Biomass size-spectra of macrobenthic assemblages along water depth in Antarctica

Several biomass size spectra of benthic assemblages were constructed along a water depth gradient on the southern coast of Livingston Island (South Shetland Islands, Antarctica). The size-spectrum for shallow bottoms (200 m) zones showed unimodal spectra with biomass peaks in the 1-2 and 0.5-1 g weight ranges respectively. Filter-feeders also affected the larger size classes at intermediate depths, whereas they were almost absent in deeper waters. The slope of the normalized size-spectrum at shallower bottoms (-0.76) was different from those of intermediate (-1.25) and deeper (-1.31) zones. This clearly indicated 2 contrasting faunal strategies: a biomass increase with size in shallow waters, whereas the biomass decreased with size in deep waters. Estimates of total secondary production were calculated using allometric equations published in the literature. Results indicated a decrease of total secondary production along water depth, with 15 g C m-2 yr-1 in shallow waters, 9 g C m-2 yr-1 at intermediate bottoms and 8 g C m-2 yr-1 at deep bottoms. The pattern of the biomass size spectrum for shallower waters suggested that there was a predictable and regular supply of food, which allowed accumulation of biomass in the larger size classes corresponding to filter-feeder organisms. Conversely, the concentration of biomass in smaller size classes of the spectra for intermediate and deeper waters pointed to more unpredictable and fluctuating food conditions arriving from the overlying layer to the deeper sea floor. Sufficient evidence exists in the literature to indicate that a tight pelagic-benthic coupling was causing biological enhancement of a suspension-feeding macrofauna at shallow bottoms, and that below 100 m depth the effects of the coupling were rather weak.Versión del editor2,483

Azken hiru hamarkadetan Euskal Herriko kostaldean klima-aldaketak komunitate bentonikoetan (flora eta fauna) izan duen eragina

Errezela eratzen duten makroalgek, oro har, beherakada bortitza izan dute, eta horrek ekosistemako prozesuetan izango dituen eraginak ez dira oraindik ondo ezagutzen. Ikerketa honek Bizkaiko Golkoko hegoaldean 20 urte inguruko aldian substratu gogorreko ekosistema bentonikoak aztertu ditu, non Gelidium corneum makrofitoak beherakada nabarmena izan duen. Errezelak atzera egitearen edo aldaketaren tasa ikertu da, bai eta errezel-menpeko diren organismoen (algak eta ornogabeak) egitura taxonomiko eta funtzionalean ondorioak ere. Gure emaitzek erakutsi dute 2008an aldaketa garrantzitsuak zakarki gertatu zirela eta ondoren ez dela berreskuratze-seinalerik izan. Galera esanguratsuenak makroalga konplexu eta iraunkorrak diren formetan gertatu dira eta, aldiz, epifitoak diren eta ez diren suspentsiboroetan ere, alga sinple soropilduak ugaritu dira. Aldi berean, espezieen aberastasunak, algen dentsitateak eta flora eta faunaren ekitatibitateak gora egin dute. Ikerketaren 1. aldian (1998-2007), alga eta fauna espezie elkartuen talde koherenteak batera aldatzen dutela ikusten da. Hala ere, 2008tik aurrerantz finkatutako komunitate berrian algen eta ornogabeen arteko elkarte espezifikoak falta dira. Gure emaitzek flora eta fauna espezieen arteko ereduak daudela adierazten dute. Patroi hauek ekosistema bentonikoaren funtsezko espezie eta ezaugarri funtzionalen galeren ondorioak hobeto ulertzen lagunduko dute.; Canopy-forming macroalgae are globally facing drastic declines and the consequences for ecosystem processes remain still little known. The present investigation analyses in a 20 years period the retreat of shallow subtidal rocky benthos communities in the southern Bay of Biscay, where the macrophyte Gelidium corneum has suffered a notable decrease. The rate of change of canopy retreat was investigated as well as the effects of the decline on the taxonomic and functional structure of canopy-dependent organisms (algae and invertebrates). Our results show that major changes occurred abruptly in 2008, and no signs of recovery have been recorded afterwards. Major losses arose in complex perennial macroalgal forms together with epiphytic and no epiphytic suspensivores while simple turf-forming algae proliferated. At the same time, species richness, algal density and both flora and fauna evenness increased. There exist groups of coherent species of flora and fauna that covary during the first part of the studied period. However, from 2008 onwards the new established community lacked algal-invertebrate specific associations. Our results highlight patterns between flora and fauna species help to better understand the consequences of the loss of key species and functional traits for the benthic ecosystem

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

Detecting human mitigation intervention: Effects of sewage treatment upgrade on rocky macrofaunal assemblages

