TEMPO: NETWORK USING ACOUSTIC TELEMETRY FOR POSIDONIA OCEANICA BEDS MONITORING

Transcription

1 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring TEMPO: NETWORK USING ACOUSTIC TELEMETRY FOR POSIDONIA OCEANICA BEDS MONITORING ( Posidonia oceanica beds Posidonia oceanica (L.) Delile is an endemic seagrass (marine phanerogam) from Mediterranean sea. The plant is composed on leaf shoots, roots and rhizomes generaly buried within sediment. The assemblage of rhizomes, leaf bases, roots and sediment that fills the interstices is called «matte». Except the leaves, dead parts of the plant are almost rot-proof explaining their long conservation (hundreds or thousands of years) within the matte (Boudouresque et al., 2006). The matte settles the meadow down and plays an important role in seabed stabilization. Posidonia oceanica beds occupy a limited area (1-2 % of Mediterranean seabeds = millions of ha (Rico-Raimondino, 1995; Pasqualini, 1997)). However, they constitute the most complex 1. Posidonia oceanica flower ; 2. Three fruits 3. Floating Posidonia oceanica grains and fruits. biocenosis of Mediterranean (Molinier and Picard, 1952; Pérès and Picard, 1964; Boudouresque and Meinesz, 1982) and are the bases of the costal water richness (Molinier et Picard, 1952; Cinelli et al., 1974; Boudouresque and Meinesz, 1982). Their ecological role is major: primary production, oxygen production (Drew and Jupp, 1976 ; Caye, 1980; Bedhomme et al., 1983; Bay, 1978), water transparency by trapping particules in suspension (Blanc and Jeudy De Grissac, 1984), base of numerous food chains (Vélimirov, 1984), spawning areas, nursery, shelter against predars or permanent habitat for thousands of animal and plant species (Boudouresque et al., 2006). In several coastal areas, Posidonia oceanica beds are in regression. The causal facrs are diverse: layout along the coast (direct destruction, changes in hydrodynamics and sedimentation (Andromède, 2013)), pollutions (hydrocarbons, pesticides, heavy metals, organic matter, suspended solids, macro waste), anchors, etc (Boudouresque et al., 2009). Because of its importance and ecological requirements, Posidonia oceanica is a bio-indicar species commonly used for the water quality moniring. Thus, Posidonia oceanica is a biological element used measure the ecological status Posidonia oceanica seagrass bed. of coastal water bodies in the Mediterranean as requested by the Water Framework Directive (WFD, 2000/60/EC). It is therefore necessary monir this habitat in time and space. TEMPO, a moniring network for Posidonia oceanica beds Supported by the Water Agency Rhône Mediterranean and Corsica, the TEMPO network was created in 2011 and extends over the entire French Mediterranean coast bordered by the three regions Corsica, Provence-Alpes-Côte d'azur (PACA) and Languedoc-Roussillon (LR). TEMPO s objectives are collect descriptive data on the dynamics of Posidonia seagrass beds and monir their changes over time and space. All of these data aim complete data obtained otherwise and evaluate in fine the environmental quality of coastal water bodies. These data also meet the environmental objectives of the Marine Strategy Framework Directive (MSFD, 2008/56/EC) such as maintain or resre of biodiversity and functioning of coastal ecosystems, strengthen the conservation of seagrass areas or identify sites with degraded natural habitats. -1-

2 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring Localization of the sites Each TEMPO site is monired at the end of spring (May-June) every three years with a one year lag from one region another. The first field campaign was conducted in Corsica in 2011 at 19 sites. This network was completed in 2012 by 13 sites located mainly in LR region and in 2013 by 21 sites in PACA region. Other sites surveyed in 2008 by Andromède with acoustic telemetry were included in the network (Descamp et al., 2009). TEMPO currently includes 60 sites distributed between 5 and 40 meters deep. Localization of the TEMPO sites Materials and methods The method chosen for the moniring is non-destructive, accurate, and uses many reference points. It takes in account three types of measures: a general description of the site, a map of the lower limit of Posidonia bed using acoustic telemetry, and measures of vitality at the lower limit. 1) General description of the site At each site, the GPS coordinates are recorded from the boat. They correspond the location of permanent markers such as "surveyor" anchored in the ground and marking the corners of the permanent quadrat used for telemetry. The diver notes water temperature, visibility, botm type, and identifies the pressures observed on the site. The choice of the disturbances surveyed follows the recommendations of the document concerning moniring methods for Posidonia oceanica within Natura 2000 sites from Languedoc-Roussillon (Blouet et al. 2011) and the methodological guide for evaluating the conservation state of Natura 2000 marine habitats (Lepareur, 2011). This information is obtained on the basis of literature review, aerial phographs and supplemented by field observations. Three types of disturbance parameters are identified and described below. a. Physical disturbances - Artificialization of the environment: The presence or absence of artificialized structures (embankments, rip-rap, concreting, groynes, pipelines, cable ducts, port facilities, etc.) is noted on the base of literature reviews, aerial phographs and field observations. -2-

