Habitat Mapping in Gilbert Bay, Labrador: A Marine ...

Habitat Mapping in Gilbert Bay, Labrador: A Marine Protected Area Phase III Final Report

Submitted by: Alison Copeland Department of Geography Memorial University St. John’s, NL A1B 3X9

Dr. Evan Edinger Department of Geography Memorial University St. John’s, NL A1B 3X9

Philippe Leblanc Dept.of Geography Memorial University St. John’s, NL A1B 3X9

Dr. Trevor Bell Department of Geography Memorial University St. John’s, NL A1B 3X9

Dr. Rodolphe Devillers Department of Geography Memorial University St. John’s, NL A1B 3X9

Dr. Joseph Wroblewski Ocean Sciences Centre Memorial University St. John’s, NL A1C 5S7

Standing Offer No. F6161-070001/001/XAQ Requisition No. F6161-07 0012 Draft final report, March 7, 2008

Habitat Mapping in Gilbert Bay Marine Protected Area, Phase III final report

Cover image caption: Shoreline habitats in The Shinneys. Nearshore portions of The Shinneys were not mapped using multibeam sonar, due to shallow water and numerous hazardous shoals. The Shinneys constitutes the primary spawning and juvenile habitat for Gilbert Bay cod, yet little is known about the habitats Gilbert Bay cod use in the Shinneys.

Recommended citation: Copeland, A., Edinger, E., Leblanc, P., Bell, T., Devillers, R., Wroblewski, J., 2008. Marine Habitat Mapping in Gilbert Bay, Labrador – A Marine Protected Area. Phase III final report. Marine habitat mapping group report # 08-01, Memorial University of Newfoundland, St. John’s, 71 p. Marine Habitat Mapping Group. Trevor Bell, Alison Copeland, Rodolphe Devillers, Philippe Leblanc Department of Geography, Memorial University of Newfoundland, St. John’s, NL A1B 3X9. Evan Edinger Departments of Geography and Biology, Memorial University of Newfoundland, St. John’s, NL A1B 3X9.

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Overview.

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Table of Contents. Overview ………………………………………………………………… iii Table of Contents ………………………………………………………… iv List of Figures …………………………………………………………….. vi List of Tables ……………………………………………………………… ix Research Objectives and Rationale ………………………………………. 1 Research Approach ……………………………………………………….. 5 Field Methods …………………………………………………………….. 6 Laboratory Methods ……………………………………………………

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Substrate classification …………………………………………… 12 Video substrate and faunal analysis ……………………………… 13 Statistical analysis ………………………………………………………... 14 Interpolation from sounding lines to bathymetric maps ………….. 14 Depth-substrate relationships in areas without multibeam coverage … 15 Faunal analysis ……………………………………………………. 15 Results ……………………………………………………………………. 17 Substrates observed ……………………………………………... 17 The Shinneys ……………………………………………………

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River Out ………………………………………………………….. 33 Mogashu Tickle …………………………………………………… 37 Potential bedrock wall habitats …………………………………… 42 Habitat Classification …………………………………………….. 43 Defining mappable habitat types ………………………………….. 49


Study Highlights and Future Directions …………………………………

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Summary ………………………………………………………………….. 59 References Cited ………………………………………………………….. 60 Appendix A: Bathymetric and substrate profiles in The Shinneys ………. 62 Appendix B: Faunal list …………………………………………………... 67 Appendix C: sediment grain size and organic content ………………….. 71

