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Fine-scale habitat characterization
of The Gully, the Flemish Cap, and
the Orphan Knoll, Northwest Atlantic,
with a focus on cold-water corals
, Evan Edinger
and Rodolphe Devillers
Fisheries & Aquatic Sciences Program, School of Forest Resources & Conservation, University of
Florida, Gainesville, FL, United States
Geomatics Program, School of Forest Resources &
Conservation, University of Florida, Gainesville, FL, United States
Department of Applied
Geoinformatics & Spatial Planning, Czech University of Life Sciences Prague, Prague, Czech Republic
Department of Geography, Memorial University of Newfoundland, St. John’s, NL, Canada
Department of Biology, Memorial University of Newfoundland, St. John’s, NL, Canada
This case study focuses on the characterization of fine-scale habitats associated with cold-water corals
in three areas off Eastern Canada. Remotely operated vehicle (ROV)-based video, oceanographic, and
bathymetric data were collected in 13 dives ranging from 200 to 3000 m deep at The Gully, the
Flemish Cap, and the Orphan Knoll. Maps of potential habitats were produced and spatially compared
with different taxa distributions, and species distribution models were computed to quantify the
association of different environmental factors with cold-water corals. Results highlighted significant
differences in corals’ environmental preferences at all taxonomic levels. Results also showed the
importance of collecting high-resolution chemical and oceanographic data as their integration with
geomorphometric variables (e.g., aspect, rugosity, slope, topographic position) provides a more
comprehensive picture of environmental niches. The exploration of cold-water coral habitats helped
identify many cases of co-occurrences with a variety of other taxa including many deep-sea sponges.
Keywords: The Gully; Flemish Cap; Orphan Knoll; cold-water corals; deep-sea sponges;
geomorphometry; oceanography; potential habitats; ROV; surrogacy
This study describes fine-scale benthic habitats in three areas off Eastern Canada
(Northwest Atlantic Ocean), with a particular focus on cold-water coral habitats. The Gully,
Seafloor Geomorphology as Benthic Habitat.
©2020 Elsevier Inc. All rights reserved.
the Flemish Cap, and the Orphan Knoll (Fig. 44.1) are known to offer diverse habitats and
to shelter relatively high levels of biodiversity. Ecological marine units (see Sayre et al.,
2017) found in those three areas are generally characterized by cool (,70 m deep) to very
cold waters ( .70 m deep), normal salinity, moderate oxygen levels, medium nitrate levels,
and low phosphate and silicate levels.
Located at the edge of Canada’s continental shelf, The Gully is the largest submarine
canyon in eastern North America and extends from 150 m deep to depths greater than
2000 m. The eastern side of The Gully is characterized by recessional moraines that can
reach several kilometers long and tens of meters in height (Cameron et al., 2016). On the
west side smaller canyons and channels are characterized by ledges, terraces, and steep
slopes of sandstone and semiconsolidated mudstone (Fader and Strang, 2002; Mortensen
and Buhl-Mortensen, 2005). Sandwave fields are also found at the head of The Gully
(Cameron et al., 2016). Mortensen and Buhl-Mortensen (2005) highlighted the geomorphic
and habitat diversity of The Gully.
The Flemish Cap is a continental fragment forming an isolated offshore bank about 600 km
east of the island of Newfoundland, Canada (Piper, 2005). It extends from 126 m deep to
more than 3000 m deep at the bottom of the continental slope (Shaw, 2006). The Flemish
Cap is characterized by steep sides and by narrow and abrupt margins (Funck et al., 2003);
its southern margin has numerous faults and tilted blocks (Welford et al., 2010). The
Flemish Cap has a low sedimentation rate (Huppertz and Piper, 2010), and is one of the
only places at continental shelf depth in Atlantic Canada that does not have extensive
deposits of late Pleistocene glacial till covered with younger proglacial and Holocene
postglacial terrigenous sediment (Piper, 2005; Edinger et al., 2011), allowing continuous
occupation of sponge grounds since the last glacial maximum at least (Murillo et al., 2016).
