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.
Journal Article Summary
-Messick,G.(1994). Hematodinium perezi infections in adult and juvenile blue crabs Callinectes sapidus from coastal bays of Maryland and Virginia, USA. Diseases of Aquatic Organisms.19:77-82.
- In Coastal bays of Maryland and Virginia, USA, adults and juvenile blue Crabs (Callinects sapidus) were severely infected with the parasitic dinoflagellate Hematodinium perezi.
The methods:
-monthly samples of live and dead adults, juveniles, and early juveniles were collected using both commercial traps and an otter trawl in coastal bays near ocean city, Maryland, and Franklin city.
- Information on sexes, sizes, number of molting, and the stages were noted.
- The cells of all the crabs were studied and exposed to some chemicals to check under microscopes for the parasite.
- a stable condition (pH, salinity) was used.
Results:
- from August through November, prevalence was higher in small crabs than in large crabs.
- There was no difference between males and females in the prevalence.
- Different morphological forms of the parasite were observed.
- Severely infected crabs had reduced hemocyte numbers.
Discussion:
-this report was the first documentation of hematodinium in early-juvenile blue crabs.
- The end results showed that the prevalence was as high as 100% in one sample of early
juvenile crabs.
- Also, the results suggest that prevalence of the infection is higher in post-molting than in pro-molting crabs.
- Seasonality was due either to environmental factors such as salinity, temperature, or photoperiods, which may control the life cycle of the parasites. Or to the possibility that summer mortality of infected crabs was so high that by fall and winter only uninfected and lightly infected crabs remained to be sampled, thus reducing prevalence.
- In Coastal bays of Maryland and Virginia, USA, adults and juvenile blue Crabs (Callinects sapidus) were severely infected with the parasitic dinoflagellate Hematodinium perezi.
The methods:
-monthly samples of live and dead adults, juveniles, and early juveniles were collected using both commercial traps and an otter trawl in coastal bays near ocean city, Maryland, and Franklin city.
- Information on sexes, sizes, number of molting, and the stages were noted.
- The cells of all the crabs were studied and exposed to some chemicals to check under microscopes for the parasite.
- a stable condition (pH, salinity) was used.
Results:
- from August through November, prevalence was higher in small crabs than in large crabs.
- There was no difference between males and females in the prevalence.
- Different morphological forms of the parasite were observed.
- Severely infected crabs had reduced hemocyte numbers.
Discussion:
-this report was the first documentation of hematodinium in early-juvenile blue crabs.
- The end results showed that the prevalence was as high as 100% in one sample of early
juvenile crabs.
- Also, the results suggest that prevalence of the infection is higher in post-molting than in pro-molting crabs.
- Seasonality was due either to environmental factors such as salinity, temperature, or photoperiods, which may control the life cycle of the parasites. Or to the possibility that summer mortality of infected crabs was so high that by fall and winter only uninfected and lightly infected crabs remained to be sampled, thus reducing prevalence.
Crab Cake Recipe
Crab cakes with green onions and seasonings, from Coweyes Brown.
INGREDIENTS:
2 6-1/2 oz. cans back fin lump crab meat or 3/4 lb. fresh crab (about 2-1/2 cups)
2 tbsp. reduced-fat mayonnaise
1 Tbsp. Worcestershire sauce
Several drops hot pepper sauce
4 green onions, chopped
2 Tbsps. dry mustard
Salt and freshly ground pepper, or to taste
2 egg whites
1 cup cracker crumbs
Olive oil spray
PREPARATION:
Drain crab meat and flake with a fork, picking out any shell or cartilage. Put crabmeat in a bowl. Add the mayonnaise, Worcestershire sauce, hot pepper, green onions, dry mustard, pepper and salt. Blend in the egg whites. Shape into 4 cakes about 4 inches across. Place cracker crumbs on a plate and season with salt and pepper. Roll crab cakes in crumbs, making sure both sides are coated. Heat a nonstick skillet on medium heat. Spray with olive oil spray. Add crab cakes and cook 5 minutes. Turn and cook 5 more minutes.