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List of Figures. Figure 1: Locations of management zones associated with Gilbert Bay Marine Protected Area and place names used in the report. Figure 2: Benthic substrate map for entire bay. Figure 3. Substrate map of Zone 1B of the Gilbert Bay Marine Protected Area, including The Shinneys and River Out. Figure 4. Alison Copeland operating the Garmin 178C GPS-sonar and Shark Marine Drop video systems. Figure 5. Philippe Leblanc readying the Petit Ponar hand-deployed grab sampler. Figure 6: Locations of all video and grab samples collected in Zone 1B in 2007 on multibeam backscatter intensity data. Figure 7: Locations of drop video stations in Leg Island Basin to assess potential bedrock wall habitats. Figure 8. Location and numbers of video transects collected in River Out, Mogashu Tickle, and The Shinneys. Figure 9. Video frame grab of muddy gravel substrate, line 16R, Inner Shinneys. Fig. 10. Sandy gravel substrate. Transect 17, Inner Shinneys. Fig. 11A. Coralline algal encrusted gravel substrate, transect 16, Inner Shinneys. Figure 11B . Example of coralline-algae-encrusted-gravel substrate class, as recovered in grab sampler. Fig. 12A. Gravelly mud substrate. Figure 12B. Gravelly mud substrate, Transect 25, Inner Shinneys. Fig 13. Mud substrate. Transect 17, Inner Shinneys. Fig. 14A. Nearshore gravel substrate, Transect 25, Inner Shinneys. Fig 14B. Nearshore gravel substrate, Transect 25, Inner Shinneys. Fig 15A. Sponges, rhodoliths, and sea stars on gravel, Mogashu Tickle Gravel.

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Fig 15B. Gravel with sun star and dead scallop shell, Mogashu Tickle gravel. Fig 16A. Bedrock wall habitat, , site 418, Leg Island Basin. Fig 16B. Bedrock wall, site 409, Leg Island Basin. Figure 17. Distribution of substrates along bathymetric and video transect lines that were surveyed in the inner part of The Shinneys, overlad over multibeam backscatter. Figure 18. Distribution of substrates along bathymetric and video transect lines surveyed in the Inner Shinneys, overlaid over substrate map generated from multibeam backscatter (Copeland et al., 2007a). Figure 19A: Bathymetric profile along line 25, labeled by substrate type. Figure 19B. Bathymetric and substrate profile, transect 28, Barr Tickle. Figure 20. Boxplot showing depth distribution of video transect points in the Shinneys. Figure 21. Linear and exponential regression lines of depth and substrate code in The Shinneys. Figure 22: Fledermaus image of substrate classification draped over bathymetry, River Out (Copeland et al., 2007a). Figure 23. Substrates in River Out, overlaid above multibeam backscatter. Figure 24 Substrates in River Out, overlaid over substrates interpreted from multibeam sonar (Copeland et al., 2007a). Figure 25A. Location of frame grab of muddy gravel occurring on steep slopes near mouth of Snook’s Arm, end of transect 7, River Out. Figure 25B. Bathymetric and substrate profile of transect 7, near mouth of Snook’s Arm, River Out. Fig. 26A, Soft coral, Gersemia rubiformis, on gravel, Mogashu Tickle gravel. Fig 26B. Basket star, Gorgonocephalus, Mogashu Tickle. Figure 27. Substrates in Mogashu Tickle, River Out, and the outer Shinneys, overlaid over multibeam backscatter data. Figure 28. Substrates in Mogashy Tickle, River Out, and the outer Shinneys, overlaid over subsrate classification based on multibeam sonar (Copeland et al., 2007a).


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Figure 29A. Nearshore gravel substrate, shallow water portions of transect 9, Mogashu Tickle. Figure 29B. Bathymetric and substrate profile, transect 9, running across Mogashu Tickle. Figure 30. Boulder gravel, site 419, Leg island Basin. Figure 31: 3-dimensional multidimensional scaling (MDS) plot of video sampled biota. Figure 32: 3-dimensional multidimensional scaling (MDS) plot of biota from grab samples.