While the Flemish Cap was apparently not glaciated during the last glacial cycle, it is
strongly influenced by sea ice and icebergs that deliver mixed lithology clasts ranging from
coarse sand through to large boulders, making hard substrates (e.g., boulder-strewn bedrock,
coarse sand with ice-rafted debris) predominant (Shaw, 2006). The hydrodynamic
conditions around the Flemish Cap, influenced by the Labrador Current, the Deep Western
Boundary Current, the Gulf Stream, and the North Atlantic Current, favor a higher level of
primary and secondary production than the rest of the Canadian continental shelf (Maillet
et al., 2005; Stein, 2007).
The last site, the Orphan Knoll, is a foundered fragment of continental crust - a portion of
continental crust that has sunk to depths below the typical depth of the continental shelf -
formerly linked to the Canadian continental margin (Ruffman and van Hinte, 1973;
Enachescu, 2004). While it is less known than the other two areas because of its depth (but
see Ruffman and van Hinte, 1973), recent investigations at the Orphan Knoll established the
presence of a variety of geomorphological features, including seamounts, valleys, terraces,
736 Chapter 44
Map of Eastern Canada showing the three study areas, with the location of the different ROV
dives identified by a star. Examples of the distribution of individual organisms along three
transects—those with a red star—are also shown. The pie charts describe the ratio of observations
of corals, sponges, and other taxa for each of the three areas, and the associated absolute
number of observations. For example, 1616 corals were observed during the six dives at the
Orphan Knoll, representing 8% of all observations recorded on the Orphan Knoll.
and steep slopes (Pe-Piper et al., 2013). The top of the Orphan Knoll, at about 1800 m
deep, contains abundant enigmatic mounds, generally 50150 m high, which together form
a plateau (Parson et al., 1984). Several possible origins for those mounds have been
proposed, including block-faulted bedrock (Meredyk, 2017), a karst plateau of Paleozoic
carbonates (Parson et al., 1984), cold-water coral bioherms (van Hinte et al., 1995), or
hydrocarbon-related mud-volcanos (Enachescu, 2004). Like the Flemish Cap, the Orphan
Knoll was likely not covered by ice during the last glacial maximum and is influenced by
the Labrador Current (Shaw, 2006; Shaw et al., 2006).
This case study focuses on smaller areas located on the slopes of The Gully and the
Flemish Cap, and on the top and sides of the Orphan Knoll and Orphan Seamount.
Naturalness, condition, and trend
Table 44.1 summarizes the condition and trend of the three study areas. While those
describe the entire extent of the features, the smaller surveyed areas had different levels of
naturalness than the features they are on. For instance, one of the surveyed areas at the
Flemish Cap had been trawled. However, most other areas were in more rocky habitats and
did not seem to have been impacted, at least by fishing.
The Gully has long been recognized for its biodiversity, including sensitive benthic fauna
such as corals and sponges, and for its resident population of northern bottlenose whales.
Groundfish fisheries, particularly bottom longline fishing for Atlantic Halibut, have been
long established on its margins. More recently, The Gully is surrounded by extensive
hydrocarbon production activities on the Sable Island Bank, including gas pipelines from a
Table 44.1: Summary of the condition and trend at the three study areas.
score Baseline Trend Confidence Notes
G6 in deeper
2000 Steady High Largely intact, with the exception of some of the
shallower portions of the MPA. The MPA has
been largely monitored since 2004.
G6 in deeper
1900 Steady High Heavily fished in shallow waters, only exploratory
fishing has occurred in deeper waters, which
now has fishery closures.
G7 1900 Steady High Too deep for fishing, no active exploratory oil
and gas drilling. Risk of decline if oil and gas
exploratory drilling expands to the western side
of the Knoll.
