Gecarcinus (moon crab) Breeding?

[PoetaCorvi]

Not looking for responses along the lines of “It’s impossible don't bother” etc etc. Hermit crabs were impossible to captive breed until they weren’t.

I’ve been putting research into the natural life cycles of moon crabs. I have just acquired a young male/female pair. I am not absolutely positive I have the correct species ID, but it is the genus Gecarcinus.

They’ll be in a 40 gallon breeder. For now it’ll be a pretty standard moon crab setup, but will be modified to experiment with inducing breeding/egg release as I learn more.

I was looking for more information/testimonies regarding the captive breeding and raising of these. One paper I found attempted to raise them from eggs (unsure if they captive bred or wild caught these), only one survived to megalopa and it died before becoming a juvenile. The methods used to raise them are not elaborated on.

There are a number of environmental factors I’m brainstorming how to recreate. Mimicking a rainy season with Asbolus beetles is easy enough, but I imagine it’s fairly different with these larger and smarter crabs. I’m unsure if the seasonal use of a fogger could be adequate, if I have no better ideas I will attempt this, open to suggestions!

The one I’m really lost on is recreating tides. In theory I’ve thought of some kind of timed water pump that adjusts the water levels, but I have absolutely no idea how I could accomplish this. I am also unsure if mimicking waves would be necessary.

Then there’s raising the zoea. My first thought was some kind of kreisel tank, there are some available on the market for raising jellyfish ephyrae. I need to do further research in sourcing adequately small plankton to feed them.

At some point they will need to surface and move to land. I am unsure how to enable this while still maintaining the appropriate environment for larvae. My thought is I could move them to a semi-terrestrial setup once they are megalopae (maybe using some sort of sifter that could catch the megalopae but not the zoea), since this seems to be when they start heading for shore? At the very least they are capable of self propulsion, so they wouldn’t need the kreisel afaik. I could just keep them in the semi aquatic tank and give them however much time they need to surface.

I eagerly welcome any advice! I’ve heard there is one instance of captive breeding and raising being achieved, but I cannot find the firsthand documentation of this.

 

[Liquifin]

From my understanding, breeding them is difficult because of how little we actually know about them and their breeding seasons/cycles. We know what months they're active, but not their temperatures, water salinity, acidity, and other minor factors that add up to the whole picture. There is a lot of speculation, but no actual tested information as to how to breed them properly in captivity. Some say they require brackish water and other say otherwise. Is it impossible? No. But what makes it difficult is how much effort and resources it'll take to just attempt and try. And then you have to dedicate years to perfect it. Which, if you add up all the costs and time, it just doesn't make it worth it.

 

[Ultum4Spiderz]

From my understanding, breeding them is difficult because of how little we actually know about them and their breeding seasons/cycles. We know what months they're active, but not their temperatures, water salinity, acidity, and other minor factors that add up to the whole picture. There is a lot of speculation, but no actual tested information as to how to breed them properly in captivity. Some say they require brackish water and other say otherwise. Is it impossible? No. But what makes it difficult is how much effort and resources it'll take to just attempt and try. And then you have to dedicate years to perfect it. Which, if you add up all the costs and time, it just doesn't make it worth it.

Wow sounds tough , better to stick to with proven species. I’ve never kept crabs But I’m sure the OP can find a decent species.

 

[PoetaCorvi]

From my understanding, breeding them is difficult because of how little we actually know about them and their breeding seasons/cycles. We know what months they're active, but not their temperatures, water salinity, acidity, and other minor factors that add up to the whole picture. There is a lot of speculation, but no actual tested information as to how to breed them properly in captivity. Some say they require brackish water and other say otherwise. Is it impossible? No. But what makes it difficult is how much effort and resources it'll take to just attempt and try. And then you have to dedicate years to perfect it. Which, if you add up all the costs and time, it just doesn't make it worth it.