INGREDIENTS:
2 6-1/2 oz. cans back fin lump crab meat or 3/4 lb. fresh crab (about 2-1/2 cups)
2 tbsp. reduced-fat mayonnaise
1 Tbsp. Worcestershire sauce
Several drops hot pepper sauce
4 green onions, chopped
2 Tbsps. dry mustard
Salt and freshly ground pepper, or to taste
2 egg whites
1 cup cracker crumbs
Olive oil spray
PREPARATION:
Drain crab meat and flake with a fork, picking out any shell or cartilage. Put crabmeat in a bowl. Add the mayonnaise, Worcestershire sauce, hot pepper, green onions, dry mustard, pepper and salt. Blend in the egg whites. Shape into 4 cakes about 4 inches across. Place cracker crumbs on a plate and season with salt and pepper. Roll crab cakes in crumbs, making sure both sides are coated. Heat a nonstick skillet on medium heat. Spray with olive oil spray. Add crab cakes and cook 5 minutes. Turn and cook 5 more minutes.
Other Crab Diseases
Pepper Spot" Disease
Pepper Spot Disease is caused when a crab becomes infected with a parasite, and then that parasite becomes infected by another parasite (called a hyperparasite.) The disease is easily seen as tiny black specks (approximately 0.5mm in diameter) which are visible throughout the crab's tissues.
Initially, the crab becomes infected by the parasitic flatworm (fluke) Microphallus bassodactylus. Next, the encysted fluke becomes infected by the parasitic protozoan Urosporidium crescens. The very small, brownish, protozoan multiplies inside the larval worm and increases in size until the worm is completely consumed and replaced by spores. The large number of dark spores distinguishes each cyst as a visible black speck and results in the condition called "buckshot," "pepper spots," or "pepper" crabs.
Crabs are not affected by the disease but it can affect the aesthetics of t he meat by making it appear unappetizing. However, the cooking process kills the parasites and renders the crabmeat completely safe to eat.
"Pepper spot" is common on the Chesapeake Bay's Eastern Shore (affecting more than 30 percent of crabs from some locations.) It appears be related to water salinity. The disease is spread by any of four species of snails which are found in shallow low-salinity estuaries. The infected snails release the infective free-swimming fluke larva (cercaria) which penetrate the crab. Many crabs are infected with the fluke which can barely be seen without a microscope. It isn't until the fluke itself becomes infected with the protozoan hyperparasite, becoming visible, that people exhibit apprehension (Jeff Shields, VIMS.)
Bitter" Crab Disease
(Dinoflagellate blood disease)
Bitter Crab Disease (BCD) is caused by a blood parasite, Hematodinium perezi, a type of dinoflagellate. (Dinoflagellates are single-celled, microscopic algae.) The parasite consumes oxygen from the crab's blood and tissues which causes it to become weak and lethargic, and to eventually die.
Hematodinium sp. can produce epizootics (an outbreak of disease affecting many animals of one kind at the same time.) Epizootics have been reported in Maryland, Virginia, Georgia, and Florida. The disease is most prevalent in warm, relatively shallow, high salinity waters. The parasite is found in the ocean-side bays of the Delmarva (short for Delaware, Maryland, and Virginia) Peninsula in the spring and fall, and spreads to the lower reaches of Chesapeake Bay in the fall.
In October 1996, the prevalence of BCD along the Virginia portion of the Delmarva Peninsula varied from 20 to 50 percent in legal sized crabs. Lower prevalences (1 to 10 percent) were noted for crabs caught at the mouth of the Bay. In November, the prevalence is generally low during the pre-breeding and ovigerous (sponge crab) seasons.
Once infected, the parasite grows rapidly inside the crab (up to 100 million parasites/ml of blood) over the course of 3 to 6 weeks. The crab's blood changes to a milky-white color and loses it clotting ability.
Signs of Infection
Watermen will find dead or dying crabs in their traps or crabpots. Infected crabs are weak, lethargic, have drooping limbs and mouthparts, and often die during handling. When cooked, the crabmeat has a chalky texture and a bitter aspirin-like flavor (the disease has no known impact on people who eat infected crabs.)
Early stages of the disease can only be detected under a microscope. Late stages of the disease can cause the crab's shell to turn pink as if partially cooked (see photo above.)
"Cotton" or "Cooked" Crab Disease
The microsporidium Ameson michaelis, a parasite that invades and destroys cells, causes severe muscle disintegration that results in a condition known as "cotton" crab or "cooked" crab disease. Infected tissue appears opaque (white) while the crab is still alive. Cooked meat is cottony in texture and poorly flavored. The parasite can be transmitted via cannibalism; and since as much as 25 percent of a blue crab's diet is other blue crabs, it is surprising that the parasite is only found at low prevalences (less than one percent, Shields, pers. obs.)