738 Chapter 44
number of wells. The Gully was voluntarily closed to oil and gas exploration in the late
1990s to protect the resident whales, and the area was officially protected as a Marine
Protected Area (MPA) in 2004. Bottom longline fishing for Atlantic Halibut is still
permitted in the shallow portions of the MPA, but most of the Gully itself is closed to all
fishing (DFO, 2008).
In international waters managed by the Northwest Atlantic Fisheries Organization (NAFO),
the Flemish Cap has an extensive fishery for a variety of groundfish species. While the
upper parts of the Flemish Cap have been extensively trawled, the deeper portions have had
limited impact from fisheries. European Union fisheries surveys encountered abundant
sponges and cold-water corals in deep portions of the Flemish Cap, which have enjoyed
temporary protection under NAFO fishery closures for Vulnerable Marine Ecosystems since
2012. The Flemish Pass, the deepwater channel between the Flemish Cap and the Grand
Banks, has been an active area for hydrocarbon exploration for more than 10 years, with
several major petroleum discoveries in the last 5 years. None of these have yet been
developed to the production stage.
Unlike the Flemish Cap, the Orphan Knoll is too deep for most commercial fishing. In 2006
NAFO protected the Orphan Knoll from fishing activities, except for experimental trawl
fisheries. While there have been extensive oil industry seismic surveys of the Orphan Knoll,
exploratory drilling has taken place within the Orphan Basin, to the west, but not directly
on the Orphan Knoll.
High-resolution bathymetric, video, and environmental data were collected in July 2010
using the Remotely Operated Vehicle (ROV) CSSF ROPOS (Canadian Scientific
Submersible Facility Remotely Operated Platform for Ocean Science), at depths ranging
from 200 to 3000 m at The Gully (two overlapping transects), the Flemish Cap (five
distinct transects), and the Orphan Knoll (six distinct transects) (Fig. 44.1). The total length
covered by the transects is about 120 km. The bathymetric data were collected using an
Imagenex 837 A DeltaT3000 multibeam system mounted on the ROV. ROPOS
simultaneously collected downward-looking and forward-looking video observations from
about 2 m above the seafloor, in addition to a variety of high-resolution chemical and
oceanographic data (e.g., conductivity, density, nitrogen saturation, pH, plume anomaly,
pressure temperature, thermosteric anomaly). While those video data have been used before
for surficial geology and coral fauna studies on some of the transects (e.g., Meredyk, 2017;
Miles, 2018), this is the first study to look at all transects and to use the bathymetric and
Cold-water Coral Habitats of the NW Atlantic 739
Geomorphic features and habitats
Bathymetric data were processed in Caris HIPS and SIPS 9.1. The level of uncertainty
associated with the data and the prevalence of artifacts in the data prevented the production
of bathymetric surfaces at a very high resolution (Lecours and Devillers, 2015). The
bathymetry was thus generated at 20 m resolution and a low-pass filter was applied to
remove the remaining outliers. A validation analysis was performed against depth values
measured by the ROV navigation system and the ROV-mounted CTD instrument. A suite
of terrain attributes was derived from the bathymetry using the TASSE toolbox for ArcGIS
v1.1 (Lecours, 2017): measures of aspect (i.e., easterness and northerness), relative
deviation from mean value (hereafter referred to as topographic position), slope, and
standard deviation (hereafter referred to as rugosity). The combination of those measures is
considered to optimize the amount of topographic variability that is captured by terrain data
(Lecours et al., 2017).
The oceanographic and chemical data were processed using the SBE Data Processing
software from Sea-Bird Scientific. For instance, hysteresis and tau corrections were
applied to raw oxygen data. Those data were collected every second, enabling a one-to-
one match of environmental data with biological observations, which were extracted from
video data and georeferenced using the ROV navigation data. Biological observations
were logged at sea to the highest possible taxonomic resolution (i.e., lowest taxonomic
level) that could be confidently assigned by experienced observers with taxonomic
expertise; taxonomic resolution varied depending on observations as variations in
illumination, turbidity, and distance and location within the field of view often prevented
a confident identification of observations to the species or genus levels. Observations
were validated in postprocessing.
