Mantis Shrimp Amazing Beautiful

Stomatopod crustaceans (mantis shrimps) possess an incredibly complex visual system, comprised of compound eyes that contain more types of photoreceptors than in any other known animal. The mantis shrimp eye’s optical arsenal includes monocular range finding capability, 12-channel colour vision, 2 channel linear polarization detection, and, in some species, the ability to detect and analyze circularly polarized light. Underlying this unparalleled array of functional capabilities is a structural diversification of a basic photoreceptive unit common to all compound eyes the ommatidium. In the following, the mantis shrimps visual prowess is described in the context of the design variations and the distribution of its ommatidia.

Mantis Shrimps shows the eye of the scaly-tailed mantis, Lysiosquilla scabricauda. It consists of upper and lower (dorsal and ventral) hemispheres separated by a narrow central band. A close examination of the eye’s surface reveals that each region consists of closely-spaced parallel rows of facets tiny ones in the hemispheres and much larger ones in the band. The hemispheres have many rows of facets but the band has only six. Looking beneath the surface reveals that each facet is the tip of an elongate structural unit, known as an ommatidium. All ommatidia are optically sensitive devices, but those in the band are the most complex, most functional, and most interesting.

The various ommatidia share certain general structural features. In particular, each ommatidium
consists of the following three sections, from top to bottom: (i) the cornea (ii) the crystalline cone (a hexagonal converging lens), and (iii) the rhabdom (rod). The rhabdom is a transparent light sensor/guide consisting of 8 photoreceptor cells a short cell (R8) sitting atop 7 long cells (R1, R2, …, R7) that are fused along a central axis. Each cell has numerous interdigitating, coplanar, finger-like constructs (microvilli) containing light-sensitive molecules. At the bottom of each rhabdom there is a conduit (axon) that conveys electrical signals to neurons. Within the framework of these general similarities, the various ommatidia have internal structural differences that give them quite different light-sensing functionalities. These will now be described.

Each ommatidium in the hemispheres is long and thin, with a rhabdom consisting of a short R8 cell on top of a ring of R1-R7 cells. There are two sets of microvilli distributed over the 8 cells. One set consists of parallel planes of coplanar microvilli, while the other set is similarly distributed in planes that are perpendicular to those of the first set. The R8 cell has both sets, but the other R1-R7 cells have one set each. This may have significance, as discussed below.

When non-polarized sunlight enters the earth’s atmosphere it interacts with atmospheric molecules and is scattered (preferentially in the blue end of the spectrum) in all directions. When viewed at an angle of 90o to the incident beam, the scattered light appears linearly polarized, meaning that the electric vector of the light wave is along a line that is perpendicular to both the incident beam and the line of sight. The sky is therefore full of linearly polarized light. Many animal species (e.g. bees, locusts) have developed an ability to use this ambient polarization to navigate even when the sun is obscured.

 The parallel planes of coplanar microvilli is suggestive of sensitivity to linear polarization. The aligned light-sensitive molecules of the microvilli will sense linear polarization by oscillating only in response to electric vectors vibrating parallel to the molecule’s vibration axis. Perpendicular planes of microvilli should therefore detect light with perpendicular planes of polarization. In the R8 cell the presence of the two sets of perpendicular planes likely has a “null” effect a linearly polarized wave enters the cell, splits into two perpendicular components oscillating parallel to each plane, and the two components recombine on exit to regenerate the original linearly polarized ray. As if nothing had happened.

The two sets of planes thereby destroy linear polarization sensitivity (LPS). However, it is not clear what happens next in the R1-R7 cells. Since each of these cells has only one set of parallel microvillar planes, it all depends on what the the receiver of the seven independent signals does with them. It could either merge them to destroy LPS or use them to advantage. Which of these actually happens is still not known.

The long axes of the ommatidia in the first few rows adjacent to the midband are skewed slightly
inwards relative to the optical axes of the ommatidia in the midband, which are perpendicular to the cornea. The ommatidia in the more distant rows have axes nearly parallel to the midband axes. It has been suggested that the intersections of these skewed optical axes from opposite sides of the midband, and hence intersections of the visual fields of these ommatidia, give rise to a monocular range-finding and speed-measuring capability. Experiments have shown that stomatopods have both monocular and binocular range-finding capability, the former being short-range and the latter longrange. Most of the ommatidia in the hemispheres, however, are parallel to each other as well as to the ommatidia in the midband, and therefore sample nearly the same narrow visual fields. No wonder mantis shrimps are constantly moving their eyes they have “tunnel vision”.

