Aggregation dynamics and foraging behaviour of striped red mullet Mullus surmuletus in the western Mediterranean Sea.

Habitat-related heterogeneity of striped red mullet Mullus surmuletus heterospecific foraging assemblages was examined off the coast of Spain. Video-based focal-follows conducted on 122 M. surmuletus assemblages (446 total individuals) revealed an array of attendant species (n = 7) with composition linked to benthic habitat complexity; bare sandy substrata were characterized by homospecific groups of M. surmuletus, while habitats with rock and vegetation attracted a variety of scrounging labrids and sparids. Although the nature of the relationship between M. surmuletus and attendants requires further exploration, the present study indicates that substratum composition can be a driving factor explaining the dynamics of this heterospecific assemblage.

Bioindicators as metrics for environmental monitoring of desalination plant discharges.

Development of desalination projects requires simple methodologies and tools for cost-effective and environmentally-sensitive management. Sentinel taxa and biotic indices are easily interpreted in the perspective of environment management. Echinoderms are potential sentinel taxon to gauge the impact produced by brine discharge and the BOPA index is considered an effective tool for monitoring different types of impact. Salinity increase due to desalination brine discharge was evaluated in terms of these two indicators. They reflected the environmental impact and recovery after implementation of a mitigation measure. Echinoderms disappeared at the station closest to the discharge during the years with highest salinity and then recovered their abundance after installation of a diffuser reduced the salinity increase. In the same period, BOPA responded due to the decrease in sensitive amphipods and the increase in tolerant polychaete families when salinities rose. Although salinity changes explained most of the observed variability in both indicators, other abiotic parameters were also significant in explaining this variability.

Monitoring the effects of wastewater treatment strategies.

Wastewater disposal in coastal waters causes widespread environmental problems. Secondary treatment is expected to reduce the adverse effects of insufficiently treated wastewater. The environmental impact of sewage disposal via 18 wastewater treatment plants was analysed using the benthic opportunistic polychaetes and amphipods (BOPA) index. In previous studies this index proved to be an effective tool for monitoring sewage pollution. The impact of these discharges was highly related to treatment level, which ranged from pre-treatment to biological, as well as to flow rates and outfall position. Locations affected by pre-treated wastewater showed environmental degradation, especially marked near outfalls with higher flow rates. At most locations, biologically treated wastewater did not cause a significant impact and an improvement in ecological integrity was detected after this secondary treatment had been implemented. The impact of discharge was highly related to chemical oxygen demand (COD), suspended solids and nutrient concentrations, which are all lower in biologically treated wastewater. A 'moderate' ecological status was observed not only near sewage outfalls with high wastewater flow rates (>1,500,000 m(3)/month) with a COD over 200 mg/l but also near those with lower flow rates but with a COD over 400 mg/l. To reduce the impact of sewage disposal, it is necessary to carry out adequate treatment, have site outfalls deep enough, and implement water recycling.

Salinity fluctuation of the brine discharge affects growth and survival of the seagrass Cymodocea nodosa.

The increase of seawater desalination plants may affect seagrasses as a result of its hypersaline effluents. There are some studies on the salinity tolerance of seagrasses under controlled laboratory conditions, but few have been done in situ. To this end, Cymodocea nodosa shoots were placed during one month at four localities: two close to a brine discharge; and the other two not affected by the discharge, and this experiment was repeated four times. The results obtained showed a decrease in growth and an increased mortality at the localities affected by the brine discharge. An increase was detected in the percentage of horizontal shoots in respect to vertical shoots at the impacted localities. It is probably that not only the average salinity, but also the constant salinity fluctuations and slightly higher temperatures associated with the brine that may have caused physiological stress thus reducing C. nodosa growth and survival.

Distribution of Sipuncula in the Gulf of Valencia and Cape Nao (western Mediterranean).

The present study analyses the distribution and diversity of sipunculan species inhabiting soft substrata in the Gulf of Valencia and Cape Nao (western Mediterranean) in relation to the characteristics of the sediment. Eighty-seven stations in 14 localities were sampled annually from 2004 to 2008. Nine species were reported, with Aspidosiphon (Aspidosiphon) muelleri being the dominant species in the area and Thysanocardia procera the most widely distributed. Pearson correlation coefficient and multivariate analysis showed how sipunculan abundances of certain species were related to the sediment characteristics, especially grain size. The shell-dwelling species A. (A.) muelleri and Phascolion (Phascolion) caupo were dominant in stations with high amount of coarse sand and gravel, while Sipunculus (Sipunculus) nudus appeared in stations dominated by fine sand with low organic content. Pn. (Pn.) caupo and T procera were reported for the first time in the study area. Moreover, it was the second record of Pn. (Pn.) caupo for the Mediterranean Sea.