"Shell Disease," "Burn Spot," or "Brown Spot" Disease
(Chitinoclastic Disease)
Chitinoclastic disease is caused by chitinivorous bacteria which causes unattractive lesions (or spots) on the shell. The lesions are ugly which can make the infected crabs unmarketable. The disease has no known impact on people who eat infected crabs.
Pepper Spot Disease is caused when a crab becomes infected with a parasite, and then that parasite becomes infected by another parasite (called a hyperparasite.) The disease is easily seen as tiny black specks (approximately 0.5mm in diameter) which are visible throughout the crab's tissues.
Initially, the crab becomes infected by the parasitic flatworm (fluke) Microphallus bassodactylus. Next, the encysted fluke becomes infected by the parasitic protozoan Urosporidium crescens. The very small, brownish, protozoan multiplies inside the larval worm and increases in size until the worm is completely consumed and replaced by spores. The large number of dark spores distinguishes each cyst as a visible black speck and results in the condition called "buckshot," "pepper spots," or "pepper" crabs.
Crabs are not affected by the disease but it can affect the aesthetics of t he meat by making it appear unappetizing. However, the cooking process kills the parasites and renders the crabmeat completely safe to eat.
"Pepper spot" is common on the Chesapeake Bay's Eastern Shore (affecting more than 30 percent of crabs from some locations.) It appears be related to water salinity. The disease is spread by any of four species of snails which are found in shallow low-salinity estuaries. The infected snails release the infective free-swimming fluke larva (cercaria) which penetrate the crab. Many crabs are infected with the fluke which can barely be seen without a microscope. It isn't until the fluke itself becomes infected with the protozoan hyperparasite, becoming visible, that people exhibit apprehension (Jeff Shields, VIMS.)
Bitter" Crab Disease
(Dinoflagellate blood disease)
Bitter Crab Disease (BCD) is caused by a blood parasite, Hematodinium perezi, a type of dinoflagellate. (Dinoflagellates are single-celled, microscopic algae.) The parasite consumes oxygen from the crab's blood and tissues which causes it to become weak and lethargic, and to eventually die.
Hematodinium sp. can produce epizootics (an outbreak of disease affecting many animals of one kind at the same time.) Epizootics have been reported in Maryland, Virginia, Georgia, and Florida. The disease is most prevalent in warm, relatively shallow, high salinity waters. The parasite is found in the ocean-side bays of the Delmarva (short for Delaware, Maryland, and Virginia) Peninsula in the spring and fall, and spreads to the lower reaches of Chesapeake Bay in the fall.
In October 1996, the prevalence of BCD along the Virginia portion of the Delmarva Peninsula varied from 20 to 50 percent in legal sized crabs. Lower prevalences (1 to 10 percent) were noted for crabs caught at the mouth of the Bay. In November, the prevalence is generally low during the pre-breeding and ovigerous (sponge crab) seasons.
Once infected, the parasite grows rapidly inside the crab (up to 100 million parasites/ml of blood) over the course of 3 to 6 weeks. The crab's blood changes to a milky-white color and loses it clotting ability.
Signs of Infection
Watermen will find dead or dying crabs in their traps or crabpots. Infected crabs are weak, lethargic, have drooping limbs and mouthparts, and often die during handling. When cooked, the crabmeat has a chalky texture and a bitter aspirin-like flavor (the disease has no known impact on people who eat infected crabs.)
Early stages of the disease can only be detected under a microscope. Late stages of the disease can cause the crab's shell to turn pink as if partially cooked (see photo above.)
"Cotton" or "Cooked" Crab Disease
The microsporidium Ameson michaelis, a parasite that invades and destroys cells, causes severe muscle disintegration that results in a condition known as "cotton" crab or "cooked" crab disease. Infected tissue appears opaque (white) while the crab is still alive. Cooked meat is cottony in texture and poorly flavored. The parasite can be transmitted via cannibalism; and since as much as 25 percent of a blue crab's diet is other blue crabs, it is surprising that the parasite is only found at low prevalences (less than one percent, Shields, pers. obs.)
"Shell Disease," "Burn Spot," or "Brown Spot" Disease
(Chitinoclastic Disease)
Chitinoclastic disease is caused by chitinivorous bacteria which causes unattractive lesions (or spots) on the shell. The lesions are ugly which can make the infected crabs unmarketable. The disease has no known impact on people who eat infected crabs.
