Testing a nearshore biophysical classification system

• Main Author: Morris, Mary
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/4409

Habitat managers in BC have identified the need for a nearshore subtidal habitat classification system to inventory nearshore biophysical resources. The objective of this thesis was to develop a nearshore habitat model, as defined by algal assemblage, substrate, depth and wave exposure. The model for the Gabriola Island study area in the southern Strait of Georgia and representative of bedrock-dominated, semi-exposed coastline was developed from two existing datasets: 1) a systematically-quantified subtidal algal survey collected in the Gabriola area; and 2) a regional physical intertidal shore-zone mapping system. Algal assemblages were determined using TWINSPAN multivariate cluster analyses of the algal dataset, and nine subtidal algal assemblages were identified. The algal assemblages were linked to four specific substrate definitions and to four nearshore depth intervals: 0-2 m, 2-5 m, 5-10 m and 10-20 m. The physical shore-zone dataset was used to extrapolate the algal assemblage results by substrate and wave exposure. Predictions from the model for nearshore substrate and algal assemblages by depth interval were compared to independendy-collected observations from eight subtidal transects at Saltery Bay Provincial Park, approximately 80 km north of the Gabriola area, in the Strait of Georgia. The predictions for the nearshore substrate descriptions from the physical shorezone data at least partly-matched the observed substrate descriptions in 86% of comparisons. Predictions for the nearshore algal assemblages by depth interval and substrate, at least partlymatched the observed algal species assemblages every time when the substrate descriptions from transect observations were used as the basis for the prediction. The complete matches were 45% of the comparisons. When the predicted substrate was the basis for the predicted algal assemblages, matches and partial-matches dropped to 89% of the comparisons, and complete matches were only 24% of the comparisons. From the nearshore biophysical habitat model, algal assemblages can be predicted with the most confidence for three general habitat descriptions: 1) shallow ( < 5 m depth), immobile bedrock/boulder substrate, 2) shallow (<7 m), sand/mud/pebble substrate, and 3) deeper than 5 m, with continuous to scattered boulder/bedrock. General estimates of 'standing crop', calculated from the biological database for the general types 1) and 3) can be used together with mapped nearshore depth intervals and predicted substrate to provide a first approximation of nearshore biomasses for these assemblages. Although these represent a 'best guess' of algal standing crop, there are currently no systematic summaries of the nearshore environment. The nearshore subtidal biophysical habitat classification model can be used as a basis for a general regional summary of the nearshore habitat in the higher wave exposure areas of the southern Strait of Georgia. === Science, Faculty of === Botany, Department of === Graduate