Crabs in the Saltwater Aquarium
No, I am not talking about our old aunts or other relatives, although they can probably fit loosely into this topic if I could throw them in my saltwater tank! For the sake of family peace, however, I have had to refrain myself during one visit. An odd circumstance arose that would have lent itself to the submergence of a crabby relative INTO my 150 gallon tank! Yet, I digress…
I am talking about crabs; all species, all genus, all colors, all shapes and all sizes. Be assured, that eventually these little hellion monsters, with evil intentions and back biting ways, will murder another creature in your tank, that you spent your hard earned money on! It’s just their nature, and they can’t be blamed. Even the ones with “small claws” have been known to cause problems, especially in a reef tank. I am sure there are a few well behaved crabs out there, but I am not risking my inhabitants on something that can be easily replaced with a less opportunistic murderer.
My first experience with the “little darlings,” was when I bought my first “clean up crew” for my 8 week old cycled 55 gallon saltwater tank. During this time, my research was quite focused on water quality, live rock, substrate, skimmers, heaters, and lighting. I did however, intend on doing research on the fish I was going to buy. After all, how can you screw up buying a “clean up crew?” …Everybody else is doing it!
My appreciation for hermit crabs were short lived. Over a period of about 4 months, the hermits, one by one, took out my snails, which of course COST more then THEY did. Yes, there was plenty of food and algae for both, perfect water parameters, and no predatory fish; so nothing else would have killed the snails. For me, the last straw was the loss of my prized Jumbo Nassarius Snail, who was one of five I had in my tank. The day I saw a hermit crab rockin’ that snail’s shell, was the day I pulled each and every one OUT of the tank and returned them to the store.
I actually have witnessed larger hermit crabs starting to attack a resting or sick fish! Then a friend of mine related a story of a puffer fish that was attacked at night, and dead by morning. She owned the puffer for a long time, and it was not sick. I remember once, when looking in someone else’s reef, I noticed a hermit crab sitting on top of a healthy SPS coral. As I observed this little beast, I noticed it was tearing the flesh off of the coral! Enough said!
If a fish dies, your nassarius snails will converge and consume, but they will never touch a live fish, only a rotting one. This will keep your water quality from deteriorating if a fish does die. This makes nassarius snails great inhabitants! Over time, I discovered that brittle starfish also do just as good of a job getting extra food that the fish missed.
Back to the crabs! Well, against my better judgment I did buy an emerald crab down the line to take care of some green bubble algae. Once again, another little monster crab had to be extracted as it threatened my Halichoeres wrasses that were napping under the sand. I swear you could hear him say, “Where did those morsels go? The algae just ain’t cutting it!” My wrasses were unusually afraid of this emerald crab as it grew. So were we…
The worst experience I’d ever had was a reef crab that hitchhiked on some live rock. I bought the rock from a gentleman whose system crashed when the power went out. This is common during hot summer days in Las Vegas. I didn’t know there was a little monster stowed away in the rock and the way I found out was not cool! One morning, my fairy wrasses came up to be fed, and I noticed that my Scott’s Fairy Wrasse was no where around. This was odd, because he was usually the first in line for breakfast. I started looking for him and found this big, black, butt ugly, reef crab slowly scraping the now gutted sides of my most expensive wrasse! The Scott’s was NOT sick and I owed him long enough to rule out disease. Why is it ALWAYS the MOST expensive fish that is killed?
Thus started my long search for this monster in the bowels of my tank after he scampered away…. sideways… the LITTLE FREAK! I found him in a twisted and gnarled piece of live rock, which of course was UNDER a bunch of other live rock! So I had no choice but to remove the rock from the tank and chase him out of the middle. That was the WEIRDEST 30 minutes of my life up to that point. With saltwater tanks, these weird minutes start to accumulate over the years… just wait, you’ll see! So I got the little turd out and put him in a refugium as I decided what his fate would be. Let’s not go there.
I started to search for fish that would not typically eat snails but WOULD eat crabs. Why? I had this suspicion he had a brother! Enter the Harlequin Tuskfish. I loved that fish! For as big and scary his teeth were, he was not even the dominant wrasse in my tank. One day, about a week after I bought him, I found remnants of yet ANOTHER reef crab on the substrate. So I blurted out, “WHO’S A GOOD BOY? WHO’S A GOOD BOY? WHOOOOOSE A GOOOOD BOY?!?!” Yes, another weird moment, as my family members looked at me perplexed; since, well, we DIDN’T have a dog!
Upon further research, the Internet supplied more and more horror stories of crabs wreaking havoc in tanks. Reef crabs include Mithrax Crabs (Mithraculus sp.) and Xanthid Crabs, and these are some of the worst culprits. The Mithraculus crabs belong to the Majidae family of “spider crabs”, which has around 200 species in 52 genera. The Xanthidae family is huge, with 133 genera and 572 known species.
A wide variety of marine crabs can be seen here, at Dr. Jungle’s Animal-Image: Saltwater Crabs
Now I am sure there are crab lovers out there, and in certain set ups, hey, go right ahead!
Yes, they are very useful, but only in the ocean. There are many seasoned writers and hobbyists who have written books that will back me up on not keeping crabs in most closed systems. One may say that there are certain crabs like the tiny blue-legged hermits that don’t cause problems. Well, except if you happen to have those little nassarius snails! So YES, I did try those and they started to kill my little nassarius snails that, by the way, were perfectly fine up to that point.
Crabs are opportunistic scavengers, not pets. They are “cute” but the snails in your tank are thinking, “Well, I know one day I will be disemboweled by that heathen.” So the snails sulk away, out of the grip of the new resident… for now.
Carrie McBirney is a team member at Animal-World and has contributed many articles and write-ups.