Density and shell-size variation of Nodilittorina lineolata (Orbigny, 1840) in the intertidal region in southeastern Brazil

Abstract

Nodilittorina lineolata is a small littorinid characteristic of the supralittoral of rocky shores but extends its vertical range to the lower midlittoral. Shell-size and density of Nodilittorina were measured at two different levels, the supralittoral and barnacle zones, in six sites along the south-eastern Brazilian coast. The sites studied varied in the degree of wave exposure. Densities were lower in the supralittoral, and higher overall values occurred on the most exposed shores. Shell size increased significantly in an upshore direction at five of the six sites. However, mean-size and the magnitude of the difference between levels varied according to the site studied. The shell-size gradient can be explained by larval recruitment in the barnacle zone and subsequent ascending migration to the supralittoral zone, where the larger individuals were found. Reciprocal transfer experiments revealed that differential mortality of large individuals in the lower levels, possibly due to lack of refuges, may also influence the size-distribution. It was also shown that some individuals can be passively transported to upper levels of the shore by wave action during storms.