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List of Tables. Table 1: Wentworth Grain Size Definitions Table 2. Numbers of video sequences of each substrate analyzed for faunal composition. Table 3: The top 10 taxa from video sampled biota, ranked in order of decreasing contribution to faunal similarity, and their percent contribution to similarity within each substrate class. Table 4: The top 10 taxa from grab sampled biota, ranked in order of decreasing contribution to faunal similarity, and their percent contribution to similarity within each substrate class. Table 5. ANOSIM results comparing faunal composition of identical substrate types in areas covered by multibeam data and areas outside multibeam coverage. ANOSIM of video data revealed significant differences between all pairs. ANOSIM of grab sampled data revealsed significant differences for muddy gravel only. Table 6: ANOSIM results table for 2007 video data. Numbers indicate probability of pvalues, in percent, i.e. p=0.05 is represented as 5.0. Table 7 : ANOSIM results table for 2007 grab sample data. Numbers indicate probability of p-values, in percent, i.e. p=0.05 is represented as 5.0. Table 8. Contributions of individual taxa in video data to faunal dissimilarity between identical substrate types in all of Gilbert Bay (2006-7 data) and zone 1B (2007-8 data). Table 9. Contributions of individual taxa in grab data to faunal dissimilarity between identical substrate types in all of Gilbert Bay (2006-7 data) and zone 1B (2007-8 data).


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Research Objectives and Rationale The primary goals of Phase III marine habitat mapping in Gilbert Bay Marine Protected Area (MPA; Figure 1) are to collect detailed data on substrate and biotic composition in Zone 1B of the MPA, especially to extend habitat classification to areas of The Shinneys outside multibeam sonar coverage, to assess the nature of unclassified areas within River Out, and describe the substrate and habitat of the Mogashu Tickle tidal rapids. A fourth research objective was to target potential rock-wall habitats in Zone 1B and in Leg Island Basin (MPA Zone 3). Bedrock wall habitats are prominent, and important, in many fjords, but our Phase II habitat maps suggested that bedrock wall habitats are rare or absent in Gilbert Bay.

Research efforts were concentrated on Zone 1B for several reasons. First, large areas of Zone 1B, especially The Shinneys, were excluded from the habitat maps generated from multibeam sonar data, because they were too shallow or too hazardous to be surveyed by the multibeam sonar launch. Second, Zone 1B, especially the Shinneys, is of particular interest because of its importance for cod spawning and juvenile habitat in Gilbert Bay. Third, River Out was identified as an area of particularly high substrate and habitat diversity, and high species diversity in Phase II of our mapping program. Furthermore, Phase II mapping showed that River Out has high abundances of coralline-algae encrusted gravel, and true rhodoliths, or mobile balls of branching coralline red algae (maerl, in European terminology). This habitat is highly biodiverse and possibly plays a role in the early life history of Gilbert Bay cod, therefore it was given special consideration in 2007. River Out also has a number of unclassified areas, where bathymetry, backscatter, and slope fell outside the statistically defined ranges of any of the six principal substrate types found within the bay. Finally, the area surrounding Mogashu Tickle,


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the narrow strait connecting River Out and The Shinneys, was identified in our Phase II report as a key area of interest for its tidal rapids, and the consequent potential for a unique and highly diverse faunal assemblage.

Figure 2: Locations of management zones associated with Gilbert Bay Marine Protected Area and place names used in the report.


Figure 2: Benthic substrate map for entire bay. Phase III mapping efforts focused on The Shinneys, River Out, and Leg Island Basin.

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Figure 3. Substrate map of Zone 1B of the Gilbert Bay Marine Protected Area, including The Shinneys and River Out. Note the extensive areas outside multibeam coverage, especially in The Shinneys. Mogashu Tickle is the narrow connection between the Shinneys and River Out.


