Reef was crawling with crabs when it died

U. FLORIDA (US) — Researchers have found an amazingly diverse record of 100-million-year-old crustaceans on a fossil reef in northern Spain.

The team reports identifying 36 decapod crustacean species, including eight new ones and the oldest-known spider crabs. Decapod crustaceans, including crabs, shrimp, and lobsters, are vital parts of the food chain, contributing to reef health and serving as food for larger marine organisms.

A study of their early evolution may help researchers better understand how present-day species are affected by reefs declining due to changes such as ocean acidification and coral bleaching, which also threaten the animals they support.


“The reef in Spain died soon after many decapods were still around. Something must have happened in the environment that caused reefs in the area to vanish, and with it, probably many of the decapods that were living in these reefs,” says study author Adiël Klompmaker, a postdoctoral researcher at the Florida Museum of Natural History at the University of Florida. “Not many decapods are known from the time after the reefs disappeared in the area.”

The location’s fauna showed a higher diversity than previously known, and included fossil crabs, hermit crabs and squat lobsters, says Klompmaker, who began research for the project as a graduate student at Kent State University. The fossils represent all dominant decapod groups found in reefs today, except true lobsters and shrimp, which may not have been preserved.

“Today’s decapods can adapt to a new environment without reefs, migrate elsewhere, or go extinct,” he says. “By documenting what happened in the past, we may provide clues as to what could happen to decapod crustaceans such as crabs, shrimp, and lobsters in today’s deteriorating reefs.”

Klompmaker researched 20 localities worldwide to determine the Koskobilo quarry is the most diverse locality for decapods in the Cretaceous period 145 to 66 million years ago. The research also shows that ancient decapods living within reefs are more diverse than those living in other parts of the ocean, which is similar to diversity patterns today.

“This shows that reefs were a popular place to feed, mate, and seek shelter for decapods,” Klompmaker says. “Thus, not much has changed from this perspective since the Cretaceous. Decapods still really like living in coral reefs, although today many different decapod families inhabit them.”

Tropical temperatures dominated the Cretaceous period and sea levels were extremely high worldwide. The quarry, which would have been underwater at the time, is now about 35 miles from the Atlantic Ocean in northern Spain, Klompmaker says. The locality’s age was determined based on ammonite fossils, ancient squid-like animals with external shells.

The study, published in the journal in Cretaceous Research, is important for understanding decapod evolution because multiple species were grouped within the same genus, rather than just one, says Francisco Vega, a paleontologist at the Universidad National Autonoma de Mexico.

“We would not expect such a high diversity at that time because there are very few records of crabs then,” Vega says. “Also, by that time, the group was represented by so many species in a reef environment, and the number of species today is about the same, which is very significant since the diversity of the communities has prevailed ever since.”

Klompmaker collected fossils in the Koskobilo quarry during three field trips in 2008, 2009, and 2010 with a team of researchers from Spain, the Netherlands, and the US. New species were identified by analyzing the morphology, or physical characteristics of the fossils, which include three-dimensional impressions of the decapod shell.

“We went there in 2008 and in the first two hours found two new species,” Klompmaker said. “That’s quite amazing—it just doesn’t happen every day.”

Source: University of Florida