Author(s): Document owner: Reviewed by: Version: 1.2 Date published: 15/01/2007 File name: Language:

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1 Title: Author(s): Document owner: Reviewed by: Mapping of benthic habitats in the Glénan archipelago Neil Alloncle, Jacques Populus, Claire Rollet, Marie-Odile Gall Jacques Populus R. Coggan (Cefas) Workgroup: MESH action: Action 4 Version: 1.2 Date published: 15/01/2007 File name: Language: Glénan Archipelago Case Study English Number of pages: 40 Summary: Reference/citation: Keywords: Case study of Intertidal & shallow sub-tidal habitat mapping in the Glénan archipelago, Brittany. Presents an inventory of data used and data collection methods. Considers problems encountered when applying EUNIS habitat classification and suggests some adaptations. Describes methodology for map production. Discusses the quality of the cartographic product obtained from multi-source data. Alloncle N., Populus J., Rollet, C., Gall M.-O., Benthic monitoring network (REBENT) Brittany Region. Mapping of benthic habitats in the Glénan archipelago. RST/IFREMER/DYNECO/ AG/06-XX/REBENT Intertidal, shallow, Glenan, REBENT, Lidar, acoustic, EUNIS, habitat map Bookmarks: Related information: PowerPoint file: "strategy...glénan"

2 Change history Version: Date: Change: /01/07 Minor editing and re-formatting by R. Coggan (Cefas) /01/07 Original submission 4

3 Mapping of benthic habitats in the Glénan archipelago Benthic monitoring network REBENT Brittany region January 2007 Neil ALLONCLE, Jacques POPULUS Page 1 of 38 Partner: IFREMER

4 Introduction 3 1. General features of the study area 3 2. Information gaps Mapping of habitats of Community interest in the frame of Natura Mapping of Zostera marina beds Bathymetric and sedimentological data from the SHOM Coastal orthophotographs Subtidal data collected by the MNHN of Concarneau New survey work Strategy of new survey work Surveying with dual hydrographic Lidar Acoustic surveys in the subtidal zone Kelp field data collection Additional intertidal field data EUNIS typology and its adaptations The EUNIS typology in the marine sector Required adaptations Additional lifeforms in the subtidal sector Additional lifeforms in the intertidal sector Interpretation The subtidal area The intertidal area Map quality: discussion and outlook Compiling data from various sources Ground truthing Metadata Information to identify the resource: Spatial information: Information about data quality: Information about constraints: Mapping quality control Intertidal area 34 Acknowledgments 37 References 37 Neil ALLONCLE, Jacques POPULUS Page 2 of 38 Partner: IFREMER

5 Introduction The Glénan archipelago is known for both its outstanding geomorphological structure and its highly diverse benthic habitats. Numerous studies have been made on this sector, many of them specific and independent. The archipelago was chosen as a reference sector within the framework of the REBENT network and provides an optimal study area for general mapping of benthic habitats made by collating data from several sources. An inventory of data used is presented first here, taking into account the wide range of resources implemented to collect these data, both in intertidal and subtidal zones. Secondly, the considerations for application of EUNIS habitat types and the methodology used for the mapping are described. Lastly, the quality of the cartographic product obtained from multisource data is discussed. 1. General features of the study area The Glénan archipelago is located in the downstream part of the Brittany precontinent, approximately 10 nautical miles south of Concarneau. It has several main islands (Saint Nicolas, le Loc h, Penfret, Drenec, Quignénec, Bananec, Cigogne ) surrounded by a chain of islets stretching over nearly 6 km from west to east and 3 km from north to south (figure 1). The area studied covers the entire archipelago in the intertidal domain and extends to the seabeds deeper than 50 m in the western section to the foot of the rocky flat supporting the archipelago in the subtidal domain. A surface area of 10,600 hectares, extending nearly 13 km from east to west and 8 km from north to south, was mapped. The intertidal sector of the study area is quite limited, representing only 300 ha compared to the 10,300 ha of the subtidal domain. At the centre of the mapped area, shallow bottoms of less than 10 m account for approximately 2,000 ha. A large number of remarkable habitats are located in the Glénan archipelago. There are extensive maerl beds at the centre and to the North-east of the archipelago. Zostera marina eelgrass beds are the main habitat in the centre of the sector. To the southwest of the principal islands, there is a large rocky flat, mostly colonised by macroalgae like kelp. Finally, although their surface area is limited, in the intertidal sector there are large belts of fucoids and large areas covered by fields of boulders which are particularly rich in terms of species present. Neil ALLONCLE, Jacques POPULUS Page 3 of 38 Partner: IFREMER

6 Figure 1: Geographic and bathymetric context of the area studied (excerpt from Ehrhold et al., 2006) Neil ALLONCLE, Jacques POPULUS Page 4 of 38 Partner: IFREMER

