Sediment Temperature Impact on Population Structure and Dynamics of the Crab Austruca iranica Pretzmann, 1971 (Crustacea: Ocypodidae) in Subtropical Mangroves of the Persian Gulf

Ocypodid crabs inhabit intertidal sandy/muddy flats of tropical and sub-tropical mangroves. Iran has three species of the genus Austruca. In contrast to A. sindensis and A. lactea, almost nothing is known about the population dynamics and its driving factors in Austruca iranica. Thus, population ecology and reproductive biology of A. iranica were studied in relation to sediment temperature and rainfall in a sub-tropical Iranian mangrove forest over a period of 13 months. Crab density and Gonado Somatic Index (GSI) were significantly correlated with sediment temperature (r2 = 0.87, p ≤ 0.05). Reproduction was restricted to spring and summer and ovigerous females appeared when both sediment temperature and rainfall had their maximum values. Rainfall triggered crab reproduction, but did not significantly correlate with crab density. Symptotic carapace width (L∞) and growth constant (k) were 16.9 mm and 1.0 yr. −1 in females (n = 251), and 18.5 mm and 0.9 yr. −1 in males (n = 325), respectively. Size frequency distributions in both females and males had a common asymmetrical bi-modal pattern with two cohorts. Total mortality was higher in females (2.74) than in males (2.29). The overall sex ratio did not differ significantly from the expected 1:1 proportion (χ2 = 20.50, p > 0.05). Size at the onset of maturity was 10.2 mm in females. In comparison to other literature on ocypodid crab species, this study revealed that A. iranica is a relatively slow growing crab, with low fecundity and mortality rates, and with a relatively long life expectancy of about two years. The results of this research are a key for establishing a management plan to conserve the population of A. iranica along the Iranian coasts