The fan mussel Pinna rudis : occurrence and association with Pontonia pinnophylax in Terceira Island (Azores, NE Atlantic).

Conference: IMMR | International Meeting on Marine Research 2014. Peniche, Portugal, 10 Jul - 11 Jul, 2014. Presentation Type: Poster Presentation.

Pinna rudis is known as one of the biggest fan mussels in the Azores, reaching a length of up to 80cm. The specimens are generally found attached by numerous byssus threads, with their pointed anterior ends buried vertically in the substratum (mud, sandy mud or gravel). However, currently there is a notorious lack of basic knowledge about this species, with no specific studies available in the literature. The objective of the present work was to study the occurrence of Pinna rudis in the coast of Terceira Island, by analysing the spatial distribution of the individuals, and investigate the symbiotic association with the shrimp Pontonia pinnophylax. Along the south coast of Terceira Island, 23 dives in 13 sites were performed using 30 meters transects. The dives were made from August to October 2004, limited by meteorological conditions. The length of each pinnid was measured in situ, and above the sediment, to avoid unnecessary removal. During the study period, 28 P. rudis were observed with a length range from 10 to 30cm. The majority measured about 10 to 15cm. The occurrence of P. rudis was not the same at the different sites selected, occurring mainly in small patches of sand in rocky bottoms. Only solitary individuals were observed. No correlation between the length of the animals and the depth of their occurrence was detected. The shrimp Pontonia pinnophylax was found living within the largest bivalves and at deeper depths. The occupancy rate of Pinna rudis by Pontonia pinnophylax was 57% (containing one or two shrimps). It is believed that the life cycles of these two species may be linked. The exact relationship between these two species remains unclear and needs to be studied experimentally; however it is believed that this is a mutualistic association.