Marine protected areas in the Mediterranean Sea

Table of Contents

Chapter 1 Mediterranean Sea Biodiversity

Chapter 2 The Perspective for Marine Conservation in the Mediterranean Sea

Chapter 3 Mediterranean Conservation Implications based on Environmental and Human Gradients

Chapter 4 MPAs Posidonia oceanica Meadows Health Indicate that Legal Protection is not Enough

Chapter 5 Evidences from a Mediterranean MPA Show that Protection Enhances Community and Habitat Stability

Chapter 6 Fish Biodiversity and Fisheries in Mediterranean MPAs

Chapter 7 The Recent Case Study about Dusky Grouper (Epinephelus marginatus) Indicate Low Connectivity between Mediterranean MPAs

Chapter 8 Response of Rocky Reef Top Predators (Serranidae: Epinephelinae) in and Around MPAs

Chapter 9 Species-Specific Export of Fish Naïveté from a No-Take Marine Protected Area in a Coastal Recreational Hook and Line Fishery

Chapter 10 Marine Protected Area or marine polluted area? The case study of the striped dolphin (Stenella coeruleoalba)

Chapter 11 Transboundary Conservation Efforts Are Needed for the Critically Endangered Species like Balearic Shearwater

Chapter 12 Socioeconomic Impacts of the National Marine Park of Alonissos (Greece) and Mediterranean Monk Seal (Monachus monachus)

Abstract

Definitions of MPAs vary from exclusionary to inclusionary. A recently revised IUCN definition of what constitutes a protected area (PA) emphasizes the conservation purpose of geographical space. ‘‘Conservation’’ is defined as the in situ maintenance of ecosystems and natural and semi-natural habitats and of viable populations of species in their natural surroundings. Prohibition or restriction of activities within a PA is usually part of the in situ maintenance. For marine sites this engenders unique management opportunities and challenges. For example, depth can be very significant in a MPA; it is difficult or impossible to put up ‘‘fences’’ around MPAs; and exploitation of resources adjacent to a reserve for commercial fishing must frequently be reconciled with conservation goals. However, the actual situation of MPAs in Mediterranean has been reported only by case studies in different regions of Mediterranean and reports of implemented projects by different organizations and NGOs. In this book all the information is well integrated and cover different scientific and management areas by considering the economic and social point of view. Although, the involved scientists, managers and experts for MPAs have different backgrounds and they can be biologist, engineers, economist or lawyers, they must at least have a Master Degree in order to understand the problematics of Mediterranean and use the book as instrument for a better management of Mediterranean and/or other World Regions MPAs, without considering only the conservation impact of MPAs.

Temporal trends indicate that overexploitation and habitat loss have been the main human drivers of historical changes in Mediterranean biodiversity. At present, habitat loss and degradation, followed by fishing impacts, pollution, climate change, eutrophication, and the establishment of alien species are the most important threats and affect the greatest number of taxonomic groups. All these impacts are expected to grow in importance in the future, especially climate change and habitat degradation. Marine experts and conservationists see great hope in the opportunities provided by marine protected areas (MPA) to counter threats to marine ecosystems. In this book, the effects of the MPAs are illustrated based on detailed analyses of the recent case studies of Mediterranean charismatic species, like monk seal, dolphins, groupers, seagrass meadows and birds (balearic shearwater). This book examines the use of MPAs as a way to restore and maintain healthy marine environments by contributing to the overall protection of critical marine habitats and resources in Mediterranean. Furthermore, it suggest the best way to manage the existing ones after providing case studies showing the actual situation of them and how to establish the future MPAs in the Mediterranean. This book is the precious instrument, full of conservation strategies based on MPA networks aimed at enhancing resilience and it may be the most effective tool to limit the negative impacts of the complex suites of threats on marine ecosystems under future scenarios of frequent and/or persistent disturbance.

The principal audiences for the publication:

- Master and PhD Students in Natural Sciences, Economy and Law
- International and/or National Experts in Ecology, Marine Biology and Coastal Management
- Representatives of Ministry of Environment, Ministry of Agriculture and Ministry of Economy in Mediterranean Countries
- Representatives of International and/or National Organizations, which aim is to improve the management of Mediterranean MPAs (for example MedPAN and Royal Albania Foundation)

Competitive publications:

1. The Status of Marine Protected Areas in the Mediterranean Sea 2012 - A study done by MedPAN in collaboration with the RAC/SPA (256 pages)
2. Marine Protected Areas 2011 - Edited by Floyd B. Mayr (143 pages)

Particular advantages this publication have compared to the competitive publications:

In comparison to the competitive publications, this book bring the latest scientific publication (of the last 5 years) about the situation of management and threats in Mediterranean MPAs. The other books explores the impacts to these intricately balanced environments include declining fish populations, degradation of coral reefs and other vital habitats, threats to rare or endangered species, and loss of artifacts and resources in the United States, but in comparison to coastal areas of United States, the threats are tremendous in such a closed sea, like it is Mediterranean Sea. Although MedPAN, the Network of Marine Protected Areas Managers in the Mediterranean, has made a lot of efforts in order to improve the management and biodiversity conservation of several MPAs, their studies results have been shown in useful technical reports, but no book has be written till now by a Project Manager (like me) working in collaboration with MedPAN.

Recent publications (past 5 years):

Rigers Bakiu, Kastriot Korro, Valbona Kolaneci: Taurine as an Important Nutrient for Future Fish Feeds of Aquaculture in Albania.

A M Tolomeo, A Carraro, R Bakiu, S Toppo, S P Place, D Ferro, G Santovito: Peroxiredoxin 6 from the Antarctic emerald rockcod: molecular characterization of its response to warming. Journal of Comparative Physiology B 10/2015; DOI:10.1007/s00360-015-0935-3

G. Sattin, R. Bakiu, A. M. Tolomeo, A. Carraro, D. Coppola, D. Ferro, T. Patarnello, G. Santovito: Characterization and expression of a new cytoplasmic glutathione peroxidase 1 gene in the Antarctic fish Trematomus bernacchii. Hydrobiologia 09/2015; DOI:10.1007/s10750-015-2488-6

Rigers Bakiu, Gianfranco Santovito: New Insights into the Molecular Evolution of Metazoan Peroxiredoxins. Acta Zoologica Bulgarica 09/2015; 67(2):305-317.

