Population Structure and Conservation Status of the White Gorgonian Eunicella Singularis (Esper, 1791) in Tunisian Waters (Central Mediterranean)
Total Page：16
File Type：pdf, Size：1020Kb
Research Article Mediterranean Marine Science Indexed in WoS (Web of Science, ISI Thomson) and SCOPUS The journal is available on line at http://www.medit-mar-sc.net DOI: http://dx.doi.org/10.12681/mms. 24984 Population structure and conservation status of the white gorgonian Eunicella singularis (Esper, 1791) in Tunisian waters (Central Mediterranean) Raouia GHANEM1,2, Jamila BEN SOUISSI1,3, Jean-Baptiste LEDOUX4,5, Cristina LINARES6 and Joaquim GARRABOU5 1 Biodiversity, Biotechnology and Climate Change Laboratory-LR11ES09, University of Tunis El Manar, Tunisia 2 Higher Institute of Fisheries and Aquaculture of Bizerte, 7080, Bizerte, University of Carthage, Tunisia 3 National Agronomic Institute of Tunisia, Tunis, University of Carthage, Tunisia 4CIIMAR/CIMAR, Interdisciplinary Center for Marine and Environmental Research, University of Porto, 4050-123, Portugal 5 Institute of Marine Sciences CSIC, Passeig Maritim de la Barceloneta 37-49, E-08003, Barcelona, Spain 6 Department of Evolutionary Biology, Ecology and Environmental Sciences, Biodiversity Research Institute (IRBio), University of Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain Corresponding author: [email protected] Contributing Editor: Carla MORRI Received: 7 October 2020; Accepted: 5 March 2021; Published online: 17 May 2021 Abstract The white gorgonian, Eunicella singularis, is thriving in Mediterranean hard-bottom communities; however, data regarding its distribution and ecology remain absent and insufficient, particularly in the southern Mediterranean Sea. In this study, the popula- tion structure and disturbance levels of the most common gorgonian in Tunisia were assessed for the first time. During two years (2015-2016), a total of 818 colonies of E. singularis were surveyed in five coastal sites, by scuba diving, between 7 to 40 m depth. Collected data included density, colony height, and extent of injury. Mean population density was 11.91 ± 7.42 colonies per m2 (mean ± SD). Mean and maximum colony heights were 16.49 ± 5.59 cm and 51 cm, respectively. Among populations, mean extent of tissue injury differed considerably, ranging from 12.47% to 58.88% and most affected colonies showed old necrosis. These data regarding the demographic structure and level of injuries are needed to provide insights into the conservation status of the Tuni- sian population of E. singularis. Indeed, data on the amount of necrosis could highlight the strength of the colonies’ exposure to mechanical impacts and are consequently crucial to study changes in their demographic structure over time. In fact, the size, struc- tures, and the high level of tissue necrosis of the colonies suggest a low conservation status of the studied Tunisian populations. Keywords: Demography; Octocoral; Tunisia; Disturbance levels; Eunicella singularis; Scientific diving. Introduction than 50% in density and biomass in impacted areas (Lin- ares et al., 2005; Cupido et al., 2008; Coma et al., 2009; Climate change is a major pressure damaging biolog- Santangelo et al., 2015). Physiological stress induced by ical diversity and ecosystems around the world by affect- climate change-related disturbances, in particular, strong ing phenology, physiology, and ecological interactions and recurrent marine heat waves (Cerrano et al., 2000; among species, causing changes in their biogeography Kersting et al., 2013; Turicchia et al., 2018; Bensoussan and altering community structure and dynamics (Har- et al., 2019) severely threaten these species and increase ley et al., 2006; Walther, 2010). Mass mortality events their vulnerability to pathogens (Rivetti et al., 2014). (MMEs) of benthic species have occurred in the last This vulnerability could be enhanced by decreasing food few decades and have been related to marine heat waves sources, caused by the stratification of the water column linked to global warming (Harley et al., 2006; Halpern et in summer, which seems to be the basis of mass mor- al., 2015; Garrabou et al., 2019; Smale et al., 2019). Over- tality events (MME’s) reported for gorgonian species in all, more than 90 species of sessile macro-invertebrates the last decades in the north-western Mediterranean Sea were affected in Mediterranean, particularly sponges and (Linares et al., 2005; Crisci et al., 2011; Huete-Stauffer gorgonians (Cerrano et al., 2000; Garrabou et al., 2009, et al., 2011; Marbà et al., 2015; Garrabou et al., 2019). 