Borer isopods (Limnoriidae) in Posidonia oceanica beds off Ustica and Panarea islands

Abstract

Occurrence of isopods borers’ of Posidonia oceanica sheaths is here reported in a survey on various Posidonia beds off the islands of Ustica (August 2021) and Panarea (September 2022). In Panarea the Posidonia beds investigated thrive under ocean acidification (OA) conditions (pH generally >7.9) due to intense CO₂ venting in three hydrothermal systems (Bottaro crater, Camp 21 and Black Point) from 8 to 23 m depth,  while at Ustica Posidonia beds occurred under normal pH conditions and were sampled from 6 to 32 m depth. All beds were settled on rocky substrates. Borer isopods, represented by Limnoria mazzellae, were observed in shoots from all sites and depths (a total of 504 specimens in 335 shoots examined). The Index of Colonization (IC= traces or animals present over the total shoot examined) was very high, ranging between 80% and 100%, and represents the highest frequency index recorded along the Italian coast.