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Horseshoe Crab (Limulus polyphemus)

Despite their name, horseshoe crabs are not true crabs. The horseshoe crab, Limulus polyphemus in popular name called Horseshoe Crab, is the only member of the Arthropoda subclass Xiphosura found in the Atlantic. Unlike true crabs, which have two pairs of antennae, a pair of jaws and five pairs of legs, horseshoe crabs lack antennae and jaws and they have seven pairs of legs, including a pair of chelicerae. Chelicerae are appendages similar to those used by spiders and scorpions for grasping and crushing. In addition, horseshoe crabs have book lungs, similar to spiders and different from crabs, which have gills. Thus, horseshoe crabs are more closely related to spiders and scorpions than they are to other crabs. Their carapace is divided into three sections: the anterior portion is the prosoma; the middle section is the opithosoma; and the “tail” is called the telson. Horseshoe crabs have two pairs of eyes located on the prosoma: one anterior set of simple eyes and one set of lateral compound eyes similar to those of insects. In addition, they possess a series of photoreceptors on the opithosoma and telson.

Horseshoe crabs are long-lived animals; after attaining sexual maturity at 9 to 12 years of age, they may live for another 10 years or more. Like other arthropods, horseshoe crabs must molt in order to grow. As the crab ages, more and more time passes between molts, with 16 to 19 molts occurring before a crab becomes mature, stops growing and switches energy expenditure to reproduction. Adult horseshoe crabs feed on a variety of bottom-dwelling organisms including marine worms, shellfish and decaying animal matter. The larvae and juvenile stages are preyed upon by many species of fish and birds and adult horseshoe crabs are known to be a food item for the threatened loggerhead sea turtle, Caretta caretta.

Horseshoe crabs are also harvested for use in biomedicine. A clotting agent in the crab’s blood,
known as Limulus Amoebocyte Lysate (LAL), is used to detect microbial pathogens in medical
intravenous fluids, injectable drugs and supplies (Rudloe, 1983). Biomedical companies purchase large crabs, which are harvested by trawlers or by hand from spawning beaches. The crabs are transported to the LAL production facility, bled, then transported back to the general harvest vicinity and released alive. LAL is currently used worldwide as the standard (FDA required) test for microbial contamination in injectable pharmaceutical products (Walls and Berkson 2000). Horseshoe crabs have also been used in eye research and the development of wound dressings and surgical sutures. In addition, horseshoe crabs are currently the primary bait used in the whelk and eel fisheries along the Atlantic coast.

This species is not currently listed as threatened or endangered; however, horseshoe crabs are an important species, both commercially and ecologically. Ecologically, horseshoe crabs are an
important component of coastal food webs. In particular, horseshoe crab eggs are the primary
source of fat for at least 20 species of migratory shore birds (Harrington 2001). Larval and juvenile crabs are also food for many species of fish and invertebrates, while adult crabs are
favored by loggerhead sea turtles and sharks (Keinath et al 1987). In addition, horseshoe crabs
have been shown to be a controlling factor in benthic species composition through their feeding
activities. There is great concern about the harvest of horseshoe crabs in the mid Atlantic and how it affects the red knot, Calidris canutus, another imperiled species.

Horseshoe crabs are relatively common in trawls in South Carolina. Based on research trawl
collections, we are able to get some ideas of relative abundance. However, there is no estimate
of population size at this time. The range of the horseshoe crab extends from northern Maine to the Yucatan Peninsula. They are particularly abundant in Delaware Bay, the center of their distribution, and in coastal areas between Virginia and New Jersey. Different populations of horseshoe crabs are thought to inhabit every major estuary along the Atlantic coast. Each population can be differentiated from the others based on size of adult crabs, the color of their carapace and pigments present in their eyes. In South Carolina, horseshoe crabs can be found in shallow estuarine areas and offshore habitats near the continental shelf.

Adult horseshoe crabs are benthic animals. Early each spring, as estuarine water temperature
approaches 20°C (68°F), adult horseshoe crabs move inshore to seek suitable spawning habitat
along intertidal beaches of the sea-islands. The characteristics associated with preferential
spawning locations are the presence of large intertidal sand flats near the spawning beach, a
depth to reducing layer greater than 30 cm (12 inches) from the surface and accretional, rather
than erosional, sediments.

Throughout the spring, females with males attached to their carapace follow flooding tides high
onto the beach, where they excavate nests and deposit thousands of eggs. During mating, the male grasps the female’s carapace and fertilizes her eggs as she deposits them in the nest cavity.
Oftentimes, other unattached “satellite” males may also fertilize some of the eggs. Mating and
nesting coincide with high tides. Nests are excavated by the female on the intertidal zone of
sandy beaches and eggs are laid in clusters. Spawning activity is especially heavy during
nighttime spring tides. Females nest several times per season, usually returning to deposit more
eggs on subsequent high tides.

After approximately two weeks, depending on temperature, moisture and oxygen levels, larval horseshoe crabs emerge from the nest. Larval horseshoe crabs are semi planktonic for about three weeks before their transition to a benthic existence. They then settle to the bottom and assume a benthic existence, typically spending their first two years in intertidal sand flat habitats near beaches where they were spawned. Adults return to deeper estuary bays and continental shelf waters after the breeding season.

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Green Crab In Habitat

The Green Crab is a small shore crab. Adults measure about 3 inches across. The color of the dorsal (top side) of the shell is a mottled, dark brown to dark green with small yellow patches. Its ventral surface (underside) can display colors of green, yellow, red, and orange. Some studies have indicated that the color of the shell may be due to the amount of time the crab spends between molting stages. A distinguishing feature that can set green crabs apart from native crabs is the array of five evenly spaced triangular spines on either side of the eyes, on the front end of the shell. The three rounded lobes between its eyes may also be used to help identify the Green Crab.

Nutrition Requirements 

The Green Crab is an omnivore, meaning that it can consume many different species of plants
and animals. Its prey includes mussels, clams, snails, polychaetes, crabs, isopods, barnacles and algae. In both field observations and laboratory experiments, the Green Crab has been observed to eat an enormous variety of prey items from at least 104 families and 158 genera in 5 plant and protist and 14 animal phyla.

Reproduction

Female Green Crabs can reproduce twice in one season, spawning up to 185,000 eggs at a time. Like all crabs, mating between Green Crabs is a lengthy process whereby the male will attached itself to the female for weeks prior to copulation, waiting for the female to molt, and before her genital pores harden. As the female approaches the molting stage, she releases pheromones (a chemical messenger) to attract males. Mature females molt only once each year, typically between July and September. Prior to the female molt, the male partner typically pairs with her and attempts to defend her from predators and competing males. This pre copulation behavior, described as pre-molt cradling, may commence many days prior to the female molt and it is at this time, and for a relatively short period after molting, the females are chemically attractive to males.

Lifecycle Stages

 Green Crab have six larval stages: 1 protozoea (hatching stage), 4 zoea (feeding stages), and 1
megalopa (the transitional stage between the planktonic larval and the sedentary adult form). The total developmental time varies with water temperature and is estimated to be between 32-62 days. The larvae of Green Crabs can survive up to 80 days and are dispersed many miles along the coast by ocean currents. It has been shown that the larvae can tolerate a wide range of temperatures (41-86°F) and salinities (20 to 30 parts per thousand). The life span of the Green Crab is about 3 years for females, and about 5 years for males.

Habitat

The Green Crab is abundant on any kind of seashore in shallow waters (upper intertidal to shallow subtidal), including estuaries. It has been located in areas well upstream from river mouths, indicating tolerance of low-salinity environments. Some studies comparing crabs with different color shells have shown that red crabs tend to dominant the subtidal zone and crabs with green shells tend to dominate both the intertidal zone and salt marshes.

Historical and Dispersal Methods

The native range of the Green Crab includes Europe and Northern Africa. It was first recorded in North America in 1817 along the Atlantic Coast. It was first collected in the San Francisco Bay in 1989 - 1990 and was most likely introduced there through ballast water. In 1993, it was collected
from Drakes Estero, Tomales Bay and Bodega Harbor. In 1994, it was discovered in Elkhorne Slough and in 1995 in Humboldt Bay. It was first observed in Oregon in 1997, Washington State in 1998, and in British Columbia in 1999. The Green Crab has successfully invaded the East and West coasts of North America, and parts of South America, Asia, South Africa, Australia, and Tasmania. Its ability to tolerate a wide range of environmental conditions suggests that it could eventually range from Baja California to Alaska.

