FAQs about Marine Crabs
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Related Articles: Crabs,
Hermit Crabs,
Related FAQs: Marine Crabs 2, Marine Crabs 3, Marine Crabs 4, By
Species/Group: Arrow Crabs, Emerald Green Crabs, Decorator Crabs/Sponge Crabs,
Fiddler Crabs,
Pom Pom Crabs, Sally Lightfoots, &
FAQs on: Marine Crab
Identification, Crab
Behavior, Marine Crab
Selection, Marine Crab
Compatibility, Marine
Crab Systems, Marine
Crab Feeding, Marine Crab
Reproduction, Marine
Crab Disease, Emerald
Green, Mithrax/Mithraculus Crabs, Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone
Eating Shrimp, Crustacean Identification,
Crustacean Selection,
Crustacean Behavior,
Crustacean
Compatibility, Crustacean Systems, Crustacean Feeding, Crustacean Disease, Crustacean
Reproduction,
Cancer antennarius
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Question about getting rid of a crab Hi, I was wondering if
you would have some advice for me. I have a pinkish crab the size of my
thumb that lives in one of my base rocks and eats my snails. There is
no practical way to get the rock out of the 80 gallon tank. Is there
any way to get this crab out of the tank? A trap or some sort? He comes
out occasionally late at night. I would appreciate any advice. Thank
you. Jerry Hirsch. <I have successfully used a trap called the
X-Terminator. It has a spring loaded closing door. -Steven Pro>
Uninvited Guest Hi Bob, <Hello> Last night I was
enjoying my tank when to my surprise this thing just crawled out of a
piece of live rock. I was quite startled seeing this as I didn't
put it there or even know it was there. <Keep looking... much
more to see> I assume it came with the box of live rock that I a
received this past summer, but this was the first time I had seen it
and it quickly crawled back into the rock. Nonetheless, it is some sort
of crab, a little smaller than a half-dollar, brown, and all hairy. In
fact it looks like a tarantula. I unsuccessfully tried to find a
picture on the web site and the Internet. <The Web/Net is
"not that complete" yet> I was wondering if you knew what
type of crab it might be, or more importantly if I should get it out of
the tank. <Mmm, bait, trap... many possibilities as to
species> Right now it is a fish only tank with a flame angel, purple
tang, flame hawk, and an orange diamond goby. I also have some snails
and hermit crabs and of course the live rock. The snails and hermit
crabs are pretty new additions and I have found a few dead snails or
should I say empty shells already. Wondering now if the hairy crab got
them?? <Could be... though the fishes you list should be in no
danger. Bob Fenner> Thanks! JJ
The Price of Getting Crabs Hi guys, back again! I love
talking to you people! <we love you too, dear> As you may have
guessed from past e-mails, I am in need of many things for my reef
tank. New Skimmer, more LR, more sand, etc. But I just realized there
is another thing I am lacking in my reef environment, sand sifters,
crabs, snails. I remember reading AND hearing that these little inverts
are about the most important part of a reef, next to LR. Is this
so? <They are extremely important to the overall health of your sand
bed.> I only have about 15 or so snails, nothing else since my wild
caught crabs all died. Which also leads me to this question: Can you
guys recommend a site where I can purchase on line? I went to many of
the links on your web page Rob, but after about 35 minutes of clicking
here and there, I decided to just go to the experts! I will say that I
went to WWW.GARF.ORG and they had what appears to be a pretty good deal
compare to the $3.99 a piece price tag at my local shop for
crabs, they had a price of about $1.00 a piece for an assortment of
crabs and snails. Of course I would hope that these inverts are very
healthy and of good size. Can you do better?? <I have heard good
things about the detritivore kits from
http://www.inlandaquatics.com/ This should inoculate your sand
with a nice variety of sand sifting creatures. -Steven Pro>
Let me know what you all think, and thank you very much for your speedy
help as always! Pam
Emerald Green crab attacks! Hi Bob, I just got back from
my favorite fish shops in Chicagoland. Realized I really do have more
time than money. Any way, I saw something there I could not believe. I
watched an Emerald crab reach out and snag a Saddlebacked
Clownfish. <This does happen... with size, hunger, Mithrax
crabs will eat most anything> It grabbed him and drug him down and
held the poor thing fast while it started to try to eat it! I quickly
got an employee and its life was spared. (maybe) Is this normal or just
a case a very hungry crab? I was thinking about picking up a few until
that event. Thanks for your input on the lights. I just purchased the
CSL ABS 4-65 watt Power Compact unit online. I also decided to buy a
75Ga. and sell the 55Ga. More room (width) for the lights, filters,
livestock etc.. Just plain easier all the way around is you ask me. Oh,
buy the way, do you need a 55Ga. tank. I know someone who is selling.
