Tracking Signals of Change in Mediterranean Fish Diversity Based on Local Ecological Knowledge

One of the expected effects of global change is increased variability in the abundance and distribution of living organisms, but information at the appropriate temporal and geographical scales is often lacking to observe these patterns. Here we use local knowledge as an alternative information source to study some emerging changes in Mediterranean fish diversity. A pilot study of thirty-two fishermen was conducted in 2009 from four Mediterranean locations along a south-north gradient. Semi-quantitative survey information on changes in species abundance was recorded by year and suggests that 59 fish species belonging to 35 families have experienced changes in their abundance. We distinguished species that increased from species that decreased or fluctuated. Multivariate analysis revealed significant differences between these three groups of species, as well as significant variation between the study locations. A trend for thermophilic taxa to increase was recorded at all the study locations. The Carangidae and the Sphyraenidae families typically were found to increase over time, while Scombridae and Clupeidae were generally identified as decreasing and Fistularidae and Scaridae appeared to fluctuate in abundance. Our initial findings strongly suggest the northward expansion of termophilic species whose occurrence in the northern Mediterranean has only been noted previously by occasional records in the scientific literature

Climate impact on Italian fisheries (Mediterranean Sea)

Global warming is increasingly affecting marine ecosystems and ecological services they provide. One of the major consequences is a shift in species geographical distribution, which may affect resources availability to fisheries. We computed the mean temperature of the catch (MTC) for Italian catches from 1972 to 2012 to test if an increase of warmer-water species against colder-water ones was observed. We further analysed the relationship among MTC, landings, fishing effort and climatic factors through a Linear Mixed Models approach. Global MTC increased at a rate of 0.12 _C per decade. Though, by considering the influence of sea surface temperature (SST), a strongest increase (0.31 _C) was estimated in southernmost areas, while in the northernmost basin (Northern Adriatic Sea) a decrease of 0.14 _C was observed. SST resulted the most relevant driver, and the relationship between MTC and SST showed a high spatial variability both in terms of strength and sign, being positively stronger in southernmost areas while negative in the northernmost basin. The result is probably underestimated since several psychrophilous and thermophilous species were not included in the analysis. However, it seems that a change towards warmer-water species has already occurred in Italian marine ecosystems. Conversely, total landings temporal dynamics seem mostly driven by changes in fishing effort rather than by MTC and climatic factors. Consequently, fishery management strategies need to focalize primarily on fishing effort reduction, in order to reduce the pressure on the stocks while increasing their resilience to other stressors, among which global warmingGlobal warming is increasingly affecting marine ecosystems and ecological services they provide. One of the major consequences is a shift in species geographical distribution, which may affect resources availability to fisheries. We computed the mean temperature of the catch (MTC) for Italian catches from 1972 to 2012 to test if an increase of warmer-water species against colder-water ones was observed. We further analysed the relationship among MTC, landings, fishing effort and climatic factors through a Linear Mixed Models approach. Global MTC increased at a rate of 0.12 A degrees C per decade. Though, by considering the influence of sea surface temperature (SST), a strongest increase (0.31 A degrees C) was estimated in southernmost areas, while in the northernmost basin (Northern Adriatic Sea) a decrease of 0.14 A degrees C was observed. SST resulted the most relevant driver, and the relationship between MTC and SST showed a high spatial variability both in terms of strength and sign, being positively stronger in southernmost areas while negative in the northernmost basin. The result is probably underestimated since several psychrophilous and thermophilous species were not included in the analysis. However, it seems that a change towards warmer-water species has already occurred in Italian marine ecosystems. Conversely, total landings temporal dynamics seem mostly driven by changes in fishing effort rather than by MTC and climatic factors. Consequently, fishery management strategies need to focalize primarily on fishing effort reduction, in order to reduce the pressure on the stocks while increasing their resilience to other stressors, among which global warming

Large-Scale Spatio-Temporal Patterns of Mediterranean Cephalopod Diversity

Species diversity is widely recognized as an important trait of ecosystems’ functioning and resilience. Understanding the causes of diversity patterns and their interaction with the environmental conditions is essential in order to effectively assess and preserve existing diversity. While diversity patterns of most recurrent groups such as fish are commonly studied, other important taxa such as cephalopods have received less attention. In this work we present spatio-temporal trends of cephalopod diversity across the entire Mediterranean Sea during the last 19 years, analysing data from the annual bottom trawl survey MEDITS conducted by 5 different Mediterranean countries using standardized gears and sampling protocols. The influence of local and regional environmental variability in different Mediterranean regions is analysed applying generalized additive models, using species richness and the Shannon Wiener index as diversity descriptors. While the western basin showed a high diversity, our analyses do not support a steady eastward decrease of diversity as proposed in some previous studies. Instead, high Shannon diversity was also found in the Adriatic and Aegean Seas, and high species richness in the eastern Ionian Sea. Overall diversity did not show any consistent trend over the last two decades. Except in the Adriatic Sea, diversity showed a hump-shaped trend with depth in all regions, being highest between 200–400 m depth. Our results indicate that high Chlorophyll a concentrations and warmer temperatures seem to enhance species diversity, and the influence of these parameters is stronger for richness than for Shannon diversityVersión del editor4,411

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

Fish diversity patterns in the Mediterranean Sea: deviations from a mid-domain model

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Un défi pour la planète : les Objectifs de développement durable en débat

Les océans jouent un rôle crucial pour la sécurité alimentaire mondiale, la régulation climatique, le cycle de l'eau et de nombreux autres services écosystémiques. L'ODD 14 entend conserver et exploiter de manière durable les océans, les mers et les ressources marines aux fins du développement durable. Cet Objectif devra se réaliser en articulant les objectifs liés à la conservation et à l'exploitation des ressources marines avec plusieurs autres ODD de l'Agenda 2030. Cette perspective permet de coupler les préoccupations environnementales, mais aussi sociales et économiques, et de recentrer les thèmes de recherche dans un cadre plus intégrateur. Les problématiques environnementales, économiques et sociales ne pourront être traitées qu'avec cet effort d'intégration et de réorientation de nos objectifs

A trophodynamic approach for the evaluation of Fishery Management Plans in the gulf of Gabes (Southern Tunisia)

An Ecopath with Ecosim food web model of the Gulf of Gabes (southern Tunisia) was constructed in order to describe its trophic structure and functioning. To assess the impacts of fisheries, an Ecosim routine was applied to predict temporal variation of catches. The model was fitted with time series data of landings for the period 1995-2008. Then, several fishery management plans were simulated by implementing different biological rest-periods. To a better evaluation of each management plan, ecological and socio-economic indicators were calculated. These indicators were used to i) establish a ranking between the fishery management plans, ii) study the effects of conservation measures on the ecosystem

Ecological correlates of dispersal success of Lessepsian fishes

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Climate change and fisheries

International audienceThere is considerable evidence that Mediterranean marine species have been shifting their ranges, migration patterns, seasonal activities and periodicities, abundances, growth and mortality rates, and consequently their trophic interactions in response to climate change and variability. These responses may ultimately have significant consequences for ecosystem productivity, biodiversity and functioning and hence for the overall goods and ecosystem services they provide, especially the production of living resources (Kirby & Beaugrand 2009,Doney et al. 2012). Climate change is an additional pressure on marine ecosystems that are already subject to many anthropogenic disturbances such as fishing activities. This is especially true in the Mediterranean Sea, where a series of human impacts co-occur and interact (Coll et al. 2010, Micheli, Halpern, et al. 2013). The consequences of climate change for marine resources need to be evaluated in this context and research and management need to take interactions between fishing, other human impacts, and climate into account (Brander 2010, Perry etal. 2010). This chapter thus has three aims: (i) to investigate the synergy between climate and fishing (a major human impact on Mediterranean marine ecosystems) and, using some examples from the Mediterranean Sea, to highlight how these two factors interact, from the individual to the ecosystem scale, (ii) to assess and quantify the consequences of climate change for the composition of fishery catches in the Mediterranean Sea, and (iii) to address the consequences of climate change for the management tools and strategies implemented in the region

Cumulative human threats on fish biodiversity components in Tunisian waters

International audienceHuman activities are increasingly impacting biodiversity. To improve conservation planning measures in an ecosystem-based management context, we need to explore how the effects of these activities interact with different biodiversity components. In this study, we used a semi-quantitative method to assess the cumulative impacts of human activities on three biodiversity components (species richness, phylogenetic diversity, and functional diversity) in Tunisia's exclusive economic zone. For each of the nine activities considered, we developed an understanding of their effects from local studies and the expert opinion of stakeholders with country-speciic experience. We mapped the cumulative effects and the three biodiversity components and then assessed the degree to which these elements overlapped using an overlap index. This is the first time such an assessment has been made for Tunisia's marine ecosystems and our assessment highlight the inappropriateness of current conservation measures. The results of this study have specific application for the prioritization of future management actions