The volcanic origin of the Azores archipelago (Portugal) gives rise to active deep sea and shallow water hydrothermal activity that affects benthic communities. Intertidal seaweed surveys were conducted at two shores affected by intense shallow water hydrothermal vents. Water temperature, acidity and salinity were monitored. Seaweed communities were found to be species poor and have a disproportionally larger number of filamentous early successional species on shores that are subject to the effect of hot and acidic freshwater of volcanic origin. There is an ecological resemblance between hydrothermally affected seaweed communities in the Azores and those affected by acid mine drainage in the UK, thus indicating that hydrothermalism can be a useful scenario for pollution studies under conditions of ocean warming and acidification.

Shallow water hydrothermal vents can be compared to polluted places due to high concentrations of heavy metals, and are thus good models for bioaccumulation studies. The present study intended to estimate the time of exposure required for the accumulation of certain elements to stabilize in specimens of Cystoseira abies-marina, to be used as a reference in future work. Cystoseira abies-marina intertidal specimens were transplanted from Mosteiros (a nonhydrothermal and pristine site) to Ferraria (with hydrothermal activity) and left there. Transplanted samples were collected after 1, 2, 4 and 8 weeks and the concentrations of Cd, Mg, Mn and Zn were measured through flame atomic absorption spectrophotometry. Although further studies with increased periods of exposure are needed because the concentration of these elements never stabilized in the collected samples, there is strong evidence that increased time of exposure led to increased concentrations of Cd, Mg, Mn, but not Zn. These results are consistent with the assumption that C. abies-marina is bioaccumulating some of the heavy metals and can thus be a good indicator for polluted waters.