<Do post this on the Chatforum: http://talk.wetwebfotos.com/ Bob
Fenner> Thanks Zimmy
Mithrax (emerald) crab Dear Robert, I have a 25 gallon
reef tank and thinking of getting a Mithrax (emerald) crab to help
control hair algae; will it bother my Sally lightfoot crab? I have had
her for close to a year, I would sure be sad if it were to be eaten.
<This is a possibility, especially in such small quarters... but not
too large a one> Also, I keep my tank from 74 to 78 degrees would an
abalone do Ok and I do have a skimmer. Any help is greatly appreciated!
<I would skip on the abalone. Please read over the mass of algae,
control and related articles and FAQs stored on WWM: Index here:
http://www.wetwebmedia.com/acidalkph.htm for much more on your choices.
Bob Fenner>
Mithrax Crab / Bubble Algae Question Bob, About a month
ago, I wrote to you about a bubble algae problem I was beginning to
have. Well, now it is a huge problem. I have been trying to remove it
by hand, but this seems to be a losing battle. In your reply to my
earlier e-mail you mentioned that Mithrax sculptus, the Green/Emerald
Crab is known to eat bubble algae so I'm thinking of adding one (or
more) to my tank. My questions are. a) will it bother the banded coral
shrimp and 2 common cleaner shrimps I have and b) will it bother / eat
any corals or clams?? Also, any other ideas for eliminating this pesky
algae would be greatly appreciated. Thanks for your help again! Phil in
San Diego <Very rare to have Mithrax crabs bother other crustaceans,
corals, or clams... try one per fifty gallons or so... and start
small... like one inch across the carapace in size. Bob
Fenner>
Re: more feeding <<JasonC here...>> I also
got a Blue Boxer Crab, I could not find much Information about them.
Any ideas what they eat. <<just about anything they run into, or
that runs into them...>> My LFS said brine shrimp <<that
would work. Cheers, J -- >>
Sally Light Foot? Hi Bob. I was reading about the
Percnon gibbesi, the Nimble Spray Crab on your site. Is this crab also
known as the Sally Light Foot crab? <Mmm, maybe... perhaps sold,
labeled as this by some... though the "real" Sally Lightfoot
Crab is Grapsus grapsus> Does it need to be able to get out of the
water periodically? <Yes> Any further tips on keeping this crab
healthy? <Do use your search engines here. Not much that is
practical/husbandry known about these crabs. Bob Fenner> Gracias.
Zimmy
Fiddler Crabs? Hi. Thanks for all your previous help in
the past, both directly and through the creation of this site.
<You're welcome> My problem is this. I have a 35 gal tank
that I added 10 Trochus and 10 Astrea snails to about a month and a
half ago. Since then they have slowly died off to the point of about
six. I find many upside-down on the sand bed, and, up until now, I had
thought they had fallen off the Live Rock. However, I had failed to
realize that I had been given a "gift" of a Fiddler Crab
about two weeks prior to the addition of the snails. <The
"Trojan" gift crab...> At least that's what it was
called, and it looks like one (has the eye stalks, but doesn't have
the one, large claw--I'm assuming this is because its female. But
the Bad News Bears and Walter Matthau taught us what happens when one
assumes). <Well put> After the addition of the Fiddler, it
disappeared for months and I believed it to be dead due to lack of a
place to dry out. However, a few nights ago I found it out and crawling
around the rocks. My questions are these: Is this crab causing the
demise of my snails? <Maybe... are their bodies missing?>
Will it hamper my plans to add more invertebrates (mushrooms, leather
corals, star polyps, feather dusters, shrimp)? <Maybe... I would
pull it> If it is...then how do I get rid of it because I
haven't seen it except for that one night? Please excuse the long
email, and thanks very much. Michael Rathwell BTW Kingsley from
Aquarium Arts in Phoenix says hello. <Ah, say hello back for me
please. I would "bite the proverbial bullet" and drain, take
out the rock... and remove the crab at this point. Luckily a thirty
five gallon is not "that big". Please see here:
http://www.wetwebmedia.com/movingaq.htm re input on "moving"
aquariums, about the same list of steps, tools, materials as you'll
be doing. Bob Fenner>
Re: Fiddler Crabs? Thank you again. The snails did have
their bodies removed, but could this have also been from decomposition?
<Not that quick... a few days...> In response to your moving
idea, could a trap not be rigged up with a little bit of bait?
<Yes... a few types described on our principal site:
WetWebMedia.com> I have seen these mentioned on various internet
sites for the removal of pesky bristleworms, violent Mithrax crabs, and
other things. Would this sort of thing work for Fiddlers?