Differences in mean environmental conditions were statistically evaluated to assess
whether they were similar in the three areas. While The Gully generally presented
some minor differences (e.g., lower oxygen and nitrogen concentrations) when
compared to the other two areas, those differences were not statistically significant.
Following the approach detailed in Lecours et al. (2017), correlation and principal
component analyses were then performed to reduce the number of variables used for
the habitat mapping exercise. For example, those analyses identified relationships
between temperature and nitrogen saturation and between slope and rugosity in this
area. In the end, oxygen concentration, salinity, temperature, depth, rugosity,
topographic position, and aspect (i.e., easterness and northerness) were selected as
uncorrelated variables that were the most representative of this particular environment.
Because fine-scale data collected along transects do not characterize the environment at
a scale suitable for the identification of relevant geomorphic features, habitat maps
were produced using this combination of variables under the assumption that terrain
740 Chapter 44
attributes would serve as proxies for the presence of intermediate-scale (20100 m)
Following methods from Brown et al. (2012) and Lecours et al. (2016), an unsupervised
approach to habitat mapping was used to generate a map of potential habitats for each of
the three study areas. The multivariate clustering algorithm in ArcGIS Pro v.2.1.3 was used
to identify potential habitats, that is, classes that maximize similarity within themselves
while maximizing differences among them. A pseudo-F-statistics was used to determine the
optimal number of classes. Boxplots of standardized values for each environmental variable
were then analyzed to characterize each class, that is, to identify which environmental
factors make a class distinct from the others.
Results are summarized in Table 44.2 (The Gully), Table 44.3 (the Flemish Cap), and
Table 44.4 (the Orphan Knoll), and an example of the resulting classified transects is
shown in Fig. 44.2. Despite being the smallest area, the statistically optimal number of
classes for The Gully was the highest, with 14. The classifications for the Flemish Cap
and the Orphan Knoll respectively identified seven and eight statistically different
potential habitats. Some similarities can be found in the three different maps of potential
habitats. For example, flat areas located on topographic lows were identified as distinct
habitats at both The Gully (Habitat G14) and the Flemish Cap (Habitat F7), where they
respectively accounted for 2% and 31% of the surveyed areas. The Orphan Knoll also had
a similar potential habitat (Habitat O6), which covered about 39% of its surveyed area,
although it differed from habitats G14 and F7 by the fact that the topographic position
variable was on average similar to the other classes. In some cases, those results provide
insights into the presence of some specific geomorphic features. For instance, habitat G6,
which is characterized by waters that are shallower than the average for this dataset and a
low complexity seafloor located at topographic highs, could very likely represent
In order to assess whether or not those potential habitats were associated with specific
taxa, habitatspecies associations were identified by spatially comparing the biological
observations extracted from the downward-looking camera to the habitat classes. Taxa
with more than 50% of their observations belonging to one specific habitat class were
associated with that class, and confusion matrices were built to evaluate the
classifications. Results are summarized in Tables 44.244.4; four of the potential habitats
at The Gully and at the Flemish Cap were found to be strongly associated with specific
taxa, compared to five at the Orphan Knoll. Those habitats cover 41% of the surveyed
area at The Gully, 67% of the area at the Flemish Cap, and 58% for the Orphan Knoll.
Some of the potential habitats were highly associated with only a few species. For
instance, Habitat F1, which covers about 10% of the surveyed area at the Flemish Cap
Cold-water Coral Habitats of the NW Atlantic 741
and was characterized by topographic highs in deep and cold waters, was only associated
with the presence of one species of bamboo corals (Keratoisis sp.). On the other end,
some potential habitats were associated with many different taxa. While the accuracy of
the three classifications was not very high (ranging between 62% and 70%), those maps
of potential habitats provide insights into some of the taxa’s environmental preferences.
