HR: 09:30h
AN: OS31A-07    [PDF]
TI: Use of Vesicomyid Clams as Proxies for Ageing Submarine Landslide Events
AU: * Barry, J P
EM: barry@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AU: Whaling, P J
EM: whpa@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AB: Age dating of submarine landslides and other geologic events that produce tsunamis is desirable, but difficult. Estimation of the time of failure" for submarine slides may be possible using proxies for age, including estimates of the time of colonization of animals on landslide scars or associated features. For submarine landslides in methane-rich strata, chemosynthetic biological communities (CBCs) will likely colonize the site, and establish a `baseline' for estimating the age of the slumping event. Vesicomyid clams are conspicuous members of methane seep environments (CBCs) worldwide, and are the dominant megafauna inhabiting eastern Pacific seep communities. Although several geological settings, including subduction zones, mud volcanoes, submarine landslide scars, and submarine canyon settings are associated with the presence of CBCs, the principal geological processes that regulate their distribution remain unresolved. Nevertheless, vesicomyid clams commonly colonize sites of recent erosion or slope failure events on continental margins, where access to sulfide-rich fluids is possible. CBCs in Monterey Bay include a fairly high diversity of vesicomyid clams (10+ species), which are somewhat segregated by geochemical conditions, water depth, and perhaps other factors. Seep sites with highest sulfide ($>$10.0 mM) and methane ($>$2.0 mM) concentrations in pore waters are dominated by {\it Calyptogena kilmeri}, while {\it C. pacifica} is the principal species at sites with low sulfide ($\sim$0.1 mM) and methane ($\sim$0.0 mM) levels. Time-lapse observations suggest that variation in sulfide levels may stimulate clam movement. These two species cohabit individual seeps but exhibit very different sulfide physiologies and growth rates. {\it C. kilmeri} is well-adapted to higher sulfide tolerance, which may enable high rates of production by bacterial symbionts, high carbon intake, and high rates of growth compared to {\it C. pacifica}. Growth rates of {\it C. kilmeri}, calculated from tagged individuals, was $\sim$10 mm/y, with individuals reaching an maximum size of $\sim$120 mm in approximately 10 y. In contrast, although the sulfide physiology of {\it C. pacifica} is more efficient in some ways than {\it C. kilmeri}, it is restricted to low sulfide microhabitats ($<$1.5 mM), and exhibits very low rates of growth. All {\it C. pacifica} tagged grew less than 1 mm/y, indicating a period of 50-75 y, or more, to attain asymptotic size near 65 mm. The density and size structure of populations of {\it C. kilmeri} and {\it C. pacifica}, as well as other CBC organisms may be useful in constraining the timing of slumping events associated with tsunamis. While knowledge of the growth rates and size versus age relationships of vesicomyid species enhance their value in aging submarine slope failure events, the observed wide differences in growth rates among species also complicates interpretation of the colonization history following landslide events.
UR: http://www.mbari.org/benthic/coldseeps.htm
DE: 1815 Erosion and sedimentation
DE: 4211 Benthic boundary layers
DE: 4512 Currents
DE: 4558 Sediment transport
DE: 8102 Continental contractional orogenic belts
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting