Mud crab (mangrove crab)

This is a regulated species. See the size, take and possession limits for tidal waters.

Scientific name : Scylla serrata

Description 	

large crabs with a smooth, broad carapace
can grow to more than 25 cm shell breadth (2 kg), with males generally growing larger than females
have nine similar sized spines each side of their eyes
hind legs are flattened for swimming
have very robust claws, used for crushing shells
vary from dark olive-brown to greenish-blue and blue-black
patterns of lighter coloured dots cover the walking legs.

Distribution 	

can be found along the entire Queensland coast in sheltered estuaries, tidal flats and rivers lined with mangroves
inhabit tropical to warm temperate waters from Exmouth Gulf in Western Australia to the Bega River in New South Wales.

Habitat 	

a marine and estuarine animal
usually found in shallow water but berried females occur well offshore
favour a soft muddy bottom, often below tide level.

Diet 	

omnivorous scavengers and are also cannibalistic, eating other crabs as well as barnacles, bivalves and dead fish.

Size and possession limits 	

minimum size - 15cm
possession limit - 10
female mud crabs are protected throughout Queensland and are therefore prohibited from being in anyone's possession without a permit.

Mud crab (mangrove crab)(Scylla serrata)

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Scylla serrata
From Wikipedia, the free encyclopedia
Scylla serrata
CSIRO ScienceImage 10696 Mud crabs are caught measured tagged and released as part of the research into the effectiveness of green zones in Moreton Bay.jpg
Scientific classification
Kingdom: 	Animalia
Phylum: 	Arthropoda
Subphylum: 	Crustacea
Class: 	Malacostraca
Order: 	Decapoda
Infraorder: 	Brachyura
Family: 	Portunidae
Genus: 	Scylla
Species: 	S. serrata
Binomial name
Scylla serrata
(Forsskål, 1775)

Scylla serrata (often called mud crab or mangrove crab, although both terms are highly ambiguous, as well as black crab) 
is an economically important species of crab found in the estuaries and mangroves of Africa, Australia and Asia. 
In their most common form, the shell colour varies from a deep, mottled green to very dark brown.

Contents

1 Distribution
2 Ecology
3 Aquaculture and consumption
4 References
5 External links

Distribution

The natural range of Scylla serrata is in the Indo-Pacific. It is found from South Africa, around the coast of the Indian Ocean to the Malay Archipelago, 
as well as from southern Japan to south-eastern Australia, and as far east as Fiji and Samoa.
The species has also been introduced to Hawaii and Florida.

Ecology

A study on tidal flats in Deception Bay in Queensland found juvenile crabs (20–99 mm or 0.8–3.9 in carapace width) were resident in the mangrove zone, 
remaining there during low tide, while subadults (100–149 mm or 3.9–5.9 in) migrated into the intertidal zone to feed at high tide and retreated to subtidal waters at low tide.
Adults (150 mm or 5.9 in and larger) were caught mainly below the low tide mark, with small numbers captured in the intertidal zone at high tide.

These crabs are highly cannibalistic in nature; when crabs undergo moulting, other hard-shelled ones sometimes attack the moulting crabs and devour them. 
The females can give birth to a million offspring which can grow up to 3.5 kg (7.7 lb) in size and have a shell width of up to 24 cm (9.4 in) wide.
Aquaculture and consumption
Scylla serrata from Karwar, India.

Interest in the aquaculture of this species has been high due to the high demand/price for them, high flesh content, and rapid growth rates in captivity. 
In addition, they have a high tolerance to both nitrate[4] and ammonia (twice that of the similar sized Portunus pelagicus), which is beneficial because ammonia-N is often the most limiting factor on closed aquaculture systems.
Their high ammonia-N tolerance may be attributed to various unique physiological responses which may have arisen due to their habitat preferences.
However, their aquaculture has been limited due to the often low and unpredictable larval survival. 
This may be due to inadequate nutrition, disease, "moult death syndrome" (due to their highly cannibalistic behaviour during the megalopa stage), 
inadequate protocols (e.g. suboptimal environmental conditions), or a combination of all.

