Abundance, diversity, and behavior of larvae collected near southern Mariana back-arc vents

In 2010 we conducted the first cruise dedicated to vent fauna at the southern Mariana back-arc spreading center. Cruise YK10-11 on R/V Yokosuka was one of several to this region as part of the Japanese multi-disciplinary TAIGA program. Here, we report on larvae collected in large-volume plankton pumps deployed near vents on- and off-axis at ~3000-m depth. Total abundances of larvae were on the order of 10 per m^3 at Snail (on-axis) and Archaean (2-km off-axis), and an order of magnitude less at Urashima (5-km off-axis). An interesting finding is in the comparison between the abundance and higher taxonomic composition of larvae in the Mariana samples vs. samples taken near East Pacific Rise (EPR) vents. Although the characteristic megafauna at the Mariana back-arc vents are "hairy gastropods" (Alviniconcha hessleri), the larvae were dominated by polychaetes. In fact, polychaete abundances in the Mariana samples at Snail vent exceeded all previous sampling at the EPR, while abundances of gastropod larvae in the Mariana samples were at or less than the 25% quartile of all previous sampling at the EPR.

Identification of larvae to species is important for relating larval supply to benthic community structure, population genetics, and metacommunity models. In the Mariana pump samples we categorized a total of 13 morphotypes of polychaete larvae and juveniles, corresponding to 15 genetic phylotypes. Although molecular genetic identification (cytochrome c oxidase subunit I) indicated that most of the polychaete larvae belonged to species not yet recorded in public databases, one larva was identified to the family Alvinellidae - to our knowledge, the first genetic confirmation of a vent-endemic polychaete larva collected in the plankton. We sorted 15 morphotypes of gastropod larvae which we assume are all different species (half so far have been confirmed by genetic identification). Additional larval types collected in lesser abundance were barnacle cyprids, bivalve larvae, and planula-like larvae.

Although collected at ~3000-m depth, many larvae were alive and active on board ship. We conducted shipboard visualization of larval swimming behavior in a vertically-oriented chamber at 1 atm in light. We analyzed swimming trajectories of 3 different morphotypes (assumed different species) of polychaete larvae. Mean speeds for net vertical displacement were approximately 0.5 mm/s upward (slightly greater downward), and these estimates may be important to consider in physical/biological models of larval dispersal between vents. Mean 3D swimming speeds, important for encounter rates with settlement cues, were approximately 1 mm/s upward (slightly greater downward). Although we must consider several caveats when interpreting these results (e.g., pressure, light, small size of chamber), the swimming speeds of the deep-sea polychaete larvae are on the lower end but well within the range of speeds reported for shallow-water polychaete larvae. We posted online a video clip showing swimming behavior of one of the polychaete larvae as well as a gastropod larva (Shinkailepas sp., hatched from an egg case) (http://ventlarvae.blogspot.com/2010/12/presentation-at-agu-fall-meeting....).

Snail and Archaean are two of the vents protected in the Volcanic Unit of the Marianas Trench Marine National Monument, and results of our local-scale study will be considered in the regional context of connectivity and ecosystem management in the Monument.

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First Name: 
Stace
Last Name: 
Beaulieu
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+1-508-289-3536
Affiliation: 
Woods Hole Oceanographic Institution
First Name: 
Susan
Last Name: 
Mills
Affiliation: 
Woods Hole Oceanographic Institution
First Name: 
Hiromi
Last Name: 
Watanabe
Affiliation: 
JAMSTEC
First Name: 
Florence
Last Name: 
Pradillon
Affiliation: 
IFREMER
First Name: 
Shigeaki
Last Name: 
Kojima
Affiliation: 
University of Tokyo
First Name: 
Lauren
Last Name: 
Mullineaux
Affiliation: 
Woods Hole Oceanographic Institution
Choose keywords that are most applicable to your abstract. (Three maximum.): 
Biogeography
Distribution and abundance
Early life history (reproduction, dispersal, settlement, recruitment)
Abstract ID: 
CBE5-141