A Method For Marking Small Juvenile Gastropods

Methods used to identify individual organisms consistently over time have been invaluable tools in ecological studies, enabling reliable assessments of time-dependent parameters such as growth and mortality, and an accurate determination of their variance. These methods have proved to be particularly amenable to gastropods owing to the presence of an external shell on which marks or tags can be applied with little or no adverse effects on the animal. Marking and tagging techniques have enabled the study of several ecological parameters in adult marine gastropods, including growth (Frank, 1965; Hughes, 1972; Palmer, 1983; Gosselin & Bourget, 1989), mortality (Frank, 1965; Hughes, 1972), movements (Frank, 1965; Chapman, 1986), and foraging behaviour (Menge, 1974; Hughes et al., 1992). Small organisms, however, can pose considerable problems for individual marking (Southwood, 1978). As a result, marking and tagging methods have seldom been applied to newly hatched or recently settled juvenile marine gastropods. Several methods have been developed for simultaneously labelling large numbers of invertebrate larvae (Levin, 1990), and some of these methods may be applicable to juvenile gastropods. The usefulness of these methods, however, is limited because all animals receive the same label and, consequently, individual animals cannot be recognized. To my knowledge, no method of individually marking very small juvenile marine gastropods has been documented. In fact, it is sometimes perceived that small juveniles cannot be individually marked due to their small size and sensitivity (Frank, 1965; Palmer, 1990). The object of this paper is to present a simple method of marking early juvenile gastropods, which consists of applying colour codes to the shells of individuals as small as 0·9 mm in length.