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The aim of a series of works recently performed at ISMAR was to provide new useful information for a better understanding of the mechanisms by which bacteria settlement causes corrosion on Stainless Steels (SS) and similar active-passive alloys exposed to seawater. In this work, the evolutions of cathodic current, bacteria population, and electronic structure of the passive layer were investigated on SS samples polarised at fixed potentials during their exposure to natural seawater. It was found that, during the first phase of biofilm growth, cathodic current increase is proportional to the number of settled bacteria at each fixed potential. However, the proportionality factor between settled bacteria and cathodic current depends on imposed potential. In particular, the proportionality factor strongly decreases when the potential is increased above a critical value close to −150 mV Ag/AgCl. This effect seems to be correlated with the electronic structure of the passive layer. Indeed, the outer part of the passive layer on tested SS was found to behave like a conductor at potentials more active than −150 mV Ag/AgCl, and like an n-type semiconductor at more noble potentials.

In this study, we screened eight terpenes isolated from the organic extract of Sphaerococcus coronopifolius for their antifouling activity in order to find possible new sources of non-toxic or less toxic bioactive antifoulants. The anti-settlement activity (EC 50 ) and the degree of toxicity (LC 50 ) of S. coronopifolius metabolites was evaluated using larvae of the cirriped crustacean Amphibalanus (Balanus) amphitrite (cyprids and nauplii) as model organism. For five of eight tested metabolites EC 50 was lower than 5 mg/L. The most promising results were observed for bromosphaerol (3), which expressed an EC 50 value of 0.23 mg/L, in combination with low toxicity levels (LC 50 >100 mg/L). The therapeutic ratio-an index used to estimate whether settlement inhibition is due to toxicity or other mechanismsis also calculated and discussed.

Ostreopsis cf. ovata is a harmful benthic dinoflagellate, widespread along most of Mediterranean coasts. It produces several toxins and variable amount of mucus that may totally cover substrates, especially during the stationary phase of blooms, in which cells are aggregated. Studies on different aspects of the biology and ecology of Ostreopsis spp. are increasing, yet knowledge on toxicity mechanism are still scarce. In particular, the potential active role of the mucilaginous matrix has not yet been proved, although when mass mortalities have occurred, organisms were reported to be covered by the typical brownish mucilage. In order to better elucidate toxicity dependence of direct/indirect contact with O. cf. ovata cells, we carried out toxicity bioassays exposing Artemia salina nauplii and ephyrae of Aurelia aurita, as a innovative model organism in ecotoxicology, to several treatments of O. cf. ovata culture. Simultaneously, molecular and chemical analysis were performed to validate our methods and characterize the toxic profile. Our results have reported higher effects when a direct contact between model organisms and intact microalgal cells occurs (LC 50-48h < 4 cells/ml on A. salina, EC 50-48h = 9 cells/ml on A. aurita), anyway also growth medium devoid of microalgal cells but containing O. cf. ovata mucilage caused significant toxic effects. Moreover, the connection between the thecal plates, pores, trychocysts and the mucilaginous matrix was explored by way of atomic force microscopy (AFM) to investigate cell surface at a sub-nanometer resolution, providing a pioneering description of the inner side of O. cf. ovata thecal plates.

The main aim for this document is to report after the Biofouling Monitoring Program (BMP) aiming at identifying major organisms responsible for biofouling in different geographical areas, as an input to the development and application of a more suitable approach to any specific region. This report is strongly linked to the JERICO deliverable D4.3 “Report on Biofouling Prevention Methods”, available at http://www.jerico-fp7.eu/deliverables/d4-3-report-on-biofouling-prevention-methods.