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

The ampharetid polychaete Amphisamytha galapagensis Zottoli, 1983 is known from hydrothermal vent sites in the eastern and western Pacific, and has been reported from the Atlantic. Pacific specimens are apparently conspecific, but closer examination of the global species is necessary. We examined ecological and reproductive features for an explanation of the wide distribution of this species, which is unusual among vent animals (unique, if truly global in distribution). The worm, present 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 substratum area but also colonizes active smokers, sediments and other animals. A. galapagensis is gonochoric, and all stages of egg and sperm development were present in populations sampled at different times of the year, Eggs reach 240 mum in diameter and fecundity is relatively high; no modifications in sperm ultrastructure were seen. From comparison with other polychaetes, we propose that A. galapagensis undergoes continuous reproduction with external fertilization resulting in demersal, lecithotrophic larvae. The proposed reproductive mode of A. galapagensis is not unique among vent animals, and shows no unusual adaptation 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 population genetics, systematics and development is important in a species that could provide much insight into the evolution of ecological and life history patterns at ephemeral island habitats