The effects of experimental protocol and behaviour on evaporative water loss during emersion in three species of rocky shore gastropods

Abstract

Evaporative water loss in intertidal gastropods as determined by a technique using repeated measures under ambient fluctuations of temperature and relative humidity provided a reasonably replicable estimate of percent total body water loss and evaporative water loss rates for the eulittoral fringe species, Nodilittorina unifasciata. However, the pattern of percent total body water loss during emersion by the eulittoral gastropod Nerita atramentosa determined at different times and localities differed significantly, especially during the first week of emersion. Differences in water loss during emersion are attributable in part to environmental circumstances but also especially to differences in behaviour fostered by the different local desiccating conditions. The manner by which evaporative water loss was determined significantly affected the percent total body water lost during emersion in the above species and Nodilittorina australis. Specimens subjected to repeated measures demonstrated higher percent total body water loss than those which were not subjected to repeated handling. Water loss determined by the latter method, however, was considerably more variable from one measurement period to the next. There was very little difference in the rate of water loss between specimens subjected to different experimental procedures after the first few days of emersion. Reasons favoring the use of repeated measures procedures are discussed.