ABSTRACT
Ontogenetic changes in body colouration are known to occur in some benthic marine invertebrates and have been associated with ecological shifts in diet and physiological tolerance. It is not known, however, whether ontogenetic colour changes are common among benthic marine invertebrate species or which mechanisms control these changes in body colour. This study therefore examines the degree of lightness in body coloration (converted to greyscale); the specific goals were to determine (1) the proportion of species that undergo a change in body colour lightness from a sample of 15 intertidal species, (2) if changes in lightness during ontogeny are associated with changes in microhabitat use, and (3) if diet or exposure to light affects the production of shell pigmentation in the snail Nucella ostrina, which are known to hatch white but later add coloured pigments to new shell growth. For each of the 15 species that I examined, 60-140 individuals of varying sizes were collected, weighed, and their body lightness index was quantified using digital imaging. Six motile species were then analyzed for a microhabitat shift during ontogeny. Of the 15 species studied, 11 underwent some degree of change in body colour lightness during ontogeny. Six of those 11 species had a change in body colour lightness of at least 10% between the 10 smallest and 10 largest individuals. The study of microhabitat use by six motile species revealed only one (a hermit crab) that substantially changed microhabitat use during ontogeny; two species partially changed microhabitat use during ontogeny, one other species showed no change, and results were inconclusive for the last two species. The last experiment revealed that N. ostrina hatchlings raised in the dark remained significantly lighter in colour than those exposed to light and that diet did not appear to impact shell colour, indicating that the production of dark shell pigmentation in this species is stimulated by exposure to bright sunlight.