For instance, many coral genera were found to favor areas of topographic highs and
higher rugosity, which suggest a relationship to elevated and complex seafloor topography
and geomorphic features.
Table 44.2: Summary of the characteristics of potential habitats at The Gully as defined by the
unsupervised classifications, and of the specieshabitat spatial relationships.
Main habitat characteristics
(distinctive from other
of area (%)
Habitat G1 Areas of topographic lows GFan sponges GAcesta
Habitat G2 Warmer waters with high
salinity and low oxygen
Habitat G3 Shallower waters GPolymastia sp. 20.5
Habitat G4 Areas with higher rugosity
Habitat G5 Coldest waters with high
Habitat G6 Shallowest waters with low
rugosity seafloor located on
Habitat G7 Warmer waters 1.2
Habitat G8 Areas with the highest
oxygen and lower salinity
Habitat G9 Colder waters 2.0
Habitat G10 Areas of topographic highs 10.2
Habitat G11 Deepest waters with high
Habitat G12 Areas of topographic lows
with lower oxygen
Habitat G13 Deeper waters 13.4
Habitat G14 Flat areas on topographic
742 Chapter 44
Overall, more than 65,600 individual organisms were observed on the video data from the
downward-looking camera, of which 19,969 were corals and 24,468 were sponges. As
highlighted in Tables 44.244.4, other observations include, for example, various bivalves,
Table 44.3: Summary of the characteristics of potential habitats at the Flemish Cap as defined
by the unsupervised classifications, and of the specieshabitat spatial relationships.
(distinctive from other
classes) Associated corals
of area (%)
Habitat F1 Topographic highs in
the deepest, coldest
GKeratoisis sp. 10.1
Habitat F2 Shallower, warmer
Habitat F3 Higher rugosity areas
with lower oxygen
Habitat F4 Shallower waters with
lower salinity and
Habitat F5 Shallowest, warmest
waters with high
Habitat F6 Higher oxygen
Habitat F7 Flat areas on
Cold-water Coral Habitats of the NW Atlantic 743
brittle stars, cephalopods, crustaceans, sea anemones, starfishes, tube-dwelling anemones,
urchins, tube worms, and ribbon worms. Inconsistencies with the reporting of observations
make it challenging to generalize them, particularly at higher taxonomic resolutions (e.g.,
species, genus). In addition to observations of individual organisms (e.g., one coral colony,
one sponge, or one urchin), areas with a concentration of a taxon that was too high to count
(high to full coverage of a video frame, e.g., sponge grounds) were identified. As such, 134
sponge concentrations were recorded at The Gully (including 49 concentrations of
Polymastiidae), 17,502 at the Flemish Cap (of which 910 were identified as encrusting
Table 44.4: Summary of the characteristics of potential habitats at the Orphan Knoll as defined
by the unsupervised classifications, and of the specieshabitat spatial relationships.
other classes) Associated corals
of area (%)
Habitat O1 Areas of
Habitat O2 Shallowest areas of
with lower oxygen
Habitat O3 Deepest, coldest
waters with high
Habitat O4 Shallower waters,
Habitat O5 Deeper waters with
Habitat O6 Flat areas 38.5
Habitat O7 Warmer waters with
Habitat O8 Warmest waters
with low salinity
levels and high
744 Chapter 44
sponges), and 5108 at the Orphan Knoll. Over a thousand concentrations of Ectoprocta
were also found on the Flemish Cap.