Rigers Bakiu, Anna Maria Tolomeo, Gianfranco Santovito: Positive selection effects on the biochemical properties of fish pyroglutamylated RFamide peptide receptor (QRFPR). Italian Journal of Zoology 08/2015; DOI:10.1080/11250003.2015.1071437

Chapter 1 Mediterranean Sea Biodiversity

Abstract

The Mediterranean Sea is a marine biodiversity hot spot. In this chapter you can read the extract of a combined extensive literature analysis with expert opinions in order to update publicly available estimates of major taxa in this marine ecosystem and to revise and update several species lists. It was also assessed the overall spatial and temporal patterns of species diversity and identified major changes and threats. These results listed approximately 17,000 marine species occurring in the Mediterranean Sea. However, all the reported estimates of marine diversity are still incomplete as yet—undescribed species will be added in the future by other scientists. Diversity for microbes is substantially underestimated, and the deep-sea areas and portions of the southern and eastern region are still poorly known. In addition, the invasion of alien species is a crucial factor that will continue to change the biodiversity of the Mediterranean, mainly in its eastern basin that can spread rapidly northwards and westwards due to the warming of the Mediterranean Sea. Spatial patterns showed a general decrease in biodiversity from northwestern to southeastern regions following a gradient of production, with some exceptions and caution due to gaps in our knowledge of the biota along the southern and eastern rims.

Biodiversity is also generally higher in coastal areas and continental shelves, and decreases with depth. Temporal trends indicate that overexploitation and habitat loss have been the main human drivers of historical changes in biodiversity. At present, habitat loss and degradation, followed by fishing impacts, pollution, climate change, eutrophication, and the establishment of alien species are the most important threats and affect the greatest number of taxonomic groups. All these impacts are expected to grow in importance in the future, especially climate change and habitat degradation. The spatial identification of hot spots highlighted the ecological importance of most of the western Mediterranean shelves (and in particular, the Strait of Gibraltar and the adjacent Alboran Sea), western African coast, the Adriatic, and the Aegean Sea, which show high concentrations of endangered, threatened, or vulnerable species. The Levantine Basin, severely impacted by the invasion of species, is endangered as well.

Introduction to Mare mediterraneum

The Mare mediterraneum (in Latin) describes the Mediterranean as a ‘‘sea in the middle of the land.’’ This basin is the largest (2,969,000 km2) and deepest (average 1,460 m, maximum 5,267 m) enclosed sea on Earth (Figure 1a). Situated at the crossroads of Africa, Europe, and Asia, the Mediterranean coasts have witnessed the flourishing and decline of many civilizations. The region was an important route for merchants and travelers of ancient times, allowing for trade and cultural exchange, and today it is notable for contributions to global economy and trade. Its coasts support a high density of inhabitants, distributed in 21 modern states, and it is one of the top tourist destinations in the world, with 200 million tourists per year (National Oceanic and Atmospheric Administration, 2009).

The Mediterranean Sea connects through the Strait of Gibraltar to the Atlantic Ocean in the west and through the Dardanelles to the Sea of Marmara and the Black Sea in the northeast. In the southeast, the Suez Canal links the Mediterranean to the Red Sea and the Indian Ocean (Figure 1a).

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Figure 1. Biogeographic regions and oceanographic features of the Mediterranean Sea. (A) Main biogeographic regions, basins, and administrative divisions of the Mediterranean Sea, (B) Annual mean sea surface temperature (uC) (2003, NOAA), (C) Annual mean relative primary production (2002, Inland and Marine Waters Unit, Institute for Environment and Sustainability, EU Joint Research Centre, Ispra, Italy), and (D) maximum average depth (m) (NOAA).

In the Strait of Sicily, a shallow ridge at 400 m depth separates the island of Sicily from the coast of Tunisia and divides the sea into two main subregions: the western (area = 0.85 million km2) and the eastern (area = 1.65 million km2).

General oceanographic conditions in the Mediterranean have been previously described in detail (e.g., Bethoux, 1979; Hopkins, 1985; Pinard et al., 2006; Bas, 2009). It is a concentration basin: evaporation is higher in its eastern half, causing the water level to decrease and salinity to increase from west to east. The resulting pressure gradient pushes relatively cool, low-salinity water from the Atlantic across the Mediterranean basin. This water warms up to the east, where it becomes saltier and then sinks in the Levantine Sea before circulating west and exiting through the Strait of Gibraltar.

The climate in the region is characterized by hot, dry summers and cool, humid winters. The annual mean sea surface temperature shows a high seasonality and important gradients from west to east and north to south (Figure 1b). The basin is generally oligotrophic, but regional features enrich coastal areas through changing wind conditions, temporal thermoclines, currents and river discharges, and municipal sewage (Estrada, 1996; Zavatarelli et al., 1998; Bosc et al., 2004) (Figure 1c). The basin is characterized by strong environmental gradients (Danovaro et al., 1999), in which the eastern end is more oligotrophic than the western. The biological production decreases from north to south and west to east and is inversely related to the increase in temperature and salinity.

The Mediterranean has narrow continental shelves and a large area of open sea. Therefore, a large part of the Mediterranean basin can be classified as deep sea (Figure 1d) and includes some unusual features: high homothermy from 300–500 m to the bottom, where temperatures vary from 12.8°C–13.5°C in the western basin to 13.5°C–15.5°C in the eastern, and high salinity of 37.5–39.5 psu. Unlike in the Atlantic Ocean, where temperature decreases with depth, there are no thermal boundaries in the deep sea of the Mediterranean (Emig and Geistdoerfer, 2005).

Shelf waters represent 20% of the total Mediterranean waters, compared with the 7.6% of the world oceans, and therefore play a proportionally greater role here than in the world’s oceans. Shelves in the south are mainly narrow and steep (e.g., Moroccan, Algerian, and Libyan coasts, with the exception of the Gulf of Gabés), while those in the north are wider (e.g., the north and central Adriatic Sea, the Aegean Sea, and the Gulf of Lions) (Figure 1d). These features influence the morphology and constrain the connections to the Atlantic, the Red Sea, and the Indian Ocean (Bas, 2002).

The enclosed Mediterranean had a varied geological history, including isolation from the world ocean, that led to its near drying out during the Messinian crisis (5.96 million years ago) and to drastic changes in climate, sea level, and salinity (Maldonado, 1985; Garcia-Castellanos et al., 2009). The geological history, biogeography, ecology, and human history have contributed to the Mediterranean’s high cultural and biological diversity (Myers et al., 2000; Fredj et al., 1992; Boudouresque, 2004; Danovaro and Pusceddu, 2007)

The recent marine biota in the Mediterranean Sea is primarily derived from the Atlantic Ocean, but the wide range of climate and hydrology have contributed to the co-occurrence and survival of both temperate and subtropical organisms (Sara, 1985; Bianchi and Morri, 2000). High percentages of Mediterranean marine species are endemic (Tortonese, 1985). This sea has as well its own set of emblematic species of conservation concern, such as sea turtles, several cetaceans, and the critically endangered Mediterranean monk seal (Monachus monachus). It is the main spawning grounds of the eastern Atlantic bluefin tuna (Thunnus thynnus) (Delaugerre, 1987; Groombridge, 1990; Reijnders et al., 1997; Bearzi et al., 2004; MacKenzie et al., 2009).