3 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring - Damages (with anthropogenic origins) on matte: Observation and census blocks of matte rn out, traces and paths due the action of trawls and anchors, holes, etc.. The goal is determine the number of damages within the site and the percentage of damaged surface. b. Biological disturbances The presence of invasive Caulerpa spp (Caulerpa taxifolia, Caulerpa racemosa) and rhodobiota is noted and the surface covered by these species is estimated by divers. c. Pollutions The different sources of pollution observed (on aerial phographs and in situ by divers) within and around the sites are noted: - Potential sources of nuisance: Rivers and their outlets, rejections of water treatment structures, harbors, rip-rap, dredging releases, etc.. are identified. - Thickness, color, smell of the oxidized layer for muddy sediments - Macrowastes: nets and other fishing gears, lost anchors, moorings. Their volume and dangerousness are estimated. - Hydrocarbon traces where required. 2) Cargraphy of the seagrass bed lower limit using acoustic telemetry a. Acoustic telemetry Based on the principle of 3D acoustic interferometry, acoustic telemetry allows the positioning (at a centimeter-level) of objects located at several tens of meters from a submerged antenna (submersion at each dive). The acoustic positioning is an alternative method conventional marking (RSP, Charbonnel et al., 2000b). This method allows easily multiply the number of mapped points ( points surveyed instead of ten with RSP ) while avoiding putting many tags up that can damage the meadow or be lost ( Descamp et al. 2005; Descamp et al, 2011). Many lower limits of seagrass beds have already been mapped using this method (Descamp et al., 2007; Descamp et al., 2009; Deter et al., 2010; Descamp et al., 2011). Temporal surveys showed how this methodology is able highlight local progressions or regressions within the seagrass bed (Deter et al., 2010; Descamp et al.,2011). The machine used for this type of measurement is Aquameter D100 (company PLSM ). At each site, a permanent quadrat of several hundred square meters is defined using a maximum of four markers anchored in the ground. These permanent markers are used for local positioning. Diver mapping the lower limit of Posidonia oceanica beds with the Aquameter -3-

4 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring 1. Beacon anchored within the ground marking one of the four corners of the permanent quadrat; 2. Antenna submerged at each dive and used for the positioning by acoustic telemetry A mobile pointer and its standard cane give the whole a length of one meter in order detach from the botm and avoid the problems of reflections and / or masking acoustic waves. Lightweight and portable, the pointer has a mini keyboard and LCD screen, allowing the diver point out the limits of the meadow be positioned and sre them in memory (the memory pointer is over 1500 points). The pointer has the ability take 10 readings per point and average them aout in order increase accuracy. The base supports up eight pointers (eight divers) simultaneously, thereby increasing the speed readings. The lower limit of the seagrass bed located in the permanent quadrat is mapped precisely by acoustic telemetry with a minimum of one point every 50 cm. The presence and position of pen shells Pinna nobilis, protected species are identified and mapped. 1. Mini keyboard and LCD screen connected the aquameter pointer; 2. Spot of seagrass being mapped by a diver. -4-

5 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring b. Data operating The data are retrieved from the pointer on the computer via an infrared interface, and processed by the operating software Aqualog PLSM. The data are then imported in a Geographic Information System (GIS) in dxf format. Each point statement (seagrass spot, isolated shoot, mark, and existing beacon) is the subject of a specific layer. The outline of seagrass spot or of seagrass bed limits is made by joining the points closer and closer. GIS software is then used calculate surfaces and thus follow the evolution of the meadow in surface and position. Data operating with GIS. 3) Vitality measures at the lower limit of the seagrass bed Non destructive vitality measures are done by divers in situ at the lower limit of the seagrass bed. a. Lower limit type and depth The deepest extension limit (lower limit) of the seagrass bed is measured by divers using an electronic depth gauge. The limit type is defined according the conventional classification of Meinesz and Laurent (1978) and a more recent classification (Montefalcone 2009). According Meinesz and Laurent (1978), a progressive limit is characterized by the presence of plagiotropic rhizomes arranged alongside the direction of the slope without matte building. The sharp limit is clean, without dead matte downstream of the limit (stable ecosystem). The regressive limit presents an extended dead matte area covered or not by the sediment downstream of the limit itself. Some bundles of leaves remain below the current limit (disturbance and regression of the seagrass bed). According Montefalcone (2009), new types of limits are enumerated: shaded, sharp or erosive limit with for each one a natural or erosive label according the presence or absence of dead matte, and a regressive limit with patches of living or dead Posidonia oceanica (Appendix 1). b. Shoot density Shoot density (number of shoot with living leaves per m²) is calculated using 30 quadrats of 20 x 20 cm at the lower limit (PergentMartini and Pergent 1996, Charbonnel et al., 2000a, b). A quadrat of 20 x 20 cm corresponds the smallest representative surface (Panayotidis et al., 1981). Its value is then extrapolated 1 m². These quadrats are randomly thrown from a height of 1.5 m without avoiding sand spots (unless they are very large). The density varies with depth and environmental conditions (light, substrate type). Due the high light intensity near the surface, a seagrass bed has very high density values in shallow areas, although they are much smaller deeper (lower limit) or in areas with high turbidity (Pergent et al. 1995). A diver is counting leaves shoot for density estimations. A grid of simplified reading integrating depth has been proposed (Pergent et al., 2008; PergentMartini et al., 2010.) and classified seagrass beds in four categories according the density values measured by depth: high, good, normal, poor and bad condition (Appendix 2). -5-

6 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring c. Dislodging of Posidonia rhizomes Posidonia rhizomes are characterized by an horizontal (plagiotropic rhizomes) and / or vertical (orthotropic rhizomes) growth. Vertical growth is the cause of matte building and allows the plant fight against the landfill, due sedimentation. The rhizomes dislodging generally reflects the existence of a sedimentary deficit on the seagrass bed. The observation of this parameter allows determine quickly and precisely the hydrodynamics and sediment movements that take place within the area. In addition, a significant dislodging causes a weakening of plant, which increases its vulnerability anchoring and trawling. Measurement of rhizome dislodging is performed according the conventions defined by Posidonia oceanica shoots with nonboudouresque et al. (1980) in Boudouresque et al. (2006): dislodged rhizomes - For plagiotropic rhizomes, dislodging is the distance between the sediment and the lower part of the rhizomes - For orthotropic rhizomes, dislodging is the distance separating the sediment from the base of the leaves, subtracted of 2 cm. Ten measures (x3 replicates) are performed within quadrats 20 x 20 cm randomly arranged. A dislodging scale (low, medium, high) is proposed, based on average values measured along the markings. Dislodging measures (Threshold values) Interpretation 5 cm 5 15 cm 15 cm Low dislodging Medium dislodging High dislodging Evaluation scale for dislodging in function of mean values measured along the marks (Charbonnel et al., 2000). Results One card per TEMPO site is available on the cargraphic platform It includes a description and a map of the Posidonia oceanica bed by acoustic telemetry, phographs taken within the site, and measures of vitality with a national comparison. 1. Map of a Posidonia oceanica bed (site of Ajaccio) realized with acoustic telemetry; 2.3. General views of the seagrass bed lower limit at Ajaccio. -6-

7 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring With a return on site every three years, a detailed analysis of the seagrass bed temporal evolution is done by comparing the micro-mapping. The evolution of the state of the meadow (stability, progression, regression) is quantified in m². Temporal dynamics of a meadow (TEMPO site = Digue de Marseille) between 2008 and The vitality measurement data are used calculate an ecological quality index for the site: the BiPo (Biotic index using Posidonia oceanica; Lopez y Royo et al 2010.). The BiPo takes in account the lower limit depth (in m), type, the mean shoot density (at - 15 m) and the length of leaf shoot (at - 15 m). The EQR (Ecological Quality Ratio) is then calculated by averaging the four EQR' (one EQR' per measured parameter, see table below). Parameters measured and reference values used for the BiPo calcul. Densities and leaf length should be measured at -15 m. (Lopez y Royo et al., 2010). -7-

8 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring The EQR is then used determine the ecological status of a site according the classification of the WFD (see table opposite). Ecological status (WFD) EQR High 0,775-1 Good 0,55-0,775 Moderate 0,325-0,55 Poor 0,1-0,325 Bad 0-0,1 For TEMPO, we compare our data for the lower limit depth and type the BiPo reference values calculating the EQR corresponding these two parameters. Even if the shoot density parameter is not measured at -15 m but always at the lower limit, we calculate an EQR 'for this parameter. For a given parameter, its value can be associated with a picrial cursor repositioning the observed value within the regional context (minimum, maximum and average values observed within a region (Corsica, PACA, LR) for all sites sampled in this region). Legend of the picrial cursor associated each detailed parameter: Minimal, maximal and average values observed for each parameter at all of the sites sampled in mediterranean sea. Each color corresponds one fifth of the values extend observed at the chosen comparison scale, i.e. water body, region (Provences-Alpes-Côte d Azur (PACA), Corsica, Languedoc-Roussillon (LR)) or Mediterranean for the concerned parameter. Examples of EQR and EQR values obtained at TEMPO sites Cap Roux, Juan, Agay Ouest and Cap Nice Est in 2008 and/or 2013 in PACA region. Maps presenting the EQR and EQR values for the parameters «lower limit typology», «lower limit depth», «shoot density per m²» of each TEMPO site can be realized at a national, regional or local scale (see next page). -8-

9 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring Map presenting EQR values of several TEMPO sites. Map presenting EQR values of several TEMPO sites. -9-

10 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring Network carriers a) Water Agency RMC Created by the Water Act in 1964, the Water Agency is a public institution of the State under the supervision of the Ministry in charge of sustainable development. Its mission is contribute improving water management, fighting against pollution and protecting aquatic environments. The Water Agency focuses on three main areas: the fight against pollution; the conservation and management of water resources; the support for the improvement of knowledge and cooperation betweenstakeholders in the water secr. Since the early 1990s the Agency has led specific actions on Mediterranean coastal and offshore waters. Website: b) Andromède Océanologie Andromède océanologie is a French independent company, highly experienced, able conduct any type of project linked the study and valuation of the marine environment. Andromède océanologie activities are organized in three divisions: - Consulting: Andromede is doing bathymetry, habitats cargraphy, species invenries, but also ecological engineering and management plans. - R&D: it focuses on the production of scientific knowledge, mainly on the two richest ecosystems in terms of biodiversity in the Mediterranean Sea: Posidonia seagrass and the coralline. This division is also responsible for improving the moniring of coastal waters by evaluating the ecological status of these ecosystems through TEMPO, RECOR and SURFSTAT networks. - Valuation. Its main missions consist in the valuation and exploration of the underwater environment and the dissemination of knowledge the general public through the management of Laurent Ballesta s image bank. Andromède also makes documentaries, exhibitions, books, articles and illustrations in the mainstream press. To better educate the public about the beauty and fragility of the underwater world, our office in Carnon (34) consists of an image gallery, a specialized library, a retail space dedicated the marine environment as well as a diving center (Andromède Plongée Bio). Website: Bibliographic references ANDROMEDE Cargraphie évolutive des herbiers de Posidonie en Région PACA depuis Document de synthèse, contrat Œil d Andromède/Agence de l eau. 81p. BAY D., Etude in situ de la production primaire d un herbier de posidonie, Posidonia oceanica (L.) Delile, dans la baie de Calvi, Corse. Thèse Faculté des Sciences, Université de Liège : BEDHOMME, A.L., THELIN, I. BOUDOURESQUE, C.F., Mesure de la production primaire des feuilles de Posidonia oceanica : modification de la méthode de ZIEMAN. Botanica Marina. 26 : BLANC J.J., JEUDY DE GRISSAC A., Erosions sous-marines des herbiers à Posidonia oceanica Méditerranée. International Workshop on Posidonia oceanica beds, BOUDOURESQUE C. F., JEUDY BLOUET S., LENFANT P., DUPUY DE LA GRANDRIVE R., LAFFON J-F, CHERE E., COURP T., GRUSELLE MC., FERRARI B., PAYROT J, Mise en cohérence des méthodes de suivis des herbiers de posidonies des sites Natura 2000 marins du Languedoc-Roussillon. Rapport ADENA-CNRS/EPHE/UPVD/CEFREM-CG66-AAMP, Fr 48p. BLOUET S., LENFANT P., DUPYU DE LA GRANDRIVE R., LAFFON J-F., CHERE E., COURP T., GRUSELLE MC, FERRARI B., PAYROT J Mise en cohérence des méthodes de suivis des herbiers de posidonies des sites Natura 2000 marins du Languedoc-Roussillon. Rapport ADENA-CNRS/EPHE/UPVD/CEFREM-CG66-AAMP, Fr., 48p. BOUDOURESQUE C.-F., MEINESZ A Découverte de l herbier de Posidonie. Cahier du Parc national de Port Cros, 4:

11 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring BOUDOURESQUE C.-F., BERNARD G., BONHOMME P., CHARBONNEL E., DIVIACCO G., MEINESZ A., PERGENT G., PERGENT-MARTINI C., RUITTON S., TUNESI L., Préservation et conservation des herbiers à Posidonia oceanica. RAMOGE publication. Fr : CAYE G Sur la morphogenèse et le cycle végétatif de Posidonia oceanica (L. Delile). Thèse docrat 3 cycle, Université Aix-Marseille II, Fr. : CHARBONNEL E., BOUDOURESQUE C.F., MEINESZ A., BERNARD G., BONHOMME P., PATRONE J., KRUCZEK R., COTTALORDA J.M., BERTRANDY M.C., FORET P., RAGAZZI M.., LE DIREAC H L., 2000a. Le Réseau de Surveillance Posidonies de la Région Provence- Alpes-Côte d Azur. Première partie : présentation et guide méthodologique. Année Région PACA, Agence de l Eau RMC, GIS Posidonie, CQEL 13, CQEL 83, Conseil Général 06, GIS Posidonie publ. : CHARBONNEL E., BOUDOURESQUE C.F., MEINESZ A., BONHOMME P., BERNARD G., PATRONE J., KRUCZEK R., COTTALORDA J.M., BERTRANDY M.C., FORET P., BRICOUT P., RAGAZZI M., CADIOU G., LE DIREAC H L., 2000b. Le Réseau de Surveillance Posidonies de la Région Provence-Alpes-Côte d Azur. Seconde partie: résultats du suivi GIS Posidonie publ., Marseille, Fr.: CINELLI F., COLANTONI P., FRESI E., SOLAINI P., La prateria sommersa. Subacqueo. 1 (9) : DESCAMP P., PERGENT G., BALLESTA L., FOULQUIE M., Underwater acoustic positioning systems as ol for Posidonia oceanica beds survey. Compte Rendus Biologies de l Académie des Sciences. C.R. Biologies 328 : DESCAMP P., BALLESTA L. HOLON F., Suivi de deux herbiers de posidonie dans la réserve marine de Cerbère Banuyls : baie de Tancade et anse du Pin Parasol. Contrat Conseil Général des Pyrénées Orientales. L OEil d Andromède publ. DESCAMP P., HOLON F., BALLESTA L., Microcargraphie par télémétrie acoustique de 9 herbiers de posidonie pour le suivi de la qualité des masses d eau côtières méditerranéennes françaises dans le cadre de la DCE. Contrat L Œil Andromède/Agence de l Eau, CRLR, CRPACA. Andromède publ., Montpellier, Fr. :1-59p. + annexes. DESCAMP P., HOLON F., BALLESTA L., GUILBERT A., GUILLOT M., BOISSERY P., RAIMONDINO V., DETER J., Fast and easy method for seagrass moniring: Application of acoustic telemetry precision mapping of Posidonia oceanica beds. Marine Pollution Bulletin. 62: DETER J., HOLON F., DESCAMP P., Surveillance de l herbier de posidonie Année Evaluation de l évolution de l herbier de Posidonie entre 2000 et 2010 sur le litral des Maures dans le cadre de l observaire marin du SIVOM. Rapport Final. Contrat SIVOM du litral des Maures et Andromède Océanologie publ. : 67 p. DREW E.A., JUPP B.P., Some aspects of the growth of Posidonia oceanica in Malta. Underwater Research, Academic Press, London. p LEPAREUR F., Evaluation de l état de conservation des habitats naturels marins à l échelle d un site Natura 2000 Guide méthodologique - Version 1. Février Rapport SPN 2011 / 3, MNHN, Paris, 55 p. LOPEZ Y ROYO C., CASAZZA G.,PERGENT-MARTINI, C., PERGENT G A biotic index using the seagrass Posidonia oceanica (BiPo), evaluate ecological status of coastal waters. Ecological Indicars. 10: LOPEZ Y ROYO C., PERGENT G., ALCOVERROE T., BUIAC M.C., CASAZZAD G., MARTÍNEZ-CREGOE B.,PÉREZ M., SILVESTRE F., ROMERO J The seagrass Posidonia oceanica as indicar of coastal water quality: Experimental intercalibration of classification systems. Ecological Indicars. 11 :

