Hi Frog,
Bewdy, a topic I can really sink my teeth into as a fisheries biologist and frequent scourer of fish markets while I'm in Indo!
The main species of crabs I've seen over there is what we call in Oz by the common name of Green Mud crab (
Scylla serrata) which are found in mangrove areas and like to bury in the mud of said areas. They get very, very big and we have plagues of them here in Oz to in our northern regions. Sadly, I doubt the population is really that healthy, certainly not in the Java/Bali/Lombok regions as their is really little or no fisheries regulation in these areas and the mangrove forests are in a hideous state if they remain at all, a lot of them have been ripped out for development and the creation of aquaculture industries. I don't know for certain, but I'm guessing that a lot of the crabs seen at the markets and restaurants in these areas actually come from farms nowdays. Back in 1999 I spent a bit of time in north Bali as part of a Uni trip and we were trying to 'crack' the life cycle of mud crabs to initiate the farming of these suckers, they could well have done it as most of the crabs I've seen seem to be a fairly uniform size and in reality quite small for wild caught crabs (Well under what we would call legal size here in WA). I doubt there is much of an export market, I can't imagine the price would allow for it as crabs don't generally get that good a price in international markets, certainly nothing like lobsters and shrimp (or what we call prawns here in Oz) and should be transported live (as crabs don't freeze well like lobsters or shrimp) which is expensive to do. Our shallow water crab fisheries here in Oz are almost solely for domestic markets
The other crabs I've noticed in relatively good numbers is the Blue Swimmer crab (
Portunus pelagicus) or what West Ozzies know as Blue Manna crabs and Asians call the Flower crab and similar to the Blue crab that you have over there in the US (and use for soft shell crab, I believe?). These are the blue, flat backed suckers with slimmer claws. They come from sandy and muddy bottoms and aren't tolerant to leaving the water like Mud crabs. They are a lot fiddlier to eat than Mud crabs but a lot sweeter on the palate. There are a whole heap of other species that I have noticed but won't bore you with the details, Indonesians don't seem to be particularly fussy about the size of the crabs they eat (or any other seafood for that matter) so that brings into play a whole heap more varieties than what we would normally eat in western countries. Interestingly, some species of colourful tropical coral reef crabs are toxic and I have noticed some of these species for sale at our big fishmarket in Java, near Banyuwangi

. Heaven help the poor sucker that buys them, a day or two of magic mushroom-esque hallucinations ahead ha ha ha!

As a rule of thumb for Indo, only eat crabs that have rounded 'swimmerets' as their last pair of legs (opposite end to the nasty bitey bits).
My bride is a big fan of crabs so one of her first excursions when she arrived here in West Oz (she's been here 3 weeks now) was going crabbing. We collected 20 nice big suckers easily and she's been eating crab all week! She certainly doesn't want to return to Indo anytime soon and it's not even lobster season yet! In the mean time she's got a freezer full of fish, prawns and scallops to munch through, poor bugger.........
Cheers
Adam