<Possibly> Seeing as how the residents of my soon-to-be mini-reef
are only 2 red Firefish, 1 smith's blenny, 1 Featherduster, and 6
(numbers slowly declining) snails the moving shouldn't be a
problem, but I would rather not mess with restarting a tank (thoughts
of re-cycling and ammonia spikes sicken me, <Shouldn't have to
be recycled... just put back what was in there... including much of the
"old" water> especially when only 1 week away from putting
in the first corals). And to think...all of this work for a $4 crab!
Thank you for your advice and help. Michael <Be chatting. Bob
Fenner>
Crab misidentification, correction on WWM Mr. Fenner,
You have a picture of the Pacific rock crab, Cancer antennarius,
labeled as a Dungeness crab, Cancer magister at your site:
http://www.wetwebmedia.com/swcrabs.htm <Thanks much for this i.d.
Will post your msg., the correction tomorrow. Bob Fenner> Chris Hunt
Marine Scientist SAIC-Science Applications International
Corporation
Big Ole Crab This is probably the strangest question you
will get all day! While cleaning the pool in the back yard I discovered
the biggest crab I have ever seen running around on the bottom. It is
about 8-10 inches wide with two very large claws. It's body is
light tan with a purple tint and the claws have a tint of blue to them.
I don't know how long it has been there but would like to get it
out and turn it loose in it's proper environment. Do you think he
is salt water of fresh? We live fairly close to both but have never
seen anything quite like him before. <Bizarre... maybe someone is
pulling a prank... I would remove the crab (with a big net) and set it
out near the beach. It will return to the sea if this is where it
belongs. Bob Fenner>
Dungeness crab R & D Hi Robert, Thanks for the
comments and advice my previous email about observing Dungeness crab
behavior in and out of our traps. We'll be able to get filter
seawater from the Seattle Aquarium which is nice since it is only 3
miles away. We'll need about 3,500 gallons. <Do consider, study
the need to bolster alkalinity. The facilities I help with use simple
baking soda, sodium bicarbonate (Arm & Hammer) here... Inexpensive,
readily available... to boost alkalinity, maintain pH at a safe
level... otherwise, w/o much in the way of soluble substrate
present/water flowing over... even with 3,500 gallons these values can
slip dangerously, quickly...> Any idea on how much air we need
aerate the pool and keep the environment good for active crab activity
?? <Not much if it's just one, a few crabs in this volume... I
would use a sump (separate container, like a big Rubbermaid tote...
horse/cow drinking size.) to have the water overflow from the main
system (run it through a protein skimmer (will aerate here par
excellence) then through some sort of biological filtration (to convert
ammonia/ammonium from crab wastes (produced continuously whether you
feed or not, and from your demo. baits...). Perhaps a good idea to have
a few "Aquarium Service" companies come out and bid on the
mechanicals, install... to get their ideas. Bob Fenner,
www.WetWebMedia.com> Thanks, Ed
Crab Skeleton Bob, what is with your accuracy? <Have
been credited, accused, cursed/blessed with intuition> You were
right on, not that there was a smiling cat, but the Banggai was
unfortunately lost. Have you witnessed the spontaneous loss of this
hardy fish, and if not what could it mean for the rest of my stock
(going to perform water change tonight)? <Good idea to execute this
change> But here's the question. I know how much I stocked the
tank. . . There were four crabs total in there. Three Mithrax and one
Sally Lightfoot. When my girlfriend was getting the Banggai out of the
tank while I was at work, she also discovered (on its back) what she
described as the Sally Lightfoot crab dead. But then when I got home I
spotted him eating happily. . . <Likely just a shed
exoskeleton... best to leave these in place (maybe behind the rocks)
for the animals to ingest, re-use> Also, all of the other crabs were
spotted at the same time in other parts of the tank, four crabs total.
Do these guys do the same thing that my cleaner shrimp do with their
skeletons?? <Yes> Could this specimen come from the rock?
<Doubtful> You're the best, separate query on the way.
<Mmm. Bob Fenner>
Dungeness crab (holding facility/gear) Hi Robert,
<Howdy> Our company manufactures crab and lobster traps.
We're purchasing a 12' wide x 31" high wading pool to set
up as a crab observation tool. We want to watch Dungeness crab, and
perhaps lobster later, as they crawl into our traps and try to get out.