The Green Crab can be dispersed by aquacultural activities, aquarium trade, live food trade, ship ballast water, ship/boat hull fouling, local currents, and by human activities such as boating.

The biggest concern for the Green Crab is its ability to displace native species through
competition and predation. For example, they pose a direct threat to shorebirds, as they have similar diets. In invaded areas, the Green Crab occurs principally along sheltered embayments. It normally requires planktonic (larvae) dispersal, usually by human assistance or unusual oceanographic events such as El Ninos, to expand its ranges between embayments. The pattern of invasion and range extension for the Green Crab appears to consist of periods of stasis followed by rare events of long distance dispersal when conditions are favorable.

The importance of this observation is that even though the Green Crab has not been observed to have spread further north than British Columbia in recent years, a sudden change in weather patterns and currents can create a condition by which the Green Crab can successfully establish itself in Alaska. Even though it has not currently been observed in Alaskan waters, the potential for invasion will always be a possibility in the face of global climate change. Overall, there are seven qualities making this crab a perfect invasive species: a high reproductive rate, a high
dispersal potential, a rapid growth rate, an extremely broad habitat adaptability, wide temperature and salinity tolerances, an extremely broad diet, and the lack of natural enemies such as parasites.

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Europe Green Crab and Green Crab

A native of Europe and Northern Africa, the green crab has invaded the Atlantic and Pacific coasts of North America, South Africa, Australia, South America, and Asia. In North America, the distribution of green crabs now extends from Newfoundland to Virginia and from British Columbia to California. Green crabs live up to 4-7 years and can reach a maximum size of 9-10 cm (carapace width). The life cycle alternates between benthic adults and planktonic larvae. Green crabs are efficient larval dispersers, but most invasions have been attributed to anthropogenic transport. The green crab has successfully colonized sheltered coastal and estuarine habitats and semi-exposed rocky coasts. It is commonly found from the high tide level to depths of 5-6m. It is eurythermic, being able to survive temperatures from 0 to over 35oC and reproduce at temperatures between 18 and 26oC. It is euryhaline, tolerating salinities from 4 to 52o/oo. It is reasonably tolerant of low oxygen conditions.

Green crabs prey on a wide variety of marine organisms including commercially important bivalves, gastropods, decapods and fishes. Impacts on prey populations are greater in soft-bottom habitat and in environments sheltered from strong wave action. The species potentially competes for food with many other predators and omnivores. The predominant predators of green crabs include fishes, birds, and larger decapods. The effects of green crabs have been of particular concern to shellfish culture and fishing industries, as well as eel fisheries. Control efforts have included fencing, trapping and poisoning. Commercial fisheries for green crab have reduced its abundance in parts of its native range.

The European green crab or shore crab Carcinus maenas (hereafter, “green crab”) is ranked among the 100 ‘worst alien invasive species’ in the world (Lowe et. al. 2000). In many ways it could be considered a model invader. A native of coastal and estuarine waters of Europe and Northern Africa, it has successfully invaded the Atlantic and Pacific coasts of North and South America, as well as South Africa, Australia, and Asia. It is a voracious omnivore and aggressive competitor with a wide tolerance for salinity, temperature, oxygen, and habitat type. A large number of planktonic larvae are produced, and dispersal occurs at all life history stages (Cohen et al. 1995).

Green crab was first detected in Canadian waters in 1951 when the introduced New England population spread into Passamaquoddy Bay in the Bay of Fundy (Leim 1951). In reference to its arrival, Hart (1955) wrote:

The green crab (Carcinides maenas), which has entered and spread throughout the Bay of Fundy since 1950, has become our most serious clam predator. It destroys adult clams as well as those of seed size. Feeding experiments conducted this year have demonstrated that it will also destroy young oysters and quahaugs. Studies of its spread show that there is serious risk of its extending its range to the Gulf of St. Lawrence where it might do enormous damage.

