Hydrobiologia 503: 9–19, 2003. M.B. Jones, A. Ing´ olfsson, E. ´ Olafsson, G.V. Helgason, K. Gunnarsson & J. Svavarsson (eds), Migrations and Dispersal of Marine Organisms. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. 9 Dispersal at hydrothermal vents: a summary of recent progress Paul A. Tyler 1 & Craig M. Young 2 1 School of Ocean and Earth Science, University of Southampton SOC, Southampton SO14 3ZH, U.K. 2 Oregon Institute of Marine Biology, University of Oregon, P.O. Box 5389, Charleston, OR 97420, U.S.A. E-mail: pat8@soc.soton.ac.uk Key words: dispersal, larvae, seeps, vents, Vestimentifera Abstract The discovery of hydrothermal vents along the Galapagos Rift in 1977 opened up one of the most dynamic and productive research themes in marine biology. In the intervening 25 years, hydrothermal vent faunas have been described from the eastern, northeastern and western Pacific, the mid-Atlantic Ridge and the Indian Ocean in the region of the Rodriguez Triple Junction. In addition, there is evidence of hydrothermal signals from the Gakkel Ridge in the Arctic, the central and southwest Indian Ridges and the Scotia Arc in Antarctica. Although often per- ceived as a continuous linear structure, there are many discontinuities that have given rise to separate biogeographic provinces. In addition, the intervening 25 years have seen a massive increase in our understanding of the biological processes at hydrothermal vents. However, how vents are maintained, and how new vents are colonised has been relatively poorly understood until recently. This review addresses the known larval development of vent-endemic invertebrates. The distribution of larvae in relation to the hydrothermal plume, and the ocean ridge in general, are discussed and the experimental evidence of larval longevity and transport are discussed using such variables as gene flow and larval development rates. The concept of larval dispersal along the mid-ocean ridge is discussed in relation to dispersal barriers and relates the known biogeography of hydrothermal vent systems to both local and evolutionary processes. Introduction The discovery of hydrothermal vents along the Galapagos Ridge in 1977 forced marine biologists to reassess the energy available for primary production in marine ecosystems. Up to that time, with a few minor exceptions, all energy for primary production was believed to derive ultimately from the sun in the form of photosynthetic primary production. With the discovery of hydrothermal vents, and subsequently cold seeps, a new energy source was discovered that originated beneath the seabed. In the case of hy- drothermal vents, this energy source was hydrogen sulphide used by chemolithoautotrophic bacteria for primary production, the products of which could be transferred to supply the nutritional requirements of the host organism. The discovery of cold seeps further demonstrated that chemical energy could be used for significant primary production, in this case, being in the form of methane and hydrogen sulphide. At vents, hydrogen sulphide was available as a product of sea- water passing through the fractured basalt of the mid ocean ridge, being heated, reacting chemically with the surrounding rock and all the sulphate being re- duced inorganically to hydrogen sulphide (Van Dover, 2000). At seeps, hydrogen sulphide is made available by the bacterial reduction of sulphate using methane and the release of carbon dioxide and hydrogen sulph- ide (Sibuet & Olu, 1998). Hydrogen sulphide is also made available by the biological degradation of or- ganic matter. Thus at seeps (and some vents) it is not uncommon for the hosts of thiotrophs and methano- trophs to live side by side, and, in some cases, bacteria capable of methanotrophy and thiotrophy can be found in the same host. In addition, seeps may be fuelled by particulate organic matter from pelagic production or by allochthonous organic matter carried into the sea by large rivers.