The effectiveness of secondary vs primary treatments of wastewaters in mitigating the effects of sewage discharge on the multivariate structure and diversity of rocky invertebrate assemblages was assessed over a nine-year period through a beyond-BACI experimental design. Assemblages from different tidal levels (i.e. mid-shore, low-shore, 3 m and 8 m subtidal) were sampled at the impact location (I) and three control locations (Cs) at a hierarchy of spatial scales. The improvement in water treatment significantly changed the structure, diversity and cover of low intertidal assemblages. Faunal cover at 8 m subtidal increased significantly after the treatment upgrade at I. The secondary treatment also affected patterns of spatial heterogeneity between I and Cs for mid-shore and 3 m subtidal assemblages. This study demonstrates that powerful experimental designs combined with univariate and multivariate analytical approaches are fundamental in distinguishing the subtle effects of human impact from those of natural processes

First record of the sipunculan worm Phascolion (Phascolion) caupo Hendrix, 1975 in the Mediterranean Sea

Specimens of the sipunculan worm Phascolion (Phascolion) caupo Hendrix, 1975 have been collected for the first time in the Mediterranean Sea, thus increasing the number of known sipunculan species of up to 36 in this area. They were encountered on soft bottoms from the coast of San Pedro del Pinatar (Western Mediterranean). Thirty specimens were collected at a depth ranging from 32.6 to 37.2 m, mainly in sandy substrata with high load of silt and clays. 80% of the individuals were found inhabiting empty shells of gastropods or empty tubes of serpulid polychaetes.This study was funded by “Mancomunidad Canales del Taibilla”

Quantitative analysis of macrobenthic soft-bottom assemblages in South Shetland waters (Antarctica)

Macrobenthic assemblages were investigated at 26 stations located around Livingston Island, Deception Island and the Bransfield Strait at depths ranging from 42 to 671 m. Representatives of 30 major taxa were found. The maximal density was 5,260 specimens·m−2 at Livingston Island; the mean abundance per station ranged from 160 to 4,380 specimens·m−2. The total biomass of the macrozoobenthos declined with depth, with mean values of 3,201 g·m−2 at shallower depths ( 100 m). After multivariate analysis (cluster analysis, MDS) based on Bray-Curtis dissimilarities, most stations could be assigned to one of three groups on the basis of distinct biomass differences between sites. The first cluster with a rich Ascidiacea biomass is common on shallower bottoms. The second, with Ophiuroidea as a characteristic group, is common on deeper bottoms. The absence of an ‘indicator’ taxon is characteristic of the remaining cluster of those stations with the lowest biomass values. No significant correlations were detected between macrobenthic biomass and any sediment parameters measured, probably because part of the benthos (i.e. the epifauna) could be better explained by the coupling with a highly productive water column. The role of the epi-infauna sensu Gallardo as the main factor structuring benthic assemblages in the investigated area is discussed.S

Changes in the biomass and dominant feeding mode of benthic assemblages with depth off Livingston Island (Antarctica)

To elucidate spatial assemblage patterns during 2 consecutive austral summer seasons, we sampled intensively the macrofauna from 73 stations located at the southern coast of Livingston Island. Representatives of 28 higher taxonomic groups were used for the faunal analysis. While two faunal descriptors (i.e. group richness and total biomass) changed markedly with increasing water depth, total density remained relatively constant. Sessile suspension-feeders belonging to the Ascidiacea and Porifera dominated at shallower depths (100 m) obtained 0.37 g. This faunal discontinuity, primarily influenced by depth-related variables, is suggested to be directly related to food availability.Versión del editor1,445

Quantitative analysis of macrobenthic soft-bottom assemblages in South Shetland waters (Antarctica)

Macrobenthic assemblages were investigated at 26 stations located around Livingston Island, Deception Island and the Bransfield Strait at depths ranging from 42 to 671 m. Representatives of 30 major taxa were found. The maximal density was 5,260 specimens·m−2 at Livingston Island; the mean abundance per station ranged from 160 to 4,380 specimens·m−2. The total biomass of the macrozoobenthos declined with depth, with mean values of 3,201 g·m−2 at shallower depths ( 100 m). After multivariate analysis (cluster analysis, MDS) based on Bray-Curtis dissimilarities, most stations could be assigned to one of three groups on the basis of distinct biomass differences between sites. The first cluster with a rich Ascidiacea biomass is common on shallower bottoms. The second, with Ophiuroidea as a characteristic group, is common on deeper bottoms. The absence of an ‘indicator’ taxon is characteristic of the remaining cluster of those stations with the lowest biomass values. No significant correlations were detected between macrobenthic biomass and any sediment parameters measured, probably because part of the benthos (i.e. the epifauna) could be better explained by the coupling with a highly productive water column. The role of the epi-infauna sensu Gallardo as the main factor structuring benthic assemblages in the investigated area is discussed.Versión del editor1,445