S. serrata can be kept easily in home aquaria when smaller, but will outgrow small setups. 
They are very active and will eat almost any conventional sinking pellets; they also consume some small fish pieces and vegetable matter. 
They are tolerant of most water conditions and are generally a very hardy and entertaining species.

Generally cooked with their shells on, when they moult their shells, they can be served as one of many types of soft-shell crab. 
Some consider them to be among the tastiest of crab species, and demand for them is large in South and Southeast Asian countries, where they are often bought alive in the markets. 
In the northern states of Australia and especially Queensland, mud crabs are relatively common and generally prized above other seafood by the general public.

Mud crabs can be killed by placing them in a freezer for up to two hours before cooking.[6]
=================
Species Name: 
Scylla serrata Forskål, 1775

Common Name(s):
Serrated Swimming Crab, Giant Mud Crab, Edible Mud Crab, Mangrove Crab

Synonymy:
Cancer olivaceus Herbst, 1796
Cancer serratus Forsskål, 1755
Lupa tranquebarica H. Milne-Edwards
Portunus tranquebaricus Fabricius, 1798
Scylla tranquebarica var. oceanica Dana, 1852
Scylla oceanica Estampador, 1949
Scylla serrata paramamosain Estampador, 1949

Species Description:
The serrated swimming crab, Scylla serrata, is a non-native species in Floriad whose current status in the state is uncertain. 
It is a robust crab belonging to the family of swimming crabs (Portunidae) to which the familiar blue crab, Callinectes sapidus, also belongs.

The carapace has four blunt frontal teeth and each anterolateral margin has nine similarly sized broad teeth. 
The chilipeds (claws) are robust with several well developed spines and the rear legs are flattened into swimming appendages as is typical of members of the portunid family. 
Individuals are grayish green to purple-brown and variable in color with small irregular white spots on the carapace and swimming legs (Motoh 1979, Perry 2007, GSMFC).


Potentially Misidentified Species:
Although Scylla serrata is unlikely to be confused with other portunid crabs found in Florida, taxonomy of the species in its native Indo-Pacific range is confusing, 
with several genetically distinct Scylla species (i.e., S. serrata, S. tranquebarica, S. oceanica, and S. paramamosain) commonly all being lumped together as S. serrata 
(Fuseya and Watanabe 1996, Tamaki et al. 2001).

II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
Scylla serrata inhabits muddy bottoms, mangrove marshes, and river mouths in estuarine environments (Motoh 1979). 
It is native to the Indo-Pacific and has been introduced to Florida, Hawaii, and elsewhere, most often intentionally in attempts to establish populations of this commercially important species.

S. serrata have been reported from south Florida several times, although a 2000 study failed to locate any specimens (Baker et al. 2004). 
The population status of the species in Florida is currently unknown.

IRL Distribution:
Although Scylla serrata occurrence in the IRL has been noted in the literature (e.g., Poss et al. 2000), 
there is no evidence of established populations currently occurring in the region.

III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
This large crab can exceed 18 cm in carapace width (Stephenson and Campbell 1960, Eldredge and Smith 2001). 
The FAO Species Identification and Data Programme suggests a maximum male carapace width of 25-28 cm and a maximum weight of 2-3 kg (FAO/SIDP undated).

Abundance:
Scylla serrata does not currently appear to occur in appreciable numbers anywhere in Florida.

Reproduction:
Studies indicate Scylla serrata become reproductively mature starting at around 90 mm carapace width, often within the first year of life (Robertson and Kruger 1994, Knuckey 1996).

Male crabs approach female crabs before the femeles have undergone a precopulatory molt, grasping them with their chelipeds and first pair of walking legs and carrying them around for up to several days until the females molt. 
On molting, males turn the females over and initiate copulation, 
delivering non-motile spermatozoa that may be retained by the females for up to several weeks to months before being used to fertilize multiple clutches of up to 2 million eggs each (Chen 1976). 
Hill (1996) notes that females bearing egg masses on their pleopods migrate offshore where the eggs hatch in a few weeks.