Sunday, October 28, 2007
news paper article about fossile records of blue crabs
Corolla Crab is an Oldster
By Daryl L. Law, Hart Matthews/Sentinel Staff
Copyright ©1996 Outer Banks Sentinel
------------------------------------------------------------------------------
--
Not too long ago, Jerry Alexander was kicking around the beach in Corolla when he stumbled across something from a long, long time ago. He found a fossil that scientists believe could be 1.5 million years old.
The Kill Devil Hills-based artist was looking for fulgurite, a tubular rock made when lightning strikes sand and fuses it into a "lightning rock," as he calls it.
But what Alexander came across had a fairly recognizable shape, one most seafood lovers would know as a blue crab.
"It's a Jimmy, and it's well done," Alexander jokes as he shows off his prized find.
The specimen is nearly complete, something that makes it rare. It weighs just less than 7 ounces and measures 5 inches from tip to tip, making it "a keeper," Alexander mused.
The crab is basically black, hard as a rock, and between its claws and body is calcite cement that is commonly found with fossils. Most of the legs and all of the body or carapace is intact.
"When I found it, I didn't notice it as a crab," Alexander said. "Then I brushed it off and said 'Voilà! What do I have here?'"
Alexander said he thought it might be a crab caught up in fulgurite, but three days after the find, he took it to a fossil seminar held at the N.C. Aquarium on Roanoke Island.
When visiting lecturer JoAnne Powell saw the crab, she knew it was an extremely old fossilized specimen. Alexander says everyone's eyes opened wide.
"I went over to the aquarium and stopped the show," he said. "Right away [he snaps his fingers] she said it could be 3 million years old. That's when man started walking upright if you believe in that evolution stuff.
Powell, the curator of education at the N.C. Maritime Museum in Beaufort, collects fossils as a hobby. In geologic time, her initial estimate was relatively close, give or take a million and a half years.
"'Fossiling' is my fun thing to do," she said. "I'm a biologist, not a paleontologist." Powell said the specimen did excite her because it is so rare; not many are found in the Carolinas.
She made a photo copy of the crab and sent it to Florida biologist Roger Portell, who is a fossil crab specialist.
Based on the photo copy, he estimated that the crab was from the Pleistocene epoch, which ranged from 10,000 to 1.6 million years ago.
It fell a little short of the earlier estimate of 3 million years, but Portell needs to get a look at the claws to diagnose the age properly, he said.
As the senior biological scientist for the Florida Museum of Natural History at the University of Florida in Gainsville, Portell has seen a lot of fossils.
He has studied a large number of crab specimens, which are fairly common in Florida's fossil record, many of them big stone crabs. He said he's studied parts of fossil crabs that are 40 million to 45 million years old.
He's eager to see the Corolla crab because its intact.
"It's unusual to find a complete specimen," Portell said. "Most of them are in bits and pieces. If it is a Pleistocene crab, they virtually haven't changed."
He also explained that this crab was probably rapidly buried in mud or sand, which encased it and allowed it to be preserved while the fossilization process slowly took over.
Since it was covered quickly, scavengers didn't have a chance to pick it apart, Portell added. The crab was more than likely buried beneath the ocean floor. But, it could have simply been buried on the beach too.
Portell theorized that the fossil came into shore after storm-charged underwater erosion uncovered it. Just from looking at the photo copy, he said he could tell the fossil had been rolling around on the bottom for a while because it was a little beat up.
No matter how old it is, Portell would like Alexander to donate it to the Florida or any other museum so it can be studied and put on display for everyone to enjoy.
The scientist explained that a lot of unique specimens are out there, but unfortunately they don't always make it into scientific institutions and often end up catching dust on someone's mantle.
"Even if it's only 10,000 years old, it's still a fossil and really neat—it's an excellent find," he said.
By Daryl L. Law, Hart Matthews/Sentinel Staff
Copyright ©1996 Outer Banks Sentinel
------------------------------------------------------------------------------
--Not too long ago, Jerry Alexander was kicking around the beach in Corolla when he stumbled across something from a long, long time ago. He found a fossil that scientists believe could be 1.5 million years old.
The Kill Devil Hills-based artist was looking for fulgurite, a tubular rock made when lightning strikes sand and fuses it into a "lightning rock," as he calls it.
But what Alexander came across had a fairly recognizable shape, one most seafood lovers would know as a blue crab.
"It's a Jimmy, and it's well done," Alexander jokes as he shows off his prized find.
The specimen is nearly complete, something that makes it rare. It weighs just less than 7 ounces and measures 5 inches from tip to tip, making it "a keeper," Alexander mused.
The crab is basically black, hard as a rock, and between its claws and body is calcite cement that is commonly found with fossils. Most of the legs and all of the body or carapace is intact.
