Recovery of the seagrass Zostera marina in a disturbed Mediterranean lagoon (Etang de Berre, Bouches-du-Rhoˆne, Southern France)

Please download to get full document.

View again

of 5
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Document Description
Hydrobiologia (2005) 539: Ó Springer 2005 DOI /s Short Research Note Recovery of the seagrass Zostera marina in a disturbed Mediterranean lagoon (Etang de Berre, Bouches-du-Rhoˆne,
Document Share
Documents Related
Document Transcript
Hydrobiologia (2005) 539: Ó Springer 2005 DOI /s Short Research Note Recovery of the seagrass Zostera marina in a disturbed Mediterranean lagoon (Etang de Berre, Bouches-du-Rhoˆne, Southern France) Guillaume Bernard 1, * Patrick Bonhomme 1 & Charles F. Boudouresque 2 1 GIS Posidonie, Parc scientifique et technologique de Luminy, Marseille Cedex 09, France 2 UMR DIMAR, Centre d Oce anologie de Marseille, Universite de la Me diterrane e, Parc scientifique et technologique de Luminy, Marseille Cedex 09, France (*Author for correspondence: Received 13 February 2004; in revised form 30 July 2004; accepted 8 September 2004 Key words: Zostera marina recovery, brackish lagoon, disturbance Abstract Until 1966, Berre lagoon (Provence, southern France) was a salty lagoon with a highly diversified marine fauna and flora. Increased inputs of freshwater from a hydroelectric plant led to the desalination and stratification of the lagoon. Following these changes, a wide diversity of species disappeared, including the eelgrass Zostera marina, a keystone species which previously constituted extensive meadows in the lagoon. After almost three decades of absence, patches of eelgrass were observed in 2001 and 2002 but the success of future recolonization by this community is uncertain. Introduction Until the late 1960s, meadows of the eelgrass Zostera marina Linnaeus were widespread in the Berre and Va ne brackish lagoons (Bouches-du- Rhoˆ ne, southern France, Mediterranean; Fig. 1a) from 1 to 6 7 m depth. At that time, the hydrological conditions of the lagoon were similar to those of the adjacent shallow coastal water: mean salinity was stable and close to 30 psu, except for the areas next to natural freshwater inputs (rivers). Water temperatures showed wide seasonal variations, from 2.5 to 25.0 C (Gourret, 1907; Decrock, 1914; Huve & Huve, 1954; Huve, 1960; Mars, 1966). From 1966, the diversion of the Durance river towards the Saint-Chamas hydroelectric power plant and into the Berre lagoon, resulted in (i) heavy input of freshwater; (ii) the decline of surface water salinity; (iii) stratification with freshwater at the surface and more salty water at depth (under calm conditions); (iv) entrophication and unstable ecological conditions (Minas, 1974, 1976; Stora, 1976; Stora et al., 1995; Ne rini, 2000; Ne rini et al., 2000). In the early 1970s, the Zostera marina stands underwent a dramatic decline; they were first reduced to a narrow belt of m width, limited to 3 m depth (Riouall, 1971, 1972a, b; Huve et al., 1973) and progressively disappeared from the Berre and Va ne lagoons. The last sighting of this species was in 1973 (Riouall, 1973, 1977). The Salinity tolerance of Z. marina is quite exceptional for a seagrass: the species can occur from fully marine water and more or less stable brackish water down to a salinity of 5 psu (Hartog, 1970; Kamermans et al., 1999; Katwijk et al., 1999). Vegetative growth occurs between 10 and 15 C and generative shoots are produced between 15 and 20 C (Hartog, 1970), which fits well with Mediterranean populations, though other populations may thrive in different temperature ranges (Silberhorn et al., 1983). Other factors known to affect the occurrence of Z. marina are: turbidity (Ibarra-Obando et al., 1997; Katwijk et al., m Z. marina patches (july 2002) m Montpellier Marseille Nice m 4.3 m 91 (c) La Mède oil terminal Perpignan Mediteranean (b) m W N S E