There are several unique and endangered habitats, including the seagrass meadows of the endemic Posidonia oceanica, vermetid reefs built by the endemic gastropod Dendropoma petraeum, coralligenous assemblages (Green and Short, 2003; Ballesteros, 2006; Safriel, 1966; Goren and Galil, 2001), and deep-sea and pelagic habitats that support unique species and ecosystems (Sarda et al., 2004; Sarda et al., 2009; Gili et al., 1998). Many sensitive habitats exist within the coastal ecosystems. There are 150 wetlands of international importance for marine and migrating birds, and some 5,000 islands and islets (Blondel and Aronson , 2005; IUCN-MED, 2009; Bellan-Santini et al., 1994 ).

The region has numerous laboratories, universities, and research institutes dedicated to exploring the sea around them (CIESM , 2009). In addition to the unique geologic, biogeographic, physical, and ecological features, the current understanding of the high biodiversity of the Mediterranean Sea is built on the long tradition of study dating from the times of the Greeks and Romans.

Historical documentation began with Aristotle, who contributed to the classification and description of marine biodiversity, and was followed by the work of Plinius (Historia naturalis, liber IX) in the first century B.C., Carl von Linné in the eighteenth century, and many others to the middle of the nineteenth century (Risso, 1826–1827 ; Costa and Costa , 1836–1871 ; Olivi ,1972; Nardo, 1847). The first deep-sea investigations began at the end of the nineteenth century (Milne-Edwards,1882; Giglioli, 1882; Adensamer,1898). The expeditions of the R.V. ‘‘Calypso’’ by Jacques-Yves Cousteau in the Mediterranean during the 1950s and 1960s provided as well valuable material that supported many important publications on the Mediterranean diversity. The history of ecological research and species discovery in the region has been thoroughly reviewed by Riedl (Ried, 1983), Margalef (Margalef, 1985), and Hofrichter (Hofrichter, 2001), though mostly confined to the western Mediterranean.

Numerous detailed taxonomic inventories now exist, most of which are specific to sub-regions or to a range of organisms (SIBM,2009; Koukouras et al., 2007; Zabala et al., 1993; Morri et al., 2009; Pipitone and Arculeo, 2003; Cartes et al., 2009; Gallardo et al., 1993; Ribera et al., 1992; Abelló et al., 2002; Templado et al., 2006). Efforts continue to provide complete datasets of taxonomic groups for the entire basin (Carpine and Grashoff , 1975; Arvanitidis et al., 2002; Bouillon et al., 2004; Voultsiadou, 2009; Zibrowius , 1980; Zabala and Maluquer , 1988; Logan et al., 2004; Bellan-Santini et al., 1982; Udekem d’Acoz Cd, 1999; Koukouras et al., 2001; Mavidis et al., 2005), although they need periodic updates. Freely available databases for macroorganism inventory include the Medifaune database (Fredj and Maurin, 1987), the Food and Agriculture Organization Species Identification Field Guide for Fishery Purposes (Fischer et al.,1987), the FNAM (Fishes of the North-Eastern Atlantic and the Mediterranean) atlas (Whitehead et al., 1986), and the ICTIMED database ICTIMED , 2009).

However, Web-based datasets often lack updates, because of limitations in funding or expertise, and in general, the marine biodiversity of the Mediterranean is less known than its terrestrial counterpart (Blondel and Aronson ,2004; Costello,2006). There are still important gaps at population, community, habitat, and sub-region levels, as well as in basic information about taxonomy distribution, abundance, and temporal trends of several groups (Costello et al., 2006; Boero, 2003).In some areas biodiversity data exist, but it is not easily accessible, because the inventories are not publicly available (CIESM, 1997). Data are also lacking to evaluate the conservation status of many species (UCN-MED,2009). The Mediterranean region has been inhabited for millennia, and ecosystems have been altered in many ways (Bas, 2009; Boudouresque, 2004; Margalef, 1985; Hughe, 1994). Therefore, impacts of human activities are proportionally stronger in the Mediterranean than in any other sea of the world (Blondel and Aronson, 2005).

Therefore, combined natural and anthropogenic events shaped the biodiversity of the Mediterranean Sea in the past and are likely to continue to do so. Within this complex framework, the aims of writing this chapter were threefold:

1. Review available estimates of Mediterranean marine biodiversity, including new estimates of less conspicuous organisms, updating previous checklists, and incorporating living organisms from microbes to top predators.
2. Describe the main spatial and temporal patterns of biodiversity, including innovative ways of describing these patterns.
3. Summarize the main drivers of change and threats to marine biodiversity.

Several authors ([436] have collated available information, generated coherent patterns, and identified the current state of knowledge and information gaps, challenges, and prospects for future research. These scientists embrace the concept of biodiversity in its broader definition as the variation of life at all levels of biological organization, but they have focused our efforts on documenting species-level diversity.

Diversity estimates in the Mediterranean

Several analysis [436] revealed approximately 17,000 species occurring in the Mediterranean Sea (Table 1).

Table 1. Taxonomic classification of species reported in the Mediterranean Sea

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State of knowledge: 5 = very well known (.80% described, identification guides ,20 years old, and current taxonomic expertise); 4 = well known (.70% described, identification guides ,50 years old, some taxonomic expertise), 3 = poorly known (,50% species described, identification guides old or incomplete, no present expertise within region), 2 = very poorly known (only few species recorded, no identification guides, no expertise), 1 = unknown (no species recorded, no identification guides, no expertise). ND = No data. Number of experts and number of identification guides correspond to the list provided in File S2, listing several experts and taxonomic guides by taxa, although this is not an exhaustive list of experts by taxonomic group in the Mediterranean Sea. (1) Sources: databases, scientific literature, books, field guides, technical reports (see File S2); (2) Nu of experts provided in File S2, listing several experts by taxa, although this is not an exhaustive list of experts by taxonomic group in the Mediterranean Sea; (3) Identification guides cited in File S2; (4) This number is highly uncertain (see text section The biodiversity of the ‘‘smallest’’); (5) corresponding to macrophytobenthos; (6) 10 species reported within the Chlorophyceae (Volvocales) and Prasinophyceae (Chlorodendrales, Pyramimonadales) are unicellular and can be considered to be phytoplanktonic, although they thrive in mediolittoral and supralittoral pools and have been classically included in the checklists of marine macroalgae.

