ADAPTATIONS OF 6 INFAUNAL BIVALVE SPECIES OF CHILE - COEXISTENCE RESULTING FROM DIFFERENCES IN MORPHOLOGY, BURROWING DEPTH AND SUBSTRATE PREFERENCE

Differential colonisation of substrata was shown to be a very importan t factor in the coexistence of six infaunal bivalve species studied he re: Gari solida (Gray, 1828), Semele solida (Gray, 1828), Protothaca t haca (Molina, 1782), Venus antiqua (King and Broderip, 1832), Tagelus dombeii (Lamarck, 1818) and Ensis macha (Molina, 1782). Two elements w ere distinguishable: A horizontal zonation (preference for certain sed iment types), and a vertical zonation (burrowing depth in the substrat um). Morphological characteristics such as body axes orientation, shel l length-height ratio, shell weight and adductor weight are explained as resulting from varying environmental living conditions, a quality o f the niche occupied by individual. According to the multi-dimensional niche, different environmental ranges were found for each species red ucing competition and permitting coexistence in the same environment.