Variability in the Structure of Epiphytic Assemblages of in Relation To

Variability in the structure of epiphytic assemblages of in relation to human interferences in the Gulf of Gabes, Tunisia Mounir Ben Brahim, Asma Hamza, Imen Hannachi, Ahmed-Riadh Rebai, Othman Jarboui, Abderrahmen Bouain, Lotfi Aleya To cite this version: Mounir Ben Brahim, Asma Hamza, Imen Hannachi, Ahmed-Riadh Rebai, Othman Jarboui, et al.. Variability in the structure of epiphytic assemblages of in relation to human interferences in the Gulf of Gabes, Tunisia. Marine Environmental Research, Elsevier, 2010, 70 (5), pp.411. 10.1016/j.marenvres.2010.08.005. hal-00631670 HAL Id: hal-00631670 https://hal.archives-ouvertes.fr/hal-00631670 Submitted on 13 Oct 2011 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Accepted Manuscript Title: Variability in the structure of epiphytic assemblages of Posidonia oceanica in relation to human interferences in the Gulf of Gabes, Tunisia Authors: Mounir Ben Brahim, Asma Hamza, Imen Hannachi, Ahmed Rebai, Othman Jarboui, Abderrahmen Bouain, Lotfi Aleya PII: S0141-1136(10)00120-0 DOI: 10.1016/j.marenvres.2010.08.005 Reference: MERE 3471 To appear in: Marine Environmental Research Received Date: 25 March 2010 Revised Date: 31 July 2010 Accepted Date: 16 August 2010 Please cite this article as: Ben Brahim, M., Hamza, A., Hannachi, I., Rebai, A., Jarboui, O., Bouain, A., Aleya, L. Variability in the structure of epiphytic assemblages of Posidonia oceanica in relation to human interferences in the Gulf of Gabes, Tunisia, Marine Environmental Research (2010), doi: 10.1016/ j.marenvres.2010.08.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. 1 Variability in the structure of epiphytic assemblages of Posidonia oceanica in relation to 2 human interferences in the Gulf of Gabes, Tunisia 3 4 5 6 Mounir Ben Brahim1, 2, Asma Hamza 2, Imen Hannachi 1, 2, Ahmed Rebai3, Othman Jarboui2, 7 Abderrahmen Bouain1 and Lotfi Aleya*4 8 9 10 1 Université de Sfax, Faculté des Sciences Sfax. Route Soukra Km 3.5, BP: 802, 3018 Sfax. 11 Tunisia 12 2 Institut National des Sciences et Technologies de la Mer, Centre de Sfax, Rue Madagascar, 13 BP 1035, Sfax, CP 3018, Tunisie. 14 3 Centre de Biotechnologie de Sfax, Route Sidi Mansour Km 6, Sfax, Tunisie 15 4 Université de Franche-Comté, Laboratoire de Chrono-Environnement, UMR CNRS 6249 1, 16 Place Leclerc, F-25030 Besançon cedex, France. 17 18 *Corresponding author: [email protected] 19 Phone: 03 81 66 57 64 20 Fax: 03 81 66 57 97 21 22 23 24 25 1 Abstract 2 In this study we evaluate whether the pattern of spatial variability of the macro-epiphytes 3 assemblages of leaves of Posidonia oceanica differed in relation to anthropogenic 4 interference in the Gulf of Gabes (southern coast of Tunisia). A hierarchical sampling design 5 was used to compare epiphytic assemblages at 5m depth in terms of abundance and spatial 6 variability at disturbed and control locations. The results indicate that the biomass and mean 7 percentage cover decreased at locations near the point of sewage outlet in comparison to 8 control locations. These losses were related to the distance from the source of disturbance. 9 This study revealed that the diversity is reduced in disturbed locations by the loss of biomass 10 and the mean percentage cover, explained by means of a multiple-stressor model which plays 11 an important role in the macro-epiphytes setting. It is urgent to propose the best management 12 plans to save the remaining P. oceanica meadow in the Gulf of Gabes and its associated 13 epiphytes. 14 15 16 Keywords: Macro-epiphytes ; Posidonia oceanica ; disturbance ; spatial variability ; Gabès G ulf. 17 Gulf. 18 19 20 21 22 23 24 25 26 1 1. Introduction 2 Over the past 20 years, the Gulf of Gabes, on the southeast coast of Tunisia, has produced 3 more than 65% of the annual fish yield in Tunisia (Ben Mustapha, 1995; C.G.P., 1996), being 4 favoured by widespread seagrass beds widely recognized as key ecosystems in temperate and 5 tropical infra littoral habitats (Hemminga and Duarte, 2000; Boudouresque et al., 2009). 