Embryology:
Fratini and Vannini (2002) report an extended larval duration for Scylla serrata. 
Experimental work by Nurdaini and Zeng (2007) reveal a mean larval development time to the megalopa stage ranging from 20.6-22.6 days at 25°C, 
shortened by several days at higher developmental temperatures. These authors also noted 100% larval mortality at 15 ppt salinity and high survival at salinities above 20 ppt. 
This finding is consistent with observed migration of egg-bearing females to high-salinity offshore waters prior to spawning.

IV.  PHYSICAL TOLERANCES

Temperature:
Adult and subadult Scylla serrata are broadly eurythermal, while larvae exhibit a somewhat narrower tolerance. 
Islam and Bhuiyan (1981-82) report an impressive tolerance range of 3-45°C for Scylla serrata in the Karnafully River estuary, Bangladesh.
Mwaluma (2002) indicates that successful pen culture of the species could be carried out in waters that ranged seasonally between 25°C and 36°C. Hill (1974), 
however, notes considerable larval mortality at temperatures above 25°C. 
The author also reports larval tolerance of temperatures as low as 5°C, although individuals become inactive below 10°C.

Hydrology:
Adult Scylla serrata are broadly eurohaline, although individuals other than spawning females preferentially inhabit brackish inshore habitats. 
Chen and Chia (1996) report specific metabolic responses allowing animals to persist at low salinities (i.e., amino acid catabolism and formation of ammonia to reduce osmolality at 10 ppt) as well as high salinities 
(i.e., initiation of urea synthesis and moderation of nitrogen excretion at 40 ppt).

V.  COMMUNITY ECOLOGY

Trophic Mode:
Scylla serrata is principally a carnivore, preying on small invertebrates such as molluscs, crustaceans, polychaetes, and on small quantities of detritus and plant material (Eldredge and Smith 2001).

Associated Species:
No obligate associations with Scylla serrata are known, although infestation of the gill chambers of the crab by cyprid larvae of stalked barnacles of the genus Octolasmis has been documented (Jeffries et al. 1992).

VI. INVASION INFORMATION

Invasion History:
Eldredge and Smith (2001) report a native Indo-Pacific distribution of Scylla serrata as likely encompassing East and South Africa to Tahiti, north to Okinawa, and south to Australia and New Zealand.

In 1962, Approximately 30 pairs of S. serrata were intentionally released to coastal waters in Collier County on the Gulf coast of Florida in an effort to establish a commercial crab fishery (Perry 2006). 
This introduction failed to lead to an established population and the present status of the species in Florida is currently unknown.

S. serrata was also intentionally introduced to Hawaii between 1926 and 1935, with established populations resulting from these efforts noted by 1940 (Edmondson and Wilson 1940). 
Established populations now reportedly occur off of Maui, Hawaii, and Kauai (Eldredge and Smith 2001).

Although most initial introductions of S. serrata were intentional releases for the purposes of establishing commercial fisheries, the protracted larval period likely confers high dispersal potential to populations of new recruits (Fratini and Vannini 2002).
The species has successfully spread through most of the Indo-Pacific, now occurring in Japan, the Philippines, Indonesia, East and South Africa and the Red Sea (Eldredge and Smith 2001).

Potential to Compete With Natives:
Ecological impacts resulting from introduction of Scylla serrata into areas in which the species has become established have yet to be assessed. 
The animal has been described as an active, aggressive species (Motoh 1979) and some degree of competition with co-occurring native species is likely.

Possible Economic Consequences of Invasion:
Scylla serrata is economically important as both a wild-harvested stock and a commercial aquaculture product and it commercially harvested in those areas to which it has been intentionally introduced and where established populations have resulted 
(Samonte and Agbayani 1992, Perry 2006). Large-scale negative economic impacts resulting from introduction of this species have not been reported.