We make some entrance devices for the traps that we would like to
observe as to their effectiveness. Our web site is
www.neptunemarineproducts.com. <Neat> Any advice on how extensive
of a system I will need to keep the crab alive and active would be
appreciated. I suspect we would only need a couple of weeks to observe
the crab's behaviour in relation to our entrances. After that, a
crab feed! <Take a look here: http://wetwebmedia.com/cntfiltbiz.htm
re centralized filtration systems in the ornamental aquatics
business... same gear, principles apply... and any/all else on our site
(www.WetWebMedia.com) that is linked, is unknown to you... And make it
known if I can be of further help... Am tempted to suggest a "skid
unit" more for the pool industry than a more expensive "live
holding system" unit here... If cost is a concern... But would
like to know that I/we weren't otherwise changing the test
animal/prey's behavior by neglecting good water quality. Bob
Fenner> Sincerely, Ed Wyman
What else? (crab, lighting questions) Bob, I have a
question that I was hoping you could help me with. My tank is a 46
gallon bow front containing approx. 30 pounds of live rock, some
cleaner crabs/snails, and few feisty little damsels. (I also received a
small greenish crab reminiscent of an emerald crab but with stockier
claws and orange eyes that is nocturnal as a free gift with a larger
piece of live rock; so far he has been quite the little gentleman)
<Keep your eye on this recruit> The filtration consists of a
Magnum canister hang-on with a bio-wheel, a Visi-jet protein skimmer,
and two small powerheads (one submersed the other hanging). The tank is
36" in length and is currently lit by one normal 30watt 50/50 by
Coralife. The tank has been up for about 6 months. After extensive
research and keeping a close eye on the chemical balance and salinity I
have decided to move into a reef tank but have run into a problem with
lighting. There is no canopy to fit this odd shaped tank. <Better,
best to fashion one of your own> I have read that power compacts
(possibly a smart lamp) could be used but am concerned with the heat
atop the tank. It is covered by a glass tank top which the strip sits
on. Do compact flour. give off enough heat for me to worry about heat
fluctuations or the top cover glass breaking on my tank? <Not
to the extent of breaking the tank, no.> Let me know what you think;
I respect your opinion. Thank you, Mike Stewart <We might want to
talk/chat about specifics... design... but ballasting (electronic) can
be easily remoted... Do read over Ozreef's for input on
construction...: http://www.ozreef.org/> PS: I realize 46 is rather
small for a reef (40 being your personal minimum) but it was a gift
from my wife. I would hate to give it up until we could afford a nice
size tank of larger range with a fitting canopy. <I understand. Be
chatting my friend. Bob Fenner> Michael L. Stewart
Crabs and lighting Bob Thank you for all your help I
really appreciate having some one to ask all these questions to. I have
two questions for you. I deal with Two LFS and I am getting conflicting
information from them. <If you keep asking me, you'll
likely have a dozen!> One store tells me that emerald crabs are reef
safe and will not eat corals, polyps, or fish the other store says that
they will. <Hmm, here we go... Most of the time, small Mithrax crabs
won't harm sessile invertebrates... But there are many cases of
larger ones doing so...> So if you could resolve that question for
me I would appreciate it. I have three in my 46 gal tank now so I need
to know what to do. <This is a bunch in a small system... You, they
will likely be okay for a good long time... as they shouldn't grow
that much, that fast in such a setting> My other question is I have
a 36in JBJ compact light with 4 36 watt 10K bulbs on my 46 gal tank.
One LFS tells me that is plenty light for a brain and candy cane coral
the other store says it is not enough and that I need metal halides.
You are going to be the tie breaker please let me know your thoughts.
<You have sufficient light... the shop has a hankering to sell you a
chiller... Bob Fenner> Thank You Jason
Fiddler Crabs I have a 55 g. marine aquarium with 45
lbs. LR. I was recently given a VERY surprise present of a fiddler
crab. I've never seen one of these mentioned in any marine
article. <On our site: http://wetwebmedia.com/swcrabs.htm>
What do they eat? <Meaty bits of this and that> Will they
harm my fish (I am planning on a tank of blennies, gobies and other
small fish) or invertebrates (snails, an emerald crab, and fan worms)?
<Slow, sedentary to sessile invertebrates may be in trouble if your
crab gets hungry...> And how will I keep this guy happy?
<Need to have a place to get out, dry a bit... and cover to hide in,
reharden their exoskeleton during molting events. Bob Fenner> Thank
you very much for your time. Mike Rathwell
Stowaway Crab Robert, I purchased a finger leather coral
and subsequently discovered a small stowaway crab on the live rock to
which the leather was attached. He was black and about the size of my
pinky fingernail. Well he disappeared for about 6 months and then
showed up significantly larger. He has very large black front claws,
his body is about the size of a half dollar and is dark brown with
white lines. His legs are brown and hairy. I recently lost a plate
coral and wonder if he is responsible. <Possible> Any idea what
type of crab he might be? Is he a pest in a reef tank? If so, how do I
catch him? <Only the last... please read over the
www.WetWebMedia.com site under "marine crabs" and associated
FAQs. Bob Fenner> Your incites are appreciated Karen
O'Reilly
Filstar XP2 canister filter Hey Bob, I would like to add
the new Filstar system by Rena to my established 30 gallon reef set-up
(about 1year). I believe my Eclipse 3 system is not powerful enough
anymore (What do you think?). <A good addition as a reef filter
system> I have been adding more corals lately and believe it's
time for a filtration change. I was wondering which steps I need to
take when changing filtration systems. <Run both... if not
continuously, at least for a month> I was mainly worried with
biological lose and possible nitrate increase. Your input is always
appreciated in such technical matters. Look forward to your advice.
