Population and reproductive biology of the fiddler crabUcathayeriRathbun, 1900 (Crustacea: Ocypodidae) in a tropicalmangrove from Northeast Brazil

Abstract

Population and reproductive biology ofUca thayeriRathbun, 1900 were studied for the firsttime in a tropical mangrove. Absolute density, sex ratio, population structure, handedness,breeding season and fecundity were investigated. Seven transects were delimited in a man-grove area of the Pacoti River, Northeast of Brazil (3 4300200S/38 3203500W). On each tran-sect, ten 0.25 m2squares were sampled on a monthly basis during low tide periods fromSeptember 2003 to August 2004. A total of 483 crabs were obtained, of which 250 weremales, 219 non-ovigerous females, and 14 ovigerous females. TheU. thayeripopulation pre-sented bi-modal size frequency distribution, with males and non-ovigerous females notdiffering significantly size-wise. Ovigerous females were larger than males and non-ovig-erous females. The overall sex ratio (1:1.07) did not differ significantly from the expected1:1 proportion. The major cheliped was the right one in 50% of the males. The observeddensity was of 8.5 individuals/m2, with the specimens being found mostly in shaded areas.Ovigerous females were found in 5 months of the year, coinciding with the rainy season,suggesting that the population ofU. thayeripresents seasonal reproductive events. Juvenilecrabs were more abundant during the dry period, while larger crabs were found mainlyduring the rainy period. The fecundity of the studied population was much smaller thanthat of subtropical populations of this species. The regression analysis shows that thenumber of eggs increases linearly with the increase of carapace width.