Posidonia bonsai: Dwarf Posidonia oceanica shoots associated to hydrothemal vent systems (Panarea Island, Italy)

Very small-sized shoots of the Mediterranean seagrass Posidonia oceanica, defined as “bonsai” shoots, were found in areas with most intense CO2 emissions and low pH associated four vents systems off Panarea island (Aeolian Archipelago, Sicily, Southern Tyrrhenian Sea). Bonsai sampled September 2021 October 2022: Bottaro crater (8 m depth), Camp 7 (16 21 m), Black Point (20 m) Hot/Cold Points (10 m). They had 2–6 leaves, adult-intermediate leaves 5–21 cm long 3.5–7 mm wide, leaf shoot surface ranging 4.8 44.5 cm2, biomass between 16 89 mg (d.w.). These values all significantly lower (t-test p < 0.006–0.0001) than those measured normal-sized collected within control sites not affected by gas emissions. 86–89% surface, 61–75% measured. The sheath thickness bonsai was very (0.1–0.8 mm), temporal trend along rhizome (lepidochronology) showed an irregular pattern, without clear cyclical seasonal variation typical shoots. reasons size reduction lack cycle lepidochronology are discussed light plant acclimatization constraints imposed continuous exposure to stressful conditions seawater acidification presence phytotoxic gases (e.g. hydrogen sulfide) vents.