Moulting & growth
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Other genera

  Moulting & growth is divided into a section on other genera, considered here, and sections on CANCER and HANDEDNESS presented elsewhere.
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Carcinus

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Research study 1
 

graph showing growth of the 1998 year-class of green crabs Carcinus maenusA decade after its discovery in San Francisco Bay in ca.1988, European green crabs Carcinus maenus had appeared in Oregon, Washington, and southern British Columbia.  Growth of this 1998-year class has been faster than that recorded on the east coast of North America and in Europe (see graph).  However, life spans are similar in all groups, at about 4-6yr, and by now the northern component of the invasion is well into its 3rd generation.  Although coastal currents have not favoured renewed larval recruitment from California populations, the Oregon and Washington populations appear to be self-recruiting, and the species seems to be here to stay.  Behrens Yamada et al. 2005 Biol Invasions 7: 309.

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Chionoecetes
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Research study 1
 

photograph of tanner crab Chionoecetes opilio with sea anemone growing on its back, courtesy Bill Eichenlaub, National Park ServiceMoulting in crustaceans is under endocrine control, with the ecdysteroids responsible being synthesised and secreted from so-called y-organs.  Some species, such as lobsters and Cancer-crabs, moult continuously throughout their lives, while others, such as many or all spider crabs, reach a terminal moult after which they never moult again.  Since the y-organ secretory activity is controlled by a moult-inhibiting neuropeptide hormone known as MIH, then cessation of moulting can occur either by degeneration of the y-organs, or by continual production of MIH, or perhaps some combination of both.  Removal of eyestalks, with consequent removal of the source of MIH, has long been known to stimulate moulting in crustaceans.  In east-coast soft-shelled crabs Callinectes sapidus, for example, eyestalk removal has been used commercially for decades.  As for tanner crabs Chionoecetes opilio in the Bering Sea, research has recently confirmed that both sexes undergo a terminal moult.  A defining experiment in the present study, which is focused on confirming that males as well as females undergo terminal moults, is to show that eyestalk removal in older males does not lead to increased levels of circulating ecdysteroids as it does in younger males or in terminally moulted females.  Tamone et al. 2005 Integr Comp Biol 45: 166. Photograph courtesy Bill Eichenlaub, National Park Service & Tamone et al. 2007 Proc 4th Glacier Bay Sci Sympos.

NOTE referred to as being anecdysic

 

 

Indication of a terminal moult having occurred in
a crustacean is often signified by the presence
of growths of other organisms on the exoskeleton,
such as barnacles, tunicates or, in the case of
this tanner crab C. opilio, presence of a large
sea anemone Metridium sp. 0.3X

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Emerita
 
Research study 1
 

photograph of mole crabs Emerita analoga
Mole crabs Emerita analoga are suspension-feeders, so growth will depend on amount of organic particles available as food.  A comparison of two locations in California, Santa Barbara (Goleta Bay) and Santa Cruz Island (only 42km apart) shows that growth of Emerita in the latter is one-third that in the former.  Moulting frequency is half as often at Santa Cruz Island than at Santa Barbara (frequency=36-63d and 18-26d, respectively).  The author notes that Santa Cruz Island is bathed by much clearer water than Santa Barbara, and that water temperatures are about 3oC lower in Santa Cruz Island than in Santa Barbara at different times of year.  Fusaro 1978 Fish Bull 76: 369.

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Hemigrapsus & Pachygrapsus
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Research study 1
 

histograms of % increase in size of shore crabs Hemigrapsus oregonensis and Pachygrapsus crassipes in Bodeg Bay, Californiaphotograph of limbs of Dungeness crab showing autotomy schedule in a study of limb regenerationCrabs that lose limbs replace them within a moult or two.  It has long been known that limb loss and replacement influences intermoult duration in decapods (leading to either longer or shorter intermoult periods depending upon species), but the effect on size increase at the next moult is not as well known.  Studies at the Bodega Marine Laboratory, California on shore crabs Hemigrapsus oregonensis and Pachygrapsus crassipes show that limb regeneration reduces expected size at subsequent moult and that the effect of limb loss is additive.  The authors induce crabs to autotomise either 2, 4, or 8 limbs by squeezing the merus portion of each limb (see photograph on Left; note that the crab featured is a Cancer magister, just for convenience).

Results show, first, that there is no regeneration if moulting occurs within 15d of autotomy. In regenerating crabs, post-moult body size is smaller, and the effect appears to be additive with greater limb loss (see histograms on Right; no statistical tests are applied to the data).  As to why there is a decrease in post-moult size, the authors offer 2 explanations.  The first, and simpler one, is that with the additional fluid required to expand the new limb buds, there is less available for carapace expansion.  However, in an experiment (using 8-limb “autotomees”) in which the 8 new limb buds are removed before they can expand (and use up fluid), size increase is still the same as in specimens in which the 8 limb buds are allowed to expand.  The second and perhaps more convincing explanation offered by the authors is that energy allocation is programmed early in the preceding pre-moult period and is adjusted commensurate with the degree of expected limb regeneration.  Kuris & Mager 1975 J Exp Zool 193: 353.

NOTE  an 8-limb removal leaves the crab with only the pair of 4th walking legs.  Under lab conditions where the treatment crabs are isolated from other crabs, mortality from these treatments is surprisingly low (<5% in both treatment and control groups).  The authors note that loss of 8 limbs would be unusual in nature.  In their collections of H. oregonensis, totalling 10,000, only a single specimen is found with 6 limbs missing, and none is found with 7-8 limbs missing

NOTE  this suggests that the moult cycle is already programmed and is not changed by loss of limbs.  In this case, there is no reduction in post-moult size

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Lopholithodes

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Research study 1
  graph showing growth of box crabs Lopholithodes foraminatus to the first crab-instar stageResearchers at the University of Victoria, British Columbia are able to rear zoea larvae of the box crab Lopholithodes foraminatus through to Crab 1 instar stage with 72% survival (see graph). Survival is noted to be poor for later stages, although some individuals apparently reach the 5th crab instar at about 28wk post-hatching. Duguid & Page 2009 J Mar Biol Assn UK 89: 1607.
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Paralithodes

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Research study 1
 

A study of growth of red-king crabs Paralithodes camtschaticus in Bristol Bay, Alaska by researchers principally from the University of Washington reveal slower growth than found in other areas of Alaska.  The 8-9yr from settlement to reach reproductive maturity in this population is photograph of red-king crab Paralithodes camtschaticusconsiderably longer than the graph showing growth of red-king crabs in Bristol Bay, Alaska6yr recorded in other stocks, such as at Unalaska and Kodiak (see graph).  The authors suggest that the difference may owe, in part, to slower growth from settlement to 3yr of age in Bristol Bay, and they discuss possible causes.  Loher et al. 2001 Fish Bull 99: 572.

 




Red-king crab Paralithodes camtschaticus 0.6X

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Petrolisthes

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Research study 1
 

photograph of porcellain crab Petrolisthes cinctipesThe moulting cycle of the anomuran Petrolisthes cinctipes is described for specimens collected at Cape Arago, Oregon and kept in the laboratory (13oC).  For the first 72h after moulting, a crab is completely soft, and is inactive and nonfeeding.  It may be another 4-5d before the crabs commence feeding.  Intermoult period in Petrolisthes is about 100-110d, long in comparison with other crabs.  In early premoult the carapace begins to soften and within 5d is thin and easily depressible.  The actual casting off of the exoskeleton may take 6-8h and appears to the author to be energy-demanding.  Duration between 2 successive moults is about 115-130dThe author provides a detailed schedule for the moulting process.  Kurup 1964 Biol Bull 127: 97.

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