White Paper Title: 
Larval transport along the East Pacific Rise

Larval dispersal is an essential component to determining both the biogeography and adaptive capabilities of hydrothermal vent invertebrates. R2K-related projects studying larval dispersal along the 9N segment of the East Pacific Rise (EPR) have combined modeling and physical and biological observations to investigate mechanisms of larval transport and estimate population connectivity.  Observations occurred both before and after the 2006 eruption, providing a unique opportunity to determine the role of larval supply in controlling the successional sequence at vents.  Pre-eruption, established vents received the bulk of their larvae locally, within a few kilometers (Adams and Mullineaux 2008). 

The 2006 eruption eradicated local larval sources providing a natural clearance experiment which confirmed that the larval supply was predominantly local at established vents (Mullineaux et al 2010).  It also revealed that distant propagules can establish dominance after the removal of the established communities.  Thus, there is a temporal variation in population connectivity or ‘openness’ – with established vents being closed and nascent and disturbed vents being open.  The variation in population connectivity is adaptive to the unique characteristics of hydrothermal vents – specifically here the isolated and ephemeral nature.  Retention of propagules prevents excessive wastage of reproductive energy and allows for rapid establishment of abundant populations.  Change to predominantly open populations once disturbed allows for rapid initial establishment and/or replenishment of populations.  Larval dispersal, and reproductive strategies (Bayer et al 2010, Tyler et al 2009), could be part of a new synthesis of macrofaunal and megafaunal adaptations to the hydrothermal vent environment.

The post-eruption data sets could also allow us to begin to address, through integration with chemical data sets, “What controls the species composition and succession at hydrothermal vents?” - abiotic vs biotic controls; more specifically - environment (and physiological tolerances) vs. larval supply.

Due to the large number of microbiologists in this group and the recent progress in investigating microbial succession, a comparison of the factors driving microbial succession to macrofaunal succession could reveal general rules of succession at vents.

Oceanographic events also can episodically change the proportion of local vs distant propagules.  Mesoscale eddies were observed to transport larvae away from local vents (Adams et al in prep).  Multiple modeling methods suggest that these eddies could transport the larvae hundreds of kilometers between vent fields along the EPR (Adams and Flierl 2010, Adams et al in prep).  This mechanism for larval transport could also significantly contribute to the exchange of heat, chemicals, and other organic material between the hydrothermal vents and the larger ocean.  Consideration of transport to the larger ocean could enhance models of lithosphere – ocean exchange.

The new empirical estimates of larval transport provide testable hypotheses about population connectivity along the EPR.  Previous empirical estimates where seemingly at odds with genetic estimates of population connectivity. The new estimates reconcile this apparent contradiction by observing temporal variation in connectivity.  New population genetic techniques and analyses have the potential to provide an indirect and independent estimate of connectivity.