*This estimate is continuously increasing and may be as high as 1,000 species if unicellular aliens and foraminiferans are included [e.g., 206,207,208].

Of these, at least 26% were prokaryotic (Bacteria and Archaea) and eukaryotic (Protists) marine microbes. However, the data available for Bacteria, Archaea, and Protists were very limited, so these estimates have to be treated with caution (see next section), as well as data for several invertebrate groups (such as Chelicerata, Myriapoda, and Insecta).

Within the Animalia, the greater proportion of species records were from subphylum Crustacea (13.2%) and phyla Mollusca (12.4%), Annelida (6.6%), Plathyhelminthes (5.9%), Cnidaria (4.5%), the subphylum Vertebrata (4.1%), Porifera (4.0%), Bryozoa (2.3%), the subphylum Tunicata (1.3%), and Echinodermata (0.9%). Other invertebrate groups encompassed 14% of the species, and Plantae included 5%. Detailed biodiversity estimates of main taxonomic groups of benthic macroscopic primary producers and invertebrates are summarized in Table 1.

Available information showed that the highest percentage of endemic species was in Porifera (48%), followed by Mysidacea (36%), Ascidiacea (35%), Cumacea (32%), Echinodermata (24%), Bryozoa (23%), seaweeds and seagrasses (22%), Aves (20%), Polychaeta (19%), Pisces (12%), Cephalopoda (10%), and Decapoda (10%). The average of the total endemics was 20.2%. In some groups the percentage of endemics was now lower than in the past, partly due to new finding of Mediterranean species in adjacent Atlantic waters.

The biodiversity of the ‘‘smallest’’

An important bulk of species diversity was attributed to the prokaryotic (Bacteria and Archaea) and eukaryotic (Protists) marine microbes. However, the differences in the methodologies and types of studies and the continuously changing state of knowledge of marine microbial diversity make it difficult to provide species estimates for the Mediterranean (or from anywhere else) and establish comparisons.

Current methods cannot yet provide reliable estimates of the microbial richness of a system (Alonso-Sáez et al, 2007) because of (i) limited capacity to describe morphological variability in these organisms, (ii) the limited development and the biases associated with molecular techniques used to identify them, even with the use of the most powerful of these techniques, and (iii) the uncertainty in determining a ‘‘microbial species’’ and where to draw the line that differentiates one species from another.

Morphological variability is used to describe diversity of some groups of microbes, such as ciliates and microphytoplankton (Amato, 2007), but this is not useful for most nano- and almost all picoplanktonic organisms, including all Archaea and most Bacteria. Therefore, until recently, surveys of microbial diversity were mainly limited to those taxa with enough features to be described under an optical microscope. Among phytoplankton, the best-studied groups included thecate dinoflagellates, diatoms, coccolithophores, and silicoflagellates. Among microzooplankton, groups like tintinnids, foraminifers, or radiolarians attracted most attention. Much less information is available on ‘‘naked’’ auto- or heterotrophic flagellates and on small picoplankton species.

However, researchers have made efforts to obtain estimates of the dominant microbial species in Mediterranean waters. The expansion of electron microscopy in the last decades of the twentieth century helped to untangle inconsistencies in the distribution of some described species and to consolidate the establishment of a biogeography of many protist taxa. More recently, molecular techniques (metagenomics) have been used to enumerate the microorganisms present in a given sample and have completely transformed the field by changing ideas and concepts. These advances have highlighted the problems with the species concept, when applied to microbial communities, which may be based on morphology, biology, or phylogeny (Amato, 2007). Furthermore, different methodologies have biases that give different views of microbial diversity (Alonso-Sáez et al., 2007; Feingersch et al., 2009), and now we know that microdiversity is a general characteristic of microbial communities (Acinas et al., 2004), making the delimitation of ‘‘diversity’’ units difficult. To avoid some of the problems with the ‘‘species’’ delimitation, some authors prefer to use ‘‘functional diversity’’: the amount and types of microbial proteins (e.g., functions) in the sample (Venter et al., 2004), rather than ‘‘species’’ diversity.

According to the compilation published in Hofrichter (Hofrichter, 2002), the number of described protist species in the Mediterranean is approximately 4,400 (Table 1). However, this estimate requires cautious interpretation and it is likely that many morphospecies, more or less well described, will include a number of cryptic or pseudocryptic variants (Amato, 2007). Molecular methods have recently uncovered new sequences that are being associated with the organisms they represent (Massana et al., 2006). Fingerprinting techniques (Dorigo et al., 2005) have been used to compare microbial communities and establish the scale of variability of these communities. For example, Schauer et al. (Schauer et al., 2000) determined that, along the coastal northwestern Mediterranean, the time of the year was more important than exact location in determining bacterial community structure. Acinas et al. 1997 and Ghiglione et al. 2005 showed that microbial communities tend to be similar in the horizontal scale and much more variable on the vertical scale, but these techniques are not appropriate to determine the number of species present and usually refer only to the dominant organisms. Recent application of new methodologies (such as metagenomics and 454-tag sequencing) will in the near future provide more accurate estimates.

All studies to date concur in identifying members of the SAR11 group as some of the most abundant Mediterranean bacteria, comprising 25–45% of the reported sequences (Alonso-Sáez et al., 2007; Feingersch et al., 2009). These are followed by other Alphaproteobacteria, which tend to be more common in coastal regions and during algal blooms (such as Roseobacter -like). Cyanobacteria (Prochlorococcus and Synechococcus), diverse culturable (Alteromonadales) and unculturable Gammaproteobacteria and Bacteroidetes form the rest of the diversity with some differences with depth and with distance from land. Several studies have concentrated in the diversity of subgroups of these abundant bacteria in the Mediterranean (Garczarek et al., 2007; Blumel et al., 2007).

Additionally, the diversity of deep samples and the communities from which they are taken have received considerable attention in the Mediterranean. Specific and likely unique ecotypes of some bacteria appear at certain depths, (López-López et al., 2005), free-living communities appear to be as complex as epipelagic communities (Moeseneder et al., 2001), and appear to vary seasonally, as do surface communities (Winter et al., 2009). The deep-sea Mediterranean maintains several extremely peculiar and interesting ecosystems, such as the deep hypersaline anoxic ‘‘lakes’’ in the Ionian Sea that are reported to include several new and little-known microbial lineages (Yakimov et al., 2007).

