What lies within; Annelid polychaetes found in micro-habitats of coral/carbonate material from SW Indian Ocean seamounts

Abstract Individual corals, coral framework and rubble are generally quite abundant on seamounts, with carbonate materials derived from an unknown source also being found. These micro-habitats are known to often harbour higher abundance of smaller sized fauna and thus potentially increases the biodiversity of that region. However, very few studies have examined what may reside within the coral and carbonate structures themselves, if anything at all. Samples that were collected on five seamounts during a research cruise to the South West Indian Ocean Ridge in 2011, were examined opportunistically in order to determine if there were any animals to be found inside the hard coral framework/rubble material. The hard material was dissolved away using 10% acetic acid and was examined on a twice daily basis to remove any animals that had been released through the dissolution process. There were a surprising number of phyla found inside the micro-habitats created by the coral rubble/framework material including sponges, brachiopods and a number of different polychaete families. As the polychaetes were more numerous, they were investigated more closely and a total of 34 different families were identified, with the Syllidae being found in every sample examined. The methodology presented here highlights that a “controlled” weak acid dissolution can be used to release the fauna from deep inside the coral rubble/framework material. Frequent removal (twice daily or more often) of liberated material meant that the fauna released were exposed to the acid for a minimum amount of time resulting in specimens in better condition and with more identifiable features. The preliminary results also illustrate the importance of sampling the dead coral framework/rubble/carbonate material, not only to identify them for what they are, but to look more closely at the fauna residing inside the structure themselves.