Thank You, Jason <Be chatting my friend. Bob Fenner>
Re: Filstar XP2 canister filter and Sally light foot
Bob, Thanks for the reply. I just came home and found my Sally Light
Foot on its back, its not so light anymore. <Actually lighter> I
added a frog spawn and a blue Linckia starfish 2 days ago, would that
cause the crab to die or do you think its was its time. <Who
knows? What do you think?> It seemed to be very active until today??
also my pipe coral and long tentacle anemone are touching each other,
should I keep some distance between them?? <Yes> Plus my
pipe coral doesn't look so hot. <It's losing. Bob Fenner>
Thanks, Jason
Little help please (Giant Crab in Live Rock or as Live
Rock...) Dear Mr. Fenner, It has been a week or so since I last
mailed you. I must report some good news. My cleaner shrimp and tiny
1/2" neon goby are alive and well. :) <Ah, good to read> I
did have an ammonia spike but a few water changes brought that down to
zero. I am optimistic that adding that 15 pounds of live rock was a
great help. I plan to add 15 more next month. <All sounds good> I
wonder if you remember my saying how pleased I am with the live rock at
my LFS. I have quite a large and amazing stowaway who I found just last
night as more proof to the quality. The biggest crab I have ever seen.
I went through WWM and found what I believe him to be. A Spider
Decorator Crab. BIG!! I walked by my tank after lights off last night
and thought I saw a big chunk of LR falling. Then I realized it was
moving. and had claws. and mushrooms and sponges of the most amazing
color on it's back and long legs. How I missed that monster when I
was arranging the rock last week I have no clue. :) <Hope it behaves
itself going forward> I have done some research last night to learn
as much as I can about him/her. An algae muncher at night and dormant
during the day. A terror of a beloved reef keeper because of it's
need to adorn it's self. I haven't found anything stating it
will do damage to live rock. Do you know if it could do that?
<Likely so to some degree> I have no coral or anything it would
decorate with. :) I think I just need a little reassurance. Also I
wanted to ask if I should have any other food for him/her to eat?
<I would try various foodstuffs to keep your crab, um, less
crabby> Or do you think he might be better off somewhere else?
<In all honesty, yes> In any event, I thought you might
appreciate knowing what appeared from the LR I put it. I was amazed. :)
Take care and best wishes, Josie <I won't gross you out... but
have encountered hundreds of life forms on/in, as live rock... some
wee-tiny, others... Bob Fenner>
Crab eating fish Dear Mr. Fenner, First, thank you so
much for the time and information you offer fish hobbyists. Your book,
Conscientious Marine Aquarist, has been a major asset. <Ah, thank
you for your kind, encouraging words> I have had a 29 gallon
saltwater tank since January of 2000. The first 2 residents were a
sally lightfoot crab, and a pygmy angelfish, Centropyge argi. Both are
still doing well. About 7 months ago, I added a Swiss guard Basslet,
and have been very pleased with this fish as well....until today.
<Oh oh> When I arrived home from work, I found the crab eating
the Swiss guard. I can't say for certain that the crab killed the
Basslet, only that he made a meal of him. <You are right about
the likely course of events> The crab is now approximately 4 inches
across, leg to leg. Last November, I had a Gramma disappear from the
tank, and at the time blamed it on the now-departed mantis.
<Possible... Grammas are also great jumpers> My question is this:
Will a sally lightfoot kill a fish if it is able to, and/or once it has
eaten a fish, are any other small fish safe? <Yes, this species,
especially when large can/will capture and consume fishes> I
don't want to blame the crab unfairly-- I actually like the crab--
but am not willing to sacrifice fish to it either. <You may have to
settle on just the inhabitants you have now... or look to getting a
larger system with wary and aware larger fish species... Bob Fenner>
Again, thank you. Sincerely, Owen Smith
Ghost crab care Dear Bob Fenner; My parents recently
brought back two ghost crabs from the beach in a 20 gal tank with sand
for my kids. Where can I find some general info. on crab care (besides
hermit crabs)? <Look on the Net under the genus
"Ocypode"> The main thing that I need help with is what to
do to replace/clean their sand. Any info will be greatly appreciated.
