ECOLOGY AND REPRODUCTIVE-BIOLOGY OF THE HYDROTHERMAL VENT POLYCHAETE AMPHISAMYTHA-GALAPAGENSIS (AMPHARETIDAE)

The ampharetid polychaete Amphisamytha galapagensis Zottoli, 1983 is k nown from hydrothermal vent sites in the eastern and western Pacific, and has been reported from the Atlantic. Pacific specimens are apparen tly conspecific, but closer examination of the global species is neces sary. We examined ecological and reproductive features for an explanat ion of the wide distribution of this species, which is unusual among v ent animals (unique, if truly global in distribution). The worm, prese nt in 95% of the collections from the Juan de Fuca and Explorer Ridges in the northeast Pacific, occurs in a wide variety of vent habitats. It appears to take advantage of vestimentiferan tubes to increase subs tratum area but also colonizes active smokers, sediments and other ani mals. A. galapagensis is gonochoric, and all stages of egg and sperm d evelopment were present in populations sampled at different times of t he year, Eggs reach 240 mum in diameter and fecundity is relatively hi gh; no modifications in sperm ultrastructure were seen. From compariso n with other polychaetes, we propose that A. galapagensis undergoes co ntinuous reproduction with external fertilization resulting in demersa l, lecithotrophic larvae. The proposed reproductive mode of A. galapag ensis is not unique among vent animals, and shows no unusual adaptatio n for long range dispersal even though the adult distribution is wide. We propose that broad ecological tolerances, habitat flexibility and reduced dispersal may be more important in allowing establishment of A . galapagensis at new sites once it arrives. Further study in populati on genetics, systematics and development is important in a species tha t could provide much insight into the evolution of ecological and life history patterns at ephemeral island habitats