Spatio-temporal patterns in coastal zoobenthos under environmental stress

The main aim of this doctoral research was to investigate the structural and functional variations of coastal marine macrofaunal communities subjected to diversified types of impact, from natural phenomena to anthropogenic pressures. The benthic community was analysed along a temporal scale at a relatively undisturbed station located in the buffer zone of the Miramare-MPA (Gulf of Trieste). The aim of the study was to assess the temporal variability of the community structure (biodiversity, feeding- and reproductive traits) related to food sources and environmental variations. The community displayed an intermediate level of stability. The capability of the community to maintain its structure (number of individuals, species diversity and feeding strategies), despite the physical disturbance events, illustrates the resistance to natural stress exhibited by these invertebrates. The coastal area nearby the Po River delta is characterized by a high amount of organic matter loads. The aim of the study was to analyse the proportions of various primary producers contributing to the plume of suspended organic matter and the extent to which subsidies from rivers may influence the macrobenthic community structure and biomass. Changes in the trophic composition and variation in food sources determined from the isotopic signal along the river gradient were observed. Further, the study highlighted a close link between grain-size and macrofaunal structure and trophic pathways in a variable and highly hydrodynamic system such as this deltaic area. The Port of Trieste represents an area with a diffuse sediment contamination The aim of this study was to detect variation in the structure of the macrofaunal community, such as number of individuals, biodiversity and trophic functional groups, as a response to anthropogenic impacts. Species that are more tolerant to stress were observed in high numbers in vicinity of contaminated sites highlighting a clear separation among stations along the studied gradients. Overall, the environmental contamination within the harbour seems not too severe to affect the macrofaunal feeding structure. As an example of an area severely contaminated by heavy metals and synthetic organic compounds, the Mar Piccolo of Taranto was chosen. The macrofaunal community was investigated and a marked influence of contamination on the abundance and biodiversity was observed. The presence of stress-resistant species and highly reduced abundance of some sensitive organisms were registered, indicating poor conditions for the benthic ecological status of this area. To assess the influence of contamination on trophic pathways, stable isotope analysis was conducted on macrofaunal communities. These results showed that chemical contamination affected the trophic structure in the absence of intermediate consumers that link basal organic matter sources to higher predators. The functional features of polychaetes associated with levels of contaminated sediments were analysed and compared in the harbour of Trieste and in the Mar Piccolo of Taranto, using biological trait analysis. Functional identity illustrated the relationships and adaptation to contaminated sediments. In fact, high motility of the species seems to be an essential trait for living in highly contaminated sediments. This could be linked to the ability to avoid hotspots of contaminants through active movements, thus, influencing sediment reworking and especially the diffusion of contaminants towards the water column. These findings confirmed that soft-sediment macrofaunal communities responded differently to natural and, more subtly, to anthropogenic stress in the different environments. Integrative approaches provide useful tools for understanding, monitoring and assessing the ecosystem functioning in coastal environments subjected to multiple stressors.