The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats

The Mediterranean Sea is a marine biodiversity hot spot. Here we combined an extensive literature analysis with expert opinions to update publicly available estimates of major taxa in this marine ecosystem and to revise and update several species lists. We also assessed overall spatial and temporal patterns of species diversity and identified major changes and threats. Our results listed approximately 17,000 marine species occurring in the Mediterranean Sea. However, our estimates of marine diversity are still incomplete as yet—undescribed species will be added in the future. 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 was also generally higher in coastal areas and continental shelves, and decreases with depth. Temporal trends indicated 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

Population Characteristics of the Limpet Patella caerulea (Linnaeus, 1758) in Eastern Mediterranean (Central Greece)

Limpets are pivotal for structuring and regulating the ecological balance of littoral communities and are widely collected for human consumption and as fishing bait. Limpets of the species Patella caerulea were collected between April 2016 and April 2017 from two sites, and two samplings per each site with varying degree of exposure to wave action and anthropogenic pressure, in Eastern Mediterranean (Pagasitikos Gulf, Central Greece). This study addresses a knowledge gap on population characteristics of P. caerulea populations in Eastern Mediterranean, assesses population structure, allometric relationships, and reproductive status. Morphometric characteristics exhibited spatio-temporal variation. Population density was significantly higher at the exposed site. Spatial relationship between members of the population exhibited clumped pattern of dispersion during spring. Broadcast spawning of the population occurred during summer. Seven dominant age groups were identified, with the dominant cohort in the third-year class. Significant negative allometric relationships were exhibited between morphometric characteristics. Differences in growth patterns among populations were indicated

Holothurian Fisheries in the Hellenic Seas: Seeking for Sustainability

In Mediterranean, the exploitation and exportation of holothurians as food is increasing during the last 25 years, with Turkey and Greece as leading countries. In Greece, the fishery is expanding by the development of two métiers; however, official monitoring is missing, creating concerns on the future viability of the industry. To evaluate the status and future perspectives of holothurian fisheries, an extensive field survey has been completed (May 2019–July 2021) covering 162 sites dispersed in the Hellenic Seas. Field data included the assessment of the abundance of holothurians (via 100 m transect replicates), and catch per unit of effort (CNPUE and CBPUE, based on 10-min commercial fishing practices). H. tubulosa, H. poli, H. mammata and H. sanctori were fished in 41.35% of the surveyed stations. H. poli (CNPUE 168 specimens, CBPUE 22.24 kg) and H. tubulosa (CNPUE 127 specimens, CBPUE14.51 kg) were the most common species, forming locally dense populations. Mean annual catch was 275 metric tons (2016–2021) according to the processing of the units’ data; 62% of the production was made by H. tubulosa and 38% by H. poli. Our results suggest the existence of exploitable grounds in the north Aegean, the central Cyclades, and the north Dodecanese, according to the prevalent environmental conditions (organic load) and fishing pressure

Population Dynamics, Fishery, and Exploitation Status of Norway Lobster (Nephrops norvegicus) in Eastern Mediterranean

Norway lobster (Nephrops norvegicus) is one of the most valuable shellfish resources in the Mediterranean and the northeast Atlantic. Sustainable management of its fishery require long-term scientific monitoring of its stocks. Population dynamics, fishery, and exploitation status of the Norway lobster were studied over a long time series (between 2008 and 2014) in a semi enclosed gulf in Easter Mediterranean (Pagasitikos Gulf). Sampling was carried out using a commercial bottom trawl with a codend mesh size of 28 mm in three different regions within the Gulf. Sex was identified macroscopically and all individuals were measured and weighed. Growth and Age groups were investigated by analysis of length–frequency distributions of the Carapace length (CL) for both sexes. Fishing, Natural and Total Mortality, along with Exploitation rate of the total stock were estimated by the FiSAT software package. Females were further examined and classified based on their maturity stage and the size at onset of sexual maturity was estimated by Probit analysis. Temporal differences in mean CL were detected for both sexes, with a tendency of lower values each year, along with a respective increase in Fishing Mortality and Exploitation Rate, indicating the effects of fishing pressure over the population. Size at onset of sexual maturity was estimated at 32.6 mm, higher than the official mesh sizes for creels (28 mm) and gillnets (26 mm). According to the analyses, the local Norway lobster stock is over-exploited, which should be taken under consideration by the regional policy makers

Systematic, zoogeographical and ecological study of anthozoans (Actiniarians excluded) of the North Aegean continental shelf

