MEPS 414:131-144 (2010)  -  DOI: https://doi.org/10.3354/meps08717

ABSTRACT: The size structure of a population of the mussel ‘Bathymodiolus’ childressi shifts dramatically across the mussel bed encircling the Brine Pool NR 1 cold seep in the Gulf of Mexico. While the fringes of the bed are inhabited by large mussels, small juveniles are abundant only at the edge of the pool, leading to the inference that larvae settle preferentially near the source of methane. We used in situ experiments to test whether this shift in size distribution is structured by differences in larval supply, settlement, substratum selection by settling larvae, juvenile mortality, growth, or predation across the mussel bed. We investigated the variation of these factors adjacent to the pool, at the fringes of the mussel bed, and also 2 m away from the bed. Neither the supply of larvae nor the density of settlers (<0.5 mm long) collected on settlement plates differed among the 3 zones. Juveniles (mean length: 9 mm) survived and grew equally well in all 3 zones. Survival was higher in caged than in uncaged juveniles (5 to 15 mm long), but mortality of uncaged juveniles was similar at all distances from the pool, suggesting that predation alone does not cause the observed differences in size structure. We reject the prevailing hypothesis that the distribution pattern can be attributed to settlement preferences of larvae alone. We hypothesize that very early post-settlement mortality, secondary settlement, and/or later migration of juveniles play a role in establishing and maintaining the persistent pattern of size structure across this mussel bed.

KEY WORDS: Bathymodiolus childressi · Chemosynthetic communities · Deep sea · Mussel · Predation · Larval supply · Recruitment