"When I found it, I didn't notice it as a crab," Alexander said. "Then I brushed it off and said 'Voilà! What do I have here?'"
Alexander said he thought it might be a crab caught up in fulgurite, but three days after the find, he took it to a fossil seminar held at the N.C. Aquarium on Roanoke Island.
When visiting lecturer JoAnne Powell saw the crab, she knew it was an extremely old fossilized specimen. Alexander says everyone's eyes opened wide.
"I went over to the aquarium and stopped the show," he said. "Right away [he snaps his fingers] she said it could be 3 million years old. That's when man started walking upright if you believe in that evolution stuff.
Powell, the curator of education at the N.C. Maritime Museum in Beaufort, collects fossils as a hobby. In geologic time, her initial estimate was relatively close, give or take a million and a half years.
"'Fossiling' is my fun thing to do," she said. "I'm a biologist, not a paleontologist." Powell said the specimen did excite her because it is so rare; not many are found in the Carolinas.
She made a photo copy of the crab and sent it to Florida biologist Roger Portell, who is a fossil crab specialist.
Based on the photo copy, he estimated that the crab was from the Pleistocene epoch, which ranged from 10,000 to 1.6 million years ago.
It fell a little short of the earlier estimate of 3 million years, but Portell needs to get a look at the claws to diagnose the age properly, he said.
As the senior biological scientist for the Florida Museum of Natural History at the University of Florida in Gainsville, Portell has seen a lot of fossils.
He has studied a large number of crab specimens, which are fairly common in Florida's fossil record, many of them big stone crabs. He said he's studied parts of fossil crabs that are 40 million to 45 million years old.
He's eager to see the Corolla crab because its intact.
"It's unusual to find a complete specimen," Portell said. "Most of them are in bits and pieces. If it is a Pleistocene crab, they virtually haven't changed."
He also explained that this crab was probably rapidly buried in mud or sand, which encased it and allowed it to be preserved while the fossilization process slowly took over.
Since it was covered quickly, scavengers didn't have a chance to pick it apart, Portell added. The crab was more than likely buried beneath the ocean floor. But, it could have simply been buried on the beach too.
Portell theorized that the fossil came into shore after storm-charged underwater erosion uncovered it. Just from looking at the photo copy, he said he could tell the fossil had been rolling around on the bottom for a while because it was a little beat up.
No matter how old it is, Portell would like Alexander to donate it to the Florida or any other museum so it can be studied and put on display for everyone to enjoy.
The scientist explained that a lot of unique specimens are out there, but unfortunately they don't always make it into scientific institutions and often end up catching dust on someone's mantle.
"Even if it's only 10,000 years old, it's still a fossil and really neat—it's an excellent find," he said.
ANNOTATION OF PAPER
Decline of Blue Crab:
-lee.R.,Frischer.M. 2002. the Decline of the blue crab. American Scientist. Volume 92: 548-552.
Decline of Blue Crab:
Problem:
-The east coast of America has suffered a significant decline in population of blue crab.
- the east coast of Georgia the average of 3.9 million kilograms in 1957 jumped down to about 816,000 kilos in 2002 which effected the economy of the seafood market and many fishermen went bankrupt.
Hypothesis:
researchers believe that there are two main reasons for this phenomenon:
- weather changes and salinity of water.
- the occurrence of a deadly disease, called hematodinium
- those two are closly related.
Hematodinium perezi:
- Is a lethal pathogen that reproduces in the crabs' blood, the hemolymph.
-As it grows inside the crab, the parasite consumes the hemolymph cells and the primary hemolymph protein hemocyanin.
-This protein transport oxygen in crustaceans in the same way the hemoglobin performs this task in vertebrates.
-Crabs with hematodinium suffer exhaustion and sooner or later they die from suffocation -Hematodinium have decreased the population of the blue crab throughout the globule as well as France,Newfoundland, Scotland, and Alaska.
Transmission of the disease:
1)Dinospore:
- Dinospore have an important role in spreading Hematodinium.
-The dinospore leaves the crab via the gills to the surroundings (water) and remains infectious in resting stage.
- The evidence shows that the Hematodinium can be released to the water from infected crabs and passed on to the healthy crabs.
2)Cannibalism:
-the blue crabs are notoriously cannibalism, and as soon as one is weakened by disease it quickly falls pray to its neighbors.
- the laboratory studies shows that healthy crabs get infected if they are fed tissue from sick crabs.
