19 - Geomorphic Features and Benthic Habitats of a Sub-Arctic Fjord: Gilbert Bay, Southern Labrador, Canada

Abstract

Fjords are geomorphic and biological systems of great interest to geomorphology, oceanography, and marine biology. Fjords typically have complex bathymetry and host highly diverse and heterogeneous habitats, making them challenging environments for marine habitat mapping using acoustic remote sensing. The fjords of Newfoundland and southern Labrador commonly have relatively low relief, are surrounded by forested watersheds, and exist in boreal to sub-Arctic climatic conditions, making them somewhat different from archetypal fjords of the Canadian High Arctic. Gilbert Bay is a shallow-water, low-gradient, sub-Arctic fjord in southeastern Labrador, Atlantic Canada. The bay is composed of a series of basins separated by sills that shallow toward the head. A major side bay with shallow but complex bathymetry includes important spawning and juvenile fish habitat for a genetically distinct local population of Atlantic cod (Gadus morhua). Six acoustically distinguishable substrate types were identified in the fjord, with two additional substrate types recognized from field observations, including areas outside multibeam sonar coverage. Ordination and Analysis of Similarity (ANOSIM) of biotic data generalized five habitat types: hard-substrate habitats developed on cobble-boulder gravel and bedrock bottoms; coralline-algae-encrusted hard-substrate habitats; soft-bottom habitats developed on mud or gravelly mud bottoms; current-swept gravel with a unique biotic assemblage; and nearshore ice-scoured gravels in waters shallower than 5 m depth. Greatest within-habitat biodiversity was found in the coralline-algae-encrusted gravel habitat.