| Summary: | 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
|
|---|
