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Stories about dead shells

Disappearance of brachiopods and mollusks indicates environmental imbalance in oceans and rivers

MARCELOS SIMÕES/UNESPBouchardia rosea samples: most of them deadMARCELOS SIMÕES/UNESP

The Bouchardia rosea, a marine invertebrate covered by two shells no more than 15 millimeters long, previously abundant on the Brazilian coast, has become a vanishing species. During the 13 years he spent collecting specimens on the north coast of São Paulo, paleontologist Marcello Simões and his team from Paulista State University (Unesp) in Botucatu found approximately 6 thousand dead specimens and only six live specimens of the Bouchardia rosea.

“This brachiopod species, previously the most common of its kind on the Brazilian continental platform, is disappearing and may soon become extinct in the Southeast,” Simões concluded. Specimens collected on Ilha Grande island, in Angra dos Reis, on the coast of the State of Rio de Janeiro, reinforce the conclusions of the surveys conducted on the north coast of the State of São Paulo. The Bouchardia rosea, which appeared approximately 60 million years ago, is food for mollusks and crustaceans and, as the shells break up into fragments, the bottom of the sea becomes more stable and firm, thus facilitating the growth of algae and corals. The results on the Bouchardia were published in the Historical Biology journal at the end of 2009.

Karl Flessa, professor of paleontology and paleobiology at the University of Arizona in the United States, is one of the pioneers of this approach. Flessa and his team have collected mollusk shells in different parts of the world, including the Paraná River. For decades, they have kept track of the transformations occurring in the 2,330-kilometer long Colorado River, which runs through the southwestern United States. Nowadays, this river is interrupted by a succession of dams built for electric power generation and water supply for agricultural and urban use.

Flessa found that the decrease in the salt content of the water modified the distribution of the mollusk populations. The quantity of Mulinia coloradoensis specimens, a predominant mollusk species before the dams were built, decreased by 94% – at present, the Chione mollusk predominates in the waters of the Colorado River. The Totoaba macdonaldi, a fish that is almost two meters long, and the Ohocoena sinus, a water mammal that resembles the dolphin, are also vanishing species, because of the transformations in the river. Flessa organized the Center for Dead Mollusks Studies at the University of Arizona, whose page on the Internet has the following slogan: “Putting the dead to work since 1992.”

The challenge is to understand the causes for the lack of proportion between live and dead specimens and then to see if anything can be done to reduce this difference. Apparently, not much can be done in the case of the Bouchardia, because what is driving the reduction in numbers is probably a natural cause: changes in the ocean currents or in the temperature of seawater. “Other factors, such pollution, only worsen this situation,” says Simões.

Scientific article
Simões, M. G., Rodrigues, S. C.; Kowalewski, M. Bouchardia rosea, a vanishing brachiopod species of the Brazilian platform: taphonomy, historical ecology and conservation paleobiologyHistorical Biology. 21: 123-137. 2009.