Some studies have shown that bacterial richness peaks in tropical latitudes (Fuhrman et al., 2008) and concluded that at Mediterranean latitudes the number of detectable ‘‘operational taxonomic units’’ (OTUs) is between 100 and 150. Zaballos et al.,2006 arrived at a similar value that, once extrapolated, indicated a value of approximately 360 OTUs for surface waters. A slightly lower value was estimated for the coastal Blanes Bay Microbial Observatory (Alonso-Sáez et al., 2007) based on a different approach. Archaeal richness is known to be lower than bacterial richness Galand et al., and this has been seen in the Mediterranean and in other oceans. Results of these new sequencing techniques suggest that microbial richness in the sea is much higher because of the presence of a ‘‘rare biospheré’ composed of very few individuals of many distinct organism types (Sogin et al., 2006; Pedrós-Alió , 2007). Application of this technique to data from the northwestern Mediterranean indicates that the numbers should be raised to about 1,000 ‘‘bacterial species’’ per sample Pedrós-Alió et al. Again, the real magnitude of bacterial richness in the Mediterranean cannot be appreciated with the techniques available. A similar situation to that with prokaryotes occurs with small eukaryotes, which are photosynthetic, heterotrophic, or mixotrophic organisms. These small eukaryotes are found in abundances of 103–104 ml21 and have low morphological variability (Potter et al., 1997). Thus we must rely on molecular techniques to grasp their diversity. Molecular work has allowed the discovery of new groups of eukaryotes present in this smallest size class (Massana and Pedrós , 2008; Not et al., 2009). The study of Mediterranean protists has benefited from the early establishment of marine laboratories and a number of illustrated books and checklists (Trégouboff and Rose, 1957; Travers, 1975; Massutí and Margalef, 1950; Margalef, 1969; Margalef and Estrada, 1987; Kimor and Wood, 1975). More recent inventories can be found in Velasquez and Cruzado (Velasquez and Cruzado, 1995)and Velasquez, 1997 for diatoms, Gómez 2003 for dinoflagellates and Cros 2002 for coccolithophorids. The compilation of northwestern Mediterranean diatom taxa of Velasquez 1997 records 736 species and 96 genera. The checklist of Gómez 2003 contains 673 dinoflagellate species in 104 genera. Cros 2002 lists 166 species of coccolithophorids of the northwestern Mediterranean and revised the classification of several important taxa (Cros and Fortuño , 2002). Recently, the discovery of a number of combination coccospheres bearing holo- and heterococcoliths (Cros et al., 2002) fostered the recognition that holococcolithophores do not belong to a separate family, as previously accepted, but are part of a life cycle that includes holo- and heterococcolithophore stages. The biodiversity of photosynthetic nano- and picoflagellates other than coccolithophores is poorly known for most groups, as may be expected from the difficulties involved in their identification.

However, in the last decade, work using optical and electron microscopy, often in combination with molecular and culturing techniques, has considerably increased the taxonomic knowledge of many of these groups and has highlighted the potential existence of much cryptic or unknown diversity (Cerino and Zingone, 2006; Chrétiennot-Dinet and Courties , 2007). There are few taxonomic surveys of heterotrophic flagellates (Arndt et al., 2003), although many phytoplankton studies based on microscopy also included taxa from these groups. Massana et al., 2004 describes a high diversity of picoeukaryotic sequences, belonging to two groups of novel alveolates (I with 36% and II with 5% of clones), dinoflagellates (17%), novel stramenopiles (10%), prasinophytes (5%), and cryptophytes (4%). Later work has shown that these novel stramenopiles are free-living bacterivorous heterotrophic flagellates (Massana et al., 2006). Most of the biodiversity work on ciliates has focused on tintinnids or loricate ciliates, while studies involving naked ciliates tend to use groupings based on ecological morphotypes and only rarely include detailed taxonomical work (Kimor and Wood, 1975; Bernard and Rassoulzadegan, 1994; Vaqué et al., 1997; Modigh and Castaldo, 2002).

Numbers of species ranging from 40 to 68 were recorded in one to several-year surveys of various Mediterranean sites (among others Margalef and Estrada, 1987). Other groups, such as the Foraminifera, which have calcium carbonate tests, and the Radiolaria, which produce siliceous or strontium sulfate skeletons, have been the subject of many stratigraphical and paleoceanographical studies. However, biodiversity work on living Foraminifera and Radiolaria in the Mediterranean is scarce (Kimor and Wood,1975; Pujol and Grazzini,1995; Fontanier et al., 2008). Hofrichter, 2002 provided a systematic summary of the main groups and species of both autotrophic and heterotrophic protists found in the Mediterranean.

The biodiversity at high trophic levels

Species that occupy the upper trophic levels, normally beyond the level of secondary consumers, are classified as predators. They have lower diversity than other taxonomic groups, but information available is usually more detailed (Table 1). In this chapter are presented the results of reviewed data available for fish, seabirds, marine mammals, and turtles in the Mediterranean Sea.

Ground-breeding species such as seabirds (gulls and terns) are counted using census bands (Oro and Martínez-Abraín, 2007) and monitored by satellite tracking. However, procellariiforms reproduce in caves and burrows in cliffs on remote, inaccessible islets, and census methods to estimate population densities are not totally reliable. Population models, based on demographic parameters, allow researchers to estimate extinction probabilities (Oro et al., 2004).

A census of marine mammals or turtles normally uses transect data collected from aerial or boat-based sighting surveys developed to assess abundance, while movement patterns are tracked with transmitters and monitored by satellite tracking as well. Fish species are mainly studied using scuba diving or fishing techniques. There is still some discussion about diversity estimates for these taxonomic groups. For fish species, for example, several estimates of Mediterranean diversity exist: Quignard (Quignard , 1978) lists a total of 562 fish species occurring in the Mediterranean Sea; Whitehead et al., 1986 mention 589; Fredj and Maurin, 1987 list a total of 612 species (and identified 30 species as uncertain); and Quignard and Tomasini, 2000 register 664 species. Hofrichter, 2002 summarizes 648 species, and Golani et al., 2002 report a total of 650 fishes (File S2). Fish diversity estimates also change as new species are described or reclassified. The updated list of exotic fish species (CIESM , 2009) reveals that the Mediterranean currently contains 116 exotic species, although more species are likely to be cited. There is also a long-standing controversy regarding genetic differentiation among a few fish populations and sub-basins, especially of commercial species due to management implications (for example for the European anchovy Engraulis encrasicolus), although results are still under debate (Grant , 2005).