Golfe de Fos Martigues Berre lagoon Saint-Chamas La Mède Vaïne lagoon Figure 1. (a) Localisation of Berre and Va ne lagoons, Bouches-du-Rhône, Southern France, Mediterranean and the input of freshwater from hydroelectric plant (arrow). (b) Localisation of Zostera marina patches in the Berre lagoon. (c) Patches of Z. marina near La Mède, in July Boxes: number of shoots per patch (a) ), light availability (Duarte, 1991; Cabello-Pasini et al., 2003), sediment dynamics (Frederiksen et al., 2004a, b) and nutrient load (Hemminga et al., 1991; Pedersen & Borum, 1992; Short & Wyllie- Echeveria, 1996; Fonseca & Bell, 1998). The turbidity and the nutrient load, due to the heavy freshwater inflow into the Berre lagoon, the resulting wide variability of salinity and water stratification, with under calm conditions a superficial fresh water layer, are the likely causes of the decline of Z. marina in the Berre lagoon. In the Wadden sea (Netherlands), the replacement of an estuarine gradient by a variable salinity regime, with the input of freshwater regulated by sluice, also had negative consequences on Z. marina populations, making them more vulnerable to other forms of stress (Katwijk et al., 2000). 159 Observation Since 1990, the benthic macrophytes of Berre and Va ne lagoons have been extensively monitored every year (Pergent-Martini et al., 1995; Soltan & Francour, 2000; this work). Monitoring methods consisted in the exploration of 46 sites by diving, perpendicular to the shore, down to the lower limit of macrophytes (less than 2 m depth) and snorkelling between these sites, parallel to the shore along the narrow strip prone to harbouring eelgrass. Through 2000, Z. marina was never sighted, confirming its disappearance. The possibility that isolated shoots of Z. marina had escaped observation cannot be excluded though this is unlikely, considering the close monitoring network over a 10-year period. In July 2001, Zostera marina was observed, along the La Mede oil terminal harbour pier (Fig. 1b), in a sector where an extensive belt of Z. marina was formerly present (Riouall, 1973). Depth (2 m), size and number of Z. marina patches and the number of shoots per patch were recorded: 6 patches (encompassing a total of 124 shoots) were scattered within a 4 m 2 surface area. In July 2002 some of these patches had coalesced while new patches had appeared (encompassing a total of 266 shoots, Fig. 1c). It is to be noted that the observed patches were composed of isolated rhizomes, without flowers or seeds, and that shoot density remained low compared to other Z. marina meadows, such as those in the Thau lagoon (Languedoc- Roussillon, Southern France) (Laugier et al., 1999; Plus et al., 2003). The substrate was mainly composed of calcareous annelid and shell debris. Discussion and conclusion The recolonization by Zostera marina, after almost three decades of absence, may be due to an improvement in environmental conditions within the Berre lagoon. The power plant freshwater discharge steadily decreased from more than 6Gm 3 /a in 1977 to less than 2 Gm 3 /a since 1994 onwards, together with a dramatic reduction in the silt load (from 1.6 Mt/a in 1977 to 0.1 Mt/a) (Electricite de France, unpublished data). There is however no evidence of such a trend for nutrients (Kim & Travers, 1997a; b), despite a significant reduction in industrial wastewater and domestic sewage input since the 1980s. The lag time between improvement in environmental conditions and the first sighting of Z. marina raises the question of their actual role. A possible hypothesis for this delayed colonization could be the poor availability of propagules (seeds and/or cuttings); the nearest Z. marina stand lies in the open sea (Golfe de Fos; pers. obs.). In Thau lagoon, the complete recolonization of the Z. marina meadow, totally destroyed by an anoxic crisis, took place in less than 1 year, because of seeds and