Comunidades de meiofauna y foraminíferos de mucha profundidad a lo largo de un gradiente de producción primaria en el Mediterráneo oriental

Benthic metazoa and stained foraminifera (>32 μm) were studied in relation to prevailing environmental parameters in the Aegean Sea (Sporades Basin and Cretan Sea) and Levantine Basin (Ierapetra Basin) during the METEOR Cruise 40 Leg 3 (December 1997–January 1998). The sampling stations differed in nutrient contents, which were indicative of the oligotrophy of the eastern Mediterranean Sea. Meiobenthic abundance decreased significantly with depth and the total standing stock in the top 6 cm sediment layer was significantly higher at the northern stations (204-231 ind./10 cm2). In the abyssal Ierapetra Basin, the abundance for all meiobenthic taxa was minimal (10-26 ind./10 cm2). Nematodes and foraminifera were dominant and accounted together for 79-93% of the total abundance. All taxa were concentrated near the surface of the sediment and only nematodes showed a deeper penetration into the sediments in the Sporades Basin. Concentrations of chloroplastic pigments, total organic carbon and total organic nitrogen were higher in the Sporades and Ierapetra Basins than in the Cretan Sea, reflecting: (a) the different productivity levels and, thus, the higher food availability in the former than in the latter; (b) the seasonal accumulation of organic matter from the euphotic zone down to the abyssal trenches; and (c) the transportation of large amounts of sediment and organic matter in the Sporades and Ierapetra Basins, which are located at the mouth of submarine canyons, through riverine inputs, flush flooding, sediment failure and dense shelf water cascading. Meiofaunal abundances in the Aegean Sea were positively correlated with chlorophyll a, phaeopigments and chloroplastic pigment equivalent (CPE), and were not correlated with any of the remaining sediment descriptors, thus indicating the dependence of meiofauna on food availability.Durante la campaña METEOR 40/3 (diciembre 97-enero 98) se estudiaron los metazoos bentónicos y foraminíferos teñidos (>32 μm) en relación a parámetros ambientales persistentes en el mar Egeo (Cuencas de Sporades y mar de Creta) y cuenca Levantina (cuenca de Ierapetra). Las estaciones muestreadas se diferenciaron por el contenido en nutrientes, y fueron indicativas de oligotrofia en el este del Mediterráneo. La abundancia del meibentos disminuyó significativamente con la profundidad; y el total de la población en los primeros 6 cm de sedimento fue significativamente más alto en las estaciones del norte (204-231 ind./10 cm2). En la cuenca abisal de Ierapetra, la abundancia de todos los taxa del meiobentos fue mínima (10-26 ind./10 cm2). Los nemátodos y foraminíferos fueron dominantes y representaron el 79-93% de la abundancia total. Todos los taxa se concentraron cerca de la superficie del sedimento y solamente los nemátodos mostraron una penetración más profunda en la cuenca de Sporades. Las concentraciones de pigmentos cloroplásticos, carbón orgánico total y nitrógeno orgánico total fueron más altas en las cuencas de Sporades y Ierapetra que en el mar de Creta, reflejando: (a) los diferentes niveles de productividad y la mayor disponibilidad de alimento en el primero que en el segundo, (b) la acumulación estacional de materia orgánica desde la zona eufótica hacia los canales abisales y (c) el transporte de grandes cantidades de sedimentos y materia orgánica en las primeras áreas, que se encuentran en la boca de cañones submarinos, a través de los influjos de ríos, arrastre por inundaciones, fallos de sedimentos y cascadas de aguas densas de plataforma. Las abundancias de la meiofauna en el mar Egeo estuvieron positivamente correlacionadas con la clorofila a, los feopigmentos y pigmentos cloroplásticos equivalentes y no estuvieron correlacionados con ningún otro descriptor del sedimento, indicando la dependencia de la meiofauna de la disponibilidad de alimento

Ecosystem functioning under the influence of bottom-trawling disturbance : an experimental approach and field observations from a continental slope area in the West Iberian Margin

Understanding the effects of bottom-trawling induced changes in benthic community structure, diversity and ecosystem functioning across different benthic-size components is imperative to determine the future sustainability of bottom-trawling fisheries in deep-sea regions. In this study, we combined field sampling observations with a pulse-chase experiment on sediments obtained from two stations of interest along the West Iberian Margin (WIM) distinguished by different trawling pressures. We compared these two stations in terms of meio- and macrofauna (infauna) standing stocks, biodiversity and several ecosystem function proxies. These proxies included: (i) 13C uptake by bacterial communities, (ii) infauna respiration rates, (iii) penetration of 13C in the sediment, and (iv) sediment pore-water nutrient concentrations. The pulse-chase experimental results were complemented with a larger biological dataset partially compiled from previous studies in the area, to investigate structural and functional diversity ecosystem functioning (respiration) patterns across the WIM. Our observations indicated that different regimes of trawling pressure influenced both macrofaunal respiration rates with disturbed sediments predominantly composed of deposit-/detritus-feeding smaller-sized macrofauna species. Moreover, sediment biogeochemical functioning (ammonium profiles) and 13C bacterial uptake showed differences among the two disturbance regimes. On the contrary, the biomass of small-sized biota, including bacteria and meiofauna, did not show marked differences between stations. The general depletion in macrofauna species richness across impacted areas of the study region was also correlated with a reduction in total biomass and respiration, suggesting that the long history of trawling disturbance at the WIM may affect regulatory ecosystem functions. These preliminary findings alert for the impacts of trawling on crucial functions of benthic ecosystems that may be imperceptible to the current tools used in monitoring programs

Bottom-trawling fisheries influence on standing stocks, composition, diversity and trophic redundancy of macrofaunal assemblages from the West Iberian Margin

Bottom-trawling fisheries operating in Portugal (West Iberian Margin) impose one of the largest footprints per unit of biomass landed in European waters at depths greater than 200 m, affecting the seafloor integrity and the associated benthic fauna. To investigate how trawling pressure is affecting the macrofaunal assemblages, we compared the standing stock (abundance and biomass), community structure and taxonomical and trophic diversity in areas subjected to varying trawling pressure along the SW Portuguese upper slope, between 200 and 600 m. In addition to trawling pressure, several environmental variables, namely depth, grain size and organic matter, were correlated with the biological component, which suggest that the longstanding trawling pressure presents cumulative effects to the habitat heterogeneity known to characterise the West Iberian Margin fauna. Furthermore, our results showed a depletion of macro-infaunal abundances in both the fishing ground and the adjacent area (up to 3 times lower), when compared to the area not trawled. The observed decrease in abundance with increasing trawling pressure was also associated with a loss of species and trophic richness, but univariate diversity indices related with community structure (i.e. Shannon-Wiener index, Pielou's evenness) failed to detect consistent differences across areas. Also observed was a decrease in the number of taxa – trophic guilds combinations of the core assemblage (i.e. characteristic, dominant or frequent taxa) with increasing trawling pressure. We suggest that, in disturbed sediments, the lower functional redundancy resulting from the loss of species within most feeding guilds increases the vulnerability of trophic interactions and therefore of the whole assemblage to further increases in natural and anthropogenic disturbance or their synergistic effects.publishe

Deep-sea mega-epibenthic assemblages from the SW Portuguese Margin (NE Atlantic) subjected to bottom-trawling fisheries

Bottom-trawling fisheries are a common threat to the health of continental margins worldwide. Together with numerous environmental and biological processes, physical disturbance induced by trawlers can largely shape the benthic habitats and their associated assemblages. At the SW Portuguese Margin, crustacean bottom trawlers have exploited deep-sea habitats for a few decades, but its effects on the benthic biodiversity are practically unknown. During the spring-summer of 2013 and 2014, several Remotely Operated Vehicle (ROV) video transects were used to investigate mega-epibenthic abundance, composition, and diversity in soft-sediment areas subjected to varying trawling pressures off Sines and Setúbal (200–800 m). Differences in mega-epibenthic assemblages were linked with environmental changes (depth, grain size, primary productivity) and trawling disturbance. The effect of trawling was assessed between segments with similar habitat characteristics, i.e., muddy-sand bottoms between 300 and 500 m. Areas subjected to intensive trawling pressure showed a generally flattened seabed, with abundant recent trawl marks (up to 3 scars.100 m−1), indicating that the seabed physical integrity was compromised. Significant negative correlations were detected between various mega-epibenthic diversity indices [S, H′, and ET(20)] and trawling pressure (h.cell−1.y−1). Furthermore, the distinct mega-epibenthic assemblages and absence of several sessile erect morphospecies at both low and highly disturbed locations by trawling off Sines, namely all seapen morphospecies found in non-trawled areas, demonstrates the negative influence of trawling fisheries on the benthic component of the study area. Also, low dissimilarity between assemblages from the main fishing grounds and the adjacent low-disturbance locations, suggests that the potentially negative influence of trawling can extend beyond the targeted areas (e.g., by the plumes of re-suspended sediments). The observed deleterious effects of trawling on mega-epibenthic fauna together with the intensification of trawling pressure in the study area, stress the need for adequate monitoring programs and regulatory measures to halt the long-term loss of biodiversity and allow the sustainability of fisheries at the SW Portuguese Margin

