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Environmental gradients and host availability affecting the distribution of the symbiosis between Pteroclava krempfi (Hydrozoa, Cladocorynidae) and alcyonaceans in the Saudi Arabian central Red Sea

Davide Seveso*, Davide Maggioni, Roberto Arrigoni, Enrico Montalbetti, Michael L. Berumen, Paolo Galli, Simone Montano

*Corresponding author:

ABSTRACT: Interspecific associations are common in coral reefs, but those involving hydrozoans and octocorals are not widely investigated. The hydroid Pteroclava krempfi (Billard, 1919) lives in association with different alcyonacean taxa, showing a widespread distribution. However, very little information is available on the ecology of these relationships. Here, we tested for differences in the taxon-specific prevalence and habitat preference of the symbiosis and we determined ecological traits of the P. krempfi-host associations in central Red Sea reefs. Pteroclava krempfi was found associated with the alcyonacean genera Lobophytum, Rythisma, Sarcophyton and Sinularia, updating its host range and geographic distribution. The symbiosis prevalence was high in the area and especially in the inshore sites compared to the midshore and offshore ones. Rhytisma was the most common host, while the association with Lobophytum showed the lowest taxon-specific prevalence. Pteroclava krempfi did not show a clear preference for a specific alcyonacean size and an increase in the host size led automatically to an increase of the surface occupied by hydrozoans, although they rarely colonized more than 50% of the host upper surface. The spatial distribution of the hydroids on the host surface appeared related to the hosts’ genus and size as well as to the hydroids’ coverage. Despite the nature of this symbiosis requiring further investigations, P. krempfi did not seem to play a role in affecting the bleaching susceptibilities of the host colonies. The study shows that the Red Sea coral reef symbioses are more widespread than previously known and therefore should deserve more attention.