The 1000 m high D. Joao de Castro seamount lies in the middle of the Azores Archipelago (Portugal) on the hyperslow-spreading Terceira rift in the Atlantic. Hydrothermal vents were found near the top of the seamount and occurred in two distinct colour zonations, white and yellow, 50 metres apart from each other. The two zones are characterized by different physical and chemical properties. The macro-species composition at the shallow vents on top of the seamount was similar to the coastal and seamount area of the Azorean Archipelago. Preliminary data on the influence of the shallow water hydrothermal activity on the marine biota is presented here. This study suggests presence of protists and bacteria adapted to metal rich waters of this ecosystem. Several - algae and animals also inhabit this shallow water vent system. The heterogeneity of the vent fluids in the two contrasted areas is reflected by the differences found in the organisms collected and in accumulated metals in their tissues. Nevertheless, as differences have been also evidenced between species and the metals, more work needs to be carried out to understand the role of the different metal fractions in the environment and particularly in the food-web.

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