Paleoecological and geochemical techniques can be used to reconstruct the species composition, abundance, and environmental tolerances of marine shelly invertebrates prior to human alteration of the environment. The problem on the Colorado Delta, like so many other places, is that people didn't start making scientific observations until people had already modified the habitat. We estimated benthic shelly productivity before the upstream water diversions that began in the 1930s. We used field counts, satellite images, radiocarbon-dated shells and analyses of shell growth to estimate pre-diversion population densities of ~50 clams/m2. Surveys of the living shelly fauna indicate densities of only 3 clams/m2. The oxygen isotope composition of prehistoric shells of the bivalve mollusk Mulinia coloradoensis show that this once-dominant species thrived when salinity was lower than at present. The reduction in the number of shellfish has probably meant a diminished food supply for migratory waterfowl. Upstream dams and irrigation projects have profoundly changed the diversity and biological productivity of the Colorado River Delta in Mexico. Prehistoric shells can be used to reconstruct past diversity, composition, abundance, ecological interactions, growth rates, survivorship, salinity regimes, and environmental preferences. Dead shells provide a baseline to assess environmental impact in coastal areas.
keywords: Marine conservation, Conservation issues concerning marine invertebrates, Aquatic ecology

Check other C.E.A.M. pages:

Back to C.E.A.M. abstracts

Back to C.E.A.M. 2001 abstracts

C.E.A.M. Home

Return to U of A Geosciences Homepage