Energy acquisition and allocation In vesicomyid clam
Shana K.Goffredi, Ph.D.
Monterey Bay Aquarium Research Institute
Wednesday, May 30, 2001
3:00 p.m.—Pacific Forum
Symbioses involving sulfide-oxidizing bacteria and various metazoan
phyla dominate megafaunal assemblages at cold seeps and hydrothermal vents
worldwide. Vesicomyid clams are often the dominant chemosynthetic
megafauna of seep and vent environments and, due to their size and
abundance, are integral components of these deep-sea benthic communities.
Although much progress has been made toward understanding basic biological
processes enabling species to inhabit the deep sea, many aspects of the
physiological ecology, diversity, and community dynamics of these
organisms remain poorly understood.
The predominant species found living at cold seeps in Monterey Bay are
the vesicomyid clams Calyptogena kilmeri and C. pacifica.
The growth and survival of these clams depend directly upon the
productivity of their chemoautotrophic endosymbionts, which is fueled by
the oxidation of sulfide. For this reason, sulfide (energy) availability
and sulfide physiology are thought to constrain symbiont and host
production. Here we describe research concerning the productivity of two
common clam species in relation to sulfide-related environmental and
physiological parameters. Both of these species inhabit sulfide-rich
sediments and depend nutritionally on their symbionts, however, many
aspects of their life styles differ considerably. Results indicate that C.
pacifica is physiologically poised for the uptake and transport of
sulfide, as measured by increased sulfide consumption rates, sulfide
binding ability, and internal sulfide levels, as well as symbiont energy
turnover, as measured by sulfide oxidation potential, sulfur metabolism
enzymes, and bacterial densities.
Growth rates of C. pacifica, however, are considerably slower
than C. kilmeri (3% vs. 15% per year). This is surprising given
that C. pacifica possesses a seemingly greater potential to process
sulfide. This contradicts the idea that sulfide limits productivity in
these two systems and, for this reason, we believe them to be constrained
by factors other than sulfide. This research represents the first
comparative investigation of the physiological functioning of
closely-related species in chemosynthetic symbioses and elucidates the
constraints and advantages posed by different modes of sulfide (energy)
uptake and assimilation in these, and other, symbiotic organisms.
Next: Rocketship siphonophores in Monterey
Bay: Vertical abundance and distribution patterns, and dietary demand