Approximately 80 fish species are elasmobranchs, although the status of some is uncertain because of infrequency or uncertain reporting (Cavanagh and Gibson, 2007; Serena, 2005; Compagno, 2001). According to Cavanagh and Gibson, 2007, nine of these elasmobranch species may not breed in the Mediterranean, while some are rare, because the Mediterranean represents the edge of their distribution ranges. Only four batoid species are Mediterranean endemics: the Maltese skate (Leucoraja melitensis), the speckled skate (Raja polystigma), the rough ray (R. radula), and the giant devilray (Mobula mobular) (Serena, 2005).

Nine species of marine mammals are encountered regularly in the Mediterranean (Notarbartolo di Sciara, 2002; Bearzi et al., 2003; Frantzis et al., 2003; Reeves and Notarbartolo di Sciara, 2006) . Of these species, five belong to the Delphinidae, and one each to the Ziphiidae, Physeteridae, Balaenopteridae, and Phocidae. Other 14 species are sporadically sighted throughout the basin and are considered ‘‘visitors’’ or ‘‘non-residents.’’

Of the seven living species of sea turtles, two (the green and the loggerhead Chelonia mydas and Caretta caretta - Cheloniidae) commonly occur and nest in the Mediterranean, and one (leatherback turtle Dermochelys coriacea - Dermochelyidae) is regularly sighted but there is no evidence of nesting sites. The other two (hawksbill and Kemp’s riddle turtles Eretmochelys imbricate and Lepidochelys kempi - Cheloniidae) are extremely rare and considered to be vagrants in the Mediterranean (Groombridge , 1990; Camiñas, 2004; Venizelos et al., 2005; NOAA, 2007; Tomás and Raga, 2009).

Seabirds from the Mediterranean have a low diversity (15 species, File S2) and their population densities are small, consistent with a relatively low-productivity ecosystem compared with open oceans, and particularly with upwelling regions. Ten of the Mediterranean species are gulls and terns (Charadriiformes), four are shearwaters and storm petrels (Procellariiformes), and one is a shag (Pelecaniformes). Three of the ten species are endemics (Aguilar et al., 1993; Yésou and Sultana, 2000; Mínguez et al., 2003).

What is hidden in the deep?

Because of the large size of the Mediterranean deep-sea ecosystems (Figure 1d), the knowledge of the benthic deep-sea diversity is incomplete (Gage and Tyler, 1992). In the past 20 years, several studies on deep-sea sediment diversity have been undertaken in various oceans (Gambi et al., 2003; Ramírez-Llodra et al.,) but have been limited to a few taxonomic groups. However, due to technological improvements that render the deep waters more accessible, the deep-sea benthos of the Mediterranean has received increased attention and there is progress toward a more comprehensive view of the levels, patterns, and drivers of deep-sea biodiversity in this semienclosed basin (Danovaro et al.,).

Its paleoecological, topographic, and environmental characteristics suggest that the Mediterranean Sea is a suitable model for investigating deep-sea biodiversity patterns along longitudinal, bathymetric and energetic gradients across its different regions. There are few areas with depths greater than 3,000 m (Figure 1d), and typically bathyal or abyssal taxonomic groups are limited. Cold-water stenothermal species that elsewhere represent the major part of the deep-sea fauna (Emig, 1997) are also unknown in the Mediterranean Sea.

The Mediterranean abyssal macrobenthos comprises a large number of eurybathic species and only 20–30 true abyssal species. In the western basin, where the depth does not exceed 3,000 m, the abyssal fauna is less abundant than in the deeper eastern basin, where abyssal species are dominant in the Matapan trench, which is more than 5,050 m deep (Laubier and Emig, 1993). The close affinity between Mediterranean and Atlantic congeneric deep-water species suggests that the ancestors of the Mediterranean bathyal endemic species moved from the Atlantic when conditions were favorable (i.e. when larvae of deep Atlantic fauna was able to enter in the Western Mediterranean due to hydrodynamic and physico-chemical conditions allowed it). According to Pérès, 1985, the deep-water fauna of the Mediterranean has a lower degree of endemism than that of the Atlantic at similar depths. So while the Mediterranean basin is recognized as one of the most diverse regions on the planet, the deep sea in the Mediterranean may contain a much lower diversity than deep-sea regions of the Atlantic and Pacific oceans (Lambshead et al., 2002; Lambshead et al., 2000). The reasons for such a low diversity may be related to (a) the complex paleoecological history characterized by the Messinian salinity crisis and the almost complete desiccation of the basin (Krijgsman et al., 1999), and (b) the Gibraltar sill that is, potentially, a physical barrier to the colonization of larvae and deep-sea benthic organisms from the richer Atlantic fauna. These factors may explain the composition of the benthos in the deep sea of the Mediterranean (Bouchet and Taviani , 1992). It may also be that the high deep-sea temperatures (about 10°C higher than in the Atlantic Ocean at the same depth) have led to a Mediterranean deep-sea fauna that consists of reproductively sterile pseudopopulations that are constantly derived through larval inflow. These postulates were based on the analysis of the macrobenthos, characterized by life cycles with meroplanktonic larvae that are spread by currents (Higgins and Thiel, 1988).

However, the populations of the most common benthic mollusks in depths greater than 1,000 m off the Israeli coast are composed of both adult and juvenile specimens, and one species, Yoldia micrometrica, the most common and abundant species in the eastern Mediterranean, is unrecorded from the westernmost part of the sea. In addition, and though much reduced in diversity and richness compared with the deep-sea fauna of the western and central basins of the Mediterranean, the Levantine bathybenthos is composed of autochthonous, self-sustaining populations of opportunistic, eurybathic species that have settled there following the last sapropelic event (Galil and Goren, 1994; Goren and Galil, 1997; Fishelson and Galil, 2001).

Macpherson (Macpherson, 2002) and Briggs (Briggs, 2007) have suggested that within the Atlantic-Mediterranean region, the fauna (including invertebrates and fishes) of the Mediterranean is more diverse than that of the Atlantic and displays considerable endemism. For strictly deepdwelling species (e.g., the deep-water decapod crustacean family Polychelidae), the Gibraltar sill is not an impenetrable barrier for some deep-waters macrobenthic species (Abelló and Cartes,2002). Moreover, available hypotheses did not consider meiofauna diversity, which is characterized by direct development [188] but also by a small size, which allows organisms’ resuspension and drifting over wide regions. This is consistent with information on the most abundant deep-sea phylum, the Nematoda, which often accounts for more than 90% of total meiofauna abundance (Danovaro et al., 1999; Danovaro et al., 2008). Nematode diversity has been investigated only in a few areas of the deep sea in the Mediterranean: slopes of the Gulf of Lions, Catalan margin and Corsica, Tyrrhenian basin, and Eastern Mediterranean (Lampadariou and Tselepides, 2006; Pusceddu et al., 2009; Danovaro et al., 2009). Recent collections from a limited number of sites throughout the Mediterranean basin (at approximately 1,000 m, 3,000 m, and 4,000 m depth), suggest that, conversely to what was expected, the deep-sea nematode fauna of the Mediterranean basin is rather diverse.