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Research Approach Our benthic habitat classification approach relies on two important assumptions. First, we assume that substrate strongly influences the distribution of benthic biota; a relationship which has been established for nearshore and continental shelf environments elsewhere (Kostylev et al. 2001; Harney et al. 2006). Second, we assume a consistent relationship between substrate and multibeam sonar-derived values of depth, slope and backscatter (Todd et al. 1999; Kostylev et al. 2003; Ferrini and Flood 2006). The operational procedure for conducting the classification is described in our Phase II report (Copeland et al. in 2007a). In Phase III, substrate classes identified throughout the bay were extended to the shallow areas of The Shinneys using video transects coupled with georeferenced single-beam sonar bathymetry, but not backscatter. Additional substrate types were described as encountered. Faunal composition of substrates was determined using multivariate statistical analysis of video transects and grab samples. The operational procedure for conducting the classification is as follows: 1. Define major substrate classes from the measured grain-size distribution of grab-sampled sediments and visual texture descriptions of video transects. 2. Create substate-classified lines from video using substrate classes defined for the bay as a whole, and any new substrate types identified in video transects. 3. Create bathymetric profiles with substrate by combining sounder and video data. 4. Apply multivariate statistics to assess biotic composition of substrate types. Analysis of substrates and faunal composition of potential bedrock wall habitats followed methods outlined in our Phase II report (Copeland et al., 2007a).


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Field Methods The goals of the Phase III field program were to conduct grab sampling and video data acquisition along transects in Zone 1B of the MPA, in which most transects included small areas covered by multibeam sonar data, and more extensive areas without multibeam coverage. The description of bottom type and dominant biota along these transects were used to to classify and map substrates and habitats for areas outside the multibeam coverage, using categories consistent with those developed for the areas with multibeam sonar data (fig 3). In River Out, video transects were conducted to cover previously unclassified areas near the edge of the multibeam coverage and drop camera stations were placed to fill gaps within the existing substrate map. Transects were also planned to assess the nature of substrate and fauna in Mogashu Tickle. Final, drop video sites within Leg Island Basin were sampled to assess the potential for bedrock wall habitats. The fieldwork component of Phase II mapping was carried out over 12 days between September 23 and October 04, 2007, and included 5.5 sampling days in Gilbert Bay, 4 travel days, and 2.5 days lost to weather or equipment failure. Sampling was conducted primarily from ashallow-draft speedboat, with the help of the boat operator, Mr. Jim Russell. The final sampling network appears in Figure 4, and the positional data for all stations are listed in Copeland et al. (2007c). During video transects, time, position and depth were recorded using a WAAS-enabled Garmin 178C GPS-depth sounder (figure 4). This, combined with the GPS overlay on the video, allowed for video classification to be translated directly into map format, and for construction of depth-substrate profiles along each transect.


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Figure 4. Alison Copeland operating the Garmin 178C GPS-sonar and Shark Marine Drop video systems. Where possible, video transects were supplemented by grab sampling using a hand-operated Petit-Ponar grab sampler (figure 5). The Petit Ponar, rather than the larger and heavier Van Veen grab, was used. Conducting field work from the open deck speedboat precluded use of a heavy grab sampler requiring a winch or crab-pot hauler. Unfortunately, however, the Petit Ponar is not heavy enough to effectively sample some of the harder gravely substrates, so many of the grab casts were unsuccessful and were returned empty.


Figure 5. Philippe Leblanc readying the Petit Ponar hand-deployed grab sampler. After collecting subsamples for sediment texture and organic content analysis, samples were sieved through the floating mesh screen observed in the foreground.

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A total of 28 video transects were conducted in River Out, Barr Tickle, the outer Shinneys and Mogashu Tickle, and the northern side of the Inner Shinneys, and recorded on approximately 13 hours of video tape. Transects in the Barr Tickle area of the Shinneys followed safe passage lines as navigated by the skipper. Transects were not sampled in the western edge of the Inner Shinneys, because the skipper determined that this area was too hazardous. A total of 28 grab samples were collected in 2007. Of these, 16 were collected opportunistically along the video transects where substrates appeared suitable for sampling with the small ponar grab (red dots on figure 6 below). The remaining 12 were collected at stations in River Out and the Shinneys to enhance the dataset from 2006 or sample locations that remained unclassified on the Phase II map (yellow dots on figure 6 below).


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Figure 6: Locations of all video and grab samples collected in Zone 1B in 2007 on multibeam backscatter intensity data. See more detailed maps below for grab and video drop site numbering. Video transect lines are represented schematically.