Weather and water salinity:
- the research illustrate that the crabs caught during the winter are free of infections.
- the intensity of the disease increase in late spring through early summer.
- After that the crabs disappears in the summer, the crab and the disease tend to appear again in the fall.
- the hematodinium disease out break more likely when the flow of fresh water to estuarine system is reduced and the salinity is high (greater then 28 parts per thousand).
-lower salinity in estuaries seems to be associated with increased blue crab population. This suggests that the availability of fresh water was beneficial to the health of the crab population.
-The hematodinium was absent in blue crabs when the salinity was less than 11 per thousand and when the average temperature of water was below 10 degree.
-Hematodinium preferentially kills female blue crabs more then males since the female crabs must traverse high-salinity estuarine areas to reach offshore spawning ground. They are more likely to contract the disease than males.
Diagnosis:
- Diagnosing the disease depends on a detecting the parasite in the blood sample.
- When the pathogen is present in high concentration (more then 1 parasite per 300 normal blood cells) we can detect the hematodinium by using a special stain under the microscope.
- However it's hard to use this method when the concentration is low or when it is out side the crab host.
- The researchers figured out a new method which is called gene based diagnostic test.
-This method can detect the parasite in low concentrations (1/300) and used to identify the organism outside the crab.
-This diagnosing technique helped the researchers study the life cycle and distribution of hematodinium.
- there is no way to control the disease till this day.
-lee.R.,Frischer.M. 2002. the Decline of the blue crab. American Scientist. Volume 92: 548-552.
Decline of Blue Crab:
Problem:
-The east coast of America has suffered a significant decline in population of blue crab.
- the east coast of Georgia the average of 3.9 million kilograms in 1957 jumped down to about 816,000 kilos in 2002 which effected the economy of the seafood market and many fishermen went bankrupt.
Hypothesis:
researchers believe that there are two main reasons for this phenomenon:
- weather changes and salinity of water.
- the occurrence of a deadly disease, called hematodinium
- those two are closly related.
Hematodinium perezi:
- Is a lethal pathogen that reproduces in the crabs' blood, the hemolymph.
-As it grows inside the crab, the parasite consumes the hemolymph cells and the primary hemolymph protein hemocyanin.
-This protein transport oxygen in crustaceans in the same way the hemoglobin performs this task in vertebrates.
-Crabs with hematodinium suffer exhaustion and sooner or later they die from suffocation -Hematodinium have decreased the population of the blue crab throughout the globule as well as France,Newfoundland, Scotland, and Alaska.
Transmission of the disease:
1)Dinospore:
- Dinospore have an important role in spreading Hematodinium.
-The dinospore leaves the crab via the gills to the surroundings (water) and remains infectious in resting stage.
- The evidence shows that the Hematodinium can be released to the water from infected crabs and passed on to the healthy crabs.
2)Cannibalism:
-the blue crabs are notoriously cannibalism, and as soon as one is weakened by disease it quickly falls pray to its neighbors.
- the laboratory studies shows that healthy crabs get infected if they are fed tissue from sick crabs.
Weather and water salinity:
- the research illustrate that the crabs caught during the winter are free of infections.
- the intensity of the disease increase in late spring through early summer.
- After that the crabs disappears in the summer, the crab and the disease tend to appear again in the fall.
- the hematodinium disease out break more likely when the flow of fresh water to estuarine system is reduced and the salinity is high (greater then 28 parts per thousand).
-lower salinity in estuaries seems to be associated with increased blue crab population. This suggests that the availability of fresh water was beneficial to the health of the crab population.
-The hematodinium was absent in blue crabs when the salinity was less than 11 per thousand and when the average temperature of water was below 10 degree.
-Hematodinium preferentially kills female blue crabs more then males since the female crabs must traverse high-salinity estuarine areas to reach offshore spawning ground. They are more likely to contract the disease than males.
Diagnosis:
- Diagnosing the disease depends on a detecting the parasite in the blood sample.
- When the pathogen is present in high concentration (more then 1 parasite per 300 normal blood cells) we can detect the hematodinium by using a special stain under the microscope.
- However it's hard to use this method when the concentration is low or when it is out side the crab host.
- The researchers figured out a new method which is called gene based diagnostic test.
-This method can detect the parasite in low concentrations (1/300) and used to identify the organism outside the crab.
-This diagnosing technique helped the researchers study the life cycle and distribution of hematodinium.
- there is no way to control the disease till this day.
