Arctica islandica (Bivalvia) clearance rates and selective feeding in the White Sea

The ocean quahog Arctica islandica (Linnaeus, 1776) is widespread in the North Atlantic and the adjacent polar waters, including the White Sea. It has been the focus of extensive research due to its commercial value and extreme longevity. However, little is known about its trophic behavior apart from several laboratory experiments using cultured algae. In this study, clams (average shell length 23.4 ± 1.89 mm, wet weight 3.15 ± 0.85 g) were fed with plankton freshly collected from the White Sea coast. In the course of a 4-h experiment, Arctica cleared a wide spectrum of particles, ranging from picoplanktonic cyanobacteria (<2 µm) and nano-cryptophytes to diatom chains (>250 µm in length). The clearance rates measured on different plankton species ranged from 0.53 l h–1 to 4.27 l h–1. In mass-specific terms, the maximum Arctica clearance rates (6.02 l h–1 g–1 wet tissue weight) corresponded to those published earlier for intertidal mussels such as Mytilus edulis Linnaeus, 1758. The estimated prey selectivity increased non-linearly with particle size, but the clams also discriminated between prey of similar size and taxonomy. In addition to their preferred diatom phytoplankton, the clams also cleared heterotrophic dinoflagellates and other microconsumers. Based on the Arctica ingestion rates, its ration equaled ~1% of its tissue carbon per day and corresponded to an estimated growth rate of 0.003 d–1.