Behaviour and ecological importance of a mud snail (Ilyanassa obsoleta) population in a temperate macrotidal estuary

Abstract

A population of Ilyanassa obsoleta was sampled during the 8-month period when they are present in the intertidal zone in the Southern Bight of Minas Basin, Bay of Fundy. Mud snails were first observed in April, and spawning took place in late May and early June. Flesh weight increased between May and November, with the highest growth rates recorded during August and September. During November the population returned to the subtidal zone, where energy reserves are partially utilized during winter. Clustering and differential habitat selection (salt marsh or mud flat) within size classes resulted in large spatial variations in density, standing stock, and production. Production by I. obsoleta averaged 1.1 g C∙m−2 during their stay in the intertidal zone. The supply of carbon from epibenthic microalgae is insufficient to meet the requirements of this population. Detritus derived from Spartina is believed to be an important additional source of carbon. Ilyanassa obsoleta is not a major prey item of any of the better known predators in this region. Their importance to the intertidal community results from the direct (predation) and indirect (competition, disturbance, nutrient regeneration, and bioturbation) influence of their presence on sedimentary microbial processes and the resident benthic flora and fauna.