Distribution and Ecology (and fishing gear):
Distribution and Ecology:Habitat:
- Blue crabs are bottom-dwellers in every type of habitat.
- from the saltiest water of the gulf to the almost fresh water of the back bays and estuaries.
- from the low tide line to water 120 feet deep.
Distribution:
- the range of the blue crab is from Nova Scotia, down the east coast of North America, throughout the Gulf Of Mexico and the Caribbean Sea, and down down the east coast of South America to Northern Argentina.
- the blue crab has been introduced, probably via ship ballasts into Europe, north Africa, and southwest Aisa.
Environment:
Water temperature:
- from 10°C -15°C.
- water temperature above 33°C is lethal.
Water Salinity:
- salinity is important, but requirements very by life stage.
-generally optimum is 3-15 parts per thousand (ppt).
Water pH:
-tolerance range is pH 6-8.
-less than 6 is lethal.
Fishing Gears:
The most common type of commercial fishing gear is the crab pot which is a cubical wire trap with two or four entrance funnels. The pot has two chambers, a lower chamber which has the entrance funnels and the bait well and an upper chamber that is separated from the lower chamber by a wire partition that has two holes.
The blue crab's natural reaction to confinement is to swim upward. In doing so, they move into the upper chamber, thereby reducing their chances for escape. The crab pot was first introduced in Chesapeake Bay in about 1936, but was not widely used in South Carolina until the late 1950's. Crabs are also caught and sold as part of the bycatch of shrimp trawlers and after the shrimp trawling season is closed, usually in January, trawling for crabs with large mesh trawls is permitted until March 31.
Recreational blue crab fishermen employ several fishing gears and methods. South Carolina law allows individuals to fish two crab pots without a license if they are properly marked with floats bearing the owner's name. Fishing more than two pots requires a commercial crabbing license. Whether fishing from a dock or boat, recreational crab pots should have a marked float and enough line to prevent the float from being submerged at high tide. Recreational crabbers should also be careful not to leave a pot in an area that would expose the pot and crabs at low tide. Pots should be checked daily and catches can often be doubled if the pots are checked twice per day. To remove crabs, pull the wire apart and shake the crabs into a tub or bucket. Some stubborn crabs may have to be dislodged with a stick. Remember that crabs can pinch, so be very careful about putting your hand in a pot.
Drop net Crab Pot (trap) Dip net
Drop nets and collapsible traps, usually baited with herring, can be fished from docks and bridges. Another effective recreational method called "dipping" requires a long-handled dip net, several yards of string and bait. The bait, usually a chicken neck or fish head, is tied to the string and thrown into the water away from the bank. Once a tug is felt, the crabber pulls the bait and crab close enough to be quickly dipped from the water and placed into a waiting bucket. The beginner should be cautious when handling a blue crab since the pinch of the powerful claws can be extremely painful. (The inexperienced crabber should probably wear thick gloves). Always approach from the rear when picking up a crab. An experienced crabber can quickly grab the base of one of its swimming legs while holding the claws down with some object. Should a crab get a hold on a finger, it is usually best not to pull it off. First, try letting it hang; many times the crab will release and drop. If the crab will not release, use the free hand to immobilize the other claw and slowly bend the offending claw backward until the crab releases it.
Crabs can be caught during all twelve months, but become inactive in winter when water temperature falls below 50-55 degrees F. As temperatures rise in March and April, catch rates increase rapidly. The best time of year to harvest large, heavy crabs is usually from October to December. Mature females are typically near the ocean, but large males are most common in the rivers and creeks.
Sexes
Sexes:
-Brachyura - an order of crustaceans having a reduced abdomen, or "apron. Sexes can be identified by the apron:
-In the male it is shaped like an inverted T, and the claws are blue.
The male abdomen "T" shaped and the blue claws
-In the female it is broader, and the claws are red.
immature & mature abdomen and the Red Claws
Mating:
- Female blue crabs mate only once in their lives
- when they become sexually mature immediately following their pubertal molt (immediately following this molt, the female is known as a "sook.")
- When approaching this pubertal molt, females release a pheromone in their urine which attracts males
- Male crabs compete for females and will carry and protect them, "cradle carrying,“
-when the female's shell is soften, the pair will mate.
- During mating, the female captures and stores the male's sperm in sac-like receptacles so that she can fertilize her eggs at a later time.
-Once the female's shell has hardened, the male will release her and she will migrate to higher salinity waters to spawn.
Spawning :
- After mating, females migrate to high-salinity waters in lower estuaries, sounds, and near-shore spawning areas.