2019). Indeed, gorgonians (Cnidaria, Octocorallia) were Among affected species, the white gorgonian Euni- the most damaged species, with an average loss of more cella singularis (Esper, 1791) suffered different mass 362 Medit. Mar. Sci., 22/2 2021, 362-371 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 18/08/2021 10:22:07 | mortalities events the north-western Mediterranean Sea vation status, life-history traits, and population genetics causing important decreases in densities and biomass of long-lived species has improved in the last two dec- with rates of up to 90% necrosis (Coma et al., 2006; Gar- ades (Linares et al., 2008; Sini et al., 2015; Ledoux et rabou et al., 2009; Gambi et al., 2018; Turicchia et al., al., 2018), it remains rare for many key species in the 2018). The first event was reported by Harmelin (1984) Mediterranean. Such basic information is a crucial pre- at La Ciotat in the Ligurian Sea followed by an unprece- requisite for the establishment of management measures dented large scale MME in 1999 that impacted thousands to ensure the conservation of those organisms. To fill this of populations in a wide area including the Ligurian Sea, gap, the main goal of this work was to provide data on Balearic Islands, and Port Cros National Park (Cerrano demographic characteristics and the disturbance level of et al., 2000; Perez et al., 2000; Coma et al., 2006). Such E. singularis, one of the most common octocoral species events have been observed from 2002 to 2017 in many lo- in Tunisian waters. calities but particularly in the Tyrrhenian Sea (Ischia and Procida Islands, Gulf of Naples, Montecristo Island, Ta- volara Island), and the northern and south-western Med- Materials and Methods iterranean Sea (Cabo de Palos, Cabrera Island, Tabarca, Spain and Banyuls sur Mer, France) (Cigliano & Gambi, The species Eunicella singularis 2007; Gambi et al., 2006; Garrabou et al., 2009; Carella et al., 2014; Gambi et al., 2018; Turicchia et al., 2018). Eunicella singularis is characterised by a longevity Being a cold-water species, E. singularis is very sensi- reaching 25-30 years with an average growth of approxi- tive to thermal stress (Previati et al., 2010; Linares et al., mately 2-5 cm/year (Weinberg & Weinberg 1979; Munari 2013; Vezzulli et al., 2013) as demonstrated by thermo- et al., 2013) displaying higher growth rates during the tolerance experiments carried out on this species showing first year of life (Viladrich et al., 2016). This gorgonian that its exposure to temperatures greater than 26°C could presents a high rate of recruitment with large larval and have lethal consequences (Coma et al., 2009; Linares et juvenile mortality (Weinberg & Weinberg, 1979; Linares al., 2013) and thus, it can be considered as a potential et al., 2008). According to studies performed in the NW indicator of climate change impacts on Mediterranean Mediterranean Sea, the species is gonochoric with rare benthic communities (Coma et al., 2006). cases of hermaphroditism and reproduces annually in late Eunicella singularis forms dense populations in Med- May and June when the water column is fully stratified iterranean rocky coastal habitats between a few meters (Gori et al., 2007; Ribes et al., 2007). Gametogenesis dis- down to 50 m depth, mainly in the western Mediterrane- plays a seasonal pattern of development characterised by an but also in the Adriatic and Aegean seas (Carpine & a single annual maturation of the gametes (Ribes et al., Grasshoff, 1975; Weinberg, 1976, 1980; Linares et al., 2007). 2008; Gori et al., 2011a; Ghanem et al., 2018). Eunicella singularis is a photophilic species that inhabits horizon- tal or subhorizontal substrates and can be also found in Sampling design coralligenous assemblages. It is also the only Mediterra- nean gorgonian species hosting symbiotic zooxanthellae The white gorgonian displays abundant populations (Forcioli et al., 2011). in northern and eastern Tunisian coasts (Ghanem et al., While our knowledge on population structure, conser- 2018). In order to characterise the population structures Fig. 1: Study sites. Medit. Mar. Sci., 22/2 2021, 362-371 363 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 18/08/2021 10:22:07 | Table 1. Characteristics of the sampled populations including coordinates, type of habitat, type of inclination, and protection level). Locality Locality Protection Site Coordinates Habitat Inclination ID name level Sector 1 L1 Tabarka Cap Tabarka 37.10694° N 8.81° E Rocky outcrop Sub-vertical Unprotected Rocher Mérou 37.14611° N 8.871944° E Wall Vertical Unprotected L2 La Galite Pointe Mistral 37.75389° N 8.907222° E Rocky outcrop Sub-vertical MPA Les chiens 37.58889° N 8.993056° E Rocky outcrop Sub-vertical MPA Gallo 37.70139° N 9.108611° E Rocky outcrop Sub-vertical MPA Gallina 37.67556° N 9.770556° E Wall Vertical MPA Sector 2 L3 La Marsa Kobet Hwé 37.46778° N 10.5825° E Rocky outcrop Sub-vertical Unprotected Sidi Abdelaziz 37.47944° N 10.605° E Rocky outcrop Sub-vertical Unprotected L4 Zembra Capo Grosso 37.21417° N 10.8325° E Rocky outcrop Sub-vertical MPA La Cathédrale 37.15528° N 10.87083° E Small stones ---- MPA L5 Haouaria Ras Drak 37.20194° N 11.24722° E Rocky outcrop Sub-vertical Unprotected Banc Madyouna 1 37.15639° N 11.27194° E Rocky outcrop Sub-vertical Unprotected Banc Madyouna 2 37.15° N 11.27972° E Rocky outcrop Sub-vertical Unprotected and their conservation status, five localities and 13 sites Assessment of disturbance impact level were studied within two sectors including two Marine Protected Areas (MPA) (Fig. 1 and Table 1). In the north- Extent of injury per colony, type of injury (see below), west sector (1) data from six sites within two localities and proportion of healthy colonies were monitored to were collected: Tabarka and La Galite MPA.