In Cham Island - the UNESCO-recognized Biosphere Reserve, located in central coastal Vietnam - the stone crab population is used as indicators for forest and marine ecosystem health and is considered a contributing factor to the sustainable development of island communities. These violet and orange crabs used to be in danger of extinction due to over consumption by tourists.
To conserve stone crabs, a community-based sustainable exploitation and protection mechanism has been successfully implemented since 2009 with the support of three other forces (government, scientists, and entrepreneurs). Only the crabs whose shells bear official stamps are allowed to be traded during a period of six months (March-July) in five areas of Cham Island.
You can read more in Vietnamese: www.hanoitv.vn/cua-da-cu-lao-cham-d72613.html