Maximum force production: why are crabs so strong?

128

Large benthic decapods play an increasingly important role in commercial fisheries worldwide, yet their roles in the marine ecosystem are less well understood. A synthesis of existing evidence for 4 infraorders of large benthic marine decapods, Brachyura (true crabs), Anomura (king crabs), Astacidea (clawed lobsters) and Achelata (clawless lobsters), is presented here to gain insight into their ecological roles and possible ecosystem effects of decapod fisheries. The reviewed species are prey items for a wide range of invertebrates and vertebrates. They are omnivorous but prefer molluscs and crustaceans as prey. Experimental studies have shown that decapods influence the structuring of benthic habitat, occasionally playing a keystone role by suppressing herbivores or space competitors. Indirectly, via trophic cascades, they can contribute to the maintenance of kelp forest, marsh grass, and algal turf habitats. Changes in the abundance of their predators can strongly affect decapod population trends. Commonly documented nonconsumptive interactions include interference-competition for food or shelter, as well as habitat provision for other invertebrates. Anthropogenic factors such as exploitation, the creation of protected areas, and species introductions influence these ecosystem roles by decreasing or increasing decapod densities, often with measurable effects on prey communities. Many studies have investigated particular ecosystem effects of decapods, but few species were comprehensively studied in an ecosystem context. A simplified synthetic framework for interpreting eco system roles of decapods was derived from the available evidence; however, more experimental and long-term observational studies are needed to elucidate mechanisms and shed light on the longterm consequences of decapod fisheries.

Section: Discussionmentioning

confidence: 99%

Ecological role of large benthic decapods in marine ecosystems: a review

Boudreau¹,

Worm²

2012

128

“…Warner & Jones 1976, Elner 1978, Seed & Hughes 1995, Behrens Yamada & Boulding 1998, Schenk & Wainwright 2001. Because many of these biomechanical properties show little variation within species, claw size becomes the chief morphological determinant of crushing ability (Elner 1980, Lee 1993, Taylor 2000 and crabs with relatively larger claws have a foraging advantage over those with smaller claws. Fourth, claw size and strength are developmentally sensitive to diet (Smith & Palmer 1994), which opens the possibility for withingeneration trophic responses by crabs to temporal or spatial differences in prey defenses.…”

Section: Introductionmentioning

confidence: 99%

Biogeographic differences in claw size and performance in an introduced crab predator Carcinus maenas

Smith¹

2004

Introduced predators must forage effectively to persist in new areas, and effective resource use is correlated with a predator's trophic (feeding) structures. The extent to which trophic morphology responds to spatial variation in prey resistance, and the time scale of that response, however, are not well understood. The introduced European green crab Carcinus maenas, which has expanded its range in the northwest Atlantic Ocean over the last century and encountered a latitudinal cline in prey armor, offers an ideal opportunity to test for such post-invasion changes. In rocky intertidal habitats in the Gulf of Maine, southern populations of the snail Littorina obtusata are better defended than northern populations. To test for correlated differences in claw size and prey defense, green crabs and common molluscan prey were collected at southern and northern sites in the Gulf of Maine. C. maenas are heterochelous, and analyses revealed that crusher claws of crabs collected in the south were significantly larger than those of crabs from the north after adjusting for carapace width. The size of the cutter claw, however, did not differ between regions. Shell weights for similarsized snails differed among sites for 3 of the 4 species examined, but did not differ by region. To test crushing performance, southern and northern crabs were presented with increasing sizes of southern or northern L. obtusata in the laboratory. For similar-sized individuals, southern crabs were able to crush significantly larger snails than northern crabs regardless of the geographic origin of the snails. Thus, patterns in claw size and performance strongly suggest trophic responses to geographic differences in prey armor. Rapid changes in trophic morphology could facilitate the spread of this invasive species and initiate an ecological arms race if both predator and prey respond ecophenotypically to each other.

“…In their experiment, crabs grown on fully shelled mussel prey developed larger and stronger claws than did those reared on unshelled mussels. The exoskeletal remodeling resulted from changes to the underlying claw muscle brought on by different amounts of exercise in the previous molt interval ( Abby-Kalio & Warner 1984, Taylor 2000. Our experiment demonstrated exercise-induced plasticity in a heterochelous crab to natural variation in prey shell thickness and, in one temperature-by-diet treatment combination, succeeded in amplifying the existing asymmetry between cutter and crusher claw size.…”

Section: Discussionmentioning

confidence: 71%

“…Carcinus maenas uses its larger and stronger crusher claw to breach prey armor and its smaller, but more dexterous, cutter claw to manipulate items (Schenk & Wainwright 2001). Claw size correlates positively with closing force in crabs (Taylor 2000) and, thus, is probably an important determinant of foraging success for C. maenas (Lee 1993).…”

Section: Introductionmentioning

confidence: 99%

Temperature constraints on phenotypic plasticity explain biogeographic patterns in predator trophic morphology

Baldridge¹,

Smith

2008

Phenotypic plasticity in feeding structures allows invasive predators to adjust to variation in prey defenses, but the abiotic milieu may constrain the extent or rate of the response. In the northwest Atlantic Ocean, the introduced European green crab Carcinus maenas encounters latitudinal differences in shell thickness of its snail prey, Littorina obtusata, and water temperature. To determine whether claw size in this heterochelous species responds to broad-scale differences in prey armor or water temperature, we reared C. maenas on a diet of thick-or thin-shelled L. obtusata at 16 or 10°C. At the higher temperature, crusher claw size increased significantly more at the molt relative to carapace width increase for crabs raised on the thick-shelled rather than thin-shelled diet. The lower temperature inhibited trophic responses in the crusher claw by reducing foraging performance on thick-shelled snails, and lower temperature also prolonged the molt interval. Cutter claw growth showed no diet effect at either temperature. Non-additive responses to multiple cues highlight the importance of testing for phenotypic plasticity over a range of environmental backgrounds and help explain post-invasion biogeographic patterns between an introduced predator and its prey.