At bathyal and abyssal depths, levels of nematode genera and species richness are similar to those reported from other deep-sea areas of the world oceans (Danovaro et al., 2009). In the deep sea of the Mediterranean, small-bodied taxa (e.g., meiofauna) can reach a high diversity, and with the presence of a high prokaryotic diversity in the sediments of the deep-sea Mediterranean (Danovaro et al., 2009), this may change the view that the Mediterranean deep-sea biota is impoverished in comparison with its Atlantic counterpart. Endemic macrobenthic species account for approximately 13– 15% of total species number at depths from 200 m to 1,000 m, and approximately 20% at 2,000 m (Bellan-Santini et al., 1992). These estimates are similar for each taxon (Table 1) and are further supported by the continuous discovery of new species (both within the highly diverse Nematoda and in rare phyla such as the Loricifera) in different sectors of the deep Mediterranean (Danovaro et al.). Therefore, the general conclusion that the biodiversity is high in coastal systems and low in the deep sea of the Mediterranean might not hold true. Detailed references about the deep Mediterranean can be found in (Danovaro et al.).

New biodiversity

The biodiversity of the Mediterranean is definitively influenced by the introduction of new species (CIESM,2009; Galil, 2006; Galil, 2007; Zenetos et al., 2009; Streftaris and Zenetos, 2006; Streftaris et al., 2005; Galil et al., 2009; Zenetos et al., 2005; Zenetos et al., 2008). Since the first review of exotic species in the Mediterranean (Zibrowius, 1991), the studies in this topic have intensified. Now more than 600 metazoan species have been recorded as alien, these representing 3.3% of the total estimates (Table 1). However, this estimate is continuously increasing and may be as high as 1,000 species if unicellular aliens and foraminiferans are included (Galil et al., 2006; Zenetos et al., 2005; Zenetos et al.,2008). Most of these introductions are littoral and sublittoral benthic or demersal species (or their symbionts). Because the shallow coastal zone, and especially the benthos, has been extensively studied and is more accessible than deeper waters, new arrivals probably will be encountered and identified in shallow waters. The species most likely to be introduced by the predominant pathways (the Suez Canal, vessels, and mariculture) are shallow-water species.

A taxonomic classification of the alien species showed that the alien phyla most frequently recorded are Mollusca (33%), Arthropoda (18%), Chordata (17%), Rhodophyta (11%), and Annelida (8%). The data are presumably most accurate for large and conspicuous species that are easily distinguished from the native biota and for species that occur along a frequently sampled or fished coast and for which taxonomic expertise is readily available. Data are entirely absent for many of the small members of invertebrate phyla (Galil, 2008). Thus, the true numbers of alien species are certainly downward biased.

The native range of the alien species in the Mediterranean was most commonly the Indo-Pacific Ocean (41%), followed by the Indian Ocean (16%), and the Red Sea (12%), while some species have a pantropical or circumtropical distribution (19%). The actual origins of the Mediterranean populations of a species widely distributed in the Indo-Pacific Ocean may be their populations in the Red Sea, both from the Indian or Pacific oceans, or a secondary introduction from already established populations in the Mediterranean itself (Morri et al.,2009). However, and with few notable exceptions (Bucciarelli et al., 2002; Hassan et al., 2003), the source populations of alien species in the Mediterranean have not been assessed by molecular means. Even so, it is clear that most alien species in the Mediterranean are thermophilic and therefore originated in tropical seas (see Figure 2). The exceptions are exotic algae, of which the largest numbers are in the Gulf of Lions and the northern Adriatic (Verlaque, 2001; Boudouresque and Verlaque, 2002), and a few other examples (Faccia et al., 2009). As far as can be deduced, the majority of aliens in the Mediterranean entered through the Suez Canal (Erythrean aliens) (53%), and an additional 11% were introduced primarily through the Canal and then dispersed by vessels. Introductions from vessels from other parts of the world account for 22% of introduced species, and aquaculture accounts for 10%. A further 2% arrived with the introduction of aquaculture and were secondarily spread by vessels. The means of introduction differ greatly among the phyla: whereas of the alien macrophytes, 41% and 25% were introduced through mariculture and vessels, respectively, the majority of alien crustaceans, mollusks, and fish are Erythrean aliens (59%, 64%, and 86%, respectively), and mariculture introductions are few (4%, 5%, and 4%, respectively) (Galil, 2009).

The numbers of alien species that have been recorded over the past century have increased in recent decades. The increasing role of the Mediterranean as a hub of international commercial shipping, a surge in the development of marine shellfish farming over the last 25 years, and the continued enlargement of the Suez Canal have contributed to the resurgence of introductions since the 1950s. Many introduced species have established permanent populations and extended their range: 214 alien species have been recorded from three or more peri-Mediterranean countries, and 132 have been recorded from four or more countries (Galil, 2009).

A comparison of the alien species recorded along the Mediterranean coasts of Spain and France and an equivalent length of coast in the Levantine Sea (from Port Said, Egypt, to Marmaris, Turkey) showed marked differences in their numbers, origin, and means of introduction. There are nearly four times as many alien species along the Levantine coast (456 species) as along the western coast of the Mediterranean (111 species). The majority of aliens in the Eastern Mediterranean entered through the Suez Canal (68% of the total, 14% vessel-transported, 2% mariculture), whereas mariculture (42%), vessels (38%), or both (5%) are the main means of introduction in the Western Mediterranean (Galil, 2009 B.S. Galil, in preparation]. Climate change favors the introduction of Red Sea species in the southeastern Mediterranean and their rapid spreading northwards and westwards. It similarly favors species coming from the African Atlantic coasts to enter the western basin (Golani et al., 2002; Relini et al., 2000).

Spatial patterns of Mediterranean biodiversity

Longitudinal and latitudinal patterns. Describing the distribution of marine diversity is as important as quantifying it. In the Mediterranean, a northwestern-to-southeastern gradient of species richness was observed in most groups of invertebrate species analyzed here, with a highly heterogeneous distribution of species in the different regions (Table 2).

