OCS Study MMS 95 - Data Center

course of the Study, satellite and airborne remote sensing were successfullyemployed as means for detecting seepage on a regional basis (MacDonald et al .1993, in press) . A newly developed optical sensor, the laser line scan system, wasalso evaluated in a demonstration deployment .Brief description of these resultswill be presented .Subsequent chapters in this report will describe geological, geochemical, andecological effects of hydrocarbon seepage based on detailed observations andcollections at representative seep sites made during this Study .This section willplace these sites in their regional context by documenting the geographic range,frequency and possible magnitude of seepage .22 7~rpes of Seep CommunitiesFour general community types were described by MacDonald et al . (1990b) .Respectively, these were communities dominated by vestimentiferan tube worms(Lamellibrachia c .f.barhami and Escarpia n.sp .), mytilids (Seep Mytilid Ia, Ib, andIII), epibenthic vesicomyid clams (Vesicomya cordacta and Calyptogena ponderosa),or infaunal lucinid or thyasirid clams (Lucinoma sp . and Thyasircz sp .) . Thesefaunal groups display distinctive characteristics in terms of how they aggregate, thesize of the aggregations, the geological and chemical properties of the habitats inwhich they occur, and to some degree, the heterotrophic fauna that occur with them .Tube worms form dense clusters that range in size from small tangles 20 cmin diameter to continuous bush-like stands tens of meters across .Tube worms aremost often found in association with oil-laden sediment, which often contain up to10% extractable oil by weight (MacDonald et al . 1989) . The oil contributes directlyor indirectly to high local concentrations of sulfide .Mytilids generally occur in single- or double-layer beds that range in sizefrom less than 0 .5 m2 to 500 m2 (MacDonald et al . 1990a ; 1990b) . The beds are2-2