José Ignacio Saiz-Salinas

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

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

Abstract 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) and 210 g·m−2 further down (> 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.

Exploring the relationships between abiotic variables and benthic community structure in a polluted estuarine system

Abstract Assessed was the effect of a man-induced interference in an estuarine system by monitoring a set of hydrographic and sedimentary variables together with a faunal survey of intertidal mudflats. A reference site was established in a nearby unpolluted estuary. A principal components analysis (PCA) reduced the original environmental data to a few more manageable factors. PCA factor I, defined by changes in salinity at the surface of the water column and dissolved oxygen at the bottom, explained 40% of the total variance. Pair-wise correlations between different structural metrics and PCA factor I explained up to 70% of the variability observed in the community metrics. Macrobenthic communities were simpler (with minor values of abundance, diversity, evenness and a much lower value of biomass) where dissolved oxygen at the bottom of the water column was minimum. An afaunal stage developed along intertidal mudflats where anoxic conditions prevailed. There was a large “weight-of-evidence” that a depletion of dissolved oxygen was causing a severe stress to the estuarine biota.

Chapter 22 – Recovery of benthic communities in polluted systems

century, practically no waste-water treatments were in operation. Due to its beneficial coastal location and closeness to rich natural resources (iron, coal etc.), several harbour complexes developed; the most important being those of Bilbao and Pasaia (see Figure 2, in Preface). The high level of human settlement and industrial development has caused, over decades, a severe impact on both of these estuaries, mainly through a considerable amount of wastewater (largely untreated) from both urban and industrial origins (Azkona

Faunal responses to turbidity in a man-modified bay (Bilbao, Spain)

The relationship between rocky shore faunal assemblages and measured environmental variables in a small bay (Bilbao, Spain) affected by large anthropogenic interferences were examined using multivariate statistical techniques (CANOCO, PRIMER). Redundancy analysis (RDA), with forward selection of environmental variables and associated Monte Carlo permutation tests, suggested that total suspension solids (TSSs) and salinity (Sals) at the water surface made significant (<0.05) contributions to explaining the variation in the investigated faunal assemblages. Alternatively, the BIO-ENV analysis selected a subset of three environmental variables, related to turbidity, as the best explanatory variables. A constrained RDA with TSSs as the only explanatory variable revealed that turbidity was a strong variable, and accounted for a statistically significant proportion of the variance in the faunal data set. Further analyses of faunal data using a smaller subset of 14 top dominant taxa produced spatial patterns as clearly as the analysis with the full species data set (63 species). This indicated that nearly 75% of the taxonomic information could be deemed redundant for the purposes of this study. In conclusion, the weight of evidence suggests that turbidity, mainly from estuarine runoff, is causing a severe stress to the hard-bottom faunal assemblages. ©

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

Abstract 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) with a mean biomass (wet weight) estimate of 3,238 g m−2. In contrast, deeper faunal assemblages were dominated by deposit-feeding polychaetes with lower biomass values of 538 g m−2. Mean body mass for dominant groups reflected two contrasting trophic strategies: ascidians at shallower depths (<100 m) attained a value of 6 g whereas a comparable density of polychaetes at deeper 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.

Reducing effort in the use of benthic bioindicators

Abstract Hard-bottom invertebrates were visually sampled in a man-modified bay during a harbour enlargement scheme. Several environmental variables were repeatedly measured. Faunal assemblages were analysed using classification and ordination (MDS) techniques at different levels of resolution (species, families and indicators). Indicator taxa were selected from the full species data set by performing preliminary correlations between faunal and environmental variables. Similar results were observed at the three levels investigated. This suggests the existence of redundant information in the species level data set when applied to this case study. The implications of our findings for environmental monitoring are discussed.

Biomonitoring of metals under the water framework directive: Detecting temporal trends and abrupt changes, in relation to the removal of pollution sources

Temporal trends in metal concentrations, i.e. Ag, Cd, Cu, Cr, Hg, Ni, Pb and Zn, measured in soft tissues of Mytilus galloprovincialis mussels and Crassostrea gigas oysters collected from estuarine waters within the Basque Country (Bay of Biscay), have been investigated to determine if actions undertaken have improved the environmental quality of rivers and estuaries. Data compiled between 1990 and 2010 have been analysed statistically, applying the Mann-Kendall and the Mann-Whitney-Wilcoxon tests. Moreover, in those cases with significant trends, the Kolmogorov-Zurbenko Adaptive (KZA) filter was applied to detect abrupt changes. Results showed significant decreasing trends for some metals, i.e. Ni, Cu, Pb and Zn, and differences between medians. Trend lines showed abrupt changes occurring between 1998 and 2002. Therefore, observed downward trends were related to increased wastewater treatment and diversions of discharges to ocean, implemented mainly during 2000-2002.

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.

Enhanced growth in juvenile Nereis diversicolor after its exposure to anaerobic polluted sediments

Organic enrichment and anaerobic sediment conditions are the dominant anthropogenic influences on the Bilbao Estuary, resulting in the elimination of all benthic aerobic activity along 3/4 parts of its watercourse bed. To simulate the recolonization of azoic sediments by the native polychaete Nereis diversicolor, once water-oxic conditions in the estuary improve, two series of juvenile survival and growth assays were conducted, both, respectively, with and without the addition of exogenous food. Long-term exposures (about 30 days) of juveniles to azoic sediments caused no mortalities. On the contrary, an increased growth occurred in both types of tests, indicating the existence of a higher nutritional quality in the anaerobic sediments of the estuary. The ecological implications of our findings are clear; azoic sediments may be re-populated by juvenile invaders of N. diversicolor, provided that water-oxic conditions improve, through the implementation of a sewerage treatment plan promoted by the local Water Authority.