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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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