DYNAMICS OF THE ACMAEID LIMPET COLLISELLA SUBRUGOSA AND VERTICAL DISTRIBUTION OF SIZE AND ABUNDANCE ALONG A WAVE EXPOSURE GRADIENT

Abstract

The vertical distribution of the acmaeid limpet Collisella subrugosa (Orbigny) was studied on subtropical Brazilian shores. In a semi-sheltered shore at Ubatuba, monthly monitoring indicated that densities were higher in the mid-intertidal, and lower in the high- and low-intertidal. There was evidence of continuous recruitment mainly to mid- and lower levels on the shore, with a peak in the summer. Shell length increased with tidal height, and this pattern was maintained during the study period. To verify whether these results were consistent over a larger spatial scale, the vertical distribution of size, abundance, and shell shape of C. subrugosa was studied along a wave exposure gradient. Densities were not clearly related to wave action, and other sources of variation such as presence of competitors or secondary substrata appear to influence C. subrugosa distribution. Shell length increased towards the upper intertidal on more exposed shores, but no differences, or the reverse pattern was recorded on sheltered shores. These results are consistent with other studies on limpet distribution, and proposed causes include differential recruitment, migration, or microhabitat availability. Shell height increased faster with shell length in lower intertidal levels, and on more exposed sites. Foot surface area also increased faster with shell length on more exposed shores and indicate that wave action is an important factor determining shell shape in C. subrugosa. Additional sampling of upper and lower populations along a gradient of wave exposure in Florianopolis (southern Brazil) resulted in similar patterns of shell size, but the relationships between shell height and length for these populations were similar and isometric. Thus, there is a geographic variation in the vertical distribution of C. subrugosa, and possible causes include distinct physical conditions or differences in phenotypic plasticity of this limpet.