In terms of biodiversity, the Flemish Cap had the highest number of records per km
surveyed with almost 1200. With only one transect, The Gully came second with an
average number of observations per km of 549, which is about 250 more than for the
Orphan Knoll. The Orphan Knoll had significantly fewer coral observations per km than the
other areas (25 observations per km compared to 301 for The Gully and 470 for the
Flemish Cap), and The Gully had significantly fewer sponge observations per km than the
other areas (83 compared to 145 for the Orphan Knoll and 408 for the Flemish Cap). About
half of all observations on the Orphan Knoll were sponges and only 8% were corals
(Fig. 44.1). The Flemish Cap had a more balanced ratio of observations with 39% for
corals, 34% for sponges, and 27% for other organisms. Finally, The Gully had a higher
ratio of corals (55%) than sponges (15%) and other taxa (30%) combined.
The Paragorgia genus was relatively rare, with 16 observations of P. arborea at The
Gully, and only six observations at the Flemish Cap, including three of P.johnsonii.
Anthomastus grandiflorus were only identified to the species level at The Gully, but
Examples of habitat maps produced along three transects, one for each study area. The scale and
north arrow apply to the three examples.
Cold-water Coral Habitats of the NW Atlantic 745
Anthomastus sp. were abundant at the Flemish Cap with over 12,700 observations.
Acanella arbuscula were also more common at the Flemish Cap and to a lesser extent at
The Gully, but only two observations were reported at the Orphan Knoll. The Gully was
rich in Keratoisis sp.; all but one observation of K. ornata were found there.
Observations of Stylaster sp. (3) and Swiftia sp. (91) were only reported at the Flemish
Cap, and Radicipes sp. (3) were only found at The Gully. About 78% of the records of
Vaughanella sp. were from the Flemish Cap, with the others being from the Orphan
Knoll. The Orphan Knoll was mostly characterized by the presence of Chrysogorgia sp.
(579 out of 581 total observations). Overall, The Gully was the richest area in sea pens,
while the Flemish Cap was richer in soft and stony corals. On average, those two areas
had similar density of gorgonian corals. Compared to those regions, the Orphan Knoll
only displayed a higher density of black corals. Finally, The Gully presented the highest
rate of dead colonies, with an average of 8.5 observations per km (total of 34). A total
of 48 dead coral observations were made on the Flemish Cap, including 36 of
In terms of individual sponges identified at the genus level, The Gully had the highest
density of Asconema sp. and Polymastia sp. While the Flemish Cap had higher densities of
Geodia sp., the Orphan Knoll had the highest abundance of Geodiidae F. Rare observations
of Stylochordyla sp. were only reported on the Flemish Cap. Glass sponges were not
abundant at The Gully compared to the other areas. Overall most observations of ball
sponges, encrusting sponges, and fan sponges were reported at the Flemish Cap, and most
of those of vase sponges came from the Orphan Knoll. Funnel sponges, finger sponges, and
branching sponges were only reported as such for the Orphan Knoll.
The most abundant observations for taxa other than sponges and corals were ophiuroids, sea
stars, crinoids, echinoids, and anemones (both Actiniaria and Ceriantharia). Individuals of
the Aphroditidae family were only recorded at the Orphan Knoll and the presence of Acesta
sp. was only noted at The Gully.
Species distribution models (SDMs) were used to measure the statistical relationships
between cold-water corals distribution and potential environmental surrogates. Models
were produced using biological data described at different taxonomic resolutions, based
on whether or not there were enough samples to produce valid models. For instance,
SDMs were not computed for Radicipes sp. and Stylaster sp. given that they only had
three observations each. However, those observations were integrated into models
at the family and order levels (e.g., Radicipes sp. observations in the model for
746 Chapter 44
Chrysogorgiidae). Two factors influenced the number of samples: the actual number of
observations and the availability of adequate environmental data at the location of the
Observations were separated in training and test subsets (70/30) to compute a suite of
validation measures, and replications of the models with different subsets were computed
to ensure consistency and provide an average contribution of each environmental variable
to the different taxa distributions.
Overall results confirm the trade-off involved between the number of samples and thematic
scale (i.e., taxonomic resolution) when modeling species distribution (Jansen et al., 2018).