Twenty-four drop video stations were sampled to assess potential bedrock wall habitats: in

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six stations in Zone 1B, indicated as black dots in figure 6, and 18 stations in Leg Island basin (fig. 7). Potential bedrock targets were identified by high backscatter (>- 15dB) and high slope (>25°), following Copeland (2006).

Figure 7: Locations of drop video stations in Leg Island Basin to assess potential bedrock wall habitats. Red highlighted areas indicate potential bedrock wall locations with high backscatter and steep slope, while numbered black dots indicate camera drops.


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Laboratory Methods Laboratory research consisted of textural analysis of sediment samples collected in the field, identification of invertebrates collected in the field, analysis of underwater video footage, and statistical analysis of substrate and biological data.

Substrate Classification Substates were classified using visual classification of video footage and textural analysis of grab samples. Video classification of substrates followed the criteria established for visual substrate identification in Phase II of the habitat mapping program (Copeland et al., 2007a).

Textural Analysis: Sediment grab samples collected from Gilbert Bay were wet sieved to remove the mud fraction (silt and clay) from the sample. The weight of the mud that was washed out was calculated by weighing the dried sample before and after wet sieving. The remaining coarse material (sand and gravel) was dry sieved through a stack of 7 sieves with mesh sizes of −2, −1, 0, 1, 2, 3 and 4ø. These sieves represent the boundaries of the grain size classes described by Wentworth (1922) which are shown in table 1. The grain size distribution of the whole sample could then be determined by combining the weight of material in each gravel and sand sieve with the known weight of the mud fraction. The results of the grain size analysis of the grab sampled sediments were combined with observations of the seabed from the video imagery to form a complete description of the substrate at each sampling site. These descriptions were then grouped into classes.


Table 1: Wentworth Grain Size Definitions Phi unit Wentworth Grain Size (ø) Description >−8 Boulder > −6 Cobble > −2 Pebble −1 Granule 0 very coarse sand 1 coarse sand 2 medium sand 3 fine sand 4 very fine sand 256 63 to 256 4 to 63 2 to 4 1 to 2 0.5 to 1 0.25 to 0.5 0.125 to 0.25 0.0625 to 0.125 < 0.0625

gravel gravel gravel gravel sand sand sand sand sand mud

Faunal identification: Fauna collected in grab samples were preserved in 70% ethanol in the field, then transported to Memorial University for identification under binocular microscope. Faunal identifications were based on Gosner (1971, 1979), Harvey Clark (1997) and additional references (--ALISON!)

Video substrate and faunal analysis. Video transects were identified to substrate class visually, and by reference to the grab sample analysis. Following assignment to substrate class, a subsample of video segments of each substrate class were analyzed for fauna, at the presence-absence scale. The video footage of each transect line was reviewed to determine which of the 6 substrate classes from 2006 were present along it, or if any new substrates occurred. Each transect was then split into segments > 10 seconds duration of a single substrate class (Table 2). Any substrate that was observed for less than 10 seconds (eg. a patch of gravel on a mud bottom) were not separated into a distinct segment. Once the transect had been broken into substrate class segments, the segments were reviewed for biotic composition. Fauna or algae present in each segment were identified and recorded for statistical analysis.


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Table 2. Numbers of video sequences of each substrate analyzed for faunal composition. Substrate Classification Number of Video Transect Segments Muddy Gravel 35 Sandy Gravel 10 Coralline Algae Encrusted Gravel 38 Mogashu Tickle Gravel 3 Nearshore Gravel 19 Gravelly Mud 36 Mud 21 1 Fucus Mapping video transect lines. Position data in UTM coordinates from the GPS-depth sounder were downloaded to mark the position and depth of all video transects and drop video targets. Segments of each transect were assigned to substrate classes based on visual assessment of the video data, and quantitative analysis of grab sample data where available. Transects were mapped according to substrate within ArcMap 9.2, and compared with multibeam backscatter and multibeamderived substrate maps from Phase II. Bathymetric and substrate profiles for each transect were constructed by calculating the distance between each sounding point from its UTM coordinates, then plotting each transect as a cross-sectional bathymetric and substrate profile in Excel. Profiles for all transects are presented in Appendix A.

