The Gammaridea (Amphipoda) Fauna in a Mediterranean Coastal Lagoon: Considerations on Population Structure and Reproductive Biology

For two years, monthly samples were collected in Encanyissada coastal lagoon (Ebro Delta, N.W. Mediterranean Sea) to investigate certain aspects of the population structure and reproductive biology of the dominant species of amphipods. A total of 23 species of Gammaridea was collected, but only three species are frequent and abundant in the samples: Monocorophium insidiosum (Crawford, 1937), Gammarus aequicauda (Martynov, 1931), and Ericthonius brasiliensis (Dana, 1855). The abundance (CPUE) of all three species showed seasonal variation, with highs in autumn-winter and lows in summer, and with sex ratios favouring females. The breeding activity of M. insidiosum is high in winter and probably continuous throughout the year; brood size is related to the size of the female (range 1-36, mean value 10.2); total body length of ovigerous females ranged from 1.8 to 6.0 mm; the estimated growth rate was 14-43 μm d−1. G. aequicauda is the most regular species in the samples; its estimated growth rate was 21-99 μm d−1; breeding activity is continuous throughout the year, and brood size was also related to female size (range 1-87, mean value 23.6); total body length of ovigerous females ranged from 5.0 to 12.0 mm. The breeding activity of E. brasiliensis is very similar to that shown by M. insidiosum; brood size was also related to female size, but the mean number of eggs is lower than in M. insidiosum (mean value 7.7, range 1-24); total body length of ovigerous females ranged from 1.7 to 5.6 mm; its estimated growth rate was 20-56 μm d−1. /// Durante dos años, se ha realizado un muestreo mensual en la laguna costera de la Encanyissada (Delta del Ebro, NO Mediterráneo) con la finalidad de investigar ciertos aspectos de la estructura poblacional y la biología reproductiva de las especies dominantes de anfípodos. Un total de 23 especies de Gammaridea fueron capturadas, pero sólo tres fueron frecuentes y abundantes en las muestras: Monocorophium insidiosum (Crawford, 1937), Gammarus aequicauda (Martynov, 1931) y Ericthonius brasiliensis (Dana, 1855). La abundancia (CPUE) de las tres especies muestra variación estacional, siendo máxima en otoño-invierno y mínima en verano. En las tres especies, las hembras son más abundantes que los machos. La actividad reproductora de M. insidiosum es alta en invierno y probablemente continua durante todo el año; el tamaño de la puesta está correlacionado con el tamaño de la hembra (rango 1-36; valor medio 10,2); la longitud total de la