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THE EFFECT OF SHALLOW MARINE HYDROTHERMAL VENT ACTIVITY ON BENTHIC FORAMINIFERA (AEOLIAN ARC, TYRRHENIAN SEA)

Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67, 40126 Bologna, Italy

^* E-mail: panieri{at}geomin.unibo.it

An exceptional intensification of hydrothermal degassing activity occurred on November 3, 2002, to the east of Panarea, the smallest island of the Aeolian Archipelago (Tyrrhenian Sea, Italy). This event represents a unique opportunity to study benthic foraminiferal assemblages under the ecological stress of hydrothermal emissions in shallow (10–15 m water depth) environments. Benthic foraminifera (>63 µm) were collected by a scuba diver from sediments and seagrass of a Posidonia oceanica meadow off the coast of Panarea. Assemblages were studied to assess mortality and monitor the composition of benthic communities following the sudden venting event, characterized by an intensification of the emission of gases with high temperatures (40–50°C), low pH (~5), and high concentrations of HCl, HF, SO₂ and some H₂S. Surface foraminiferal assemblages were monitored during surveys on November 13–14, 2002, and May 22–24, 2003. In November 2002 (10 days after the venting event) agglutinated forms dominated the assemblages in sediment samples, whereas hyaline forms dominated the assemblages collected from the leaves and roots of P. oceanica. Six months later, in May 2003, when environmental conditions had returned to normal, sediment samples were barren of foraminifera, whereas the assemblages associated with P. oceanica were composed of allogromiids, which can be considered opportunistic pioneer species able to colonize disturbed environments.