Macrofaunal associates of marine sponges of the Andaman Islands (India), with a focus on Biemna fortis (Topsent, 1897) and its symbionts

Research on sponge-associated macrofauna from India is scarce. The current study provides a preliminary account of sponge associated macrofauna from the Andaman Islands with a focus on Biemna fortis (Topsent, 1897) and its symbionts. At least 24 species in six phyla were found associated with 15 host sponges species. Among them, number of individuals of the associated fauna was highest in Paratetilla bacca (29), while 12 sponges had only one associated species. These observations were, however, based on one sponge specimen each and does not reflect the actual numerical and taxonomical compositon of the associated fauna. Altogether, a total of 564 individuals representing 9 endofaunal taxa (belonging to six phyla) were found from B. fortis. The fauna most frequently associated with B. fortis are Ophiactis savigny with a mean +/- SE of 31 +/- 6.1 individuals followed by Nereis sp., Gonodactylus sp., anomuran crabs, hermit crabs (Paguroidea), juvenile stomatopods and Gastropoda (Conus sp. and polyplacophora). Brittle stars and polychaetes were common associates of B. foris irrespective of the sampling sites. Polycladida, bivalves (Pectinidae) and Sipuncula were observed occasionally within the canals. Endofaunal assemblage of Biema fortis was dominated by: Brittle stars > Polychaetes > Crabs. Oscule size of the sampled Biemna fortis ranged from 2 to 12 mm in diameter. Brittle stars were particularly abundant in sponges having oscules 5-6 mm in diameter, which highlights the importance of oscule size in limiting the potential predators that can enter the host. The high specificity of juvenile brittle stars and their mortality without sponge habitats suggests an obligate relationship, while other associated polychaetes and crustaceans could be facultative sponge commensals. Interactions between host sponges and their symbionts await further experimental demonstration for understanding their ecology. sont toutefois basees sur un seul specimen par espece et ne refletent pas necessairement la composition taxonomique et numerique de la faune associee. Un total de 564 individus representant 9 taxons d'endofaune (appartenant a 6 phylums) ont ete trouves associes a B. fortis. Les especes les plus abondantes etaient Ophiactis savigny avec une moyenne +/- SE de 31 +/- 6,1 individus, suivie de Nereis sp., Gonodactylus sp., des crabes anomoures, des pagurides, des stomatopodes juveniles et des Gasteropodes (Conus sp.) et des polyplacophores. Les ophiures et les polychetes etaient communes independamment du site de recolte. Polycladida, bivalves (pectinides) et siponcles ont ete occasionnellement observes dans les canaux. L'assemblage chez B. fortis etait domine par les ophiures > les polychetes > les crabes. La taille de l'oscule de B. fortis variait de 2 a 12 mm de diametre. Les ophiures etaient particulierement abondantes dans les eponges ayant des oscules de 5-6 mm de diametre, ce qui souligne l'importance de la taille des oscules dans la limitation des predateurs potentiels pouvant penetrer dans l'hote. La forte specificite de cette presence et la fortre mortalite des juveniles horsde l'habitat-eponge suggere une relation obligatoire, alors que des polychetes et des crustaces associes sont des commensaux facultatifs. Les interactions entre l'eponge hote et leur symbiontes necessitent de futures experimentations pour comprendre leur ecologie.