White Paper Title: 
Larval abundance and dispersal at deep-sea hydrothermal vents in the southern Mariana Trough: comparison to Ridge 2000 EPR ISS

Stace E. Beaulieu1, Lauren Mullineaux1, Susan Mills1, Hiromi Watanabe2, Florence Pradillon2, Shigeaki Kojima3

1Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
2 Marine Biodiversity Research Program, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka 237-0061, Japan
3Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan

Despite three decades of research on deep-sea hydrothermal vents, the processes that govern larval dispersal, settlement, and recruitment to these discrete and sometimes ephemeral habitats remain poorly understood, even at well-studied sites. To understand larval dispersal to/from vents, we are presented with many challenges which include:
- difficulties in quantitative sampling of the plankton,
- lack of physical oceanographic measurements, and
- little to no information on larval behavior.
All of these challenges are compounded by the difficulties in sampling over long-enough time scales and fine-enough temporal resolution to understand a process that has temporal variability caused by the physical environment and by reproductive biology (also not well-studied for vent-endemic fauna).

Larval dispersal drives population connectivity on short (i.e., generational) time scales and ultimately the biogeography and evolution of species on very long time scales. We have studied larval dispersal at the Ridge 2000 East Pacific Rise (EPR) Integrated Studies Site (e.g., Mullineaux et al. 2005, Mullineaux et al. 2010), including the recent LADDER project ( which incorporated physical oceanography, regional circulation modeling, and particle-tracking models (e.g., McGillicuddy et al. 2010).

In September 2010 we will collect larvae in a different biogeographic province on the other side of the Pacific, in the southern Mariana Trough (for more information on biogeographic provinces, please see Van Dover et al. 2002 and Bachraty et al. 2009). We will deploy large-volume plankton pumps at approximately 3000-m depth at Snail (also called South Backarc), Archaean, and Pika, three of the Vents (Volcanic) Unit sites in the U.S. Marianas Trench Marine National Monument. These vents near the back-arc spreading center are being studied as part of the Japanese multi-disciplinary program TAIGA (Trans-crustal Advection and In-situ biogeochemical proceses of Global sub-sea floor Aquifer). We will deploy a current meter near the Snail site (on-axis) for preliminary estimates of passive larval transport on the time scale of the cruise. We also plan to conduct experiments at 1 atm and in pressure chambers to estimate swimming and/or sinking velocities of vent larvae, important for adding behavioral information to models of larval dispersal.

We will compare the larval abundances, diversity, and preliminary estimates of dispersal between the back-arc (Mariana Trough) and the mid-ocean ridge (EPR) vents to address the question posed in the Ridge 2000 Science Plan: “Q5. What are the forces and linkages that determine the structure and extent of the hydrothermal biosphere?” Although our studies are only at small spatial scales (over several km, on single ridge segments), and the comparison between EPR and the Mariana back-arc vents can only be made at the short time scale of a single research cruise, we hope that by conducting such studies at different sites in different tectonic settings, that a more general understanding of larval dispersal between vents can be developed.

Bachraty C, Legendre P, Desbruyères D (2009) Biogeographic relationships among deep-sea hydrothermal vent faunas at global scale. Deep Sea Research I 56: 1371–1378.

McGillicuddy, D.J., Lavelle, J.W., Thurnherr, A.M., Kosnyrev, V.K. and L.S. Mullineaux, 2010. Larval dispersion along an axially symmetric mid-ocean ridge. Deep-Sea Research, I, 57, 880–892.

Mullineaux, L.S. et al. (2005) Vertical, lateral and temporal structure in larval distributions at hydrothermal vents. MEPS 293: 1-16.

Mullineaux, L.S., Adams, D.K., Mills, S.W., and Beaulieu, S.E. (2010) Larvae from afar colonize deep-sea hydrothermal vents after a catastrophic eruption. PNAS 107(17): 7829-7834, doi: 10.1073/pnas.0913187107.

Van Dover, C.L. et al. (2002) Evolution and Biogeography of Deep-Sea Vent and Seep Invertebrates. Science 295: 1253-1257.