Population Biology and Breeding Period of the Sand-Bubbler Crab Dotilla Fenestrata (Brachyura: Ocypodidae) from Southern Mozambique

Abstract

The sand-bubbler crab Dotilla fenestrata (Hilgendorf, 1869) is the most common and abundant brachyuran in the intertidal area of many East African sandy shores. Monthly sampling surveys were performed from March 2001 to February 2002 at Praia do Triunfo, Southern Mozambique. At each sampling survey, 15 stations (0.25 m 2 ) were sampled to a depth sediment of 30 cm. Crabs were identified, sexed, and measured for carapace width (mm). A total of 2456 crabs were collected of which 1247 were males (mean±sd: 5.36±0.04 mm), 938 non-ovigerous females (5.03±0.03 mm) and 271 ovigerous females (5.15±0.06 mm). The overall size frequency distribution showed a unimodal pattern suggesting a stable population with continuous recruitment. A clear sexual dimorphism was observed, with males being larger than ovigerous females, which in turn, were larger than non-ovigerous females. The overall sex ratio did not differ from 1:1. The annual reproductive cycle of Dotilla fenestrata was continuous and ovigerous females were recorded throughout the year, with peaks of occurrence during the warmer months (February-August). Despite of this continuous cycle, few juveniles were observed during the study period. These observations and the maximum size attained by adults supports the hypothesis that for this burrowing crab, recruitment may occur in different habitat than that occupied by adults. However, the studied area is favourable for growth, since the analysed population attains sexual maturity in smaller sizes than that from close areas.

Continuous reproduction and recruitment in the narrowback mud crabPanopeus americanus(Brachyura, Panopeidae) in a remnant human-impacted mangrove area

“…This result was contrary to expectations of low numbers of individuals in an environment under constant stress, such as the Araçá area. The population analysis revealed similarities to the population structure described for P. americanus and those of other tropical and subtropical brachyuran species living remote from human-impacted areas (Díaz and Conde, 1989;Mantelatto and Fransozo, 1999;Litulo et al, 2005). However, some peculiarities in the relationship to abiotic factors, as well as in certain population characteristics, were observed and are described here.…”

“…Differential mortality between the sexes and other factors that create differences in expenditures during production of offspring in each sex, such as differential growth rates, or differences between sexes during parental care, may produce innumerable deviations in the sex ratio (Willson and Pianka, 1963). This population of P. americanus is well-established and stable, mainly in terms of incorporation and mortality rates of individuals, like other intertidal populations of brachyuran crabs (Turoboyski, 1973;Snowden et al, 1991;Fransozo et al, 2000;Flores and Paula, 2002;Litulo et al, 2005).…”

Activity and feeding ofDotilla fenestrata(Brachyura: Ocypodidae) in a warm, temperate South African estuary

“…Dotilla fenestrata (Hilgendorf 1869), commonly known as the sand-bubbler crab, is a small species (Dray and Paula 1998, Gherardi et al 2002a, Flores et al 2005. It is distributed along the East African coast from Kenya to South Africa, and also occurs on Madagascar and the Comoro Islands (Barnard 1950, Hartnoll 1973, Vannini and Valmori 1981, Dray and Paula 1998, Gherardi and Russo 2001, Gherardi et al 2002a, Flores et al 2005, Litulo et al 2005. In South Africa, D. fenestrata is most abundant north of Durban (29°51′ S), but small numbers do exist in warm temperate regions as far south as the Breede River estuary (34°24′ S) (Day 1974, 1981, Branch et al 2010.…”

“…(Ocypodidae), are often abundant on soft-sediment shores in the tropics and subtropics (Fishelson 1983, Ólafsson and Ndaro 1997, Bradshaw and Scoffin 1999, Litulo et al 2005, Allen et al 2010). On such shores they play a vital role in the ecology of the infaunal community due to their burrowing and feeding activity (Bradshaw and Scoffin 1999).…”

Reproductive aspects and adaptive relative growth of the tropical crab Goniopsis cruentata

“…availability of food for parental females may be another factor leading to the higher fecundity in the dry season. This factor is often positively associated with the frequency of ovigerous females (Litulo et al, 2005). During the period of study, the frequency of ovigerous females was higher in the dry season (see Lira et al, 2013), perhaps reflecting higher food availability in this season.…”