Seasonality and zonation in the reproductive biology and population structure of the shrimp Alvinocaris stactophila (Caridea: Alvinocarididae) at a Louisiana Slope cold seep

Abstract

Ecological patterns in deep-sea chemosynthetic environments are often considered to be independent of variations in photosynthetic primary production. This study examines spatial and temporal variation in the population structure and reproductive development of the caridean shrimp Alvinocaris stactophila at the Brine Pool cold seep on the Louisiana Slope. To assess spatial variation, samples were collected by submersible from different locations at the Brine Pool mussel bed in November 2003. The proportion of males in samples declined from the outer to the inner zone of the mussel bed, while the proportion of female shrimp carrying eggs increased. This zonation may result from congregation of large ovigerous females towards the inner zone, where sulphide flux from underlying sediments may be absent or reduced. To examine temporal variation in reproductive development, oocyte size-frequency distributions were compared between August 1997, March 2002, February 2003, November 2003 and July 2004. All oocytes in early spring samples were small and previtellogenic, while summer samples contained larger vitellogenic oocytes. The largest oocytes were found in large non-ovigerous females from the autumn, while ovigerous females from the same season contained the smallest oocytes in this study. Embryos in the autumn exhibited no differentiation, in contrast to well-developed embryos from early spring that hatched into zoea larvae. These features indicate seasonal and iteroparous reproduction in A. stactophila, with females carrying embryos from autumn to early spring and releasing planktotrophic larvae to exploit a seasonal peak in surface productivity and its export.