Reproductive traits of pioneer gastropod species colonizing deep- sea hydrothermal vents after an eruption

The colonization dynamics and life histories of pioneer species are vital components in understanding the early succession of nascent hydrothermal vents. The reproductive ecology of pioneer species at deep-sea hydrothermal vents may provide insight into their dispersal, population connectivity, and ability to colonize after disturbance. An opportunity to study the reproductive traits of two pioneer gastropod species, Ctenopelta porfera and Lepetodrilus tevnianus, presented itself in 2006 after an eruption on the East Pacific Rise (EPR) eliminated vent communities near 9*50'N. Standard histological techniques were used to determine whether reproductive characteristics, such as timing of gamete release, fecundity, or time to maturation, differed from other vent gastropods in ways that might explain arrival of these two species as early colonizers. Both species exhibited two-component oocyte size frequency distributions that indicated they were quasi-continuous reproducers with high fecundity. In C. porifera, the oocyte size distributions differed slightly between two collection dates, suggesting that environmental cues may introduce some variability in gamete release. In samples collected within one year of the estimated eruption date, individuals in populations of both C. porfera and L. tevnianus were reproductively mature. The smallest reproducing C. porifera were 4.2 mm (males) and 5.4 mm (females) in shell length, whereas reproductive L. tevnianus were smaller (2.3 and 2.4 mm in males and females respectively). Most Cporifera in the population were large (> 6.0 mm) compared to their settlement size and reproductively mature. In contrast, most L tevnianus were small (< 1.0 mm) and immature. Reproductive traits of the two species are consistent with opportunistic colonization, but are also similar to those of other Lepetodrilus species and peltospirids at vents, and do not explain why these particular two species were the dominant pioneers. It is likely that their larvae were in high supply immediately after the eruption due to oceanographic transport processes from remote source populations. Thesis Supervisor: Lauren Mullineaux Title: Senior Scientist of Biological Oceanography