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 AE4 weeks at Lavos, AE3 weeks at Collelungo, and AE4.5 weeks at Zouara, for males, and AE6 weeks at Lavos, and AE5 weeks at Collelungo and Zouara, for females. The period necessary for female's sexual maturation after being born was estimated at AE10 weeks at Lavos, and AE8 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 ÿ2 yr ÿ1 ashfree dry weight (AFDW; 17.7 kJ m ÿ2 yr ÿ1 ) at Lavos, 0.12 g m ÿ2 yr ÿ1 AFDW (2.8 kJ m ÿ2 yr ÿ1 ) at Collelungo, and 0.61 g m ÿ2 yr ÿ1 AFDW (14.3 kJ m ÿ2 yr ÿ1 ) at Zouara. Elimination production (E) was estimated at 1.40 g m ÿ2 yr ÿ1 AFDW (33.5 kJ m ÿ2 yr ÿ1 ) at Lavos, 0.20 g m ÿ2 yr ÿ1 AFDW (4.8 kJ m ÿ2 yr ÿ1 ) at Collelungo, and 1.11 g m ÿ2 yr ÿ1 AFDW (26.6 kJ m ÿ2 yr ÿ1 ) at Zouara. The average annual biomass ð B BÞ (standing stock) was estimated at 0.13 g m ÿ2 at Lavos, 0.014 g m ÿ2 at Collelungo, and 0.084 g m ÿ2 at Zouara, resulting in P= B B ratios of 5.7 at Lavos, 8.2 at Collelungo, and 7.3 at Zouara, and E= B B 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.

The biology, population dynamics, and production of Talorchestia brito were studied at two sandy beaches located on the Atlantic (Portugal) and on the Mediterranean (Tunisia) coasts, respectively. The seasonal variation in abundance and the overall densities were similar in both populations. Reproduction occurred from February to September in the Atlantic, and from March to early November in the Mediterranean. The sex ratio was male biased in the Atlantic, and female biased in the Mediterranean. Based on data from the Atlantic population, both abundance and the proportion of reproductive females were positively correlated with temperature, while the proportion of juveniles in the population was positively correlated with temperature and sediment moisture. On average, individuals from the Atlantic were larger than the ones from the Mediterranean. Life span was estimated at six to nine months in the Atlantic, and five to eight months in the Mediterranean. Talorchestia brito was shown to be a semiannual species, with iteroparous females producing two broods per year, and exhibited a bivoltine life cycle. The minimum age required for males' and females' sexual differentiation and for female sexual maturation was shorter in the Mediterranean. Growth production (P) was estimated at 0.19 g m ÿ2 y ÿ1 ash free dry weight (AFDW; 4.3 kJ m ÿ2 y ÿ1) in the Atlantic population, and 0.217 g m ÿ2 y ÿ1 AFDW (4.9 kJ m ÿ2 y ÿ1) in the Mediterranean one. Elimination production (E) was estimated at 0.35 g m ÿ2 y ÿ1 AFDW (7.9 kJ m ÿ2 y ÿ1) in the Atlantic, and 0.28 g m ÿ2 y ÿ1 AFDW (6.3 kJ m ÿ2 y ÿ1) in the Mediterranean. The average annual biomass (B B) (standing stock) was estimated at 0.032 g m ÿ2 in the Atlantic beach, and 0.029 g m ÿ2 in the Mediterranean one, resulting, respectively, in P= B B ratios of 5.9 and 7.5 and E= B B ratios of 10.8 and 9.6. Like other talitrids, T. brito exhibited geographic variation in morphometrical characteristics, sex ratio, growth rates, life span, and reproduction period, with the Atlantic population presenting a slower life history.

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Zonation, biology, and reproduction of two populations of Talitrus saltator (Amphipoda, Talitridae) were studied at two different beaches: Zouaraa and Korba, respectively, in the north and northeast of Tunisia. Sampling was carried out monthly or twice a month along a transect from the shoreline up to the dunes, at Korba. Densities and mean zonations were calculated for each sampling period. Environmental factors (sand moisture, sand and air temperature, humidity, precipitation, wind direction and velocity, cloudiness, and atmospheric pressure) were simultaneously recorded and used to assess their influence on zonation, density, and other biological parameters of the species, notably the percentage of juveniles and the sex ratio. The two populations exhibited a similar zonation: a main distribution on the dunes in winter and near the shoreline in summer, and dispersion along the transect in autumn and spring. Moreover, juveniles occurred, in most cases, lower on the shore than adults, whereas no differences were observed between sexes. The two populations exhibited two different patterns of seasonal variation in density: at Zouaraa, the highest densities were recorded in winter and the lowest in summer, whereas at Korba, the population showed a totally opposite pattern. Furthermore, statistical analysis showed, from all the environmental parameters chosen, a main influence of temperature and sand moisture on the distribution and reproductive biology of Talitrus saltator. RÉSUMÉ La zonation, la biologie et la reproduction de deux populations de Talitrus saltator (Amphipoda, Talitridae) ont été étudiées dans deux sites différents, Zouaraa et Korba, respectivement, dans le nord et le nord-est de la Tunisie. Un échantillonnage mensuel ou semi-mensuel a été effectué le long d'un transect depuis la ligne de rivage jusqu'au sommet des dunes, et ce à partir de décembre 1998 jusqu'à mai 2000 à Zouaraa et de décembre 2001 jusqu'à décembre 2003 à Korba. La densité et la zonation moyenne ont été estimées pour chaque période d'échantillonnage. Les facteurs 1 )

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