The research carried out in the North Aegean Sea revealed the presence of 49 species of Anthozoa. For each of these species the following information is given: its main synonyms, the examined material, and the sampling stations from which it was collected, its main diagnostic features, its geographical distribution in the Aegean, Mediterranean and worldwide, information concerning its habitat and, where necessary, comments mainly on the identity of the species.One of the species found is described as new for the science, the species Crassophyllum thessalonicae. The great differentiation of some characteristic morphological features distinguishes it obviously from the other species (C. cristatum) of the genus.Out of the 49 species found in the North Aegean Sea, 17 are new for the fauna of the Eastern Mediterranean, 3 more (totally 20) are new for the fauna of the Aegean Sea and 9 more (totally 29) are new for the fauna of the North Aegean. So, after the additions made by our research, the anthozoan fauna of the Eastern Mediterranean counts 54 species (an increase of 45.9%), the fauna of the Aegean Sea 53 species (an increase of 60.6%0, and the fauna of the North Aegean 50 species (an increase of 138.1%).After the study of the relevant literature, it has been found that 97 species of Anthozoa have been recorded from the Mediterranean Sea, 91 of them (93.85%) from the western basin, 35 (36.08%) from the central basin, 49(590.51%) from the Adriatic, and 54 (55.67%) from the eastern basin. These differences should be attributed mainly to the very limited research carried out in the eastern and central basins compared to that carried out in the western basin.An estimation of the anthozoan fauna of the Mediterranean shows that it includes 23.71% endemic, 3.09% boreal, 14.44% Lousitanian, 13.4% Mauritanian, 32.99% Atlanto-Mediterranean, and 12.37% cosmopolitan species. The corresponding percentages for the fauna of the Aegean Sea are: 18 endemics, 26 Lousitanian, 6 Mauritanian, 36 Atlanto-Mediterranean, and 14 cosmopolitan None of the species found in the Aegean is boreal.The vertical distribution of the majority of the species found in the North Aegean Sea varies inside the known limits, according to the literature. For a considerable number of species (30.61%, 15 species) the limits of vertical distribution have been extended to greater depths.The majority of the Mediterranean (83.5%) and Aegean (87.7%) species) have been found to live in the circalittoral zone. On the other hand, the number of species found to live exclusively in one ecological zone was very low.The majority of the species (79.6%) have been found on typical hard substratum, especially rocks (67.3%). Exceptions are the species of the orders Pennatulacea and Ceriantharia, which live exclusively in mud, sand or sand-mud substrata. A considerable number of species (34.7%) were found on other animals (sponges, corals, polychaetes, mollusks, decapods, and ascidians).Most of the species have been found in the benthic assemblage of the coastal detritic bottoms, the offshore rocky bottoms, the semi-obscure and obscure caves, the superficial muddy sand in sheltered areas, and the coralligenous assemblage. The most rich in species assemblage is the corraligenous (26.5%, 13 species).In the framework of this study, 26 anthozoan species have been found associated with other animals. Among these, sponges, cnidarians, polychaetes, mollusks, decapods, and ascidians are included. The association of some of these animals with anthozoans is reported for the first time.Οι έρευνες που πραγματοποιήθηκαν στο Β. Αιγαίου αποκάλυψαν την παρουσία 49 ειδών ανθοζώων. Για κάθε ένα από τα είδη αυτά δίνονται τα κυριότερα συνώνυμά του, το υλικό που εξετάστηκε και οι σταθμοί δειγματοληψίας από τους οποίους αυτό συλλέχθηκε, τα σημαντικότερα διαγνωστικά του χαρακτηριστικά, η γεωγραφική του διανομή στο Αιγαίο, τη Μεσόγειο αλλά και σ’ όλο τον κόσμο, πληροφορίες σχετικές με την οικολογία του και όπου κρίνεται απαραίτητο, σχόλια κυρίως για την ταυτότητά του.Ένα από τα είδη που βρέθηκε, περιγράφεται ως νέο για την επιστήμη. Πρόκειται για το είδος Crassophyllum thessalonecae. Η έντονη διαφοροποίηση ορισμένων βασικών μορφολογικών του χαρακτηριστικών, το αντιδιαστέλλει σαφώς από το άλλο είδος (C. cristatum) του γένους.Από τα 49 είδη που βρήκαμε στο Β. Αιγαίο, 17 είναι νέα για την πανίδα της Ανατολικής Μεσογείου, άλλα 3 (συνολικά 20) νέα για την πανίδα του Αιγαίου και άλλα 9 (συνολικά 29) νέα για την πανίδα του Βόρειου Αιγαίου. Έτσι μετά την έρευνά μας η πανίδα της Ανατολικής Μεσογείου αριθμεί 54 είδη (αύξηση 45.9%), του Αιγαίου 53 είδη (αύξηση 60.6%) και του Β. Αιγαίου 50 είδη (αύξηση 138.1%).Διαπιστώθηκε, μετά από τη μελέτη της σχετικής βιβλιογραφίας, ότι στη Μεσόγειο ζουν 97 έγκυρα είδη ανθοζώων. Απ’ αυτά, 91 (93.81%) έχουν βρεθεί στη δυτική Μεσόγειο, 35 (36.08%) στην κεντρική, 49 (50.51%) στην Αδριατική και 54 (55.67%) στην ανατολική λεκάνη. Η διαφορά αυτή θα πρέπει να αποδοθεί στις περιορισμένες έρευνες που έχουν γίνει μέχρι σήμερα στην κεντρική και ανατολική λεκάνη σε σχέση με τη δυτική.Εκτιμήθηκε ότι η πανίδα των ανθοζώων της Μεσογείου αποτελείται κατά 23.71% από ενδημικά είδη, 3.09% είναι Βόρειας προέλευσης, 14.44% Λουζιτανικής, 13.4% Μαυριτανικής, 32.99% Ατλαντικο-Μεσογειακής και 12.37% κοσμοπολίτικα. Τα αντίστοιχα ποσοστά για την πανίδα του Αιγαίου είναι: 18% ενδημικά, 26% Λουζιτανικά, 6% Μαυριτανικά, 36% Ατλαντo-Μεσογειακά και 14% κοσμοπολιτικά ενώ κανένα από τα είδη δεν θεωρήθηκε ότι είναι Βόρειας προέλευσης.Η βαθυμετρική διανομή των περισσότερων ειδών που βρέθηκαν στο Β. Αιγαίο, ήταν μέσα στα γνωστά όρια διανομής τους. Για ένα σημαντικό αριθμό ειδών όμως (30.61%, 15 είδη), τα όρια διανομής τους επεκτείνονται προς μικρότερα ή μεγαλύτερα βάθη.Το μεγαλύτερο ποσοστό των ανθοζώων της Μεσογείου (83.5%) αλλά και του Β. Αιγαίου (87.7%) ζουν στην περιπαραλιακή ζώνη. Από την άλλη μεριά όμως, τα ποσοστά των αποκλειστικών κατοίκων κάθε μιας οικολογικής ζώνης είναι σχετικά χαμηλά.Το μεγαλύτερο ποσοστό ειδών (79.6%) βρέθηκε εγκαταστημένο πάνω σε τυπικό σκληρό υπόστρωμα και κυρίως πάνω σε βράχους (67.3%). Εξαίρεση αποτελούν τα είδη των τάξεων Pennatulacea, Ceriantharia, που ζουν αποκλειστικά σε κινητά υποστρώματα, «φυτεμένα» σε ιλύ, άμμο ή αμμοϊλύ. Ένα αρκετά επίσης υψηλό ποσοστό ειδών (34.7%) βρέθηκε εγκαταστημένο πάνω σε ζωικούς οργανισμούς (σπόγγους, κοράλλια, πολύχαιτους, μαλάκια, δεκάποδα και ασκίδια).Τα περισσότερα από τα είδη που μελετήθηκαν βρέθηκαν κυρίως στις βενθικές συνευρέσεις των παράκτιων βιογενών θρυμμάτων, των βράχων ανοικτής θάλασσας, την κοραλλιογενή, των ημισκότεινων και σκοτεινών σπηλαίων και της αβαθούς ιλυώδους άμμου σε προφυλαγμένες περιοχές. Η πιο πλούσια σε είδη συνεύρεση (26.5%, 13 είδη) είναι κοραλλιογενής.Στο πλαίσιο της έρευνας αυτής, 26 είδη ανθοζώων βρέθηκαν να σχετίζονται μ’ άλλους ζωικούς οργανισμούς. Μεταξύ των μακροβενθικών οργανισμών που βρέθηκαν να αναπτύσσουν τέτοιου είδους σχέση περιλαμβάνονται: σπόγγοι, ανθόζωα, μαλάκια, δεκάποδα, ασκίδια. Η σχέση πολλών από αυτά τα ζώα με τα ανθόζωα αναφέρεται για πρώτη φορά