12 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring MOLINIER R., PICARD J., Recherches sur les herbiers de phanérogames marines sur le litral méditerranéen français. Annales de l Institut Océanographique, Paris. 27 (3) : PANAYOTIDIS P., BOUDOURESQUE C-F., MARCOT-COQUEUGNIOT J Microstructure de l herbier de Posidonia oceanica (Linnaeus) Delile. Botanica Marine. 24 : PASQUALINI V., Caractérisation des peuplements et types de fonds le long du litral Corse (Méditerranée, France). Thèse Docrat, Université Corse : PERES J.M., PICARD J., Nouveau manuel de bionomie benthique de la mer Méditerranée. Station marine Endoume. Fr., 31 (47): PERGENT G., LEONARDINI R., LOPEZ Y ROYO C., MIMAULT B., PERGENT-MARTINI C., Mise en œuvre d un Réseau de Surveillance Posidonies le long du litral de la Corse Rapport de synthèse Contrat Office de l Environnement de la Corse et GIS Posidonie Centre de Corse, GIS Posidonie Publ., Corte : PERGENT-MARTINI C., PERGENT G., Spatio-temporal dynamics of Posidonia oceanica beds near a sewage outfall (Mediterranean - France). In: Kuo J., Phillips R.C., Walker D.I., Kirkman H. edits. Seagrass Biology: Proceedings of an International Workshop. Univ. Western Australia publ.: RICO-RAIMONDINO V., Contribution à l étude des scks et flux d éléments dans les herbiers à Posidonia oceanica. Thèse Docrat d Ecologie, Université Aix-Marseille II. Fr. : VELIMOROV B., Grazing of Sarpa salpa L. on Posidonia oceanica and utilization of soluble compounds. 1: In: International Workshop on Posidonia oceanica Beds, BOUDOURESQUE C.F., JEUDY DE GRISSAC A., OLIVIER J., (éds.), GIS Posidonie publ., Fr. This document should be cited as follows: Andromède Océanologie, Brochure presenting TEMPO, a moniring network for Posidonia oceanica beds in Mediterranean sea. Andromède Agence de l eau RMC publ. 13p

13 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring Appendices Appendix 1: Lower limit types I II Illustration of different Posidonia oceanica lower limits typologies according I) Meinesz and Laurent (1978) (progressive limit = A, sharp = B and regressive = C) and II) Montefalcone (2009) natural (a, c, e) and regressive lower limits (b, d, f, g, h, i) with R the living P. oceanica cover percentages)

14 TEMPO: Network using acoustic telemetry for Posidonia oceanica beds moniring Appendix 2: Classification of Posidonia oceanica beds according shoot leaf densities (per m²) and depth (m) after Pergent et al., 2008 and Pergent-Martini et al., Depth (m) High Good Moderate Poor Bad