VII.  REFERENCES

Edmondson C.H., and I.H. Wilson. 1940. The shellfish resources of Hawaii. Sixth Pacific Science Congress, University of California Press, Berkeley, p 241-243.

Eldredge, L.G. and C. Smith (eds.). 2001. Guidebook to the Introduced Marine Species in Hawaiian Waters. Bishop Museum Technical Report 21. Bishop Museum, Honolulu.

FAO Species Identification and Data Programme (FAO/SIDP). Undated. Scylla serrata Species Identification Sheet. Available online.

Chen T.P. 1976. Aquaculture Practices In Taiwan. Fishing News Books Limited, 1 Long Garden Walk, Farnham, Surrey, England. 162 p.

Chen J., and P. Chia. 1996. Hemolymph ammonia and urea and nitrogenous excretions of Scylla serrata at different temperature and salinity levels. Marine Ecology Progress Series 139:119-125.

Fratini S., and M. Vannini. 2002. Genetic differentiation in the mud crab Scylla serrata (Decapoda: Portunidae) within the Indian Ocean. Journal of Experimental Marine Biology and Ecology 272:103-116.

Fuseya R., and S. Watanabe. 1996. Genetic variability in the mud crab genus Scylla (Brachyura: Portunidae). Fisheries Science 62:705-709.

Hill B.J. 1974. Salinity and temperature tolerance of zoeae of the portunid crab Scylla serrata. Marine Biology 25:21-24.

Hill B.J. 1996. Offshore spawning by the portunid crab Scylla serrata (Crustacea: Decapoda). Marine Biology 120: 379-384.

Islam M.J., and A.L. Bhuiyan, A.L. 1981-82. Temperature tolerance and its impact on the distribution of mud crab in the Karnafully River estuary. Bangladesh Journal of Agriculture 6,7:38-46.

Jeffries W.B., Voris H.K., and S. Poovachiranon. 1992. Age of the mangrove crab Scylla serrata at colonization by stalked barnacles of the genus Octolasmis. Biological Bulletin 182:188-194.

Knuckey I. A. 1996. Maturity In male mud crabs, Scylla serrata, and the use of mating scars as a functional indicator. Journal Of Crustacean Biology 16: 487-495.

Motoh H. 1979. Edible crustaceans in the Philippines, 11th in a series. Asian Aquaculture 2:5.

Mwaluma J. 2002. Pen culture of the mud crab Scylla serrata in Mtwapa Mangrove System, Kenya. Western Indian Ocean Journal of Marine Science 1:127-133.

Nurdiani R., and C. Zeng. 2007. Effects of temperature and salinity on the survival and development of mud crab, Scylla serrata (Forsskål), larvae. Aquaculture Research 38:1529-1538.

Perry H. 2006. Scylla serrata. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Available online.

Poss S.G.. Aguirre, W., Crochet, N., Nates, S., Hard, S.D., and O'Connell, A.M. 2000. Nonindigeous species in the Gulf of Mexico ecosystem. Gulf Coast Research Laboratory Museum, Univ. Southern Mississippi.

Robertson W. D., and A. Kruger. 1994. Size at maturity, mating and spawning In The portunid crab Scylla Serrata (Forsskål) In Natal, South Africa. Estuarine, Coastal And Shelf Science 39:185-200.

Samonte G.PB., and R.F. Agbayani. 1992. Pond culture of mud crab (Scylla serrata) and economic analysis. SEAFDEC Asian Aquaculture 14:3-5.

Tamaki M., M. Minagawa, T. Hayashibara, M. Sano, K. Fukuoka, E. Quinitio, J. H. Primavera, H. Imai, and K. Numachi. 2001. Identification of four species of Scylla spp. by pcr-rflp analysis and species composition of Scylla juveniles in Ishigaki Island. Workshop on Mud Crab Culture, Ecology and Fisheries, Can Tho University, Vietnam, 8-10th January, 2001.

Report by:  J. Masterson, Smithsonian Marine Station
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Page last updated: December 1, 2007