# Risk Assessment of a Coastal Ecosystem from SW Spain
## 3 Results and Discussion
### Multivariate Analysis  
The principal-component analysis (PCA) identified the correlations between sediment contamination, biological responses, and the pH decrease in seawater caused by CO\({}_{2}\) enrichment in the ocean (Table 4). A total of 30 variables were used, including dissolved metals in overlying seawater (As, Cr, Cu, Fe, Ni, and Zn) and elutriate treatment (Cu, Fe, and Zn), toxicity to marine organisms (mortalities, embryo-larval development inhibition, and NMRT time after 24 h, 96 h, and 10 d of exposure), sediment characteristics (concentrations of organic matter, fines, and metals), concentrations of metals bioaccumulated in the whole body of mussels (As, Cr, Cu, Fe, Ni, and Zn) and benthic integrity (total abundance, diversity, and richness). The two main factors explained almost 75% of the original variance in the original data set. The criterion selected to interpret a variable associated with a particular factor was a loading of 0.4 or higher. Each factor is described according to the dominant group of variables. The first factor (F1, 48.41% of variance) linked all dissolved metals (except Fe) in seawater and elutriates, the metal concentration in mussels (except Zn), mortalities of amphiopods and mussels, embryo-larval development inhibition of sea urchins and mussels and the increasing proton (H\({}^{+}\)) concentration, in the other words, the CO\({}_{2}\) acidification. Furthermore, the F1 also linked negative values to the results of NMRT at 24 h, 96 h, and 10 d, and the richness of the macrobethic community. The second factor (24.93% of variance) linked all metals in sediment, dissolved Ni in the seawater and Cu in the elutriate, As and Zn bioaccumulated in the mussels, mortality of mussels, sea urchin larval development inhibition, and the values of total abundance and diversity of the macrobethic community. Moreover, negative values were linked in factor two for Cr and Fe in seawater. In general, the multivariate analysis showed that both causes can influence the adverse biological effect measured: acidification by enrichment of CO\({}_{2}\) and the metal concentration analyzed in the sediments. The ecological integrity of the macrobenthic community related to the total abundance and diversity showed to be associated with the sediment contamination of the sampling sites, though not with the pH reduction. However, previous studies showed significant changes in the structure and reductions in diversity, abundance, and biomass of the benthic communities exposed to acidification scenarios [8; 37; 38]. These results confirm the obtained results (Table 3 and Figure 4) that showed a significant (\(p<0.05\)) difference in the TRO benthic community at pH 8.0 when compared to the reference case. Therefore, the pH level probably was not correlated with these results, and the macrobenthic community could be affected by the CO\({}_{2}\) enrichment in the ocean only at highly-acidified conditions. It is known that the forms in which metals are bound in the sediments and the sediment porosity stability and grain size may influence their bioavailability and toxicity [39; 40; 41; 42; 43]. Factor one suggests that the majority of metals can increase their mobility in acidified conditions, and might cause adverse effects on marine organisms. These results were also