Subsequently, the green crab did arrive in the Gulf of St. Lawrence as well as western Canadian waters (Jamieson 2000). In all areas where the green crab has invaded, its potential for significant impacts on fisheries, aquaculture, and the ecosystem has caused concern. Numerous studies have shown the potential for green crab to adversely affect many ecosystem components, directly and indirectly, by predation, competition and habitat modification (Grozholz and Ruiz 1996). Because green crab has the ability to modify entire ecosystems, it is considered an “ecosystem engineer”.

Published estimates of the cost of green crabs in Canadian waters are incomplete and of questionable validity. Colautti et al. (2006) used economic losses attributed to 21 other non-indigenous species to propose median (52% loss) and half-quartile (20%) cases as projections of maximum and minimum cost range for any invasive species. Using these projections, the potential economic impact of green crabs on bivalve and crustacean fisheries and aquaculture in the Gulf of St. Lawrence was estimated as $42-$109 million (Colautti et al. 2006).

The only other published estimate of costs of green crab on the Atlantic coast of North America, a value of $44 million, has been shown by Carlton (2001) and Hoagland and Jin (2006) to be based on an incorrect citation in a summary paper by Pimentel (2000). Unfortunately, repeating Pimentel’s error, this estimate has been widely cited in the scientific literature as the actual cost of the green crab invasion of New England and Atlantic Canada. In fact, the $44 million represented an estimate by Lafferty and Kuris (1996) of the potential, not actual, cost of green crab for a hypothetical (at that time) invasion of the west coast up to Puget Sound.

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Blue Crab Habitat and Spamming

Despite its fearsome appearance and aggressive nature, the Blue Crab is greatly cherished in the South Carolina lowcountry. Many gourmets prefer the blue crabs sweet meat over all other locally-caught seafood. This interesting animal is often sought by recreational fishermen and it also supports a considerable commercial fishery. The blue crab requires both inshore brackish waters and high salinity ocean waters to complete its life cycle. They are common from Massachusetts to Texas and a few have been reported as far north as Nova Scotia and as far south as Uruguay. The Chesapeake Bay, North Carolina and Louisiana support the largest blue crab fisheries.
 
Although other small swimming crabs in this family (Portunidae) occur locally, only the blue crab is of any commercial or recreational importance in South Carolina. The blue crab's scientific name, Callinectes sapidus, translates to "savory beautiful swimmer." Swimming is accomplished by skulling the oar-like fifth pair of legs, the swimming legs. These paddles usually rotate at 20 to 40 revolutions per minute, but they quickly disappear into a blur as the animal darts away.

Walking is accomplished with the three pair of thin walking legs. Blue crabs almost always walk sideways clearing a path with their sharp lateral spines. The blue crabs most prominent features are the large and powerful claws which are used for food gathering, defense, digging and sexual displays. If not handled properly, blue crabs can inflict severe injury. Male crabs can be distinguished from females by the shape of the abdomen. The male has a Tshaped abdomen which is held tightly against the body until maturity when it becomes somewhat free. The immature female has a triangle-shaped
abdomen which is tightly sealed against the body.

The mature female's abdomen becomes rounded and can be easily pulled away from the body after the final molt. Large males, often called "Jimmies" by fishermen, usually have brilliant blue claws and legs. The mature females or "sooks" can be distinguished by the bright orange tips on their claws. Males typically grow larger than females, sometimes reaching seven or eight inches in point-to-point width. Some males have been reported to grow to about ten inches.

Mating and Spawning
Mating generally occurs in brackish water from February to November with peaks in March to July and in October and November. Females mate only during the final molt when they are in the soft shell condition, but males are believed to mate several times. Researchers have determined that blue crabs release chemical signals called pheromones which attract their mates. Two to three days prior to mat-ing, the male will "cradle carry" the soon-to-shed female after a rather elaborate courtship ritual. These crabs are called "doublers." The male is usually one to two inches larger than its mate.

The male protects the soft female when she is vulnerable to predators. After mating, he will continue to carry her until her shell hardens. After mating, females migrate to higher salinity water in the lower reaches of the estuary or in the ocean. Spawning occurs in near shore ocean water about one or two months after mating in spring or summer. Females that mate in fall or winter usually spawn the following spring.

