Benthic habitats of a sub-arctic fiard: the case study of Okak Bay, Labrador

Carpenter, Mallory (2012) Benthic habitats of a sub-arctic fiard: the case study of Okak Bay, Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

The objective of this thesis is to classify and map the nature and distribution of benthic marine habitats of Okak Bay. Okak Bay is an irregularly shaped, generally shallow, low elevation estuary best described as a fiard, on the central Labrador coast. Supervised classification of multibeam sonar bathymetry and backscatter data ground-truthed with substrate and biotic samples were used to map the seafloor. Cluster analysis of grain size data from 123 substrate samples indicated 7 classes: mud, sandy mud, sandy, gravelly mud, gravelly sand, kelp and bedrock/boulder. Analysis of similarity and similarity percentage analysis show that the 7 substrates support 5 statistically distinct habitats, divided into soft-bottom: mud, sandy mud, and gravelly sandy mud; and hard-bottom: kelp and bedrock/boulder. Key species comprising the soft-bottom habitats are deposit-feeding bivalves and polychaete, whereas encrusting epifauna dominates the hard-bottom habitats. The accuracy of the substrate and habitat maps was assessed at 71% and 82%, respectively. A sensitivity analysis of habitats to potential stressors suggests that kelp and gravelly sandy mud are most vulnerable to a variety of impacts including the majority of fishing activities and physical environment changes such as increases in turbidity and sedimentation, and steps should be taken to protect representative areas. The distribution and nature of habitats within Okak Bay differed significantly from others Labrador fiords, supporting the hypothesis that fiards are distinct marine estuarine systems, both physically and oceanographically, and developing a better understanding of these habitats will contribute to resource management initiatives within the central Labrador region as a whole.

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