6 However, fish production is gradually decreasing parallel to the decline of littoral beds of the 7 endemic Mediterranean seagrass Posidonia oceanica (L.) Delile species as the coastal area of 8 the Gulf is now a threatened biotope mainly due to the pressure of anthropogenic expansion 9 and dumping of large quantities of phosphogypsum and other chemical products which 10 severely impacted benthic habitats ((Hamza-Chaffai et al., 1999, Bejaoui et al., 2004). The 11 loss of the native vegetable cover in the Gulf of Gabes is estimated at 90% with the P. 12 oceanica beds being replaced by the opportunistic and caulerpenyne-producing green algae 13 Caulerpa prolifera (Forsskål) Lamouroux in deeper zones (Hamza et al., 1995; Ramos-Espla 14 et al., 2000). The remaining Posidonia meadows cover the littoral fringes at depths ranging 15 between -3 and -4 m (Hattour et al., 1998). On the other hand, most biological studies of the 16 Gulf of Gabes have dealt with the distribution of phytoplankton (Drira et al., 2008; Bel 17 Hassen et al., 2009) zooplankton (Drira et al., 2009) ciliates (Kchaou et al., 2009; Hannachi et 18 al., 2009), demosponges (Ben Mustapha et al., 2003) while seagrass species and their 19 epiphytes which are known to be highly sensitive to environmental changes (Balata et al., 20 2007; Prado et al., 2008; Montefalcone, 2009) have been given limited attention. Epiphytes of 21 seagrass not only contribute significantly to the primary production of the meadow (Buia et 22 al., 1992; Nelson and Waaland, 1997; Duarte et al., 2004), but are also more sensitive to 23 environmental changes than the plant host (Delgado et al., 1999; Nesti et al., 2008; 24 Giovannetti et al., 2010). For example, various studies reported increases in epiphyte biomass 25 parallel with nutrient enrichment (Armitage et al., 2006; Neckles et al., 1993), eutrophication 1 (Balata et al., 2008; Frankovich et al., 2009) and water quality (Meric et al., 2005). 2 Differences in the spatial heterogeneity of epiphytes (Piazzi et al., 2004; Martínez-Crego et 3 al., 2010) and shifts in species composition (Nesti et al., 2008; Fourqurean et al., 2010) have 4 also been observed. It is widely known that the distribution of epiphytic assemblages of P. 5 oceanica both on leaves (Van der Ben., 1971; Mazzella et al., 1989) and rhizomes (Piazzi et 6 al., 2002; Balata et al., 2008) can change, but these changes have not yet been explored on a 7 horizontal scale in the Gulf of Gabes. Differences in the spatial heterogeneity of epiphytes 8 (Piazzi et al., 2004) and shifts in species composition (Nesti et al., 2008; Fourqurean et al., 9 2010; Martínez-Crego et al., 2010) have also been observed. Several findings have provided 10 evidence that epiphytes are patchy at 1 to 10 cm (Kendrick and Burt, 1997; Jernakoff and 11 Neilsen, 1998) and > kilometer scales, (Vanderklift and Lavery 2000, Lavery and Vanderklift 12 2002), other studies have indicated that epiphytes may be uniform at relatively small spatial 13 scales (e.g., 0.1 m Vanderklift and Lavery 2000; <10 m, Saunders et al., 2003, Piazzi et al., 14 2004). Moore et al. (2006) reported that epiphytes biomass is uniform at the scale < 100 m 15 transect. Variability in leaves epiphytic biomass at the scale of meters may be relatable to 16 differences in shoot density (Gambi et al., 1989), and to impacts of water movements on both 17 settlement and recruitment of propagules (Trautman and Borowitzka, 1999; Vanderklift and 18 Lavery, 2000). It is, therefore, of importance to undertake a study of the effects of urban 19 pressure on P. oceanica dynamics under the impact of human activities versus control 20 conditions. To our knowledge, only the flowering and fructification of P. oceanica along the 21 coastline of the Gulf of Gabes has been the subject of studies in recent years (Hattour et al., 22 1998). As part of a comprehensive study intended to understand the dramatic decline of the 23 endemic Mediterranean seagrass P. oceanica in the Gulf of Gabes, we analyzed, for the first 24 time in this ecosystem, the structure and patterns of spatial variability of leaf macro-epiphytic 25 assemblages and tested their relationships with anthropogenic disturbance. We attempted to 1 answer the questions 1) how vulnerable are the leaf macro-epiphytic assemblages to these 2 environmental pressures? 2) Does epiphyte biomass increase parallel with organic and 3 nutrient enrichment and which members of the epiphytic community should be considered as 4 most sensitive species? And 3) Does anthropogenic disturbance modify the spatial scales at 5 which variability of the epiphytic communities is highest/lowest or also influences the 6 partition of total variability among spatial scales? We, thus, compared epiphytic assemblages 7 between locations exposed to urban and industrial effluents and control locations, and 8 examined their variability at spatial scales ranging from cm to km, using a hierarchical 9 sampling design (Underwood, 1994; Chapman et al., 1995).

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