rhizomes surviving the crisis within the sediment (Plus et al., 2003). Another hypothesis for the delayed recolonization could be the opening of a window of opportunity within the range of environmental fluctuation. To date, we cannot forecast whether the observed Z. marina patches in the Berre lagoon are the harbinger of extensive recolonization of the lagoon, which would support the hypothesis of a durable improvement in environmental conditions or whether they will be eliminated by subsequent chance climatic events or by a new anthropogenic disturbance. Acknowledgements The authors are indebted to Philippe Picon (GIPREB) for field assistance, to Michael Paul for improving the English text and to the reviewers for their critical comments on the manuscript. This study is a part of a global monitoring program of Berre and Va ne lagoons funded by GIPREB (Berre l Etang, France). References Cabello-Pasini, A., R. Mun iz-salazar & D. H. Ward, Annual variations of biomass and photosynthesis in Zostera marina at its southern end of distribution in the North Pacific. Aquatic Botany 76: Decrock, E., Le Sol. Encyclopédie des Bouches-du- Rhoˆ ne, France: 12, xv pp. Duarte, C. M., Seagrass depth limits. Aquatic Botany 40: Fonseca, M. S. & S. S. Bell, Influence of physical setting on sea-grass landscapes near Beaufort, North Carolina, USA. Marine Ecology Progress Series 171: Frederiksen, M., D. Krause-Jensen, M. Holmer & J. S. Laursen, 2004a. Spatial and temporal variation in eelgrass 160 (Zostera marina) landscapes: influence of physical setting. Aquatic Botany 78: Frederiksen, M., D. Krause-Jensen, M. Holmer & J. S. Laursen, 2004b. Long-term changes in area distribution of eelgrass (Zostera marina) in Danish coastal waters. Aquatic Botany 78: Gourret, P., Topographie zoologique des e tangs de Caronte, de Labillon, de Berre et de Bolmon. Flore, faune, migrations, etc. Annales du Muséum d Histoire naturelle de Marseille 11: den Hartog, C., The Seagrasses of the World. North Holland Publ. Co, Amsterdam: 275 pp + 63 Fig plates. Hemminga, M. A., P. G. Harrison & F. van Lent, The balance of nutrient losses and gains in seagrass meadows. Marine Ecology Progress Series 71: Huvé, H., Sur l envahissement re cent d une portion de l Etang de Berre (Etang de Va ne) par une Céramiacée du genre Spermothamnion. Rapport et Procès-verbaux des Re unions de la Commission internationale pour l Exploration scientifique de la mer Méditerranée 15: Huvé, H., A. Kiener & R. Riouall, Modifications de la flore et des populations ichtyologiques des e tangs de Berre et de Va ne (Bouches-du-Rhône) en fonction des conditions hydrologiques crée es par le déversement de la Durance. Bulletin du Muséum d Histoire naturelle de Marseille 33: Tables I III. Huvé, P. & H. Huvé, Zonation superficielle des coˆ tes rocheuses de l Etang de Berre et comparaison avec celles du Golfe de Marseille (de Carry à Sausset). Vie et Milieu 5: Ibarra-Obando, S. E., C. F. Boudouresque & M. Roux, Leaf dynamics and production of a Zostera marina bed near its southern distributional limit. Aquatic Botany 58: Kamermans, P., M. A. Hemminga & D. J. de Jong, Significance of salinity and silicon levels for growth of a formerly estuarine eelgrass (Zostera marina) population (Lake Grevelingen, The Netherlands). Marine Biology 133: van Katwijk, M. M., D. C. R. Hermus, D. J. de Jong, R. M. Asmus & V. N. de Jonge, Habitat suitability of the Wadden Sea for restoration of Zostera marina beds. Helgoland Marine Research 54: van Katwijk, M. M., G. H. W. Schmitz, A. M. Gasseling & P. H. van Avesaath, Effects of salinity and nutrient load and their interaction on Zostera marina. Marine Ecology Progress Series 190: van Katwijk, M. M., G. H. W. Schmitz, L. S. A. M. Hanssen & C. den Hartog, Suitability of Zostera marina populations for transplantation to the Wadden Sea as determined by a mesocosm shading experiment. Aquatic Botany 60: Kim, K. T. & M. Travers, 1997a. Les nutriments de l Etang de Berre et des milieux aquatiques contigus (eaux douces, saumâtres et marines; Méditerranée NW). 