Comparison of Talitrus saltator (Amphipoda, Talitridae) biology, dynamics, and secondary production in Atlantic (Portugal) and Mediterranean (Italy and Tunisia) populations

Abstract

Talitrus saltator biology, population dynamics, and reproduction were studied more or less simultaneously at three sand beaches: Lavos, on the western coast of Portugal; Collelungo, on the Italian coast of the Thyrrenian Sea; and Zouara, on the northern coast of Tunisia. The species exhibited a consistent pattern of aggregated distribution. Densities were higher at Lavos than at Collelungo and Zouara. Reproduction took place from early March to late September at Lavos and Collelungo, and from late February to early November at Zouara. The average sex ratio was favourable to males at Lavos and Collelungo, and to females at Zouara. Based on data from Lavos, the population abundance was positively correlated with temperature, while the percentage of juveniles in the population was positively correlated with temperature and sediment moisture. Adult individuals from the Atlantic population were larger than the Mediterranean ones, while newborn individuals from the Mediterranean were slightly larger than Atlantic ones. Life span was estimated at 7-11 months at Lavos, 6-9 months at Collelungo, and 6-8 months at Zouara. Cohorts born at the beginning of the reproductive period tend to have shorter lives than the ones born later in the season, with longer life spans occurring in cohorts that crossed the winter to breed in the next year. The minimum period necessary for sexual differentiation after birth was estimated at ±4 weeks at Lavos, ±3 weeks at Collelungo, and ±4.5 weeks at Zouara, for males, and ±6 weeks at Lavos, and ±5 weeks at Collelungo and Zouara, for females. The period necessary for female's sexual maturation after being born was estimated at ±10 weeks at Lavos, and ±8 weeks at Collelungo and Zouara. At the studied sites, T. saltator appeared as semiannual species, with iteroparous females appearing to produce at least two broods per year, and exhibited a bivoltine life cycle. Growth production (P) was estimated at 0.74 g m-2 yr-1 ash-free dry weight (AFDW; 17.7 kJ m-2 yr-1) at Lavos, 0.12 g m-2 yr-1 AFDW (2.8 kJ m-2 yr-1) at Collelungo, and 0.61 g m-2 yr-1 AFDW (14.3 kJ m-2 yr-1) at Zouara. Elimination production (E) was estimated at 1.40 g m-2 yr-1 AFDW (33.5 kJ m-2 yr-1) at Lavos, 0.20 g m-2 yr-1 AFDW (4.8 kJ m-2 yr-1) at Collelungo, and 1.11 g m-2 yr-1 AFDW (26.6 kJ m-2 yr-1) at Zouara. The average annual biomass (standing stock) was estimated at 0.13 g m-2 at Lavos, 0.014 g m-2 at Collelungo, and 0.084 g m-2 at Zouara, resulting in ratios of 5.7 at Lavos, 8.2 at Collelungo, and 7.3 at Zouara, and ratios of 10.8 at Lavos, 14.4 at Collelungo, and 13.1 at Zouara. The present results, combined with information from literature, revealed a geographic variation in T. saltator populations with regard to their morphological characteristics, growth rates, life spans, and life cycles.