7 2. Information gaps Several types of data were employed in the framework of the project to map benthic habitats over the entire Glénan sector. Prior to designing new surveys, the aim was to identify data sets that were suitable for use in the mapping study. Some of them were already in the form of habitat maps. In our case, for the intertidal zone and shallow bottoms to the limits of visibility of for aerial photographs, two studies conducted within the frame of Natura 2000 had earlier produced a cartography for habitats of Community interest (Le Hir, 2005) and a cartography of eelgrass beds (Le Hir, 2005). Likewise, for the subtidal zone, maps of benthic populations in the Glénan sector carried out in the framework of the REBENT network's sector-based subtidal approach (Ehrhold et al., 2006) were being finalised when our project began. Other data included historic data (sedimentary and bathymetric maps from the Hydrographic survey SHOM) which are described below. 2.1 Mapping of habitats of Community interest in the frame of Natura 2000 This mapping was done in 2004 by the TBM consultancy based on data from several sources. The baseline media for this study were coastal orthophotography for the intertidal zone and shallows (depths less than 8-10 m), the SHOM's G map modified by photo-interpretation for shallow bottoms, along with observations made on hyperbaric dives at greater depths. Ground truthing surveys were carried out (Figure 2). Localised observations made during either free-breathing or hyperbaric dives made it possible to describe the types of bottom. Each observation station was positioned using GPS with a mean accuracy of 10 metres. In the case of soft substrates, some stations were sampled for granulometric analysis and other observations were solely based on visual estimation of the grain size class. Coastal orthophotographs were processed by enhancement before being put into unsupervised categories. Ground truthing was then used to classify each pixel of the image as a habitat type with respect to its spectral signature. The resolution indicated is 1 metre. The habitats were described in accordance with the Natura 2000 typology given in detail in the Natura 2000 habitat manuals (2004). Neil ALLONCLE, Jacques POPULUS Page 5 of 38 Partner: IFREMER

8 Points de validation de terrain effectués dans le cadre de l étude Natura 2000 Figure 2: Ground truthing carried out in the framework of the Natura 2000 study 2.2 Mapping of Zostera marina beds Several specific studies dealt with Zostera marina beds (Peuziat, 2004; Le Hir, 2005; Alloncle, 2005). These studies were based on automated segmentation of orthophotographs and enabled the extremely patchy surface areas covered by seagrass beds to be described precisely (Figure 3). Comparing the eelgrass maps produced by the various studies will make it possible to monitor changes in them over time, since the studies used different generations (county-scale from 1997 and coastal-scale ones from 2000) of orthophotographs as a baseline medium. To clear up the uncertainty in determining the boundaries of some seagrass beds in the deeper zones, additional ground truthing was done in the framework of Peuziat's study (2004). Neil ALLONCLE, Jacques POPULUS Page 6 of 38 Partner: IFREMER

9 Figure 3: Zostera marina bed map and specific ground truthing points for seagrass beds 2.3 Bathymetric and sedimentological data from the SHOM The bathymetric data from minutes produced by the SHOM (The French Hydrographic Survey) are available for the entire study area. However, in checking the origin of the data (figure 4), we see that although total coverage is available, the accuracy of data from the hydrographic surveys made from 1958 to 1977 at a scale of 1:10,000 (profiles 100m apart) will not be sufficient in the very shallow water and near the coast. Interpolating the data made it possible to obtain a digital elevation model (DEM) with a resolution of 10m. However, this DEM remains of quite limited value for the foreshore area, seing the very small number of soundings made there. Neil ALLONCLE, Jacques POPULUS Page 7 of 38 Partner: IFREMER

10 Figure 4: Source of hydrographic information inset from special 'G' SHOM 7146G map. Figure 5: Source of sedimentological information, inset from special 'G' SHOM map 7146G. Glénan archipelago inside red circle. Likewise, for sedimentological data the special G map for bottom types 7146G, (SHOM-UBO, 1999) provides information about the origin of the data used (Figure 5). Some of them came from grab samples taken during the period from , others from side scan sonar surveys made in 1993 north-east of the archipelago. On figure 5 the almost total absence of sampling in the southern approaches to the archipelago can be noted. This means that the information comes only from old Neil ALLONCLE, Jacques POPULUS Page 8 of 38 Partner: IFREMER

11 sounding-lead readings taken during classic hydrographic surveys. It is also interesting to note that no mention is made of maerl in the seabed-type lists on this map (Table 1). And yet, the importance of the very abundant maerl habitat on the northern seafront has been fully recognised both for its biodiversity and economic significance. Table 1: Types of bottom list from the 7146G map G map typology Rocky bottom Pebbles Gravel Sand-gravel Sand Fine sand Clayey sand Fine clayey sand Mud Sediments containing from 50 to 100% of particles larger than 20 mm Sediments containing from 50 to 100% of particles whose size is between 20 and 2 mm Sediments containing sand and from 15 to 50% gravel Sediments containing from 50 to 100% of particles between 2 and 0.5 mm Sediments containing from 50 to 100% of particles between 0.5 and 0.05 mm Sands containing from 5 to 20% of particles less than 0.05 mm Fine sands containing from 5 to 20% of particles less than 0.05 mm Sediments containing from 20 to 100% of particles less than 0.05 mm 2.4 Coastal orthophotographs Coastal orthorectified photographs are a vital medium for mapping benthic habitats in intertidal areas. These aerial photographs, also called Ortholittoral photos, were chosen to serve as a geometric reference. They provide a synoptic display of the areas to be mapped. Interpretation of the orthophotographs by various experts, biologists and sedimentologists, made it possible to identify the main structures present (Rollet et al., 2005). In accordance with the main specifications for aerial photographs taken on regular photogrammetric surveys ensuring a 1:25000 coverage of France (county level coverage), the coastal othophotographs have an absolute accuracy of about one metre on land areas (where many calibration points are available and triangulation is of good quality). This accuracy drops to 2 to 3 m on large-sized sediment foreshores. If a value of 2 m is considered as a safe estimate of accuracy, the scale of recovery will be about 1: The scanning resolution in the field is 50 cm. The coastal orthophotography used met precise specifications: - dates and times of flights were set in advance with respect to the tidal coefficient (a measure of the tidal amplitude). In short, spring tide was required for water depth to be no more than 1 metre above LAT at all survey times; - flight lines had to be adapted to the orientation of the coasts, - a 6 km wide swath was acquired, in order to ensure coverage of foreshores and Neil ALLONCLE, Jacques POPULUS Page 9 of 38 Partner: IFREMER