I’d argue that some people (myself included) find it worth it. Right now all of the moon crabs in the hobby are wild caught. If we are able to pinpoint the conditions required to captive breed, it means a healthier captive stock and reduces the risk of damaging wild populations by over-collecting. If we didn’t try breeding something because we didn’t already know how to, we wouldn’t have nearly as many captive bred species on the market. You’re correct that there’s no tested information, so.. why shouldn’t we test the information? At some point, we knew nothing about every fish and invert in the hobby. I’m just seeking guidance on how to best practice recreating the conditions they seem to need for breeding.

 

[PoetaCorvi]

Wow sounds tough , better to stick to with proven species. I’ve never kept crabs But I’m sure the OP can find a decent species.

If we stuck to proven species then we would not have proven species. I’m already aware that this is a difficult project, but I have committed to at least trying. I just need advice on the mechanics for the setup, mostly.

 

[NMTs]

@Smotzer is the only one on here that I know of who regularly breeds crabs of any type with success. Maybe he'll have some insights that will be helpful. Good luck!

 

[somebugnerd]

To preface, I have no experience breeding terrestrial crabs, but I respect what you are trying to do. I think it makes sense to start by going to inaturalist (https://www.inaturalist.org/taxa/204112-Gecarcinus-quadratus) and checking where there are verified sightings in their native range during their reproductive season then establishing reference points for average temperature and humidity for those locations.

I also found a research paper dealing with reproductive cues and larval development in this species: https://dspace.mit.edu/handle/1721.1/62786 (this might be the same paper you mentioned)
Page 88-89 briefly describes their setup for rearing the larvae, 96-98 for larval development. Short summery, they all died, but their setup was more basic than most freshwater shrimp breeders and they don't mention much about feeding them (so I'm guessing there was a lot of cannibalism.) Still, it's worth reading chapter 4(pg. 79-), they collected a lot of good research on the behavior of the adult crabs and environmental cues for reproduction and egg release.

If you want to try mimicking tides, I think the lowest tech solution would be to drill a hole near the the bottom of the tank (low tide line) and in the side of a bucket, then epoxy a tubing connector into both and connect them with a few feet of airline tubing. Putting the bucket below the tank would cause the water to slowly drain (you can put some filter media in the tube to slow it down to a normal tide speed) and raising the bucket above the tank would cause it to slowly refill.

For the zoea, like I said I haven't worked with crabs, but with neocaridina shrimp and triops (yes, common and not picky species) I use hikari first bites and include reeds/gravel with well developed biofilm in their tank. They also sell phytoplankton/copepod culture kits for improving the micro fauna in marine tanks, they run about $25-50 on amazon.

Good luck, keep us posted on your experiment!

 

[PoetaCorvi]

@somebugnerd I appreciate the response greatly! Inat has definitely been a good resource; I'm even using it to research coastal plants I could use. I'll have to give the tank a good amount of time before adding them so the plants can develop deep roots (preventing these guys from ripping out the roots...), the main purpose of them is to maintain the slope shape I'd like to use. The bottom of the slope being saltwater, the top of the slope containing the freshwater container.

I did find a build someone made for a mangrove tank that mimicked tides automatically, timing it the same as tides would be in real life. It's a pretty impressive build.

The paper you linked is the one I read! I did also find two other papers that are extremely relevant, and seemed to have even more success with rearing larva. This one elaborates on the methods used, it seems like I would not actually need a kriesel. They are capable of self propulsion in the absence of currents. They hatch small, but not as small as I initially thought, so finding suitable food would be easier than I expected. They used newly hatched brine shrimp for the smaller zoea. They have more herbivorous habits on land, but it seems like in saltwater stages they are heavily carnivorous. The paper studies 5 of each stage (only 3 of sixth stage for whatever reason) meaning they reared at least 5 to megalopa. I don't believe they attempted to rear them to juvenile, since they were just studying the larval phases.

