Ranking sediment samples from three Spanish estuaries in relation to its toxicity for two benthic species: the microalga Cylindrotheca closterium and the copepod Tisbe battagliai

Metal and metalloid pollution in shelf sediments from the Gulf of Cádiz (Southwest Spain): Long-lasting effects of a historical mining area

The Gulf of Cádiz is an area historically affected by acid mine drainage and also by the discharge of two important rivers, the Guadiana and the Guadalquivir. Metal and metalloid (As, Cd, Hg, Pb, Zn, Cu, Cr, Ni, Mn, Fe, Al and Li) concentrations were measured in 33 surface sediment samples, collected in the continental shelf, inside the Ría de Huelva and the Bay of Cádiz, to assess the metal pollution status of this area. Geographical distribution was identified for different groups of metals: Cu, Cd, Zn, Hg and As were mainly associated with discharges of the Tinto and Odiel rivers, which have been historically affected by mining, into the Ría de Huelva. Sediments inside this Ría presented the highest concentrations of the whole area for these metals, and enrichment factors revealed that Hg and Cu pollution spread up to 20 km away from the mouth of this Ría, into the continental shelf. On the contrary, the distribution of Ni, Cr and Mn did not show a clear gradient with distance from a pollution source, and was mainly explained by geochemical factors, such as their association with fine materials. The comparison of metal concentrations with sediment quality guidelines, predicts that adverse ecological effects due to the metal pollution may be occurring in a group of stations located in the northwest corner of the studied area. Local background levels for metals in the Gulf of Cádiz were proposed and the information obtained will be useful to identify those areas where sampling must be intensified in ongoing Marine Strategy Framework Directive (MSFD) monitoring programs. These results corroborate that metal pollution is still a serious problem in the Gulf of Cádiz.

Alterations in the macrobenthic fauna from Guadarranque River (Southern Spain) associated with sediment-seawater acidification deriving from CO2 leakage

Nowadays, Carbon Storage in Sub-Seabed Geological Structures (CS-SSGS) is having much interest. Nonetheless, these technologies are still under development, especially the leakage of the stored CO2 and the consequent acidification of the environment. Therefore, the goal of this study is to test the impact of CO2-induced acidification on a macrobenthic community due to leakages from CS-SSGS using a mesocosm-based experiment. Results confirmed the significant correlation between the abundance of the species and the pH (positively), and the alkalinity (negatively). Additionally, the BIOENV analysis showed that the majority of the variability in the abundance of the total species was explained for the alkalinity. The correlation analysis showed differential vulnerabilities of different species, especially Cyathura carinata and a non-calcifier species as Hediste diversicolor. Nevertheless, these results showed the importance of taking into account the indirect effect associated with acidification processes, as metal release from sediment.

Response of copepods to elevated pCO2 and environmental copper as co-stressors--a multigenerational study

We examined the impacts of ocean acidification and copper as co-stressors on the reproduction and population level responses of the benthic copepod Tisbe battagliai across two generations. Naupliar production, growth, and cuticle elemental composition were determined for four pH values: 8.06 (control); 7.95; 7.82; 7.67, with copper addition to concentrations equivalent to those in benthic pore waters. An additive synergistic effect was observed; the decline in naupliar production was greater with added copper at decreasing pH than for decreasing pH alone. Naupliar production modelled for the two generations revealed a negative synergistic impact between ocean acidification and environmentally relevant copper concentrations. Conversely, copper addition enhanced copepod growth, with larger copepods produced at each pH compared to the impact of pH alone. Copepod digests revealed significantly reduced cuticle concentrations of sulphur, phosphorus and calcium under decreasing pH; further, copper uptake increased to toxic levels that lead to reduced naupliar production. These data suggest that ocean acidification will enhance copper bioavailability, resulting in larger, but less fecund individuals that may have an overall detrimental outcome for copepod populations.

Measuring the avoidance behaviour shown by the snail Hydrobia ulvae exposed to sediment with a known contamination gradient

This study tested the hypothesis that the snail Hydrobia ulvae will recognise differences in the contamination levels of sediment and avoid the more contaminated zones. Instead of testing avoidance behaviour in a two-compartment system, a linear contamination gradient has been devised in which several zones containing sediment with different contamination levels could be "chosen". A sediment of known severe contamination was collected and mixed with a non-toxic sediment to comprise a linear gradient with four concentrations of 0, 30, 60 and 100% contamination. Thus, the individuals were free to move between fields of different concentration (unforced conditions). During 24 h of exposure, the distribution of the organisms on fields was recorded and organisms' percentage that avoided each field was calculated for each concentration. At 30 and 60% of contamination, avoidance was around 50% for all periods of exposure. Avoidance at 100% contamination ranged between 11 and 56% (rates lower than expected). Organisms that did not avoid the 100% contamination revealed that they were inactive, indicating either that non-mobility and retraction within their shell may be alternative defence strategies, or else the high contamination may have impaired their ability to escape. The percentage of preference shown to the uncontaminated sediment ranged between 64 and 74%. The initial hypothesis was supported: H. ulvae avoids the more contaminated sediment. The assay proposed has been shown to be simple, rapid and effective; in addition, it is considered ecologically useful since the effects resulting from the avoidance are similar to the extinction of the population.

Microphytobenthos in ecotoxicology: a review of the use of marine benthic diatoms in bioassays

Contamination in coastal zones is an increasing problem that adversely affects biological diversity and the functioning of coastal ecosystems. Sediment is an important compartment of these zones since large quantities of diverse contaminants can accumulate there. Whole-sediment toxicity assays are of increasing importance, and several assay methods using mainly invertebrates have been developed. However, an important part of the benthic community, the microphytobenthos (represented principally by benthic diatoms and cyanobacteria), has surprisingly been neglected. Recently, comprehensive studies have been conducted using benthic marine microalgae with the object of establishing a toxicity assay method for sediment samples. The main results published to date in the literature and obtained by our own team have been compiled and are discussed in this review. The value and feasibility of using certain organisms of the microphytobenthos group in ecotoxicology studies are also discussed, and a sediment quality guideline based on multivariate procedure has been derived from data obtained in previous studies. Finally, future perspectives for research in this field are discussed.