-They over-winter before spawning by burrowing in the mud.
- Most females spawn for the first time two to nine months after mating, usually from May through August the following season.
- The female extrudes fertilized eggs into a cohesive mass, or "sponge," that remains attached to her abdomen until the larvae emerge.
-The average sponge contains about two million eggs and is formed in about two hours.
Life cycle:
Growth and development of the blue crab, as in other crustaceans, consist of a series of larval, juvenile, and adult stages during which a variety of morphological, behavioral, and physiological changes occur.
-Brachyura - an order of crustaceans having a reduced abdomen, or "apron. Sexes can be identified by the apron:
-In the male it is shaped like an inverted T, and the claws are blue.
The male abdomen "T" shaped and the blue claws
-In the female it is broader, and the claws are red.
immature & mature abdomen and the Red Claws
Mating:
- Female blue crabs mate only once in their lives
- when they become sexually mature immediately following their pubertal molt (immediately following this molt, the female is known as a "sook.")
- When approaching this pubertal molt, females release a pheromone in their urine which attracts males
- Male crabs compete for females and will carry and protect them, "cradle carrying,“
-when the female's shell is soften, the pair will mate.
- During mating, the female captures and stores the male's sperm in sac-like receptacles so that she can fertilize her eggs at a later time.
-Once the female's shell has hardened, the male will release her and she will migrate to higher salinity waters to spawn.
Spawning :
- After mating, females migrate to high-salinity waters in lower estuaries, sounds, and near-shore spawning areas.
-They over-winter before spawning by burrowing in the mud.
- Most females spawn for the first time two to nine months after mating, usually from May through August the following season.
- The female extrudes fertilized eggs into a cohesive mass, or "sponge," that remains attached to her abdomen until the larvae emerge.
-The average sponge contains about two million eggs and is formed in about two hours.
Life cycle:
Growth and development of the blue crab, as in other crustaceans, consist of a series of larval, juvenile, and adult stages during which a variety of morphological, behavioral, and physiological changes occur.
Description
Description:
Crabs are crustaceans with five pairs of legs:
- the first pair is modified as pinchers.
- the last four pairs are walking legs.
- the last pair is for summing to.
Size:
The shell is about 7” wide and 4” long.
It weight 1-2 pounds when fully grown.
Color:
-The back is dark or brownish green
-The abdomen, and lower legs are white.
-The claws are various shades of blue, but the claws tips of the female are red.
Crabs are crustaceans with five pairs of legs:
- the first pair is modified as pinchers.
- the last four pairs are walking legs.
- the last pair is for summing to.
Size:
The shell is about 7” wide and 4” long.
It weight 1-2 pounds when fully grown.
Color:
-The back is dark or brownish green
-The abdomen, and lower legs are white.
-The claws are various shades of blue, but the claws tips of the female are red.
the classification: blue crab:
Ruppert.E.,Fox.R.,Barnes.R. invertabrate Zoology: A functional Evolutionary Approach. seventh edition.
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Crustacea
Class:
Malacostraca
Order:
Decapoda
Suborder:
Pleocyemata
Infraorder:
Brachyura
Family:
Portunidae
Genus:
Callinectes
Species:
Callinectes sapidus
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Crustacea
Class:
Malacostraca
Order:
Decapoda
Suborder:
Pleocyemata
Infraorder:
Brachyura
Family:
Portunidae
Genus:
Callinectes
Species:
Callinectes sapidus
interesting sites for blue crab
http://www.dnr.state.md.us/fisheries/education/crab/bluecrabfacts.html
http://en.wikipedia.org/wiki/Blue_crab
http://www.chesapeakebay.net/blue_crab.htm
http://skipjack.net/le_shore/crab/
http://www.dnr.state.sc.us/marine/pub/seascience/bluecrab.html
http://www.sciencenetlinks.org/lessons.cfm?BenchmarkID=5&DocID=83
http://www.blue-crab.net/
http://www.serc.si.edu/labs/fish_invert_ecology/bluecrab/overview.jsp
http://en.wikipedia.org/wiki/Blue_crab
http://www.chesapeakebay.net/blue_crab.htm
http://skipjack.net/le_shore/crab/
http://www.dnr.state.sc.us/marine/pub/seascience/bluecrab.html
http://www.sciencenetlinks.org/lessons.cfm?BenchmarkID=5&DocID=83
http://www.blue-crab.net/
http://www.serc.si.edu/labs/fish_invert_ecology/bluecrab/overview.jsp
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