This one was released in the same year, and focuses on spawning behavior and how females try to spawn in ideal conditions. Strangely it contrasts the other paper you linked, this one claims the females spawn regardless of tide. Obviously this is an older paper, but I don't think that inherently discredits the observations. I can imagine a preference for low tides though, but I don't think tides are actually necessary for spawning in captivity, since the risks present in high tides are not present. Low tides are preferred because the larger waves of high tide are more likely to sweep females into the ocean, and the lowering of high tides may leave larva stranded in tide pools. I may keep the saltwater at a consistent level, but use something like an air stone to prevent it from being entirely still.

Of course, I can always modify the setup if it doesn't work out. I figure if a cheaper option seems reasonable, I'll start with that one before investing in an unnecessarily complicated setup lol.

 

[Odontodactylus]

Crabs are tough to breed for numerous reasons and its not exactly approachable for some species to be captive bred.

Often breeding projects are successful when labs deem it vital (such as non-crab horseshoes which are harvested for their blood, its important biologist figure that out) and really invest into the facilities and setup needed to pull it off.

Hermit crabs were difficult cause the average individual can't in a timely manner raise hermit crabs from larval to adult to mass product them publicly, there are hobbyist that did go the extra mile with a whole room setup around it, but its not commercially viable, hence why most hermit crab communities setup for 'adopting' but if they were commercially sold they'd just be permanently out of stock until field collecting occurs again, that's basically what's happening now as the 'wave' of tank raised hermits pretty much went, and considering they live up to 30 years or more have fun waiting for the next breeding pair.

Vampire crabs are by far the easiest species to breed in captivity and are highly approachable for commercial tank raised sale because they don't have a larvae stage and don't require any unique environment parameters throughout their growth. Its actually as easy as just buying like 5, making a setup, and watching them multiply.

Moon crabs I have some experience with, but not with breeding. To my understanding, you'd need a facility where you can kennel the larvae in stable saltwater, and transition them to land. The other major issue is the larvae are often cannibilistic and the mortality rate is very high for the survivors. You'll find it difficult to pinpoint what food exactly they eat at that stage (you'll be going through multiple trials trying different bottles of phyto), difficult to keep water quality pristine without damaging the larvae themselves (such as from air bubbles, pumps, water flow, etc), if you succeed after the major heavy investment not to mention obtaining and raising a breeding pair up to the point where you can begin practicing this, you'll be lucky if you manage one or two settled crabs that may not even be able to produce another generation. There's also the theory for a lot of species that phases of the moon actually correlate with timings sea life does things (it was a major break through for coral reproduction, and mantis shrimp have a lot of lunar cycles for when they do certain things), and in captivity not only is lunar difficult to replicate, but also elevation may throw off whatever effect they're using. Since these types of crabs just know when to migrate to the ocean, it likely is a lunar phase that triggers it for all of them.

To be blunt, in the saltwater hobby we don't even have tank raised crabs, and moon crabs would be just learning that + the extra step of putting them on land. Is it possible? Perhaps, is it worth it? Not really this is some lab investment to pull off and there's no guarantee lightning strikes twice. I learned that the hard way with some species.

 

[Smotzer]

Hey thanks for the mention, in guess I’m now the senior resident crabber now, eh @NMTs ?

so yeah to keep it simplr and put it bluntly, no breeding the genus Gecarcinus is not really feasible as their reproduction cycles that involve the sea is practically undoable in any reasonable matter. I will say I have pondered the thought many time over the years, but the salt water and related environmental condiaitons and food sources are quite a task.

The entire family is tricky as well. But there are other crabs that I have been working with, and a new family and speciesI am attempting but it’s difficult.

 

[catboyeuthanasia]

I've been looking into breeding reef crabs for a while now, and the one thing they have in common is that they refuse to settle. People have had very good success getting the adults to spawn and raising the larvae, but the step that Noone has been able to figure out is how to get them to go from larvae to adult. It's either something to do with temperature cues/time of year, or captive planktonic foods lacking some nutrients they need.

I would have a reef tank on standby for water (no pumps/intakes in crab tank, daily water changes from the main tank) and planktonic foods and meticulously check water temperatures along the coast of mexico. I'd also invest in a rotifer bucket since baby brine are not very nutritious.