Statistical analysis. Interpolation from sounding lines to bathymetric maps. An attempt was made to produce a continuous bathymetric map that would extend the initial bathymetric coverage derived from the multibeam soundings to the shallow water unmapped regions of The. Shinneys. Bathymetric soundings collected during Sept-Oct 2007 using the


Garmin 178C GPS-sounder were combined with the high-resolution multibeam data

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soundings in order to derive a dataset that would include all the available bathymetric data for the Shinneys and River Out sectors. The coastline from the NRCan 1:50,000 digital topographic maps was converted to points having a depth of zero meters, which has been added to the other bathymetric data. This allowed a control of the interpolation which stopped the interpolation process beyond the coastline. Interpolation procedure followed a nearest neighbour interpolation in ArcView 9.2.

Assessing depth-substrate relationships in areas without multibeam coverage. In shallow water areas of The Shinneys, without multibeam coverage, Exploratory Data Analysis (EDA) was used to visualize the depth distributions of the different substrate classes occurring in The Shinneys. Depth from the GPS-depth sounder and substrate class were compared statistically using EDA, ANOVA, and linear and exponential regression. 1-way ANOVA was used to test the hypothesis that the different classes had distinct depth distributions. Finally, linear and exponential regression were used to test the ability of depth to predict substrate class in the shallow areas of the Shinneys outside the multibeam coverage.

Faunal analysis. Species composition of the biota (both flora and fauna) was compared among sampled stations in the substrate types identified using the multivariate statistical techniques similarity percentage (SIMPER) analysis, non-metric multidimensional scaling (MDS), and Analysis of Similarity (ANOSIM).. Analysis of all biotic data was conducted at the presence-absence level. MDS and ANOSIM analysis rely upon calculation of a Bray-Curtis similarity matrix, in


which the similarity of every sample in relation to every other sample is calculated. The

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MDS ordination plot then shows the relative similarity of all samples; samples that plot close to one another are highly similar, while those plotting far from each other are highly distinct. Similarity Percentage Analysis (SIMPER) Similarity percentage analysis (SIMPER) calculates the percent contribution of each taxon to the overall internal Bray-Curtis similarity of the biota associated with each substrate class, that is, the taxa that most clearly characterize the biota occupying each substrate. SIMPER also calculates the contribution of each taxon to the dissimilarity between all the substrate classes, but only the contribution to internal similarity is presented here.

In order to extrapolate substrates and habitats from the areas with multibeam sonar coverage to those without, we compared the faunal composition of each substrate class in the whole bay, based on the Oct 2006 data, with the faunal composition of that substrate class in the shallow water areas of Zone 1B, based on the Sept-Oct 2007 data. This comparison was conducted using ordination (MDS) analysis of similarity (ANOSIM), and the dissimilarity metric in the SIMPER, all conducted within PRIMER 5.0.. The extent to which the faunal composition of each substrate in the whole bay was similar to the composition of that substrate in the shallow areas indicates the reliability of extrapolating the substrate and habitat maps from the areas with multibeam data into the shallow areas outside the multibeam coverage.


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Results. Substrates observed. In the areas of the Shinneys without multibeam coverage that were surveyed (figure 8), nearshore gravel, coralline-algae-encrusted-gravel, sandy gravel, muddy gravel, Fucus beds, gravelly mud, and mud were observed.

Figure 8. Location and numbers of video transects collected in River Out, Mogashu Tickle, and The Shinneys. In addition to the six substrate classes identified in Phase II, two additional substrate classes were recognized (see below). The characteristics of each of the eight substrate classes are described below.