Please send any info. to . Thanks, Chris Colby <Not easily kept in
captivity. Bob Fenner>
Crabs First thank you for your help in other areas of my
fish tank. This site is quickly becoming invaluable for a
research/learn what you can nut like me. <Good company> But.... I
wish that I had found this site earlier (but we only recently got on
the net....we are so out of touch!) <But catching up quickly!> I
have been going on my dealer's advice with all my critters
currently housed in my tank, but after reading your articles some of my
faith has been shattered. I was told that deco crabs were detritus
eaters and rarely bothered anything in the tank, but from what I have
read in your articles is that this can be the vicious monster that it
looks! <Yes, unfortunately> And so far it has proven true. For a
while all was well, he his and I would occasionally see him sitting on
a rock at night, nothing was eaten or bothered. Then I bought a blue
star fish. Pretty little thing, one of those things that I really
wanted and went out of my way to make sure that my dealer knew it. So I
brought this beauty home, acclimated him slowly and then plopped him
into my tank, where he promptly "oozed" under a rock and
disappeared. A couple days later I noticed that he had bites on him,
two of them suspiciously the size of my Singapore angels mouth. At that
point my husband wanted to get rid of the angel, "We never see
him". But I see him and I love him. <A great aquarium
species... best of the genus Chaetodontoplus> So first I took my
rocks apart to make sure the deco was o.k. cause I thought for sure
that the angel might get him too...ha ha ha. (By the way I suspected
the angel because I saw him taste my anemone and my sea cucumber
once...though he never did it again) So I moved the star to an area
that the angel would never be able to reach. down flat and under the
rock that the star was attached to...there, now he's safe...
not!!!! Two days later I woke up and found bits of blue flesh on the
sand and a star that was losing his leg and had several more bites on
him. So then I got to thinking. Angels don't go out at night, so
what does? The only really nocturnal thing that I had at that time was
the deco.....huh. After reading your articles I am sure this is what
happened. The star went back to my dealer for a little r&r in his
live rock tank with nothing meaner then feather worms.
<Neat> And now.....well he just did in my cute half tame emerald.
I used to hand feed the little fellow. And if he was still hungry
he'd grab my feeding tube and reach up in for some more...I got him
on some rock, so financially he was no loss. But I don't count
money, just lives. <Good for you, the planet> And the weird thing
was that before the emerald died he started spitting this weird goop
out of his mouth, that eventually covered him. <Oh, oh> I
took him out and found that his whole abdomen was missing and I could
see his lungs. Have you ever heard of these crabs spitting goo?
<Reminds me of cheesy "B" or less movies with the
"done in" actors regurgitating whatever... suspect your
Emerald/Mithrax wasn't faking...> It was clear and stringy and
reminded me of the stuff that some animals use to catch food. Or maybe
what spawning looks like, except he wasn't spawning.... Any way
thanks for all the help. And as for the deco crab.....he's going
back for a trade on something far less likely to chew on everything in
site! Maybe a rock... <Much safer. Bob Fenner>
Blue Linckia and catching evil Sally Lt foot? Hi Bob aka
Lorenzo, Bob knows about my tank, but you seem like a nice
knowledgeable guy so here goes. I would like to catch a nasty Sally
light foot (my sister's name, I should have known :-)). Anyway it
ate an otherwise healthy (but teeny- 1") False Perc. I am thinking
I will replace with Clarkiis, but that's another story. <This
does happen... Bob as Bob> Anyway he (or she) looks impossible to
catch, so how do I do it? I looked on the FAQ and couldn't find
anything. <You might be fortunate to bait this faster than lightning
crustacean out with a meaty item tied to a stout thread or bit of
fishing line... and net it out from there> Also looked on the FAQ,
as if I catch the darn thing I am thinking about a Linckia star. The
question I have is how established is my tank? Or would I need more
time? About my system I have had it going since December. It is a forty
gal breeder with 40 lbs or so of LR and 40 lbs sand (some live). Usual
perimeters are: Temp 78-80 pH 8.2 Ammonia, Nitrites 0 nitrates under 10
Alk 3-4 Ca 390-450 Phos .1-.2 I use an Ecosystem 40 and have 144 watts
PC. I have a MaxiJet 1000 for circulation. All creatures are doing well
and include: Midas blenny, juvenile Sailfin tang (who is not long for
the tank at his/her eating rate), a Common Cleaner, some Turbos, a
regular mushroom, and a Rhodactis. No deaths or anything for months
except the ill-fated clowns (one jumped out -- maybe spooked by Tang
and the other was eaten :-o). I won't put any slow creature in
until the SLF is out, but aside from that what do you think? <Would
skip a Linckia for this small system... Look for a smaller Fromia
Seastar species in its stead. Bob Fenner> --Jane J
Crab Control Bob, I discovered a crab in my 75g reef
tank a couple of months ago which I assumed to have been a hitchhiker
on my live rock. I didn't give it much thought at the time but I
did some reading which indicated that some types of crabs can be
detrimental to the tank including corals, hermit crabs, small fish, and
snails. <Yes, many crab "recruits" can get large, become
too destructive> Well - this weekend I saw him again for the first
time in about a month and he is now about the width of a quarter, light
brown (almost beige) color, and has a hairy appearance. I noticed that
he has taken refuge on the bottom of the tank under a large piece of
live rock. I monitored him for while and much to my chagrin observed
him sneaking out from his refuge and capturing small Nassarius snails
which he then transports back to his hideaway and assume he then
consumes their meat if he can. <Likely> Given the obvious
difficulty in trying to capture this nuisance - I'm writing you to
ask for any insight you may have in trapping and removing this crab
short of removing all my live rock to find him. <Do take a read
through the FAQs on Crabs on our site: www.WetWebMedia.com as well as
those on other crustacean groups... about baiting, trapping them out of
established systems. I would probably be removing yours. Bob Fenner>
Your thoughts would be appreciated.. Thanks,
Soft shell crab Hi port some living rock for my tropical
marine tank 6 weeks later spotted some damaged coral. The culprit
is a crap about 1.5 inches in size grey in colure with a soft shell
there is no discarded empty shells in the tank .The crab hides
during the day in a small hole the only time I see him is during
the night. He is growing fast, can you tell me how large he will grow
and is he a danger to my fish and anemones <Hmm, can't tell
what this animal is species-wise... but would likely pull it (bait it,
trap it out...)... some directions on how to go about this are
posted on our site: www.WetWebMedia.com. Bob Fenner>
Stow Away Crab Bob, I recently purchased your book from
FFE and find it an excellent source for information and guidance.
