What kind of (evil?) crab found its way into my sump? Can anyone ID this thing?

[Land&Sea]

So, about a month ago, I was shining the flashlight into my return pump section of my sump and I saw the “cutest” little crab (less than a half a centimeter wide) munching on some sponges, algae and detritus. It looked like the tiniest “blue leg crab” in the world. I thought, “whatever… I’ll let him live in here so he can eat algae and no one else lives in there, so no harm, right?” Well, the sneaky lil bugger found his way into my refugium, and only a few weeks later, is about 3” wide and a VERY active predator, constantly sitting with his claws up and open, looking like evil incarnate, and the second he sees any of my ghost cleaner shrimp or mysid shrimp (real mysids “americamysis bahia,” that have taken years to finally get a sustainable population in my sump and DT)…he POUNCES, and rips them into meaty lil bits. I mean, I honestly don’t care about the ghost shrimp since they have been breeding like crazy, so he may actually be helping me with my bioload by hunting them (as there are HUNDREDS in every corner of my sump…mind you, I only bought 10, lol), but I’m very actively protective of my mysids. I really love having both of them, as their larvae/babies are great free live food for my fish and corals, and they help as part of my CUC. So I wouldn’t want this crab to wipe them out. Anyway, does anyone know what this is? Will I be eating a blue leg crab dinner 6 months from now? Or is it an adult now at about 3 inches? He’s all grey, when the refugium light is off n I can actually use white light from the flashlight to see him. But, he’s also IMPOSSIBLE to catch, as he’s still the perfect size to find any little crevice, rubble rock, or macroalgae to just slide right into, and then clamp down to anchor himself. He also swims faster than most fish and is SUPER aggressive. You just look at him, and the claws are UP & OUT! Lol! Anyway, all joking aside, can anyone ID this thing? If it helps, I’m 99% sure he was a hitchhiker from stuff I bought at Gulf Coast Ecosystems, so he’s gotta be from around Florida/the Caribbean. Obviously is thriving in my tropical water, so not a cold water crab (unless they can live in warm water too). Thank you in advance for any info/advice you may have to give!! Oh, also, I hate killing anything, as it’s not his fault he’s a crab doing what crabs do best. So I was also wondering, if/when I catch this guy, can i just release it into the Long Island sound where I live? Or is that a big “no no?”Here’s a few pics:

 

[betareef]

He's one of the swimmer crabs. Our local blue swimmers grow to about 20cm and about 1kg weight they say. I can tell you they taste superb.

Do not release him into the wild. Even if he was from the local area, you don't know what he may have picked up whilst mixing it qith foreign organisms in your tank.

 

[DontWorryReefHappy]

So, about a month ago, I was shining the flashlight into my return pump section of my sump and I saw the “cutest” little crab (less than a half a centimeter wide) munching on some sponges, algae and detritus. It looked like the tiniest “blue leg crab” in the world. I thought, “whatever… I’ll let him live in here so he can eat algae and no one else lives in there, so no harm, right?” Well, the sneaky lil bugger found his way into my refugium, and only a few weeks later, is about 3” wide and a VERY active predator, constantly sitting with his claws up and open, looking like evil incarnate, and the second he sees any of my ghost cleaner shrimp or mysid shrimp (real mysids “americamysis bahia,” that have taken years to finally get a sustainable population in my sump and DT)…he POUNCES, and rips them into meaty lil bits. I mean, I honestly don’t care about the ghost shrimp since they have been breeding like crazy, so he may actually be helping me with my bioload by hunting them (as there are HUNDREDS in every corner of my sump…mind you, I only bought 10, lol), but I’m very actively protective of my mysids. I really love having both of them, as their larvae/babies are great free live food for my fish and corals, and they help as part of my CUC. So I wouldn’t want this crab to wipe them out. Anyway, does anyone know what this is? Will I be eating a blue leg crab dinner 6 months from now? Or is it an adult now at about 3 inches? He’s all grey, when the refugium light is off n I can actually use white light from the flashlight to see him. But, he’s also IMPOSSIBLE to catch, as he’s still the perfect size to find any little crevice, rubble rock, or macroalgae to just slide right into, and then clamp down to anchor himself. He also swims faster than most fish and is SUPER aggressive. You just look at him, and the claws are UP & OUT! Lol! Anyway, all joking aside, can anyone ID this thing? If it helps, I’m 99% sure he was a hitchhiker from stuff I bought at Gulf Coast Ecosystems, so he’s gotta be from around Florida/the Caribbean. Obviously is thriving in my tropical water, so not a cold water crab (unless they can live in warm water too). Thank you in advance for any info/advice you may have to give!! Oh, also, I hate killing anything, as it’s not his fault he’s a crab doing what crabs do best. So I was also wondering, if/when I catch this guy, can i just release it into the Long Island sound where I live? Or is that a big “no no?”Here’s a few pics:

Looks like a dam blue crab , I live in Naryland and that is a Blue Crab Final answer… flip him over … I wouldn’t want him around my coral

 

[DontWorryReefHappy]

They are delicious with old bay and butter…

 

[Land&Sea]

He's one of the swimmer crabs. Our local blue swimmers grow to about 20cm and about 1kg weight they say. I can tell you they taste superb.

Do not release him into the wild. Even if he was from the local area, you don't know what he may have picked up whilst mixing it qith foreign organisms in your tank.

Thank you!! And, after posting, I already thought of all the reasons NOT to release him into the the Long Island sound. So, if/when I catch it, I’m guessing I’ll have to dispatch of him humanely…or, if he gets big enough, throw him in a pot of boiling water. Bon appetit!!

 

[Reefing102]

Agree with the above. While the lighting is off, my guess is a Callinectes sapidus - Atlantic Blue Crab. Some people will raise them in separate tanks as a “neat” pet. Could see if your local aquarium wanted him, though it may be hard to explain how you got him “undersized” compared to legal collection practices.

 

[Land&Sea]

Agree with the above. While the lighting is off, my guess is a Callinectes sapidus - Atlantic Blue Crab. Some people will raise them in separate tanks as a “neat” pet. Could see if your local aquarium wanted him, though it may be hard to explain how you got him “undersized” compared to legal collection practices.

Oooh… I have a 20 gallon. Maybe I’ll keep him as a “neat pet” (if I can ever catch the little bugger). But, if I brought it to our maritime center, especially when he outgrows my 20 gal, can’t I just say I found him in my reef tank and didn’t want to kill him? I highly doubt they’ll arrest me, lol! I live in CT, so not sure what the laws are here, but im guessing they’re different than Florida (or wherever the macros and sponges he came on were collected).

 

[adamg77]

I found one as well and now have him as a feature in my 29 gallon

He is a feisty little guy! So cool

 

[twentyleagues]

I would email gulf coast ecosystems with pics and they may provide a best id and care requirements. I agree with @Reefing102 and @betareef its a type of swimming crab with those paddles. Have you tried baiting a trap or using 2 nets one to "entice" him to swim and one to catch him from behind when he does swim?

 

[Kostas Hatz]

He is very good guy to eat algae..I has an,for some years in the sump

 

[Land&Sea]

I found one as well and now have him as a feature in my 29 gallon

He is a feisty little guy! So cool

I’ve gone from “evil incarnate” to “my newest cool pet.” I’m literally aquascaping for him as we speak Now I just have to catch him, and I really don’t want to take everything outa my sump to do it, so just gonna keep trying w the net…or just wait til he’s too big to slip away, lol!

 

[Land&Sea]

I would email gulf coast ecosystems with pics and they may provide a best id and care requirements. I agree with @Reefing102 and @betareef its a type of swimming crab with those paddles. Have you tried baiting a trap or using 2 nets one to "entice" him to swim and one to catch him from behind when he does swim?

Oh yeh… I’ve tried everything possible. He’s a smart lil bugger! Put some krill in a net with another net in the other hand, and like I said, he swims faster than most fish I’ve had to catch. And there’s just so much rubble rock and macro algae in there that the second I move in for the catch he zips away and hides

 

[Land&Sea]

They are delicious with old bay and butter…

Looks like a dam blue crab , I live in Naryland and that is a Blue Crab Final answer… flip him over … I wouldn’t want him around my coral

Luckily he’s nowhere near any of my coral. I really lucked out, bc 90% of what I bought from GCE went straight into the display… the other 10% went into the refugium/sump, and that’s where I found him. But he’s picking off my grass shrimp and I don’t want him to wipe them out. So, today’s Sunday chore? CATCH THE CRAB!

 

[Fenral]

Having grown up in Maryland... That looks like dinner to me - and most crabs will eat anything they can catch. (Your in CT I see - I still have some old bay if you want it