Table 2. Species richness by taxa and regions of the Mediterranean Sea.

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N: North, S: South, W: West, E: East, Med: Mediterranean.

(1)Including NW Med, Alboran Sea, SW Med, Tyrrhenian Sea, and excluding Adriatic Sea;
(2)Including Aegean, Ionian, Levantine, and Central Mediterranean;
(3)Plateau;
(4)North Africa,
(5)Tyrrhenian Sea;
(6)Mediterranean Greece and Turkey,
(7)Italian waters;
(8)Including Thyrrenian Sea, Alboran, and SW Mediterranean;
(9)Including the Ionian Sea,
(10)There are severe gaps in our knowledge of most invertebrate taxa in the Levantine Sea,
(11)This contribution (details in supplementary material), except where noted.

Only a few exceptions were noticed so far. For example, while there was the same number of Euphausia species in the western and central basins, estimates for several other invertebrate groups were higher in the Aegean Sea than in central areas of the Mediterranean. These exceptions may be due to different species tolerance to environmental factors (such as temperature and salinity), connectivity between regions, and to the lack of data in some regions. Similar results were found for vertebrate species. There was a decreasing gradient from northwest to the southeast, while the sea around Sicily had the highest richness (375 species per 0.160.1 degree cell), followed by other northwestern coastal and shelf areas (Figures 2a–b).

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Figure 2. Spatial patterns of fish species richness in the Mediterranean Sea based on superimposed expert-drawn maps. (A) All fish species (n = 625), (B) ray-finned fish species (n = 545), (C) elasmobranchs (n = 80), (D) endemic fish species (n = 79), (E) alien fish species (n = 127) [data modified from 91]. Colors express species occurrence from blue (little or no occurrence) to red (highest occurrence). The size of the cell is 0.1x0.1 degree.

The distribution of elasmobranch species was not homogenous either, showing a higher concentration of species in the west (Figure 2c). The endemic richness gradient of fish species was more pronounced with latitude, the north side exhibiting a greater richness, and the Adriatic appearing as a hot spot of endemism with 45 species per cell (Figure 2d). Spatial patterns also showed how most of Mediterranean coastal waters have been colonized by exotic species (Figure 2e). The highest richness of exotic species occurred along the Israeli coast.

Marine mammals were concentrated in the Western Mediterranean and Aegean seas (Figure 3a).

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Figure 3. Spatial patterns of vertebrate species richness in the Mediterranean Sea based on superimposed expert-drawn maps (excluding fish species). (A) resident marine mammals (n = 9), (B) nonresident marine mammals (n = 14), and (C) resident sea turtles (n = 3), as well as sighting records (dots) of the two visiting sea turtles. Colors express species occurrence from blue (little or no occurrence) to red (highest occurrence). (D) Seabird colonies (the yellow dots show the distribution and population density of colonies in breeding pairs (bp) of Audouin’s gull: Some dots represent the epicenter of several smaller colonies in archipelagos). The size of the cell is 0.1x0.1 degree.

Of the nine resident marine mammals, eight were found in the western part of the basin. This distribution pattern was also observed for the visiting marine mammals (Figure 3b). Two of the three resident sea turtles (loggerhead, green, and leatherback turtles) occurred in the central Mediterranean and Aegean seas, while the two visiting turtles were absent from the eastern side (Figure 3c). There were fewer seabird colonies and seabird density was lower in the southeast than the northwest (Figure 3d).

Spatial patterns of benthic biodiversity in the deep sea are poorly known in comparison with other ecosystems. Available information is scarce and all presented maps and estimates include only approximations for the deep sea. In this context, metazoan meiofauna and, in particular, nematodes can be used to describe the biodiversity patterns in the deep sea.

Deep-sea nematode diversity appears to be related to that of other benthic components such as foraminifers (Gooday et al., 1998), macrofauna (Levin et al., 2001), and the richness of higher meiofauna taxa in the deep sea (Danovaro et al., 2008). Results for the deep sea of the Mediterranean show a clear longitudinal biodiversity gradient that also occurs along the open slopes, where values decrease eastward, from Catalonia to the margins of southern Crete (Figure 4a). The analysis of the Nematoda indicates that at equally deep sites, nematode diversity decreases from the western to the eastern basin and longitudinal gradients are evident when comparing sites at 3,000 m or 1,000 m depth (Danovaro et al., 2008). Complementary information on spatial patterns of the deep Mediterranean fauna can be found in (Danovaroet al.).

Additional information from the literature on spatial patterns of Mediterranean marine diversity suggests that the measurement of local a-diversity is not sufficient to draw a clear picture for the whole Mediterranean basin. Whittaker (Whittaker, 1960) defined α -diversity as the number of species found in a sample (or within a habitat), β -biodiversity as the extent of species replacement along environmental gradients (termed ‘‘turnover diversity’’ by Gray, 2000), and γ -diversity as the diversity of the whole region.

The analysis of β -biodiversity of Nematoda among different sites in the deep sea of the Mediterranean and across bathymetric and longitudinal gradients reveals an extremely high species turnover. By comparing nematode assemblages at (a) different depths, (b) similar depths in two different basins, and (c) similar depths within the same basin, the dissimilarity of biodiversity among deep-sea samples is always greater than 70% (Danovaro et al., 2008; Pusceddu et al., 2009; Danovaro et al., 2009; Zenetos et al., 2009). On average, the dissimilarity of nematode diversity between western and eastern Mediterranean at about 3,000 m depth is greater than 80% and at similar depths the dissimilarity between Atlantic and Western Mediterranean exceeds 90%. These findings indicate that each region is characterized by the presence of a specific assemblage and species composition. This has important implications for estimating the overall regional diversity (γ -diversity), but also suggests the presence of high biogeographic complexity in the Mediterranean. However, these patterns may not hold for all the taxonomic groups (Gaertner et al., 2007), and a broader comparison is needed.

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Figure 4. Patterns of benthic biodiversity in the deep sea of the Mediterranean. (A) Longitudinal patterns, and (B) bathymetric patterns of benthic nematodes along the open slopes of the European margins. Benthic biodiversity is estimated as the total number of meiofaunal taxa, and as nematode species richness (expected number of nematode species for a theoretical sample of 51 specimens).

Spatial patterns predicted with AquaMaps

Predicted patterns of overall species richness based on AquaMaps showed a concentration of species in coastal and continental waters most pronounced in the Western Mediterranean, Adriatic, and Aegean seas (Figure 5).

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