<Thank you... much good help putting it together> I have referred
to it countless times in the short time I have had it. But my question
is in regards to a stow away crab. I just received a shipment of SPS
corals from FFE for my 90 gal. reef. While the corals were acclimating
I noticed in the bag with the Bird Nest coral that a small crab was
hiding in the branches. <Not uncommon> I looked on WWM and
FFE as well as some bulletin boards, but have found no information on
my specific crab. <The site would have to be several times its
current size... it will be...> It is red, has huge claw in relation
to the it's body, and a thin yellowish band of color on each one of
it's legs. I didn't know if it is safe for a reef tank, but
doesn't seem like a good tank mate. I have a mated pair of gold
strip maroons, Mandarin, 2 cleaner shrimp, and a lawnmower blenny.
Thank you for making this hobby a much more enjoyable journey!
<Thank you for sharing it with me. I would likely remove this
"unknown" Decapod at my/your earliest convenience. Bob
Fenner> Brad Stefanko
Arrow crab, good lord! I'm in a state of confusion
and disbelief. I recently got an arrow crab to ensure that I didn't
have any bristle worms and I'm pretty sure that I now regret the
purchase. I used to have quite a plump little lion on my last tank that
died from a nasty fight with pseudomonas and I had two peppermint
shrimp in there for him to much on at will, also to give it something
to do, hunting and all. anyways they made it into the second generation
tank. only one survived and I've had it for quite some time. I saw
it last night in full health (about two inches, a "big un" by
ornamental peppermint sizes) and now my arrow crab has its maws on its
exoskeleton. I haven't seen it for about a day now... perhaps its
molted, that would be fine. but is there a chance that the arrow crab
nailed it? my arrow is insanely aggressive towards anything (I've
got 8 blue fin damsels, I'm a bit nervous there too. always do my
morning count...). can a 4in leg span arrow tackle a 2in peppermint?
<Absolutely... and it will eventually eat those Damsels as
well...> Jon Trowbridge I'm pretty sure it molted, but I'm
always nervous about the arrow. kinda wish I never got it. <You will
be more sure about that sentiment soon... see the section on
"Marine Crabs", Stenorhynchus on the WWM site... Bob
Fenner>
Crab question I've got a question regarding
Schizophrys dama (decorator crab). about how many species are in this
genus, <this genus of the family Majidae, the Sea Toads, has at
least a dozen described species, but several more undescribed as yet...
and some majids are not "decorator crabs" per se... and other
families contain "decorator" types...> and are they all in
the same genus because they 'decorate', or is it for other
reasons. <Other, morphological reasons> I started a 125g
reef tank about 5 months ago and I'm going for a semi regionally
accurate system going from the south of the barrier reef to a bit west
of Australia (Christmas island). the furthest east ill go is Fiji, and
the furthest north ill go is southern Indonesia. <Like the way you
put this> anyways, I think the whole idea of decorator crabs is
pretty cool and I'm trying to find out some information about them.
are their any species that fit in that region that you can think of?
