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Population Dynamics and Production of the Amphipod Orchestia Gammarellus (talitridae) in a Ria Formosa Saltmarsh (Southern Portugal)

2003; Brill; Volume: 76; Issue: 9 Linguagem: Inglês

10.1163/156854003322753448

1568-5403

Martin Sprung, Natália Dias,

Aquatic Invertebrate Ecology and Behavior

[Population dynamics and production of the amphipod, Orchestia gammarellus were studied for two years in a Ria Formosa saltmarsh (southern Portugal). The animals were sampled every 6th week using pitfall traps and core samples. The highest densities were recorded in the organic matter deposits during spring 1999 (core samples) and most intense activity (pitfall traps) during autumn 1998. Females lived for 8-11 months and reached up to 14 mm body length while males lived for 8-12 months and reached 17 mm body length. Reproduction was continuous and started when females were 6-7 months old. Females produced, on an average, 17 eggs each and fecundity increased with size. Sex ratio was 58% on an annual average. Daily mortality was generally high (0.9%) with higher values in spring/summer (1.8%) and lower in autumn/winter (0.5%). Significant differences in the Von Bertalanffy growth curves were found with males growing faster than females. Annual production has been calculated by the increment summation method as 1.4 g AFDW/m2 with a corresponding P/B ratio of 3.9. Production rate was highest in spring and summer 1999. It is pointed out that O. gammarellus has adopted an r-strategy to exploit this saltmarsh. A dinâmica de populacoes e a producao do anfipode Orchestia gammarellus foram estudadas durante dois anos num sapal da Ria Formosa (Sul de Portugal). Os animais foram capturados a cada 6 semanas utilizando armadilhas e cores. As densidades mais elevadas foram registadas nas zonas com depositos de materia orgânica durante a Primavera de 1999 (cores) e a actividade mais intensa (armadilhas) ocorreu durante o Outono de 1998. As femeas viveram cerca de 8-11 meses e atingiram um comprimento total de 14 mm enquanto que os machos viveram cerca de 8-12 meses e atingiram 17 mm de comprimento total. A reproducao foi continua e comecou quando as femeas tinham 6-7 meses de idade. As femeas produziram, em media, 17 ovos cada uma e a fecundidade aumentou com o tamanho. A media anual da proporcao de sexos foi de 58%. A mortalidade diaria foi geralmente alta (0.9%) com valores mais elevados na Primavera/Verao (1.8%) e mais baixa no Outono/Inverno (0.5%). Foram detectadas diferencas significativas na curva de Von Bertalanffy, crescendo os machos mais rapido que as femeas. A producao anual foi calculada pelo metodo da soma de incrementos como 1.4 g PSLC/m2 com a correspondente razao P/B de 3.9. A taxa de producao foi mais elevada na Primavera e no Verao de 1999. Pensa-se que O. gammarellus adoptou uma estrategia-r para explorar este sapal. , Population dynamics and production of the amphipod, Orchestia gammarellus were studied for two years in a Ria Formosa saltmarsh (southern Portugal). The animals were sampled every 6th week using pitfall traps and core samples. The highest densities were recorded in the organic matter deposits during spring 1999 (core samples) and most intense activity (pitfall traps) during autumn 1998. Females lived for 8-11 months and reached up to 14 mm body length while males lived for 8-12 months and reached 17 mm body length. Reproduction was continuous and started when females were 6-7 months old. Females produced, on an average, 17 eggs each and fecundity increased with size. Sex ratio was 58% on an annual average. Daily mortality was generally high (0.9%) with higher values in spring/summer (1.8%) and lower in autumn/winter (0.5%). Significant differences in the Von Bertalanffy growth curves were found with males growing faster than females. Annual production has been calculated by the increment summation method as 1.4 g AFDW/m2 with a corresponding P/B ratio of 3.9. Production rate was highest in spring and summer 1999. It is pointed out that O. gammarellus has adopted an r-strategy to exploit this saltmarsh. A dinâmica de populacoes e a producao do anfipode Orchestia gammarellus foram estudadas durante dois anos num sapal da Ria Formosa (Sul de Portugal). Os animais foram capturados a cada 6 semanas utilizando armadilhas e cores. As densidades mais elevadas foram registadas nas zonas com depositos de materia orgânica durante a Primavera de 1999 (cores) e a actividade mais intensa (armadilhas) ocorreu durante o Outono de 1998. As femeas viveram cerca de 8-11 meses e atingiram um comprimento total de 14 mm enquanto que os machos viveram cerca de 8-12 meses e atingiram 17 mm de comprimento total. A reproducao foi continua e comecou quando as femeas tinham 6-7 meses de idade. As femeas produziram, em media, 17 ovos cada uma e a fecundidade aumentou com o tamanho. A media anual da proporcao de sexos foi de 58%. A mortalidade diaria foi geralmente alta (0.9%) com valores mais elevados na Primavera/Verao (1.8%) e mais baixa no Outono/Inverno (0.5%). Foram detectadas diferencas significativas na curva de Von Bertalanffy, crescendo os machos mais rapido que as femeas. A producao anual foi calculada pelo metodo da soma de incrementos como 1.4 g PSLC/m2 com a correspondente razao P/B de 3.9. A taxa de producao foi mais elevada na Primavera e no Verao de 1999. Pensa-se que O. gammarellus adoptou uma estrategia-r para explorar este sapal. ]