Does population structure and growth of an intertidal pulmonate snail reflect environmental conditions within a small estuary?

The aim of this research was to determine if population attributes and growth of an estuarine pulmonate could be used as bioindicators of environmental conditions in New Zealand estuaries. We quantified the size distribution of the deposit feeding Amphibola crenata in areas which contrasted in contaminant inputs. Within a small estuary, location and tidal level significantly affected A. crenata density. The highest mean abundances were found at the most contaminated site, close to the waste treatment discharge point, compared with lower densities at two river sites and close to the estuary mouth. The population structure was site-specific with juveniles present in historically contaminated areas. Growth of A. crenata held in experimental cages for 6 weeks was highest for medium length individuals from close to the waste discharge point and least for individuals from the estuary mouth. Sediment surface microalgal biomass (chlorophyll a), representing the potential food supply for A. crenata was greatest at the least contaminated site, and lowest at the most polluted site. The abundance, population structure and growth rate of A. crenata are attributes that may be used as ecological bioindicators, reflecting the complex environmental conditions within New Zealand estuaries. [ABSTRACT FROM AUTHOR]