Sensitivity of tanaid Apseudes latreillei (Milne-Edwards) populations to sewage pollution.

Apseudes latreillei (Milne-Edwards) is a common and abundant tanaid in soft-bottom communities from waters off East Atlantic and Mediterranean coasts. Its sensitivity to pollution is not clear despite being an abundant and widely distributed crustacean, since it has been reported as both a tolerant and sensitive species. This paper tests the sensitivity of A. latreillei to sewage discharges in fine-sand communities along the Castellon coast (W. Mediterranean). We analysed variation in tanaid populations between sites at varying distances from sewage outfalls with respect to population density, size distribution, sex ratio and their correlation with different abiotic factors of waste water and sediment. Results showed clearly that A. latreillei populations were affected by the presence of sewage outfalls, to such an extent that sewage disposal outlets produced a decrease in population density and changes in size spectra.

Remote influence of off-shore fish farm waste on Mediterranean seagrass (Posidonia oceanica) meadows.

The aim of this study was estimating the remote influence of waste dispersed from a large off-shore fish farm complex (6197 ton year(-1)) on the near-shore Posidonia oceanica meadow (26-27 m deep) located at a distance of 3 km. Measurements of isotopic nitrogen content in epiphytes and seagrass leaf tissues, epiphyte biomass, shoot size, herbivory pressure, shoot density and seagrass meadow cover, performed in this meadow (FA area) were compared with those obtained in an undisturbed control meadow (CA area) to evaluate: (1) the remote influence of waste and (2) the impact of such influence on seagrass condition. In addition, delta(15)N measurements in particulate organic matter of natural and anthropogenic origin were used in a single-isotope mixing model to elucidate the relative contributions of these sources to the isotopic N signal measured in epiphytes and leaf tissues. Total tissue N content was similar between meadow areas, but delta(15)N signatures were significantly higher in the FA area than in the CA area both in epiphytes and seagrass leaf tissues. Results from the mixing model, together with available information on local currents and previous studies, support the conclusion that the dispersion of farm wastes over large areas (spanning kilometres) are responsible for the elevated delta(15)N signatures found in the FA meadow area. Despite this, no changes in meadow structure were detected and only some changes at the level of seagrass community (epiphytes abundances and herbivores activity) could be interpreted at the light of nutrient-induced effects in the FA area. Results from this study indicate that concentrating aquaculture facilities in off-shore areas is a strategy not totally exempt of environmental risk on near-shore sensitive habitats such as seagrass meadows.

Testing BOPA index in sewage affected soft-bottom communities in the north-western Mediterranean.

The implementation of the European directive (ELD) 2000/60/EC has produced the development of several biotic indices based in benthic communities. These indices try to summarise ecological quality status of different communities. However, a universal index that works in all situations is difficult to establish, because there are several sources of variation. Therefore, there is the need for testing and validation of these indices which is required for making management decisions on different scales, and in different regions and communities. In this study we test one of these indices, BOPA index, developed by Dauvin and Ruellet [Dauvin, J.C., Ruellet, T., 2007. Polychaete/amphipod ratio revisited. Marine Pollution Bulletin 55, 215-224] in five locations affected by sewage disposal. These disposals are often released via outfall into shallow subtidal habitats, leading to a common source of pollution in coastal marine environments. BOPA index provides a valuable overview of the gradient status of a benthic environment, discriminating between stations more affected by discharge. Nevertheless, BOPA index, used to establish the ecological quality status, seemed to overestimate the status and hence there is the need to calibrate the thresholds between EcoQs classes as defined for these medium-to-fine sand communities, which are characteristics of shallow sublittoral soft-bottoms of the north-western Mediterranean Sea.

Effect of sewage discharge in Spisula subtruncata (da Costa 1778) populations.

Sewage discharge is a common source of pollution in coastal marine waters. Several municipal treatment plants dump treated water in medium to fine sand Spisula subtruncata communities. This bivalve is generally considered a major food source for demersal fishes, and it is important as a dominant species in structuring the macrobenthic community during the spring and summer months. We sampled within five locations affected by sewage discharge along the Castellon coast (northwest Mediterranean Sea) where S. subtruncata (da Costa 1778) is a common bivalve. Van Veen grab samples were obtained for the study of the bivalve population and to characterize the sediment. The sewage discharges studied affect Spisula populations. In the stations near the outfalls, the abundance and the average size of S. subtruncata decreased. However, this effect did not correlate with sediment characteristics, such as granulometry or pH.