Muddy Gravel This class was characterised by pebbles, cobbles and occasionally boulders,

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in muddy sediment. The matrix (the sediment between the gravel) from grab samples in this class contained between 3 and 34% mud grains. Our analysis did not calculate the amount of silt and clay in the mud fraction of any of the substrate classes. Although the gravel was often draped by a thin layer of mud, this is a primarily gravel-bottom substrate. Boulder talus, where observed, consisted of coarse boulder gravel or exposed bedrock , sometimes covered in a thin layer of mud, generally on steep slopes. Potential bedrock and boulder gravel sites were mapped within the muddy gravel substrate class, because in most cases, boulder gravel was distinguished only by the coarse nature of the clasts.

Figure 9. Video frame grab of muddy gravel substrate, line 16R, Inner Shinneys. Sandy Gravel The sandy gravel class was characterised by a matrix containing over 10% sand by weight and little mud. Most of the samples in this class contained sand which fell into the ‘very coarse sand’ (0ø) to ‘medium sand’ (2ø) range on the Wentworth scale (Wentworth 1922). The gravel component of this class was similar to the previous class, and included pebbles, cobbles and angular boulders.


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Fig. 10. Sandy gravel substrate. Transect 17, Inner Shinneys.

Coralline Algae Encrusted Gravel This substrate class contained pebbles, cobbles and boulder gravel that was at least 50% covered by branching coralline red algae. Coralline algae were observed in the other gravel classes, but samples where branching coralline algae, mostly Lithothamnion glaciale, formed a significant amount of the substrate structure were placed in this coralline-algae dominated class. The rhodoliths collected were densely branched and completely composed of coralline algae.


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Fig. 11A. Coralline algal encrusted gravel substrate, transect 16, Inner Shinneys.Image shown here captures true rhodoliths with associated sea stars.

Figure 11B . Example of coralline-algae-encrusted-gravel substrate class, as recovered in grab sampler. Branching coralline red algae, Lithothamnion glaciale, form biologically structured habitat on pebble-cobble gravel. Gravelly Mud Samples in this class contained mud, occasionally with a very small amount of fine sand, and scattered gravel. Gravel of all sizes was observed, from small pebbles to boulders, scattered on a primarily mud bottom. Often a drape of mud covered the surface of the gravel.


Fig. 12A. Gravelly mud substrate – note gravel clast with associated sun star. Scaling lasers 10 cm apart.

Figure 12B. Gravelly mud substrate, not scattered gravel clasts and mollusk shells. Transect 25, Inner Shinneys. Mud Grab samples in the mud class were composed primarily of sediment grains smaller than 0.0625 mm (63μm) which fell into the silt and clay classes of the Wentworth scale (Wentworth 1922). No gravel was observed.

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Fig 13. Mud substrate. Note burrow mouth. Transect 17, Inner Shinneys.

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Nearshore gravel. This class was characterized by gravelly sediment, sometimes with

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cobbles or boulder, and usually without either sand or mud, and found in very shallow water, especially in The Shinneys.

Fig. 14A. Nearshore gravel substrate, Transect 25, Inner Shinneys.

Fig 14B. Nearshore gravel substrate, Transect 25, Inner Shinneys.


Mogashu Tickle Gravel. This class was characterized by gravelly sediment, without sand or mud, and was found only in the high-current areas surrounding Mogashu Tickle.

Fig 15A. Sponges, rhodoliths, and sea stars on gravel, Mogashu Tickle Gravel.

Fig 15B. Gravel with sun star and dead scallop shell, Mogashu Tickle gravel.

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Bedrock. This class was characterized by steeply sloping bedrock, as distinguished from boulder talus, which was included in the muddy gravel substrate. Only six sites of the 24 sampled contained true bedrock.

Fig 16A. Bedrock wall habitat, , site 418, Leg Island Basin.

Fig 16B. Bedrock wall, site 409, Leg Island Basin.