Females produce up to two million eggs, but only about one egg per million will survive to become an adult. Eggs are carried under the abdomen until they hatch. The egg mass is bright orange at first and becomes darker as the embryos mature and consume the egg yolk. Females carrying an egg mass are called "sponge crabs," and are protected by law in South Carolina. If captured, they must be returned to the water immediately. Sponge crabs usually first appear in early April and are common until August or September. Eggs hatch after about two weeks into zoea larvae which are 1/100-inch long. During the next month there are six or more larval stages before reaching the megalopal stage. 

The megalopae, which is about 1/10-inch wide, begin to migrate into the nutrient-rich estuarine waters. Very soon after settling in the saltmarsh creeks, the megalopae transform into the "first crab" stage. Crabs hatched in April or May become two to three inches wide by Nov- ember and five inches or larger by August the following year. Crabs hatched in early fall will be only -inch in width by winter. After one year, these crabs will be only three to four inches wide and will not mature until the following spring. A few crabs may live for three years but most live for less than a year. South Carolina law requires that captured crabs less than five inches in width be returned to the water.

Growth and Molting
Blue crabs, like all arthropods, must periodically shed their hard exoskeleton in order to grow. The smallest crabs shed every three to five days, juvenile crabs every 10 to 14 days and those 3 inches and larger every 20 to 50 days. Experienced crabbers can quickly spot crabs about to molt. Five to ten days before molting, a narrow white line appears just within the thin margin of the last two joints of the swimming legs. A few days before shedding, the peeler crab's narrow white lines give way to a red line, and fine white wrinkles appear on the blue skin between the wrist and upper arm. The actual molting lasts for only a few minutes as the crab pushes out the rear of the old shell.
 
The resulting soft crab, which is limp and wrinkled, will swell to normal shape and usually increase in size by 25 to 35 percent. If disturbed, the vulnerable soft shell crab can swim and walk but prefers seclusion. After a few hours, the crab's shell becomes parchment-like and is fully hardened within two or three days. During the spring, usually early April, there is a "run" of peeler crabs that lasts for about two weeks. At this time fishermen will target the female crabs that are molting into mature crabs after the winter dormancy. These crabs can be caught in "peeler pots" which are crab traps in which one or two large males are used as bait to attract the females which are ready to mate. The peeler crabs are held for a short time in shedding tanks until the molt. After molting, the soft shell crabs are removed from the water and refrigerated for sale.


Abundance and PredatorsFactors controlling year-to-year variation in blue crab stocks exert their influence early in the life cycle. Water circulation patterns controlled by prevailing winds, can either carry the larvae shoreward or sweep them away. Thus, recruitment (addition of new individuals) of megalopae and small crabs may be largely controlled by the coastal water currents and the weather. Young crabs within the estuaries are vulnerable to drought, flood, or unseasonable temperatures. A relationship seems to exist between river discharge and survival of small crabs. Small crabs survive best during years of relatively high fresh water runoff which increases nutrient input and decreases salinity.

However, too much rainfall can also flush the small crabs from the marsh. Predators claim large numbers of young crabs, and crab populations may vary from year to year according to the abundance of predators. Blue crabs are subject to predation throughout their life cycle and are particularly susceptible when they are soft during the molting process. As larvae, they are vulnerable to fishes, jellyfish and other planktivores. The megalopae and juvenile crabs are consumed by various fishes and birds, as well as other blue crabs.


Eating Habits
Blue crabs eat a variety of foods, including fishes, oysters, clams, snails, shrimp, worms and other crabs. At high tide, crabs may swim into the salt marsh to pluck snails from the tall grass. At times, they burrow into the bottom with only their eye stalks visible, lying in wait for an unsuspecting fish. Crabbers typically bait their pots with oily fishes which seem to work better than other baits. Presumably, the crabs home in on the oil or odor being released. Studies have shown that blue crabs can follow a current upstream by cris-crossing the stream bed. Crabs are opportunistic feeders, meaning they will eat what is most available regardless of their size, the season or the area they inhabit.


Fishing GearsThe 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.

Blue 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 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.

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Swimming Crabs Types Crab

Swimming crabs have certain unique characteristics that set them apart from walking crabs. Almost all crabs have five matched pairs of limbs: four pairs of “legs” and two claws. The last pair of legs (those furthest from the claws) on swimming crabs is flattened out into paddles. These legs are called swimmerets and allow the crabs to swim quite rapidly. They are also used to dig into the sand or mud. Most swimming crabs have flatter bodies and more pronounced spikes than their walking crab relatives.