12 estuaries and inlets to the salinity limit). However, the Ortholittoral 2000 shots have many flaws which make it impossible to optimise their use for interpretation (Rollet, 2003). There are very high radiometric discontinuities, and during mosaicking, adjustments for radiometric variations between the images were not optimised. This is particularly a problem on the foreshore, where the colouring is very subtle. The image is greenish, lacking in sharpness and considerably lacking in dynamics. Generally speaking, the radiometric dynamics are highly variable from one sector to another and the radiometric discontinuities can render this baseline document for the intertidal zone useless for photo-interpretation. Consulting the raw images, in digital or printed form (which must be purchased), may be necessary in order to complement the data which can be identified on the mosaic. Ortholittorale 2000 Figure 6: Coastal orthophotographs available for the study area In the Glénan sector, images were taken on 30 August 2000 at 9:30 AM. Taking photographs in summer helps to distinguish between the plant cover, particularly for Zostera marina beds. Water depth at the time of shooting was 60 cm above the chart datum. Almost the entire intertidal zone was uncovered, making this document a preferential medium for the mapping of intertidal habitats. The transparency of the water column on the site made it possible to use this medium at shallow depths, to a bathymetric limit of about 8 to 10 m below the chart datum. However, some radiometric discontinuity can be noted in Figure 6. Neil ALLONCLE, Jacques POPULUS Page 10 of 38 Partner: IFREMER

13 2.5 Subtidal data collected by the MNHN of Concarneau Monitoring of subtidal algae belts was organised within the station-based strand of the REBENT strategy framework by the MNHN (National museum of natural history) in Concarneau (Derrien, 2004). On the Glénan site, there were two stations regularly monitored by divers, the first called «Les Bluiniers» located to the Northwest of the archipelago and the second «Pen a Men» northwest of Penfret Island (Figure 10). Figure 7: Excerpt from REBENT 2004 subtidal macroalgae station monitoring Inventories of flora were taken along a leg perpendicular to the bottom's slope. In this way, the limits of each algal belt were noted and positioned with respect to the bathymetric gradient. Figure 7 gives the cruise results for the year 2004 (Derrien, 2005). Neil ALLONCLE, Jacques POPULUS Page 11 of 38 Partner: IFREMER

14 3. New survey work 3.1 Strategy of new survey work Having identified the data gaps by compiling all data under in the same mapping reference, a strategy can be drawn up to best fill the gaps, keeping in mind that a composite of imagery and relief will always best address seabed mapping needs. This strategy has to consider the main limitations of the techniques currently available as well as specific constraints inherent to the site. In this case, the potential survey legs of the coastal vessel Thalia equipped with side scan sonar was first sketched. This obviously leaves a number of gaps in the shallow water area, i.e. the area lying approximately between chart datum and -10 m. Two techniques can be employed. Airborne hydrographic Lidar is described in 3.2. It only currently provides bottom elevation with potential penetration of the light beam to metres depending on bottom reflectivity. Flying constraints impose surveying in straight flight lines, hence a rather unflexible survey design. Shallow water acoustics, namely a multibeam sonar mounted on a light vessel (see 3.3) is fully flexible, however coverage rate is very low in shallow waters (approximately 2km² per day). The animation Glenan survey strategy.ppt shows how data layers combine to provide an almost full coverage of the archipelago, starting with existing data being completed by survey outlines. In total, using the complementarity of remote sensing data and field sampling and observations, there are only few remaining gaps. However it should be mentioned that more particularly in the subtidal shallow zone, there still are a number of places not being covered by both high resolution imagery and a terrain model. This is more strikingly appearing in Figure 22 where the blue zone only features elevation data, as no imaging system could be run there. 3.2 Surveying with dual hydrographic Lidar Surveys were made in September 2005 using an airborne dual hydrographic Lidar system to collect both topographical and bathymetric data on the Glénan sector (ACS, 2005). This system provides spot measurements of the distance between the sensor and the ground (Populus, 2003; Populus et al., 2004). It uses a double beam of light, containing both infrared to determine the emerged relief and the water surface and green to penetrate the water column. The measurement density is approximately one return point per 2 m² and the vertical accuracy is 25 cm. The aircraft carrying the sensor is equipped with differential GPS with a ground beacon, providing very high accuracy (in centimetres) for its positioning. Seeing the uncertainty of the laser's trajectory (especially due to diffraction at the air/water interface) and the width of the insolation spot due to backscattering within the water column, the stated accuracy for each measurement point is 2 to 3 m at best. The signal's penetration ability will depend on the amount of suspended matter in the water column. On the Glénan site, it is around 20 m. The coverage also includes land surfaces, for which the Lidar's infrared beam is used. However the coverage is not total, since the laser is switched off for safety reasons when flying over houses or boats. This means that there are many gaps in the centre of some flight lines, particularly in the sheltered area called "the Chamber" where many boats moor. In the subtidal area, the signal does not always reach the bottom. Neil ALLONCLE, Jacques POPULUS Page 12 of 38 Partner: IFREMER

15 For instance, it can be absorbed in very dark environments or disturbed by phenomena of multiple reflections, as seen on kelp fields. This creates additional gaps in data coverage, which are detrimental to producing a complete elevation model. The footprints of the two relief coverages are seen in Figure 8. The Lidar did not reach the darkest areas to the south and the west (see Figure 1), whereas the conventional bathymetry data are insufficient for the intertidal area. Thus, the two data sets complement each other quite well. Figure 8: Footprints of bathymetry data sources, green SHOM DTM, orange Lidar survey. Three DEMs at resolutions of 2, 5 and 20 m were produced using Lidar surveys. Seeing the digitisation scale and the complexity of some zones in the study area, especially in the intertidal area, only the 2 m- resolution DEM was used (Figure 9a). To make interpretation easier, slope calculations were made on the 2 m DEM (Figure 9b) and isobaths were generated every 50 cm (Figure 9c). In spite of a high point density which provided high resolution gridding, the relatively low horizontal accuracy of the bathymetric Lidar (estimated at 3 m) did not enable a DEM to be reproduced at a scale greater than 1: This should be taken into account during interpretation, at least in the areas where these data were used. Neil ALLONCLE, Jacques POPULUS Page 13 of 38 Partner: IFREMER

16 a b c Figure 9 : Lidar DEM (2m resolution) (a), Slopes (b), isobaths (c) 3.3 Acoustic surveys in the subtidal zone The outer area of the archipelago was studied in the frame of the REBENT programme, to identify and characterise the subtidal benthic habitats. The data was acquired during the REBENT subtidal sector-based cruises 1, 2, 6 and 7 (Figure 10). A two-phase methodology was used (Ehrhold, 2003). First, side scan sonar surveys were run, using an Edgetech St DF1000 sonar towed by Ifremer's inshore research vessel Thalia at seabed depths from 20 m to over 50 m and a Reson Seabat 8101 sonar from the Survex launch (Mesuris company) on shallow bottoms of 10 and 20 m, which were inaccessible using the Thalia. After an initial, almost-simultaneous interpretation of the acoustic profiles produced, the morpho-sedimentary facies detected (with a specific acoustic signature) are validated by Shipek grab sediment samples and by video profiles. Next came a stratified biological sampling approach, based on the identification and Neil ALLONCLE, Jacques POPULUS Page 14 of 38 Partner: IFREMER

17 validation of the acoustic facies. Samples were taken using a Hamon grab. This operation made it possible to characterise benthic populations. A specific report was drawn up for each of the studies carried out in the framework of the REBENT subtidal sector-based approach (Ehrhold et al., 2006). Vessels were positioned using a differential GPS, but in the case of the DF1000, the towed fish did not have a real-time positioning system, which increased positioning inaccuracy. This imprecision varied, reaching possibly significant values depending on the currents or the fish's gyration. Figure 10: Footprint of the acoustic study and sampling carried out in the framework of REBENT subtidal sector-based surveys. 3.4 Kelp field data collection In the frame of REBENT, underwater prospection surveys targeting subtidal macroalgae were conducted by the CEVA (Seaweed research and resource centre) from 25 April to 3 May 2005 and from 23 to 27 May A potential zone of presence was determined by identifying subtidal rocks using the SHOM G map, which the TBM consultancy had modified for shallow water through photo-interpretation based on coastal orthophotographs. The prospecting area was voluntarily limited to a maximum depth of -14 m for safety reasons (diver decompression stages) and because of the extent of the area to be covered. Within this area, spot measurements of the percentages of the various kelp species present were done by scuba diving or directly through a viewer (called a Calfat glass) Neil ALLONCLE, Jacques POPULUS Page 15 of 38 Partner: IFREMER

18 for very shallow seabeds (Figure 11). In all, 914 points were recorded using a GPS in normal mode (average accuracy of 10 m). In some areas, the observations were concentrated inshore, giving no indication of the lower boundary of the kelp's distribution, which does however seem to go beyond -14 m. Very little specific data on subtidal algae are available beyond this bound. Figure 11: Ground truthing points made by the CEVA and MNHN In addition, in order to process a SPOT satellite image for the coverage rate (intertidal portion), belts of the main species of intertidal fucoids (Fucus vesiculosus, Ascophyllum nodosum and Fucus serratus) were contoured in the field using natural GPS. Over 20,000 GPS waypoints were acquired during the field missions which took place from 8 to 18 March and from 5 to 14 April 2005, making 21 days in all in the field. This means that almost all of the Glénan islands were mapped (Figure 12). Neil ALLONCLE, Jacques POPULUS Page 16 of 38 Partner: IFREMER

19 Figure 12: Belts of main fucoid species recorded in the field 3.5 Additional intertidal field data A ground truthing survey focusing on hard intertidal substrates was conducted from 31 January to 1 February 2006 within REBENT's intertidal sector-based approach. The observations entailed spot measurements taken on the boundaries of habitats along legs perpendicular to the slope, from the limits of vegetation on land to the first subtidal habitats (Figure 13). Many photos were taken on site and matched to each measurement, providing a sound basis for later interpretation of the orthophotographs. Neil ALLONCLE, Jacques POPULUS Page 17 of 38 Partner: IFREMER

20 Figure 13: Ground truthing points made in the framework of REBENT intertidal sector-based surveys 4. EUNIS typology and its adaptations 4.1 The EUNIS typology in the marine sector The habitat typology of the EUNIS (European Nature Information System) classification was chosen for mapping purposes. It is the European habitat classification reference for land, freshwater and marine areas p. This typology (EUNIS, 2004) was grounded by several authors' work (Connor et al., 1997; Davies et al., 2001; Connor et al., 2004) and is based on a habitat hierarchy (figure 14) which, for marine areas, provides access to degrees of accuracy ranging from simply distinguishing between rocky or soft sediment types (level 2), including both the mode of exposure and the type of substrate (level 3), and the concept of functional grouping of habitats (level 4), up to the precise identification of benthic populations defined by the presence of dominant species or characteristic groups of species (levels 5 and 6). Neil ALLONCLE, Jacques POPULUS Page 18 of 38 Partner: IFREMER

21 Figure 14: EUNIS ranking structure, from level 2 to 6. The interest of using this typology lies in the fact that it makes it possible for habitats to be compared on a European scale and facilitates the implementation of European directives such as the Habitats Directive and its operational tool Natura However, its application in the frame of mapping the Glénan islands area highlighted numerous technical difficulties. Either the habitats observed have not been identified in EUNIS, making the creation of a new category necessary (long and rigorous process requiring an expert benthologist's involvement) or the situation observed reveals a complex reality where several EUNIS classes are found together. In the latter case, it seems simpler to determine the habitat observed by combining EUNIS categories, which comes down to creating mosaics. Don't these "natural" mosaics represent a reality which should have a simple classification level, like a level 3 or 4? This means that the EUNIS classification, as organised in the October 2004 version, is difficult to apply for both subtidal rocks and intertidal rocks. On the rocky intertidal scale, it is very complicated to model the exposure, and the hierarchy approach by level of exposure (level 3) is impossible. In addition, the hierarchy-based approach using population analyses requires very accurate knowledge of the species present. This is impossible to acquire for the entire area in the validation time slot available during low tides. Moreover, seeing the new remote sensing techniques (satellite, airborne or acoustic images) deployed to map benthic habitats, should new entry keys be added to EUNIS? Acoustic, optical, and satellite remote sensing can all identify different sets of seabed features. There is often a mismatch of habitat classes that can be defined from remote sensing techniques (physically-defined e.g. bedrock, boulders, cobbles) and the broader classes in EUNIS (ecologically defined, e.g. exposed rock). Additionally, infrared satellite imagery and orthophotography can detect algae-dominated habitats, but these areas cannot be represented using current EUNIS codes. To produce a habitat map it is typical to combine data from several remote-sensing techniques, together with various ground truthing techniques (e.g. video, grab), to identify a set of mapping types; these are typically defined at the life form level. The current EUNIS structure doesn t always accommodate such life forms very well (e.g. fucoid types are separated by wave exposure rather than grouped together as fucoids and then by dominant species (Fucus serratus, Fucus vesiculosus). If physically-defined units (e.g. bedrock, boulders) were used in the upper hierarchy of EUNIS, it would lead to much duplication of biological units at levels 5 and 6 (e.g. the same mussel/barnacle community would be found in separate bedrock and boulder Neil ALLONCLE, Jacques POPULUS Page 19 of 38 Partner: IFREMER

22 categories). It was agreed that a suite of mapping units were required, which would allow mapping from remote sensing techniques. In EUNIS this could be handled by treating the mapping units in a similar way to habitat complexes [marine landscapes such as estuaries], i.e. as a separate list of types that can be cross-referenced to the main ecological classification. Although EUNIS level 4 goes part way to accommodating the life-form level of biological identification, it was worth considering whether further restructuring at this level would improve the classification. It was recognised that the rigid hierarchical structure of EUNIS was not suited to all uses and that mapping at different scales needed different approaches (e.g. the current structure is better for very broad-scale mapping, but not fine-scale mapping of rocky types). 4.2 Required adaptations Additional lifeforms in the subtidal sector Thus the following categories were defined, grouping several existing EUNIS classes and making it easier to describe subtidal rocks: Infralittoral rock dominated by kelp: FRMosaic010. This classification designates infralittoral rocks dominated by kelp, including all species and all degrees of exposure. The EUNIS categories involved are: 1 Kelp with cushion fauna and/or foliose red seaweeds (A3.11), 2 Sediment-affected or disturbed kelp and seaweed communities (A3.12), 3 Kelp and red seaweeds (moderate energy infralittoral rock) (A3.21), 4 Kelp and seaweed communities in tide swept sheltered conditions (A3.22) 5 Silted kelp on low energy infralittoral rock with full salinity (A3.31). Infralittoral rock dominated by fucoids: FRMosaic011. This classification designates infralittoral rocks dominated by sargassa or cystoseira. Only one EUNIS classification is concerned but it alone does not cover all the situations encountered: 1 Frondose algal communities (other than kelp) (A3.15). Infralittoral rock dominated by kelp and/or fucoids x coarse infralittoral sediments (A5.12): FRMosaic012. This classification designates mixed rock/sediment seabeds dominated by macrophytes. It can also designate pebbly bottoms dominated by seaweeds. 2 That falls under FRMosaic010 and FRMosaic011 x A5.12 Scattered kelp on infralittoral rock: FRMosaic013 This classification corresponds to the rocks of the lower infralittoral zone, where light intensity is limited and kelp becomes sparse. The classifications concerned are the Neil ALLONCLE, Jacques POPULUS Page 20 of 38 Partner: IFREMER

23 same as for the «Infralittoral rock dominated by kelp» grouping. The EUNIS categories involved are: 6 Kelp with cushion fauna and/or foliose red seaweeds (A3.11), 7 Sediment-affected or disturbed kelp and seaweed communities (A3.12), 8 Kelp and red seaweeds (moderate energy infralittoral rock) (A3.21), 9 Kelp and seaweed communities in tide swept sheltered conditions (A3.22) 10 Silted kelp on low energy infralittoral rock with full salinity (A3.31). All the EUNIS classifications included in the groupings are not necessarily reprensented in each entity described by a grouping Additional lifeforms in the intertidal sector As for subtidal rocks, it is difficult to apply the EUNIS typology to the rocky intertidal compartment. Thus the following categories were defined, grouping several existing EUNIS classes and making it easier to describe subtidal rocks: Rock dominated by cirripedia: FRMosaic001. This classification designates rocks mainly colonised by cirrided populations, all species included. It provides an initial approach without the long, meticulous determination of species which is impossible to implement using remote sensing tools. Moreover, the various species are often mixed and their altimetric distributions vary from one study site to another, a still poorly understood phenomenon. The EUNIS categories involved are: 1 Chthamalus spp. On exposed upper eulittoral rock (A1.112) 2 Semibalanus balanoides on exposed to moderately exposed or vertical sheltered eulittoral rock (A1.113). Upper mid littoral fucoids: FRMosaic002. This classification includes the upper mid-littoral rocks colonised Pelvetia canaliculata and Fucus spiralis species, but does not indicate the rate of coverage. The latter is often lower than that of the dense Ascophyllum nodosum or Fucus serratus coverage. If the cover is not significant, the zone will not be classified as such. Because the bathymetric distribution of these two species (P.c. and F.sp.) is very close, and often partly mixed up with each other, it is impossible to map the two belts separately. The EUNIS categories involved are: 1 Pelvetia canaliculata and barnacles on moderately exposed littoral fringe rock (A1.211), 2 Fucus spiralis on full salinity exposed to moderately exposed upper eulittoral rock (A1.212), 3 Pelvetia canaliculata on sheltered littoral fringe rock (A1.311) 4 Fucus spiralis on sheltered upper eulittoral rock (A1.312). Neil ALLONCLE, Jacques POPULUS Page 21 of 38 Partner: IFREMER

24 Dense fucoids of the medium mid littoral: FRMosaic004. This classification represents rocky areas with dense Ascophyllum nodosum and/or Fucus vesiculosus cover. The bathymetric distribution of these two species is almost the same. In more sheltered areas, Ascophylum nodosum is largely predominant. The EUNIS categories involved are: 1 Fucus vesiculosus on moderately exposed to sheltered mid eulittoral rock (A1.313) 2 Ascophyllum nodosum on very sheltered mid eulittoral rock (A1.314). Dense fucoids of the lower mid littoral: FRMosaic003. This category corresponds to a dense belt of dense Fucus serratus. The zone is located at the bottom of the mid-littoral, between the Ascophyllum nodosum belt and an area dominated by red seaweeds often growing upwards, mixed with Fucus serratus. One EUNIS category is involved: 1 Fucus serratus on sheltered lower eulittoral rock (A1.315). Dense fucoids of the mid eulittoral x dense fucoids of the lower eulittoral: FRMosaic005. This category is the zone where the Ascophyllum nodosum and Fucus vesiculosus belts overlap with that of Fucus serratus. A mix of the three species is found there. Sparse fucoids of the mid eulittoral: FRMosaic007. This classification represents rocky areas with scattered Ascophyllum nodosum and/or Fucus vesiculosus. No distinction is made on for the associated faunal species. The EUNIS categories concerned are: 2 Fucus vesiculosus and barnacle masaics on moderately exposed mid eulittoral rock (A1.213) 3 Mytilus edulis and Fucus vesiculosus on moderately exposed mid eulittoral rock (A1.221). 4 Ascophyllum nodosum on very sheltered mid eulittoral rock (A1.314) is also concerned, but at lower coverage rates. Sparse fucoids of the lower eulittoral: FRMosaic006. This classification corresponds to the lower eulittoral rocks colonised by Pelvetia canaliculata and Fucus spiralis species, with no distinction between the associated animal species. The EUNIS categories concerned are: 1 Fucus serratus on moderately exposed lower eulittoral rock (A1.214) 2 Mythilus edulis, Fucus serratus and red seaweeds on moderately exposed Neil ALLONCLE, Jacques POPULUS Page 22 of 38 Partner: IFREMER

25 lower eulittoral rock (A1.222). Sparse fucoids of the mid eulittoral x sparse fucoids of the lower eulittoral: FRMosaic008. This category corresponds to the overlapping zone between the previous two classifications (FRMosaic006 and FRMosaic007). Communities of rhodophyceae and robust fucoids: FRMosaic009. This classification designates the lower eulittoral zone between the last Fucus serratus and the first kelp. Various red seaweeds (Mastocarpus stellatus, Chondrus crispus, Laurencia penatifida, Palmaria palmata, Coralina officinalis, etc.) develop there, along with the fucoids Himanthalia elongata and Bifurcaria bifurcata. The EUNIS categories concerned are: 1 Coralina officinalis on exposed to moderately exposed lower eulittoral rock (A1.122), 2 Himanthalia elongata and red seaweeds on exposed lower eulittoral rock (A1.123), 3 Palmaria palmata on very exposed to moderately exposed lower eulittoral rock (A1.124) - Mastocarpus stellatus and Chondrus chrispus on very exposed to moderately exposed lower eulittoral rock (A1.125). 5. Interpretation Seeing how diverse the available data are both in terms of their themes and their resolutions, a fixed digitisation scale of 1:2000 was defined in order to reduce the related bias and produce a consistent map. 5.1 The subtidal area Studies carried out in the framework of the REBENT subtidal sector-based approach provided a characterisation of soft substrate subtidal habitats. It was not possible to make a thorough characterisation of subtidal rocky habitats. The cartographic reproduction comes from crossing biological validations with the morphosedimentary entities detected. The entities were digitised from acoustic mosaics with a resolution of 50 cm and the habitats described were then translated into the EUNIS classification. In the initial step, the sedimentary data enabled a level 4 characterisation and specific faunal analyses made it possible to reach level 5 in the classification (Figure 15). Neil ALLONCLE, Jacques POPULUS Page 23 of 38 Partner: IFREMER

26 Figure 15: Reproduction of the mapping achieved in the subtidal sector-based approach of REBENT, translated into EUNIS typology. Three data sources were used to detect subtidal rocks. In the area covered by the acoustic survey, the rocks were contoured by interpreting the sonar mosaics. The mapped habitats were then geographically repositioned in some areas, based on bathymetric Lidar data, which are more accurate for positioning. In the most inner area of the study zone not covered by sonar surveys, it was necessary to use DEMs produced using Lidar or SHOM data in the deeper areas. By interpreting the DEMs translated into slopes, combined with the isobaths, it was possible to detect the slope breaks which are characteristic of the boundary between soft and hard substrates (Figure 16). Finally, in shallow water, the use of coastal orthophotos was an invaluable addition in delimiting rocky substrates. Neil ALLONCLE, Jacques POPULUS Page 24 of 38 Partner: IFREMER

27 Figure 16: Detecting rocks using bathymetric data and its derivatives Subtidal rock habitats were characterised using data collected on hyperbaric dives by the CEVA and the MNHN of Concarneau (Figure 17). In the current state of data acquisition methods for subtidal macroalgae and seeing the difficulty of modeling the exposure at a detailed scale, it was not possible to use the EUNIS typology to characterise the habitats of the subtidal rock compartment. We therefore defined the categories grouping several already existing EUNIS classes, making it easier to describe the subtidal rocks (see below). Figure 17: Characterisation of habitats on subtidal rocks Validations made by the CEVA were limited in depth, so they were mostly used to distinguish between kelp and sargassa or cystoseira cover, and validate the presence of kelp on the large rocky flats on the edges of the archipelago. Neil ALLONCLE, Jacques POPULUS Page 25 of 38 Partner: IFREMER

28 To determine dense or sparse kelp cover, the MNHN bathymetric surveys were used (see 2.5), then extrapolated using the DEMs. Thus, the lower boundary of dense kelp was defined at a depth of 16 metres and that of sparse kelp at 22 metres. Beyond that, rocks were considered to be circalittoral rocks where faunal communities prevailed. Some isolated observations made in the framework of the Natura 2000 study were also used to characterise the hard substrate subtidal habitats. The very small amount of data on the lower bounds of the kelp with respect to the study area did not allow these habitats to be reliably delimited. The Bluiniers station was the only benchmark used to establish the bathymetry frame of reference for the belts of kelp. At the Pen a Men station on the estern side of Penfret island (Figure 1), due to the influence of a turbid plume produced by nearby maerl extraction, the lower kelp limits were considerably higher than at the Bluiniers station. However, the extent of subtidal rock which is definitely affected by this impact seems limited. Therefore these data were not used to define the bounds of the kelp belts on the adjacent zones (especially to the southeast of Penfret Island). By inputting additional information about the lower boundaries of the kelp, this mapping point could be refined. The areas of soft substrates which were not covered by the acoustic survey were characterised using data from various sources. The Community interest habitat map produced in the frame of Nature 2000 was the main medium used to characterise the habitats in that compartment. Since this work was mainly based on using coastal orthphotographs combined with ground truthing, the resulting data are reliable up to a bathymetric limit of about 10 metres. In deeper water, field observations were combined with information from SHOM G charts which are available at a much coarser scale. Since the accuracy for that part of the map was not satisfactory, in order to produce the REBENT map, we had to reexploit the Natura 2000 study's ground truthing in relation with the information given on the G chart, as well as by the adjacent entities described using more reliable methods. Since the Community interest habitats are described using habitat guide types, equivalents had to be expressed in the EUNIS typology. For soft substrates, the Nature 2000 typology classifications are expressed above all in granulometric variations. The equivalent EUNIS classes, therefore, correspond to the classification's level 4. For zostera beds, the data produced by Peuziat (2004) and Alloncle's (2005) studies were incorporated to improve the accuracy of the Natura 2000 study. Figure 18 shows the complete mapping of the subtidal benthic habitats in the study area (the intertidal zone is coloured in grey). Neil ALLONCLE, Jacques POPULUS Page 26 of 38 Partner: IFREMER

29 Figure 18: Mapping of benthic habitats in the subtidal zone. Neil ALLONCLE, Jacques POPULUS Page 27 of 38 Partner: IFREMER

30 5.2 The intertidal area The intertidal soft substrate habitats were characterised in the same way as the shallow soft bottoms, based on the data of the Community interest habitat map produced in the framework of Natura Likewise, since the habitats were defined with respect to the sediment grain-size, the equivalent EUNIS categories correspond to level 4 of the classification. Several types of data were used to map the habitats of rocky intertidal substrates. Photo-interpretation of coastal orthophotographs can, amongst other things, differentiate the rocky substrates from soft ones, fucoid covers or area colonised by red algae at the bottom of the foreshore. However, there are limits to photointerpretation based on this medium, since it is impossible to determine the fucal species and a fixed macroalgae cover can be confused with a mussel bed or beached algae. Moreover, it is difficult to determine the percentage of coverage. That is why coupling with other media, as well as ground truthing, is needed. REBENT intertidal survey data had several advantages. On the one hand, they made it possible to validate the signatures on coastal orthophotos of characteristic entities and on the other, to characterise habitats in ambiguous areas which are hard to identify using remote sensing. Those data also provided the basis for an altimetric frame of reference for intertidal macroalgae (mainly fucoids) by crossing them with Lidar DEM data. This meant that, in parts of the foreshore that could not be validated, detailed mapping of the algal belts was possible by extrapolation of the altimetric bounds using the isolines extracted from the Lidar DEM (Figures 19 and 20). Figure 19: Correlation between intertidal ground truthing and Lidar altimetric surveys. Lidar metric isocontours are referenced to chart datum. Neil ALLONCLE, Jacques POPULUS Page 28 of 38 Partner: IFREMER

31 Figure 20: Approach to digitising the boundaries of the rocky intertidal habitats. The data on the fucoid belts gathered by the CEVA were not exploited, since no data on the percentages of the different species was available for the overlapping zones between the belts. Thus the distribution of intertidal macroalgae could not be determined using that medium. When mapping the various seaweed belts, it would have been useful to employ a SPOT scene with a resolution of 5 or 10 metres taken at low water of spring tide. That would have enabled us to estimate the algal coverage thanks to the images from the infrared channel. Neil ALLONCLE, Jacques POPULUS Page 29 of 38 Partner: IFREMER

32 6. Map quality: discussion and outlook 6.1 Compiling data from various sources In the intertidal domain, as well as in shallow water, coastal orthophotography was used as the digitisation medium. Its estimated absolute accuracy is 2 metres on average. Apart from the altimetric data from the Lidar surveys (whose absolute accuracy is close to a metre), and the seaweed belt surveys done using a differential GPS (accurate to about a metre), the other media were only used for interpretation and not digitisation. On a scale of 1:2000 (1 cm on the screen corresponds to 2 m on the ground), the accuracy of the various digitisation media was compatible. In the subtidal area, the data set was more heterogeneous. The map was created using both Lidar bathymetric surveys (accurate to 3 to 5 metres) and the SHOM's DEM, as well as sonar surveys whose positioning may be uncertain in the areas where the towed fish gyrated. The bathymetric DEM was built by geostatistic interpolation of the soundings from the minutes (with a theoretical horizontal accuracy if 5 metres and a vertical one of 25 cm), meaning that the accuracy of the depth value at each mesh node is somewhat deteriorated. This heterogeneity created difficulties in digitizing the map, especially in the areas bordering the different media. Spatial adjustments consisting in translations or elastic deformations could take place in these areas, taking the most reliable media as benchmarks. However, discrepancies did not exceed about ten metres. For instance, the tops of rocks clearly visible on the orthophotographs were identified on the bathmetric Lidar data, which confirmed that the Lidar was correctly positioned. On the multibeam echosounder data acquired using the Survex craft (Ehrhold, 2006), the same rocky outcrops showed a fairly constant displacement of the same order on the acquisition line. These various difficulties and inaccuracies should be taken into account when using this cartography (Figure 21). 6.2 Ground truthing The elements below are an attempt to give qualitative and comprehensive illustration for the map. They do not reflect the spatial distribution of the different data used. Because numerous surveying techniques were used and the footprints were variable and non-exhaustive, it seems interesting to give users a preview of the footprints in map form (Figure 22), so that they can adjust their judgment if need be. It should be noted in this figure that since no particular colour was given to the ortholittoral footprint, it is shown as a red outline. The ground truthing point density is also indicated. We decided not to indicate a simple density by surface unit, but to relate the density to the polygons of the habitats present, in order to account in this way for the heterogeneity. The density, varying from zero to about 5 points per polygon, was calculated on squares of 500 m per side and is represented by increasingly dense hatching in Figure 22. It should be noted that this marking does not distinguish the quality of the ground points, where are quite different in nature, as shown above. Improvements in the symbology are still needed to better account for these quality criteria. This could go Neil ALLONCLE, Jacques POPULUS Page 30 of 38 Partner: IFREMER

33 as far as two quality maps, for instance, one illustrating the remote-sensing data and the other the ground data. 6.3 Metadata Metadata are basically data about data: they make it possible to document the data so that any user can unequivocally interpret them. They contribute to the quality of the cartographic product. The Agency for the development of electronic administration (ADAE) reasserted «the importance of having metadata for geographic data interoperability» in February It is currently finalizing the French profile of the ISO standard devoted to describing geographic information. As for all the maps presented in the REBENT framework, this ISO standard was selected to document the map of benthic habitats in the Glénan archipelago. Although they are constrained by the tool used, in this case the ArcCatalog data manager in ArcGIS, the metadata on the Glénan fulfill the Core of the ISO standard and incorporate, insofar as possible, the ADAE's recommendations (see ISO metadata appendix of the Glénan archipelago benthic habitat map REBENT, 2006). This more specifically concerned the following information: Information to identify the resource The first piece of information concerns the metadata title, which is taken from the map itself. The name of the REBENT project, which made it possible to create this cartography of the Glénan islands, is added, along with the year of publication, i.e A more detailed description is provided in the summary: presenting the various contributing scientists, the methods used, and the EUNIS habitat typology with a link to the EEA's internet site. The digital map's various reference dates (creation-publication-printing) are indicated and should be compared with the period at which the data was collected (time scope). Five experts were selected as contacts for the Glénan cartography, each with their own specific expertise Spatial information The extended Lambert II spatial reference system is used for all REBENT maps. The scale of the Glénan cartography data set is 1:2000. The resource footprint is indicated in two different units: decimal degrees and metres. Neil ALLONCLE, Jacques POPULUS Page 31 of 38 Partner: IFREMER

34 Neil ALLONCLE, Jacques POPULUS Page 32 of 38 Partner: IFREMER Figure 21: Map of benthic habitats in the Glénan sector

35 Figure 22: Map showing the different techniques used in mapping the Glénan archipelago, as well as the ground-truthing effort (ortholittoral coverage footprint is shown as a red outline) Neil ALLONCLE, Jacques POPULUS Page 33 of 38 Partner: IFREMER