The general relationship between body size and density dubbed the energetic equivalence rule has been applied several habitats or organisms, and has been reported many results that supported to this. This relationship is linear with a slope of -0.75. However, almost studies were analyzed at species level, nevertheless analysis of relationship at individual level was also important. And, this hypothesis was not always adapted with technical or biological problems.

In order to evaluate hypothesis of the energetic equivalence rule at both species level and individual level, field observation was conducted using by mobile molluscan assemblages in inter-tidal boulder shore of Amakusa, Southwestern Japan.

As a result, I suggested new optimum relationship between body size and density at individual level, not species level, because energy flux was constrained and not constant with biotic and abiotic factors.