Life history, aspects of reproductive biology and production ofCorophium orientale (Crustacea: Amphipoda) in Monolimni lagoon (EvrosDelta, North Aegean Sea)

摘要

Monthly samples of Corophium orientale were collected during February 1998-February 1999 in both parts of Monolimni lagoon (0.3 < Sal. < 6 psu, 2 < Temp. < 28.5 degree C). Corophium orientaleshowed a semiannual life cycle. In the southern part, breeding occurred from early spring to mid autumn having three peaks, in early spring, early summer and early autumn, and three cohorts were produced, a spring cohort, a summer cohort and an overwintering one. In the shallower innermost northern part of Monolimni lagoon, breeding peaked in mid-spring and, also, in early autumn, and two discrete cohorts, a spring and an overwintering one, were produced. A lack of large individuals, attributed to a temporary size - selective predation by migrating shorebirds, was observed during summer. That lack possibly contributed to the hiatus in reproduction. Photoperiod seemed to be a more important cue than temperature in the initiation of the reproductive cycle, while extremely low salinities (<1 psu) did not deter breeding. Females attained maturity at a smaller size in late spring and, especially, in summer than in early spring at lower temperatures. Brood size was a function of females' body size. Females, matured during summer at high temperatures, showed the lowest brood size, body length ratio. Mean brood size was small (12-13 early embryos) and embryo loss during development high (54%), possibly due to a negative effect of low salinities. A 1:1 sex ratio existed in the small body length classes, but females preponderated in the large ones. The spring cohort in the southern part, which developed at moderate temperatures, showed the highest growth rate (40 mu m day super(-1)). Secondary production of C. orientalecalculated by Hynes's method gave a mean annual density of 4562.5 and 9327.6 ind. m super(-2), a mean annual crop (B) of 1.03 and 2.67 g DW m super(-2), an annual production (P) of 6.91 and 22.54 g DW m super(-2) and a P/B ratio of 6.7 and 8.4 in the northern and southern part of the lagoon, respectively.