| Sumario: | The life cycle and growth of the mud-snail Heleobia australis was studied in the Bahía Blanca estuary (Argentina) from April 2008 to April 2010. Four age classes were identified. This species recruits once a year, during summer. In general, the recruits (< 2.5 mm) represented a small percentage of the total population. The growth rate of H. australis declined with increasing animal size and showed a marked seasonal pattern for the population under study: lower rate during winter and higher rate in summer. A life cycle of approximately 30 months (~2.5 years) was estimated for the population of H. australis in the Bahía Blanca estuary. This population shows variations in growth rate, abundance of recruits, and shell size in relation to more northerly populations. Several factors like parasitism, predation, environmental features, and anthropogenic action may be interacting to produce these differences. This work constitutes the first long-term study of the life cycle of cochliopids. Heleobia australis appears to be a long-lived species and exhibits variations in its life cycle that seem to be influenced by biological and physical variables. Long-term studies that include biological interactions and spatial features of the microhabitats are needed to elucidate patterns in life-history traits of H. australis along its distribution range.
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