Macrofauna of Canadian arctic fjords

Abstract

Deposition of fine glacial sediments in Canadian arctic fjords decreases downfjord from the source. Soupground substrates near the head give way to softgrounds and then to firmgrounds in the outer regions. Intertidal areas are strongly affected by sea ice. Faunal communities reflect substrate characteristics. The muddy, soupground substrate supports a community of benthic infauna, in which errant polychaetes such as Nereis pelagica coexist with mobile deposit-feeding bivalves, including Portlandia arctica, Nucula belloti and Nuculana pernula. Forms are typically inflated and possess attached bristle-like hydrozoans. The firmground communities are dominated by epifaunal species, especially pectens, Chlamys islandica or Delectopecten groenlandicus, old shells of which litter the bottomcreating shell pavements. Hardground communities occur on sidewalls and in microcosm on isolated ice-rafted cobbles to form faunal islands. Shell and gravel surfaces support epifauna including anthozoans (octocorals), bryozoans, tunicates, porifera and serpulid polychaetes. Echinoderms, especially ophiuroids (brittlestars) dominate the epifaunal communities, increasing in species diversity, density and size toward the mouths of the fjords. Intertidal areas support a biota dominated by bivalves, polychaetes and fucoid algae. In the subarctic marine zone, a distinct subarctic macrofauna consisting of Macoma balthica, Mytilus edulis, Arenicola marina, Littorina saxatilis and Semibalanus balanoides cohabit with panarctic shallow-water species such as Hiatella arctica, Mya truncata and Musculus discors. In the arctic marine zone, the intertidal macrofauna consists solely of panarctic shallow-water species, including Macoma calcarea and Balanus balanus, in addition to H. arctica, M. truncata and M. discors.