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.

This abstract has been translated to other languages (File S1).

/pdf/the-biodiversity-of-the-mediterranean-sea-estimates-patterns-38y4s7jond.pdf

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

Trabajo presentado en el 39th CIESM Congress, celebrado en Venecia, Italia, del 10 al 14 de mayo de 2010

/pdf/biodiversity-of-the-mediterranean-sea-estimates-patterns-and-2mjs6mi5cx.pdf

Biodiversity of the Mediterranean Sea: estimates, patterns and threats

The role of Posidonia oceanica in promoting sediment stability and accretion was studied in a 15 m deep meadow at Fanals Point (NW Mediterranean, Spain) by comparing particle deposition within the meadow and adjacent bare sediment. Small sediment traps were used to measure deposition within and above the meadow and over bare sand. A model, based on measurements of particle deposition at increasing distances from the bottom, was used to partition the total depositional flux between primary (sediment particles deposited for the first time at the measuring site) and resuspended deposition (sediment particles that have been previously deposited at the measuring site). Measurements were conducted monthly over a year to establish the magnitude and seasonality of deposition, and to form a balance of particle transport at the annual time scale. Significant differences in total deposition were found over time, ranging from 1·5 to 500 g DW m−2 d−1, including those between bare and vegetated sediments. The effect of P. oceanica in increasing primary deposition at an annual scale was modest, however, P. oceanica significantly buffered sediment resuspension, which was reduced more than three fold compared to the unvegetated bottom. The annual flux of deposition was dominated by settling of resuspended materials, which represented 85% of the total flux within the meadow, but 95% of the total deposition on bare sand. Thus, seagrass meadows reduce resuspension in the NW Mediterranean littoral, thereby contributing to increased sediment retention and, therefore, reducing erosion in the coastal zone.

Sediment Retention by a Mediterranean Posidonia oceanica Meadow: The Balance between Deposition and Resuspension

Acquisition of phototrophy is widely distributed in the eukaryotic tree of life and can involve algal endosymbiosis or plastid retention from green or red origins. Species with acquired phototrophy are important components of diversity in aquatic ecosystems, but there are major differ- ences in host and algal taxa involved and in niches of protists with acquired phototrophy in marine and freshwater ecosystems. Organisms that carry out acquired phototrophy are usually mixotrophs, but the degree to which they depend on phototrophy is variable. Evidence suggests that 'excess car- bon' provided by acquired phototrophy has been important in supporting major evolutionary innova- tions that are crucial to the current ecological roles of these protists in aquatic ecosystems. Acquired phototrophy occurs primarily among radiolaria, foraminifera, ciliates and dinoflagellates, but is most ecologically important among the first three. Acquired phototrophy in foraminifera and radiolaria is crucial to their contributions to carbonate, silicate, strontium, and carbon flux in subtropical and trop- ical oceans. Planktonic ciliates with algal kleptoplastids are important in marine and fresh waters, whereas ciliates with green algal endosymbionts are mostly important in freshwaters. The photo- trophic ciliate Myrionecta rubra can be a major primary producer in coastal ecosystems. Our know- ledge of how acquired phototrophy influences trophic dynamics and biogeochemical cycles is rudi- mentary; we need to go beyond traditional concepts of 'plant' and 'animal' functions to progress in our understanding of aquatic microbial ecology. This is a rich area for exploration using a combina- tion of classical and molecular techniques, laboratory and field research, and physiological and ecosystem modeling.

/pdf/acquired-phototrophy-in-aquatic-protists-1mdt944u1i.pdf

Acquired phototrophy in aquatic protists

Zooplankton abundance, biomass (biovolume) and taxonomic composition were studied within an annual cycle (August 1995-October 1996) in the Bay of Blanes (northwest Mediterranean). Weekly zooplankton sampling included oblique tows made with a 200 μm Juday-Bogorov net, and vertical tows made with a 53 μm net, to adequately sample both mesoplankton and the smaller zooplankton fractions. Total zooplankton abundance showed high variability, lacking any clear seasonal pattern. However, the different species within the zooplankton community displayed a clear succession throughout the year. In general, cyclopoid copepods (Oithona spp.) and cladocerans (Penilia wirostris) dominated the summer and autumn communities, whereas in winter and spring, calanoid copepods (Clausocalanus spp., Paracalanus sp. and Centropages typicus) were predominant. The zooplankton annual cycle in the Bay of Blanes does not resemble those of other Mediterranean littoral areas, probably due to the inherent particularity and variability associated with open coastal environments. On average, the abundance of organisms estimated with a traditional 200 μm Juday-Bogorov net was 8.1 times lower than the values obtained with a 53 μm net. Even if only organisms >200 μm collected in the 53 μm tows were considered, the total abundance within the 53 μm net was still 4.4 times higher than the estimates from the Juday-Bogorov net. These results suggest the need for accurate samplings of the entire zooplankton assemblage when characterizing the structure and dynamics of zooplanktonic communities.

/pdf/annual-zooplankton-succession-in-coastal-nw-mediterranean-193uv5lpr3.pdf

Annual zooplankton succession in coastal NW Mediterranean waters: the importance of the smaller size fractions

/pdf/dynamics-of-ciliate-abundance-biomass-and-community-1feyubb6u5.pdf

Dynamics of ciliate abundance, biomass and community composition in an oligotrophic coastal environment (NW Mediterranean)

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Dynamics of ciliate abundance, biomass and community composition in an oligotrophic coastal environment (NW Mediterranean)