Density,distribution and population structure of <Emphasis Type="Italic">Opusia indica</Emphasis> (Ocypodoidae: Camptandriidae) in a coastal mangrove creek in Pakistan |
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Authors: | Noor Us Saher Naureen Aziz Qureshi |
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Institution: | 1.Centre of Excellence in Marine Biology,University of Karachi,Karachi,Pakistan;2.Department of Fisheries and Aquaculture,University of Veterinary and Animal Sciences,Lahore,Pakistan |
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Abstract: | The density, distribution and population structure of Opusia indica were studied through transects method. Two transects were delimited in a mangrove area of Korangi creek (24°79′ N/67°20′
E). On each transect, three 0.25 m2 quadrats were sampled at three tidal levels on a monthly basis during low tide. A total of 1919 crabs were obtained, of which
775 were males, 945 were non-ovigerous females and 199 were ovigerous females. Density of crabs varied between 198 m−2 to 798 m−2. The density and size distribution showed significant difference from low tide level to high tide level and were positively
correlated with the percent moisture, percent organic matter and sediment structure. Based on carapace width (CW) males were
significantly larger than the females indicating sexual dimorphism. The monthly size frequency distribution of crabs showed
recruitment of juvenile crabs (< than 4 mm) nearly throughout the year except in few months. The monthly sex ratio deviated
from 1:1 throughout the year, with female bias (χ
2 = 31.633, P = 0.001 and df =11). Breeding was seasonal with peaks in SW monsoon. Size at sexual maturity based on smallest ovigerous
female was CW = 4.0 mm. The average number of eggs per female were 2066 ± 479 (n = 25). Positive linear relationship was observed between the size of the female crabs and the egg numbers (r
2 = 0.554). |
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