Net Fisheries’ Métiers in the Eastern Mediterranean: Insights for Small-Scale Fishery Management on Kalymnos Island

Small-scale fisheries constitute an important component of coastal human societies. The present study describes the small-scale net fisheries on Kalymnos Island (south-east Aegean Sea) that harbors the largest small-scale fleet in the eastern Mediterranean Sea. In addition, this study aims to evaluate their characteristics and economics. Relevant métiers were identified through a multivariate analysis by inputting the main resources and fishing gear data that were recorded during landings. Four main practices were observed being used as fishing gears, gillnets and trammel nets, targeting the species Mullus barbatus, Boops boops, Mullus surmuletus, Scorpaena porcus, and Sepia officinalis. Further analysis, which incorporated data concerning the type of the gear used, revealed 11 distinct métiers. Most of these métiers are practiced by other Mediterranean small-scale fisheries as well, in terms of target species, gear and seasonality. However, the métier that had its target species as B.boops is not practiced in other Mediterranean small-scale fisheries. The seasonal rotation of métiers was determined by the availability of different species rather than their market price. The results revealed the difference in fishing practice used by the fishermen in the study area compared to other fishing practices in the Mediterranean Sea. In particular, the fishermen of this study area targeted more species (B.boops) with a very low market price. They also provided essential information for the development and implementation of management plans aiming at the sustainability of small-scale fisheries

