Exploring the role spatial scale plays in marine habitat mapping using multiscale geomorphometric analyses

The study of terrestrial ecosystems at various spatial and temporal scales has proven beneficial for
understanding a number of important ecological processes, but has not received the same level of
attention in marine ecology, largely due to a more difficult access to data at multiple scales. Broadscale
data can miss patterns linked to local-scale processes. While Remotely Operated Vehicles
(ROV) allow the collection of high resolution data in the deep sea, such detailed data sets are not
necessarily the most appropriate for understanding distributions. In most studies, the scale of analysis
is often arbitrarily based on the available data, which can be misleading if the scale of analysis does
not match the scale of ecological process under investigation. Spatial scale is therefore probably one
of the most misunderstood concepts in marine habitat mapping.

The research presented here aims to further explore the role that spatial scale plays in
understanding and mapping deep-sea benthic habitats. Environmental and topographic variables are
known to be important to understand the spatial distribution and spatial ecology of benthic organisms
and habitat structures at several scales. We apply an approach which studies these variables and
patterns across a continuum of spatial scales, using different resolution bathymetric datasets, in order
to create a continuous range of scales.

We present preliminary results obtained from the application of this multiscale approach to coldwater
coral habitats in Canada. High-resolution multibeam sonar, video and oceanographic data were
collected in 2010 and 2011 in the Northwest Atlantic (Flemish Cap and Orphan Knoll, near
Newfoundland) and on the Pacific continental shelf (Strait of Georgia, British Columbia), using the
Canadian ROV ROPOS. Multibeam bathymetric data were collected using the ROV either close to the
seafloor (1-2m height), and/or at an altitude of 20m off-bottom. Vessel-mounted multibeam
bathymetric data are also available from both study areas. These data allowed bathymetric models
(grids) of the seafloor to be generated at the following spatial resolutions: ROV-derived bathymetry,
ranging from 0.1 to 1m resolution; vessel-mounted multibeam bathymetry ranging from 2 to 50m
resolution; General Bathymetric Chart of the Oceans (GEBCO) derived grids at 30-seconds resolution
(around 865m at this latitude). Observations of corals were obtained from the ROV video data at the
local scale, and from scientific trawl surveys at the regional scale.

Using these data, the importance of seafloor morphology in structuring coral habitats was studied
across the range of spatial scales in order to characterize their respective niche and to define their
most appropriate scale for which to investigate their predicted distribution. Geomorphometric attributes
(e.g. slope, aspect, curvatures) were measured for each bathymetric datasets, with a particular
emphasis given to attributes expressing the complexity of the seafloor, such as Bathymetric Position
Index (BPI) and Vector Ruggedness Measure (VRM). Linear correlations were calculated between
geomorphometric attributes and area-normalized presence of six functional groups of corals: soft
corals, small gorgonians, large gorgonians, sea pens, stony cup corals, and black corals.

Using the GEBCO bathymetry and the observations from scientific trawl surveys, depth showed a
positive relationship with all the functional groups except soft corals. Slope was positively correlated
with cup corals, soft corals, and small gorgonians. Standardized fine-scale and broad-scale BPI were
negatively correlated with black corals and sea pens, but positively correlated with soft corals. Finescale
BPI presented a negative correlation with stony cup corals and small gorgonians, but not broadscale
BPI. VRM was positively correlated with all coral groups except soft corals: the three scales of
measured VRM had a relationship with small gorgonians, the broadest scale with stony cup corals,
and the two finest with sea pens.

More analyses are required to explore more geomorphometric attributes and the multicolinearity
effect between them, and to understand the complex interactions between the different morphological
characteristics of the seafloor and cold-water coral habitats at different scales.

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