Abstract
A population of the intertidal, ovoviviparous, cirolanid isopod Annina mesopotamica was studied at the Al-Chibassy tributary of the Shatt Al-Arab river from 14 May 1973 to 29 April 1974, and at the Garmat-Ali river of the Shatt Al-Arab, Basrah, Iraq from 5 November 1984 to 30 June 1986. Population density varied between 128 to 5760 individuals m−2 with a mean of 1218 m−2. Highest numbers occurred between June and September. Breeding extended for most of the year except November/January to February/March, although ovigerous females were present throughout the year. The incubation period varied with season, and was ca. 2 weeks during the warmest period, and about a month at lower temperatures. Egg numbers varied between 4 to 66 with mean 24. Brood size was linearly proportional to female size. The size frequency distribution of the population was polymodal with a predominance of females over males. Four different types of growth curves were found: exponential, concave, convex, and intermediate between concave and convex. Growth rate varied between 0.63 and 2.19 mm month−1. Mortality was higher among summer cohorts. Life span varied between 5 and 11 months.
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