missing a single crusher cheliped did not differ significantly from that of intact crabs. Blue crabs compensated for the loss of a crusher by using the cutter cheliped and opposite first walking leg to forage. In contrast, crabs missing both chelipeds experienced a greater feeding handicap; their consumption of clams was significantly lower than that of intact crabs. The low incidence of individuals missing both chelipeds suggests that such injury does little to diminish blue crab predation on M. arenaria populations.

The Role of Phenotypic Plasticity in Marine Biological Invasions

The outcome of a species introduction depends, in large measure, on the abilities of the invader and species in the receiving community to respond to their new environments. A successful invader must survive changing environmental conditions at all stages leading to and following its introduction. Residents in the invaded community, in turn, must cope with environmental changes that result from the arrival of the new species. Adaptive responses (i.e., those that confer a fitness benefit) by either party have been viewed primarily to result from evolutionary changes in fixed traits in populations (Thompson 1998; Mooney and Cleland 2001; Cox 2004). Although intense selection can result in rapid phenotypic shifts across generations (Huey et al. 2000; Gilchrist et al. 2001; Reznick and Ghalambor 2001), this process does not encompass fully the dynamic nature of many invasions. A burgeoning literature indicates that individual organisms are capable of modifying ecologically important physiological, morphological, behavioral, and life-history features within a lifetime in response to environmental cues (Harvell 1986; Stearns 1989; Kingsolver and Huey 1998; Schlichting and Pigliucci 1998; West-Eberhard 2003; DeWitt and Scheiner 2004a). This phenomenon, known as phenotypic plasticity, provides a means by which an invader can respond relatively quickly to its new biotic or abiotic environment. Similarly, phenotypic plasticity may allow resident species to mitigate changes wrought by the invader. The role of adaptive phenotypic plasticity in biological invasions, however, has been largely ignored in marine settings. Our understanding and interpretation of marine biological invasions will be incomplete on several counts if we fail to acknowledge or test for the potential influence of phenotypic plasticity. First, phenotypic plasticity can provide a mechanistic explanation to understand and predict (1) why and how some individuals or species invade and others do not, (2) what the ecological effects and eventual ranges of the invader might be, and (3) how native species might respond to the introduction. In particular, knowledge of the type, direction, and magnitude of induced responses is critical if we are to decipher direct and indirect ecological effects stemming from species introductions. Second, recognition of phenotypic plasticity’s

Correction for Verling et al. , Supply-side invasion ecology: characterizing propagule pressure in coastal ecosystems

Correction for ‘Supply-side invasion ecology: characterizing propagule pressure in coastal ecosystems’ by Emma Verling, Gregory M. Ruiz, L. David Smith, Bella Galil, A. Whitman Miller and Kathleen R. Murphy (Proc. R. Soc. B 272, 1249–1256. (doi: 10.1098/rspb.2005.3090)). A reference was omitted from the print version of this paper; the missing reference is as follows: Simberloff, D. 1989 Which insect introductions succeed and which fail? In Biological Invasions: a global perspective (ed. J. A. Drake, F. Di Castri, R. H. Groves, F. J. Kruger, H. A. Mooney, M. Rejmanek & M. H. Williamson), pp. 61–75. Chichester, UK: Wiley & Sons Ltd.