2 Les nitrates. Marine Nature 5: Kim, K. T. & M. Travers, 1997b. Les nutriments de l Etang de Berre et des milieux aquatiques contigus (eaux douces, saumâtres et marines; Méditerranée NW). 4 Les nitrites. Marine Nature 5: Laugier, T., V. Rigollet & M. L. De Casabianca, Seasonal dynamics in mixed eelgrass beds, Zostera marina L. and Z. noltii Hornem., in a Mediterranean coastal lagoon (Thau lagoon, France). Aquatic Botany 63: Mars, P., Recherches sur quelques e tangs du littoral méditerranéen français et sur leurs faunes malacologiques. Vie et Milieu 20: Minas, M., Distribution, circulation et évolution des e léments nutritifs, en particulier du phosphore minéral, dans l étang de Berre. Influence des eaux duranciennes. Internationale Revue der gesamten Hydrobiologie 59: Minas, M., Oxygène dissous et saturation dans un milieu de forte production organique (étang de Berre). Roˆ le d une halocline sur leur distribution et sur les rapports oxygènephosphate. Notion de bilan. Hydrobiologia 51: Nérini, D., Analyse statistique de processus physiques et chimiques en océanologie coˆ tière à l aide d une méthode de re gression et de classification par arbre décisionnel. Application à l étude d un milieu fortement perturbé: l étang de Berre. PhD thesis, Université de la Me diterrane e, 105 pp. Nérini, D., J. P. Durbec & C. Manté Analysis of oxygen rate time series in a strongly polluted lagoon using a regression tree method. Ecological Modelling 133: Pedersen, M. F. & J. Borum, Nitrogen dynamics of eelgrass Zostera marina during a late summer period of high growth and low nutrient availability. Marine Ecology Progress Series 80: Pergent-Martini, C., R. Semroud, V. Rico-Raimondino & G. Pergent, Localisation et e volution des peuplements de phanérogames aquatiques de l e tang de Berre (Bouches du Rhoˆ ne France). Proceedings of the 39th national meeting of the Association Francaise de Limnologie, 1995 (Jul 3 7); Corte, France: Plus, M., J. M. Deslous-Paoli & F. Dagault, Seagrass (Zostera marina L.) bed recolonisation after anoxia-induced full mortality. Aquatic Botany 77: Riouall, R., Inventaire floristique des e tangs de Berre et de Va (années ). Bulletin de la Société des Sciences naturelles et d Archéologie de Toulon et du Var 23: Riouall, R., 1972a. A propos des Entéromorphes des e tangs de Berre et de Va ne. Bulletin du Muséum d Histoire naturelle de Marseille 32: Riouall, R., 1972b. Contribution à l étude de la flore des e tangs de Berre et de Va ne (Bouches-du-Rhoˆ ne). PhD thesis. Université Aix-Marseille, 518 pp. Riouall R., Contribution préliminaire à l étude de la flore de l e tang de Berre. Rapport et Procès-verbaux des Réunions de la Commission internationale pour l Exploration scientifique de la mer Me diterrane e 21: Riouall, R., Evolution de la flore benthique des e tangs de Berre et de Va ne (Bouches-du-Rhoˆ ne) de 1971 à Bulletin du Muséum d Histoire naturelle de Marseille 37: Short, F. T. & S. Wyllie-Echeverria, Natural and humaninduced disturbance of seagrasses. Environmental Conservation 23: 161 Silberhorn, G. M., R. J. Orth & K. A. Moore, Anthesis and seed production in Zostera marina L. (eelgrass) from the Chesapeake Bay. Aquatic Botany 15: Soltan, D. & P. Francour, Monitoring system of benthic macrophytes communities in Berre and Va ne ponds: development of a new strategy. Journal de Recherche oce anographique 25: Stora, G., Evolution des peuplements benthiques d un e tang marin soumis à un effluent d eaux douces. Bulletin d Ecologie 7: Stora, G., A. Arnoux & M. Galas, Time and spatial dynamics of Mediterranean lagoon macrobenthos during an exceptionally prolonged interruption of freshwater inputs. Hydrobiologia :
Similar documents
View more...
Search Related
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks