Benthic ecosystem functioning

The main aim of this doctoral research project was to assess the benthic ecosystem functioning in areas subjected to multiple and diffuse impacts. The Aeolian Islands, originated by the volcanic activity and characterised by continuous gas emissions and presence of thermal vents on the surrounding seabed, represent a good natural laboratory for global warming and carbon capture and storage (CCS) leakage studies. The aim of this work was to investigate to what extend the high CO2 alone and in combination with the high temperature affects the microphytobenthic abundance and its community composition (Chapter 1). A further objective was to detect a possible change in the primary production rate in relation with these two variables. Higher microphytobenthic densities were recorded at the vent stations and values were even more pronounced in relation with high temperature. On the other hand, high microphytobenthic abundances were coupled with low community richness and diversity. The gross primary production estimates were strongly coupled with the microphytobentic abundance values. We observed several diatoms with morphological deformities, The Port of Trieste represents an area with a diffuse sediment contamination as it is subjected to diverse impacts: the shipbuilding activities, the iron and steel plant, the petroleum industry and the port activities. The aim of this study (Chapter 2) was to detect any variation in the structure of the microbenthic community, both as active phototrophic and resting microbenthos, and the possible differences in the primary production and respiration at stations subjected to different anthropogenic impacts. The total microbenthic abundance did not vary among stations. On the other hand, the structure of the community gave more information. In particular, the analysis based on the active and resting microbenthic community structure highlighted a clear separation among stations close to the productive activities from the more distant ones and the reference station, indicating a contamination effect on those communities. As an example of an area severely contaminated by heavy metals and synthetic organic compounds, the Mar Piccolo of Taranto was chosen. Firstly, the microphyto- and macrozoobenthic communities were investigated and a marked influence of contamination on the abundance and biodiversity of those two communities was detected (Chapter 3). To further asses the overall trophic status of the benthic ecosystem, an integrated study of the active phototrophic and resting microbenthic stages, combined with the main photoautotrophic pathways, was conducted (Chapter 4). Furthermore, although the Mar Piccolo is very shallow, the benthic system was scarcely productive, likely as a consequence of the accumulated contaminants in the surface sediments that probably interfere with the proper functioning of the benthic ecosystem. Contrary to the benthic ecosystem, the pelagic one was very productive and a clear seasonal succession of different sized plankton phototrophs was observed (Chapter 5). To have a better overall view and provide some insights into the benthic-pelagic coupling, the primary production and heterotrophic prokaryotic production in the water column were integrated with those in the sediments and related to the origin of the organic matter pools based on the analysis of stable isotopes (Chapter 6).