Deep-Sea Biodiversity in the Mediterranean Sea: The Known, the Unknown, and the Unknowable

Deep-sea ecosystems represent the largest biome of the global biosphere, but knowledge of their biodiversity is still scant. The Mediterranean basin has been proposed as a hot spot of terrestrial and coastal marine biodiversity but has been supposed to be impoverished of deep-sea species richness. We summarized all available information on benthic biodiversity (Prokaryotes, Foraminifera, Meiofauna, Macrofauna, and Megafauna) in different deep-sea ecosystems of the Mediterranean Sea (200 to more than 4,000 m depth), including open slopes, deep basins, canyons, cold seeps, seamounts, deep-water corals and deep-hypersaline anoxic basins and analyzed overall longitudinal and bathymetric patterns. We show that in contrast to what was expected from the sharp decrease in organic carbon fluxes and reduced faunal abundance, the deep-sea biodiversity of both the eastern and the western basins of the Mediterranean Sea is similarly high. All of the biodiversity components, except Bacteria and Archaea, displayed a decreasing pattern with increasing water depth, but to a different extent for each component. Unlike patterns observed for faunal abundance, highest negative values of the slopes of the biodiversity patterns were observed for Meiofauna, followed by Macrofauna and Megafauna. Comparison of the biodiversity associated with open slopes, deep basins, canyons, and deep-water corals showed that the deep basins were the least diverse. Rarefaction curves allowed us to estimate the expected number of species for each benthic component in different bathymetric ranges. A large fraction of exclusive species was associated with each specific habitat or ecosystem. Thus, each deep-sea ecosystem contributes significantly to overall biodiversity. From theoretical extrapolations we estimate that the overall deep-sea Mediterranean biodiversity (excluding prokaryotes) reaches approximately 2805 species of which about 66% is still undiscovered. Among the biotic components investigated (Prokaryotes excluded), most of the unknown species are within the phylum Nematoda, followed by Foraminifera, but an important fraction of macrofaunal and megafaunal species also remains unknown. Data reported here provide new insights into the patterns of biodiversity in the deep-sea Mediterranean and new clues for future investigations aimed at identifying the factors controlling and threatening deep-sea biodiversity

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

Distribución del meiobentos en fondos batiales del Mediterráneo: Una comparación entre lugares distantes

In order to study the distribution of meiobenthos (Metazoa and Foraminifera) at bathyal depths along a west-east productivity gradient in the Mediterranean Sea, stations along the continental slopes of the Balearic Sea, west Ionian and east Ionian Seas were sampled during the DESEAS Trans-Mediterranean Cruise in June-July 2001. Standing stock of total meiobenthos differed considerably among the sampling stations, with marked differences occurring between sampling depths and sites. At 600 m depth, meiobenthic abundances were slightly higher over the Balearic continental slope, whereas at the deeper stations (800 m and 1500-1700 m), abundances were significantly higher in the west Ionian Sea. Significant relationships were found between the abundances of major groups and the chloroplastic pigments, indicating that food availability is a major factor controlling the distribution of meiobenthos. Apart from the overall differences in productivity between the western and eastern Mediterranean Sea, local hydrographic features and topographic differences greatly influence the spatial variability of the environmental parameters within each sub-basin and thus the distribution of meiobenthos in the bathyal zone.Para el estudio del meiobenthos (Metazoa y foraminifera) en los fondos batiales del Mediterráneo a lo largo del gradiante de productividad oeste-este, se hicieron muestreos en la plataforma continental del mar Balear y del mar Jónico oriental y occidental, durante la campaña transmediterránea DESEAS (junio-julio, 2001). La biomasa permanente del meiobentos total difiere considerablemente entre las muestras de las distintas estaciones y profundiades. A 600 m de profundidad las abundancias de meiobentos fueron un poco más altas en la plataforma de Baleares, mientras que en las estaciones más profundas (800 y 1500-1700 m), las abundancias fueron significativamente más altas en el Jónico occidental. Se encontraron relaciones significativas entre las abundancias de los grupos mayoritarios y los pigmentos cloroplásticos, indicando que la disponibilidad de alimento es el principal factor que controla la distribución del meiobentos. Aparte de las diferencias globales entre la productividad del mediterráneo oriental y occidental, son las características hidrográficas y las diferencias topográficas quienes influencian fuertemente en la variabilidad espacial de los parámetros ambientales en cada sub-cubeta, y por tanto, en la distribución del meiobentos en la zona batial