Every summer, hundreds of whale sharks gather off the Yucatan Coast near the Mexican tourist hubs of Cancun, Isla Mujeres and Isla Holbox. The sharks congregate 32 km offshore to gorge on the eggs of a fish called the little tunny, skimming them from the ocean’s surface with enormous, gaping mouths. In recent years, the spectacle has attracted legions of tourists to snorkel alongside the graceful, slow-moving giants.

Such crabs have specially evolved to a more compact size so that they can hide in the nooks and small spaces within the coral reefs.

However, as coral reefs are being progressively lost worldwide (by as much as 80 percent in the Caribbean), these crabs risk losing their homes.

This conclusion was reached after Post Doctoral Associate Dr Adiël A. Klompmaker and his team compiled the body size measurements of 792 species of prehistoric crabs and lobsters, and concluded that habitat appears to be a factor in the evolution of crustacean size.

During their molting season, the concentration of methyl mercury in the seawater at Año Nuevo State Reserve was 17 times higher than normal. Scientists then found the toxin inside the shedded skin and hair that had been taken for analysis.

The mercury in the elephant seals comes from the fish and mussels they consume, which themselves have been exposed to high mercury levels in the seawater.