Blue Crab

The Blue Crab has an olive green to brown body with points on each side. The underside of the blue crab is white. The crab gets its name from the brilliantblue colored claws and legs. The tips of the claws are red or orange and can be used to determine the sex of the crab. Males have red or orange coloration only at the very tips, while the red or orange in females covers more of the claw.

Lady Crab

 The Lady Crab is a small, rounded crab with a collection of red and purple calico spots. The markings serve as a camouflage both to defend against predators and to help them ambush their primary prey, small fish. Found on the sandy shoals just offshore, the Lady Crab often buries itself, leaving just its eyes and antennae exposed.

Speckled Crab

This crab is identified by the large number of white dots on its brown to olive shell. The Speckled Crab has a flat shell with points on both sides, similar to the Blue Crab. Like most swimming crabs, their body design works just as well for digging as it does for swimming. Their coloration helps them blend in with the sandy sediments. Speckled Crabs are often found in tide pools.

Walking Crabs

Walking crabs get their name because all of their legs end in points. Because these crabs can not swim, they navigate the ocean and river bottom using their 4 matching pairs of legs. Walking crabs shells are generally more dome-shaped than those of swimming crabs.

Ghost Crab

These land-dwelling crabs can be seen scurrying quickly (up to 10 mph) along the beach between dusk and dawn. Ghost Crabs have 1.5- to 2-inch square, beige colored bodies that allow them to “disappear” into the sand. Mainly a land crab that burrows in the dry sand, Ghost Crabs wet their gills at the water's edge and the females enter the ocean to lay eggs in the salt water. While not very large, Ghost Crabs can prey on sea turtle hatchlings. They also eat coquina clams and flying insects that they catch in mid-air.

Spider Crab

This crab looks like a large spider with a bumpy brown, pear-shaped body and long legs. Spider Crabs are often found on mud bottoms, clinging to marsh grasses, or riding along on Cannonball Jellyfish. A Spider Crabs rough shell collects bacteria and plankton. This coating encourages the growth of other plants and animals on the shell surface. Nicknamed the “decorator crab,” Spider Crabs use this coating to disguise themselves. The shell decorations also are a source of food for the crab.


Stone Crab

Growing to over 5 inches across with massive claws, the Stone Crab is prized for its meat. Care must be taken, however, because the massive claw of an adult Stone Crab can easily crush the finger of an inattentive crabber. Because of their slow growth rate, only the larger of the two claws is taken at harvest. The crab is returned to the water where the missing claw will regenerate. Stone Crabs are purplish-tan in color with a thick oval body and black “finger tips” on the claws.

Hermit Crab

Hermit Crabs are unusual in that their hard outer shell covers just their head and claws, not their entire bodies like other crabs. To protect their fragile bodies, Hermit Crabs find and move into empty snail and whelk shells. Their bodies are specially designed so that their two back pairs of legs hook into the protective shells. They cannot be removed without destroying the animal. Hermit Crabs found on Kiawah are not the same as those sold in pet stores. Our local Hermit Crabs live in salt water and cannot survive out of the water for a prolonged period.

Marsh Crabs 

Two types of marsh crabs are found on Kiawah. The first species, the Wharf Crab (also known as the Grey Marsh Crab, Square-Back Marsh Crab, or Friendly Crab) is found in the higher marsh areas and bordering regions. When you are out for a stroll, these small, dark-colored crabs with square, flattened shells often surprise you by darting across the bike path or beach access. The other species is the Marsh Crab, or Purple Marsh Crab, which prefers the lower areas of the marsh where it constructs a burrow with a mud “chimney.” It has a square body like its relative the Wharf Crab, but has a thicker body. As the name implies, the coloration of the Marsh Crab is typically purple and they are often mistaken for young Stone Crabs. However the tips of the Marsh Crabs claws are light-colored and their legs are “fuzzy."


Fiddler Crabs

Fiddler crabs occur in both sandy and muddy environments and are very common along creeks and mud flats around Kiawah. The male Fiddler Crabs large, white claw is unmistakable. Males are typically seen waving this claw back and forth in a territorial display. Females in habit the same areas as males, but are often harder to spot since they lack a large, bright-colored claw. The male uses his single smaller claw (and the female uses her two small claws) to scrape up mud and sediment for food. They are excellent burrowers and their holes can sometimes extend down more than 2 feet. These burrows have an added benefit of aerating the marshes and preventing the “rotten egg” smell associated with some saltwater marshes.


Crabbing
Crabbing is a popular activity on Kiawah Island. A simple crabbing set-up consists of string, a chicken neck for bait, and a long-handled net for scooping the crabs up. Remember, blue crabs must be more than 5 inches across the back, tip to tip, to keep. One of the best places to crab on the island is the Kiawah River Bridge.

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Emperor Red Snapper

The Emperor Red Snapper family Lutjanidae contains more than 100 species of tropical and sub-tropical fish known as snappers. Most species of interest in the inshore fisheries of Pacific Islands belong to the genus Lutjanus, which contains about 60 species. One of the most widely distributed of the snappers in the Pacific Ocean is the common blue stripe snapper, Lutjanus kasmira, which reaches lengths of about 30 cm. The species is found in many Pacific Islands and was introduced into Hawaii in the 1950s.

Although most Emperor Red snappers live near coral reefs, some species are found in areas of less salty water in the mouths of rivers. The young of some species school on sea grass beds and sandy areas, while larger fish may be more solitary and live on coral reefs. Many species gather in large feeding schools around coral formations during daylight hours. Snappers feed on smaller fi sh, crabs, shrimps, and sea snails. They are eaten by a number of larger fish. In some locations, species such as the two-spot red snapper, Lutjanus bohar, are responsible for ciguatera fish poisoning (see the glossary in the Guide to Information Sheets).


Emperor Red Snappers have separate sexes. Smaller species have a maximum lifespan of about 4 years and larger species live for more than 15 years. Many common species grow to sizes of 25 to 35 cm and reach reproductive maturity at about 45 per cent of their maximum size (that is, 11 to 16 cm in the most common species).

Emperor Red Snappers generally spawn throughout the year in warmer waters but during the warmer months in cooler waters. Many snappers travel long distances to particular areas along outer reefs and channels to breed (in spawning aggregations), often around the time of the new moon and full moon. During breeding, females (~) release eggs (often more than 1 million) and these are fertilised by sperm released by males (|). In most reef associated snappers, fertilised eggs hatch within a day or two into small forms (larval stages) that drift with currents for about 1 month. Less than one in every thousand of these small floating forms survives to settle on a reef as a young fish (juvenile). And less than one in every hundred juveniles survives the period of 3 to 8 years that it takes to become a mature adult capable of reproducing. Emperor Red Snappers are most often taken by using baited hooks and hand lines but are also caught by using spears, traps and gill nets.

Many snappers are caught as they gather in large groups to breed (in spawning aggregations). Fishing in this way is destructive as these breeding fi sh are responsible for producing small fi sh, many of which will grow and be available to be caught in future years.


Minimum size limits for snappers have been applied in some countries (e.g., 30 cm length from the tip of the mouth to the middle of the tail). However, the particular species of snapper is not usually stated. Taking into account the wide variation between Emperor Red Snapper species, this size limit would be of little use in protecting larger species. Size limits should be applied to individual species. Some countries have restricted fishing methods to the use of hook and line only. Catch (bag) limits have also been applied but such a measure is usually inappropriate in community-based fisheries. Locally managed fi sh reserves (no-take areas) could be established but, for species that travel long distances to spawning sites, these will not protect reproducing fi sh. However, if spawning times and areas are known by local fishers, the following management actions are possible:



- A ban on fishing during the times that fi sh form spawning aggregations, which may require a number of short closures (say for 3 to 4 days) around the periods of new moon and full moon, depending on the particular species.

- A ban on fi shing at known spawning areas or sites; such sites may include particular areas along outer reefs and channels where snappers are known to gather to breed. Additional community actions could include:
 
support for local national minimum size limits or (if not available) set community based minimum size limits at about 50 per cent of the maximum size of the species; A ban on the use of gear such as gill nets which catch too many fish, a restriction on small-mesh gill nets, enforcing a minimum mesh size may allow smaller fish to escape and grow to a size when they can reproduce.

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