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Habitat Mapping in Gilbert Bay Marine Protected Area, Phase III final report 26 Substrate distributions and bathymetry in the Inner Shinneys. The distribution of these substrates in the inner Shinneys is presented in figure 17, along with

the backscatter map for the areas covered by the multibeam data. The depth profiles indicate a trough running WSW-ENE, approximately parallel to transect 25 filled with mud and gravelly mud, with bedrock ridges covered in coralline algae-encrusted gravel and muddy gravel to the W, E, and S, and the shore to the N. The bedrock ridge to the south of line 25 is also manifest as the two small islands separated by line 18. Similarly oriented bedrock ridges separating muddy troughs are likely to occur in the area SE of the multibeam coverage, but north of Barr Tickle. Contrary to expectations, Barr Tickle is not uniformly shallow nearshore gravel, but also contains considerable areas of mud and gravelly mud.

Continuity of substrate distributions. Mapping of substrate types from video transects in conjunction with the substrate classified multibeam data (figure 18) verified the substrate classifications in the multibeam data, and showed that the substrate distributions are generally continuous from the multibeam-covered areas to the areas outside multibeam coverage.

Following two pages: Figure 17. Distribution of substrates along bathymetric and video transect lines that were surveyed in the inner part of The Shinneys, overlad over multibeam backscatter. Figure 18. Distribution of substrates along bathymetric and video transect lines surveyed in the Inner Shinneys, overlaid over substrate map generated from multibeam backscatter (Copeland et al., 2007a).


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Habitat Mapping in Gilbert Bay Marine Protected Area, Phase III final report 29 Attempted interpolation from survey lines to continuous bathymetry. The sounding lines collected in the Inner Shinneys during Sept.-Oct. 2007 were too sparse to

allow a reliable mapping of the bathymetry, although several lines collected provided useful information on the bathymetric variability in the Shinneys. Some shallow water regions of the Shinneys were not surveyed at all, as the skipper did not want to risk an accident in these zones. Indeed, the boat struck a rock and broke a propeller in Barr Tickle. The sounding lines in other parts of the Shinneys were too sparsely positioned offer reliable interpolations, as the seabed in the shallow water of the Shinneys is highly variable. A complete bathymetric map was generated but, as its reliability was very variable, it has not been used to derive a substrate or habitat map, nor released. To be able to use the information without taking a risk of over-interpreting the data, one would need to carefully understand the initial data used and the interpolation process. The production of a reliable complete bathymetric map of the shallow waters of Gilbert Bay would be possible, but would require considerable additional small boat time to collect a high density of bathymetric survey lines.

Substrate-Depth relationship in the Shinneys. The relationship between depth and substrate class in the Shinneys, including both areas covered by multibeam and not covered, was fairly consistent, and is well illustrated by line 25 (figure --). Nearshore gravel occurred in the shallowest waters, as did sandy gravel, in many but not all cases. Coralline-algal-encrusted-gravel and muddy gravel occurred in slightly deeper water, while gravelly mud and mud occurred in deeper troughs. Figure --- shows a similar profile for transect 28, in Barr Tickle. Profiles for all survey lines are included in appendix A.


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Video transect #25 1600

1400

1200

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0 0.0 -2.0

-6.0 -8.0 Nearshore gravel

-10.0

Depth (m)

-4.0

Coralline algae encrusted gravel

-12.0

Gravelly mud Mud

-14.0

Muddy gravel Sandy gravel

-16.0 Distance (m)

Figure 19A: Bathymetric profile along line 25, labeled by substrate type. Note the general, but not absolute, relationship between substrate and depth. Video transect #28 0

100

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1000

0.0 -1.0 -2.0

Depth (m)

-3.0 -4.0 -5.0 -6.0 -7.0 Coralline algae encrusted gravel

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Gravelly mud

-9.0

Muddy gravel

-10.0 Distance (m)

Figure 19B. Bathymetric and substrate profile, transect 28, Barr Tickle. Note abundance of gravelly mud, and general but not uniform location of coralline algae and muddy gravel on ridges, but gravelly mud in troughs.


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Statistically, however, the relationship between depth and substrate was not strong. The water depths in which the different substrate classes in the Shinneys were found varied significantly (figure --- boxplot, ANOVA F(6,3968) = 489, p