Population Dynamics, Fishery, and Exploitation Status of Norway Lobster (<i>Nephrops norvegicus</i>) in Eastern Mediterranean

Norway lobster (Nephrops norvegicus) is one of the most valuable shellfish resources in the Mediterranean and the northeast Atlantic. Sustainable management of its fishery require long-term scientific monitoring of its stocks. Population dynamics, fishery, and exploitation status of the Norway lobster were studied over a long time series (between 2008 and 2014) in a semi enclosed gulf in Easter Mediterranean (Pagasitikos Gulf). Sampling was carried out using a commercial bottom trawl with a codend mesh size of 28 mm in three different regions within the Gulf. Sex was identified macroscopically and all individuals were measured and weighed. Growth and Age groups were investigated by analysis of length–frequency distributions of the Carapace length (CL) for both sexes. Fishing, Natural and Total Mortality, along with Exploitation rate of the total stock were estimated by the FiSAT software package. Females were further examined and classified based on their maturity stage and the size at onset of sexual maturity was estimated by Probit analysis. Temporal differences in mean CL were detected for both sexes, with a tendency of lower values each year, along with a respective increase in Fishing Mortality and Exploitation Rate, indicating the effects of fishing pressure over the population. Size at onset of sexual maturity was estimated at 32.6 mm, higher than the official mesh sizes for creels (28 mm) and gillnets (26 mm). According to the analyses, the local Norway lobster stock is over-exploited, which should be taken under consideration by the regional policy makers

Population Characteristics of the Upper Infralittoral Sea Urchin Arbacia lixula (Linnaeus, 1758) in Eastern Mediterranean (Central Greece): An Indicator Species for Coastal Water Quality

The black sea urchin (Arbacia lixula, Linnaeus, 1758) is a non-edible marine echinoderm of high ecological importance with the potential to affect marine ecological communities. A. lixula were sampled monthly for one year from the supralittoral fringe at two locations in the Pagasitikos Gulf, in the north-western Aegean Sea. Morphometric characteristics exhibited significant spatiotemporal variation. The population in closer proximity to treated sewage effluent outflow exhibited significantly higher biometric relationships resulting in possible improved physiological conditions. Spatial distribution exhibited a clumped pattern of dispersion, consisting of predominantly six age classes. The dominant cohort was the four-year age class, comprising 31.2% of the total population. Significant negative allometric relationships were exhibited between all morphometric characteristics. The maximum approximate age of the total A. lixula population was estimated at 15.27 years. The von Bertalanffy growth equation for the entire population was estimated as: test diameter = 62.881&times;1&minus;e&minus;0.196&times;Age+1.147. The gonadosomatic index indicated a seasonal cycle with a peak in late spring. The approximate age of sexual maturity was estimated at 4.45 years. We observed a significantly higher number of females than expected at the site in closer proximity to the treated sewage effluents (32% of total female number)

Population Characteristics of the Mid-Littoral Chthamalid Barnacle C. stellatus (Poli, 1791) in Eastern Mediterranean (Central Greece)

Barnacles are key space-occupiers in rocky shore communities on European coasts. Barnacles of the species Chthamalus stellatus (Poli, 1791) were collected between June 2014 and May 2015 from two sites, two stations per each site with varying degree of exposure to wave action and anthropogenic pressure (trampling), in the Eastern Mediterranean (Pagasitikos Gulf, Central Greece). This study addresses a knowledge gap in population characteristics of C. stellatus populations in the Eastern Mediterranean, assessing population structure and allometric relationships. Patterns of distribution and abundance (density and percentage cover) were studied both temporally (seasonally) and spatially (water level and site). Morphometric characteristics exhibited spatiotemporal variation. Population density was significantly higher at the site with higher wave exposure. The population cover exhibited high levels of similarity among shore levels, both spatially and temporally. Spatial distribution exhibited a clumped pattern of dispersion in autumn, winter, and spring, mainly in the sheltered site. Six dominant age groups were identified, with the dominant cohort in the third-year class. Significant negative allometric relationships were exhibited between all morphometric characteristics. Differences in growth patterns among populations were indicated, with a higher rate of growth at the site of lower wave exposure