Monday, October 29, 2007
Molting
When a blue crab has grown sufficiently to require a larger shell, the following events occur:
Precdysis (pre-molt or “peeler” stage) :
-Molting hormones are released.
-The hypodermis detaches from the existing hard shell. The hypodermis is a layer of cells -directly beneath the shell.
-The hypodermis produces enzymes which begin to dissolve the shell components. Much of the existing shell is recycled causing it to become thin. Inorganic salts are resorbed from the shell and stored internally.
-A new inner soft shell slowly forms underneath the existing shell. When this new shell has fully formed, the crab will be ready to molt.
Ecdysis (molting or “busting” stage):
-The crab stops eating and seeks shelter in order to avoid predation. During this process the crab is highly vulnerable to predators, including the two-legged variety!
-The crab rapidly absorbs water which causes its tissues to swell and split the old shell open across the back between the lateral spines. Fracture planes in the claws split open to allow the claws to be pulled through.
-The crab begins the slow, arduous process of backing out of its old shell, which is then discarded.
-The newly molted crab pumps water into its tissues in order to inflate the shell to its new size.
-The new shell will be roughly one-third larger (33%) than the old shell. The new shell reaches its full size within six hours after molting.
Postecdysis (postmolt or “soft shell” stage):
-The salvaged inorganic salts are rapidly redeposited to help thicken and harden the new shell. -The new shell will only harden in water (the hardening process stops if the crab is removed from the water) and will take approximately two to four days to fully harden.
Over time, as the crab slowly grows inside its new shell, tissue water is replaced with protein. Once there is no more room left to grow inside this shell, the whole molting process starts over again.
Precdysis (pre-molt or “peeler” stage) :
-Molting hormones are released.
-The hypodermis detaches from the existing hard shell. The hypodermis is a layer of cells -directly beneath the shell.
-The hypodermis produces enzymes which begin to dissolve the shell components. Much of the existing shell is recycled causing it to become thin. Inorganic salts are resorbed from the shell and stored internally.
-A new inner soft shell slowly forms underneath the existing shell. When this new shell has fully formed, the crab will be ready to molt.
Ecdysis (molting or “busting” stage):
-The crab stops eating and seeks shelter in order to avoid predation. During this process the crab is highly vulnerable to predators, including the two-legged variety!
-The crab rapidly absorbs water which causes its tissues to swell and split the old shell open across the back between the lateral spines. Fracture planes in the claws split open to allow the claws to be pulled through.
-The crab begins the slow, arduous process of backing out of its old shell, which is then discarded.
-The newly molted crab pumps water into its tissues in order to inflate the shell to its new size.
-The new shell will be roughly one-third larger (33%) than the old shell. The new shell reaches its full size within six hours after molting.
Postecdysis (postmolt or “soft shell” stage):
-The salvaged inorganic salts are rapidly redeposited to help thicken and harden the new shell. -The new shell will only harden in water (the hardening process stops if the crab is removed from the water) and will take approximately two to four days to fully harden.
Over time, as the crab slowly grows inside its new shell, tissue water is replaced with protein. Once there is no more room left to grow inside this shell, the whole molting process starts over again.
swimming rhythms in Blue Crab
-forward,J.(2004). Endogenous swimming rhythms underlying secondary dispersal of early juvenile blue crabs, Callinectes sapidus Endogenous. ScienceDirect.316:91-100.
-Blue crab, Callinectes sapidus Rathbun, megalopae settle in seagrass or other complex submerged aquatic habitats in estuaries, where they metamorphose to the first juvenile (J1) crab stage.
-Within tidal areas, early juveniles (J1–2) leave such nursery areas by undergoing secondary dispersal during nocturnal flood tides.
- This article determined whether J1–2 blue crabs have a biological rhythm in vertical swimming activity that contributes to secondary dispersal. Endogenous rhythms in vertical swimming were determined for:
(1) J1–2 crabs collected from two estuaries with semi-diurnal tides.
(2) J1 crabs that metamorphosed from the megalopal stage in the laboratory the day after collection.
(3) premolt megalopae that metamorphosed to J1 crabs under constant conditions during the experiment.
-In all cases, a circadian rhythm was present in which crabs swam vertically during the time of night in the field.
-The time of peak vertical swimming did not correspond to the time of flood tide at the collection sites, but did consistently occur at night, with a mean around midnight.
-While responses to environmental factors probably control the onset and end of vertical swimming by early juvenile blue crabs during flood tides in tidal areas, a circadian rhythm underlies secondary dispersal at night.
-Blue crab, Callinectes sapidus Rathbun, megalopae settle in seagrass or other complex submerged aquatic habitats in estuaries, where they metamorphose to the first juvenile (J1) crab stage.
-Within tidal areas, early juveniles (J1–2) leave such nursery areas by undergoing secondary dispersal during nocturnal flood tides.
- This article determined whether J1–2 blue crabs have a biological rhythm in vertical swimming activity that contributes to secondary dispersal. Endogenous rhythms in vertical swimming were determined for:
(1) J1–2 crabs collected from two estuaries with semi-diurnal tides.
(2) J1 crabs that metamorphosed from the megalopal stage in the laboratory the day after collection.
(3) premolt megalopae that metamorphosed to J1 crabs under constant conditions during the experiment.
-In all cases, a circadian rhythm was present in which crabs swam vertically during the time of night in the field.
-The time of peak vertical swimming did not correspond to the time of flood tide at the collection sites, but did consistently occur at night, with a mean around midnight.
-While responses to environmental factors probably control the onset and end of vertical swimming by early juvenile blue crabs during flood tides in tidal areas, a circadian rhythm underlies secondary dispersal at night.
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