When the crab population suffers from over harvesting, it has a big effect on lots of other organisms, because removing only one organism in a certain ecosystem affects most of the ecosystem, be it directly or indirectly. The organisms that the crabs eat start to grow in number, organisms that were out competed by the crabs move in and start taking over their niche in the food chain, organism that prayed on the crabs are losing pray, so have to find another alternative and develop different hunting techniques.