The average accuracy of the models generally increases with higher taxonomic resolution
(e.g., genus at 0.93 compared to order at 0.90), except when the number of samples is too
low (e.g., at the species level). Generally, models built using a finer taxonomic resolution
(e.g., species level) included more explanatory variables than models produced at a broader
thematic scale (e.g., family level). This may relate to the spatial scale at which habitats are
described, and whether species are generalists or specialists. At finer taxonomic resolutions,
the different variables contributing to explaining the distribution of coral species and genera
had generally a more balanced contribution among them, as opposed to broader taxonomic
resolutions for which the distribution of families or orders were generally explained by two
or three variables with a higher mean percentage of contribution.
At the species level, only four series of SDMs could be produced due to the limited number
of observations for other species (Table 44.5). Of those, models computed for Paragorgia
arborea, which linked their distribution to temperature and salinity, were not considered
accurate enough by validation statistics. The models for the three other species all identified
different environmental variables as drivers of their respective distribution. Results indicate
that the distribution of Acanella arbuscula is driven by a range of factors, including oxygen
concentration, temperature, depth, northerness, and rugosity. The picture is simpler for
Table 44.5: Percentage contribution of environmental variables for species distribution models.
Variable Acanella arbuscula Anthomastus grandiflorus Keratoisis ornata Paragorgia arborea
Depth 17.1 9.1 65.9 7.3
Easterness 8.6 13.8 0.3 0.7
Northerness 15.7 68.6 18.3 2.9
Oxygen concentration 27.4 8.5 10.9 3.1
Rugosity 13.1 0.0 1.4 0.0
Salinity 0.1 0.0 1.5 9.4
Temperature 18.1 0.0 1.5 76.4
Topographic position 0.0 0.0 0.3 0.0
Mean AUC 0.92 0.84 0.94 0.61*
The top two contributors are indicated in bold font. The asterisk indicates absence of statistical significance.
Cold-water Coral Habitats of the NW Atlantic 747
Table 44.6: Percentage contribution of environmental variables for genus distribution models.
Variable Acanella Acanthogorgia Anthomastus Chrysogorgia Desmophyllum Flabellum Keratoisis Paragorgia Paramuricea Swiftia Vaughanella
Depth 52.4 0.8 20.8 32.8 1.3 5.2 2.5 28.3 49.6 44.1 41.8
Easterness 1.4 47.7 2.3 0.7 6.2 0.8 1.2 17.1 27.1 2.7 8.9
Northerness 10.4 0.4 23.5 2.8 47.8 38.0 2.0 1.4 10.5 20.8 9.0
30.7 43.7 0.9 5.4 0.5 8.1 52.5 2.4 0.3 4.1 5.4
Rugosity 0.4 0.4 4.7 8.4 43.0 29.8 8.4 27.0 9.7 23.3 18.0
Salinity 1.3 0.2 1.8 1.8 0.1 1.0 22.7 0.0 0.0 0.7 4.5
Temperature 1.2 4.5 21.6 32.8 0.4 9.0 10.4 11.4 2.5 0.9 8.6
2.2 2.3 24.3 15.3 0.6 8.1 0.4 12.5 0.2 3.4 3.8
Mean AUC 0.88 0.87 0.85 0.99 0.90 0.99 0.93 0.92 0.89 0.99 0.97
The top two contributors are indicated in bold font.
Table 44.7: Percentage contribution of environmental variables for family distribution models.
Variable Acanthogorigiidae Alcyoniidae Caryophylliidae Chrysogorgiidae Flabellidae Isididae Nephtheidae Paragorgiidae Plexauridae
Depth 1.8 56.3 2.4 46.6 4.8 8.7 2.5 17.1 77.2
Easterness 55.2 5.1 1.0 0.3 0.5 1.1 0.1 25.5 2.1
Northerness 0.2 13.1 29.4 6.7 43.0 3.9 1.4 2.6 8.5
36.0 2.6 0.3 1.6 7.3 84.1 94.6 1.8 3.3
Rugosity 1.8 3.5 64.3 1.0 27.8 0.6 0.0 18.7 4.2
Salinity 0.0 0.7 0.1 0.7 0.7 0.5 0.2 0.0 2.1
Temperature 2.3 13.3 1.8 20.9 8.6 0.9 0.5 21.5 1.4
2.7 5.4 0.6 22.2 7.2 0.2 0.6 12.7 1.0
Mean AUC 0.86 0.82 0.95 0.97 0.99 0.88 0.89 0.92 0.94
The top two contributors are indicated in bold font.
Anthomastus grandiflorus: northerness and easterness, which are known to be surrogates of
currents that bring food to corals and clear them of sediments (Tong et al., 2016), were
identified as the main drivers of this species’ distribution. Finally, depth, northerness, and
oxygen were identified as surrogates of Keratoisis ornata’s presence.
At the genus level (Table 44.6), the drivers of Acanella sp. are simplified from those
specific to A. arbuscula: depth, oxygen, and northerness are the main variables that were
found to explain this genus’ distribution. Depth was also one of the main factors explaining
the presence of about half of the genera. Many of the genera were impacted by one of the
components of aspect (i.e., easterness or northerness), and oxygen concentration was
important for Acanthogorgia sp. and Keratoisis sp. Scleractinian corals (e.g., Desmophyllum
sp., Flabellum sp.) were found in areas of higher rugosity. Salinity was only found to be
significant for Keratoisis sp., perhaps indicating a preference for a particular water mass,
while temperature and topographic position were relevant mainly for Anthomastus sp. and
At the family level (Table 44.7), bamboo corals (i.e., Isididae) and Nephtheidae were highly
influenced by oxygen concentration. Depth was among the most influential variables once
again with a contribution greater than 10% for four families. Northerness, oxygen
concentration, rugosity, and temperature contributed to explaining the distribution of a third
of the families. Similarly to some of their corresponding genera, topographic position
remained a predictor of the Chrysogorgiidae and Paragorgiidae families.
While remaining satisfactory, the accuracy of the different models at the order level was
lower than at the other taxonomic level (Table 44.8). Depth was identified as one of the
main drivers of coral distribution at this thematic resolution. Easterness and northerness,
and thus likely currents were found to explain soft and black corals’ distribution. Rugosity
was identified as a surrogate for soft and stony corals, while temperature would be a
surrogate of the presence of black corals, gorgonians, and sea pens.
Table 44.8: Percentage contribution of environmental variables for order distribution models.
Variable Alcyonacea Antipatharia Gorgonacea Pennatulacea Scleractinia
Depth 14.4 24.2 78.1 11.3 22.8
Easterness 36.3 20.1 0.7 0.4 0.7
Northerness 6.6 11.8 1.2 0.9 9.2
Oxygen concentration 3.7 1.4 2.7 2.2 0.4
Rugosity 33.7 3.1 2.0 0.7 63.6
Salinity 1.6 3.2 1.2 0.6 0.2
Temperature 1.9 33.9 12.8 83.8 3.0
Topographic position 2.0 2.3 1.2 0.1 0.1
Mean AUC 0.88 0.90 0.86 0.89 0.95
The top two contributors are indicated in bold font.
Cold-water Coral Habitats of the NW Atlantic 749
Many thanks are due to Arnaud Vandecasteele for his assistance with the processing of the oceanographic data,
to Vonda Wareham and Shawn Meredyk for helping with the identification of taxa from the video data, and to
everyone involved in data collection. This work was supported by a Natural Sciences and Engineering Council
of Canada (NSERC) Alexander Graham Bell Scholarship (VL), NSERC Discovery Grants (EE, RD), an NSERC
ship time grant, and Fisheries & Oceans Canada International Governance Strategy.
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