Niche adaptation in two marine gastropods, Monodonta turbiformis and M. turbinata

Several behavioural, physiological and morphological parameters were studied in two marine gastropods to better define niche differences between the species. M. turbiformis is adapted to a broader more variable niche where as M. turbinata has more stringent niche requirements. This study demonstrated that M. turbinata as compared with M. turbiformis has: a) greater foot muscle strength, b) shorter more squat shell form, c) greater body weight per shell weight and d) greater foot size per body weight. M. turbiformis has a) greater resistance to desiccation and low temperature and b) a more slender shell form. Qualitatively, M. turbiformis appears less effected by elevated temperatures to 40° C. In the laboratory, M. turbinata is more sensitive to crowding. In the field, M. turbinata is found principally in high energy situations with respect to surf action or water flow on or over rocks to which it is attached. On the other hand, M. turbiformis is exclusively found in relatively quiet, shallow water, behind barriers protected from all but the most violent sea action. These data and observations are consistent with M. turbiformis being adapted to a niche with greater extremes with respect to temperature, desiccation and possibly oxygen and metabolic waste product levels. M. turbinata, in part due to its foot muscle strength and shell morphology, is adapted to a high energy niche which would be less varied with respect to the parameters described.