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Semele solida and Tagelus (Tagelus) dombeii are two tellinacean bivalves which coexist in the lower intertidal zone of a sandflat in south-central Chile but follow different feeding strategies. Wheras T. (T.) dombeii is a suspension-feeder, S. solida is a facultative deposit-feeder. In this study, digestive gland indices and reproductive cycles were described in relation to annual food availability and related to their feeding modes. Results showed that gonadic index cycles were similar for both species, with highest values being observed during the spring when water temperature was still on the rise and microflagellate and centric diatom density was at its peak. However, histological analyses indicated that the spawning period of T. (T.) dombeii extended from November 1995 to March 1996 and from August 1996 to January 1997, whereas S. solida presented a continuous spawning period that extended from September 1995 to December 1996. Results suggest that extended spawning throughout the winter by S. solida is a consequence of its ability to feed on bottom deposits when food in suspension is low.

The scope for growth (SFG) calculated on measurements of physiological variables in juvenile of the predatory gastropod Chorus giganteus was compared with the actual growth under an energetic point of view. The continuous increase in the amount of food ingested and absorbed by C. giganteus was clearly related to the body size of the snails. The pronounced increase in the metabolic processes of respiration and excretion at the end of the study was related with the high rates of growth experienced by the snails under the experimental conditions. These results were supported by the correlation analysis where ingestion rate (r=0.99), oxygen consumption (r=0.88) and excretion rate (r=0.89) were significantly correlated with the actual growth (P≤0.05). Comparing the estimated growth curve (SFG) with that directly measured on juvenile individuals of C. giganteus, a high similarity in results was observed. The high sensitivity of the scope for growth argues for the use of this index as an adequate tool for estimating the growth of juvenile gastropod molluscs without interference from reproductive processes such as gametogenesis and spawning which may produce corresponding rises and falls in the biomass of individuals. Scope for growth is thus validated as a reliable measurement of the physiological/energetic condition of the organism, representing an effective index for indirect estimation of the growth of a species.