Variation in abundance and size-structure of populations of the small chiton, Acanthochitona retrojecta

Abstract

Hierarchically-nested sampling designs were used to test hypotheses about the population ecology of the small chiton Acanthochitona retrojecta (Pilsbry) in coralline algal turf on rocky shores near Sydney, Australia. Spatial sampling in January 1998 demonstrated that these small chitons were more abundant in mid- than in low-shore areas and more abundant on shores north of compared with those south of Sydney Harbour. Densities of A. retrojecta were extremely high, often exceeding 3500/m2. Temporal sampling showed there was little variation in the total abundance of A. retrojecta at scales of weeks and months. Nevertheless, there were significantly more juvenile chitons in June and July, which was offset by a reduction in the abundance of adults at the same time. The lengths of chitons ranged from 0.59 mm to 9.56 mm and size-frequency distributions demonstrated that A. retrojecta recruits continuously throughout the year. Several aspects of the population ecology of A. retrojecta differed greatly from those of previously studied species of larger chitons. These differences may be a function of the unique biology of A. retrojecta or be related to its unusually small size. More information is needed on other species of small chitons before general patterns of difference can be properly evaluated. © The Author 2005. Published by Oxford University Studies, all rights reserved.