perhaps some or the kind that use anemones as their main defense
system? perhaps boxer crabs? any help would be neat <Best way to
approach this IMO/E is to select for the animals on the basis of where
they were actually collected... Schizophrys are not "reef
safe" as the case with most all crabs... Do look into "The
Modern Coral Reef Aquarium, volume 3" here... for about the most
up-to-date, complete coverage of potential Decapod additions. Sven and
Alf's website link can be found on the WWM sites Link Pages.>
Jon Trowbridge oh, I've seen some online places that sell anemone
decorators and I'm wondering s they sell the baby anemones on them,
do they (anemones) usually end up living? or would I get a bag with a
crab and a lot of goo.... <The associated anemones live/ship about
as well as their hosts... both generally arrive in good condition. Bob
Fenner>
Crab question Hello Bob- I recently purchased a bright
pink hard coral from a mail order company. After placing it in my reef
tank I noticed a very small crab approx. 1/8th of an inch from claw to
claw that came with the coral and appears to be guarding the coral as
his territory. If anything comes within range of the coral the crab
gets between the object and his coral with his tiny claws extended. I
have searched every internet sight I can find, to see what type of crab
this could be and am hoping you may have an idea. He is mostly white
with rust red claws. Thanks for any info Sincerely, Carol Gibbs <A
few possibilities here... and do agree with your assessment... this
crab is likely "guarding its turf"... For starter's, of
works that are widely available, see Allen and Steene's
"Indo-Pacific Guide" under both corals of the genera Porites,
Pocillopora and crustaceans/decapods... Bob Fenner>
A Bunch of stuff, with the Crab the "butler" who
did it Hello Mr. Fenner, I emailed you about a month ago when I
received some "extras" anemones in a recent fish shipment
because it took the company so long. I really appreciate your advice
and gave them to my local aquarium store. The white beaded is living in
an employees tank and doing great paired up with an anemone fish, I was
thrilled. <Very good to hear/read> The other pink tip is a
permanent residence at the store and has his good/bad days. I just
received my first two pair of Seahorses on April 2. Tank bred and
raised on frozen Mysis shrimp, I just got my first problem with trapped
air bubbles in one males pouch. I think! <Very common... and can be
real trouble> I have also read about trapped air bubbles under the
skin or ingested and/or problems with undissolved gases in your water
affecting buoyancy. <Yes> I recently discovered a very large,
very red crab, he must have hidden very well indeed, will this guy
threaten my horses? <Possibly, yes... if hungry, for sure> I also
had a arrow crab and peppermint shrimp who disappeared (eaten) and
I'm thinking this red guy is the culprit. <Likely...> I
looked at the pictures of the crabs on your section but didn't see
any like him. Very large front claws( mandibles?), white horizontal
stripes down his legs, no shell (like hermits). <Would take a few
lifetimes to assemble such an index... with images... a worthy goal...
I put a few on as I pass through, get new images...> Is there a trap
I can use to get him if he poses a threat? <Yes, or a tethered
bait... see the WWM site re pests/removal here...> He has buried
himself under my 100 lb.. of Live rock, haha, I can't move it. I
also have a 55 gal. brackish and would love to see more inf. on the
various fish, especially puffers, no one seem to know how they breed
etc.. <Need to get to this section... there is a nice Scat article
in FAMA this issue (May)...> I also have another question and have
asked my aquarium store but no one else has seen it. I have a variety
of different crabs all small but the previously mentioned one, one type
however, pale red, hairy legs & body goes up to the very top of my
live rock and spits-spews out white dots (bugs? eggs?) they swirl
around for a few days and then are gone. What is it doing?
<Don't know... maybe reproductive dispersal...> Once I
noticed hundreds of plankton-type white organisms swimming around for
days, then gone. I hear of people talking about calcium etc... are
these just worries for the reef aquarist? <Concerns? Yes... one of
many possible ways of judging water quality... an important
variable...> Currently I only check for pH, ammonia, nitrates,
nitrites, salinity. I do have live sand, rock, fan worms, gorgonians,
some kinds of corals, but I'm looking at a species only tank with a
few Dragonets, BTW what do Dragonets eat exactly? <A wide range of
interstitial fauna... crustaceans, worms, mollusks and more that live
in, between sand grains... the water column...> Sorry for so many
questions. I'm amazed at your wide range of knowledge on so many
different topic. Thank you for your time and patience, its greatly
appreciated. <You are welcome my friend. Let your curiosity and
wonder lead you to further study, enjoyment. Bob Fenner>
Mithrax Crabs... no carte blanche guarantees... Hello
Mr. Fenner In your previous writing's on your site you have stated
that the Mithrax crabs are good bubble algae and Bryopsis eaters. I
very much would like to have a few in my 120 Berlin system. Will they
be ok with my red leg, and blue leg crabs and all of my corals? How
many would you recommend for my tank? As always , I am grateful for
your site, books and advise. Thank you , and take care. <I would try
four or so small individuals of the Emerald Crab <Mithrax>
here... but no guarantees... there are numerous cases of this species
trying out other crabs, even corals from time to time... Get one inch
or so individuals... chances are they will leave your other life alone.
Bob Fenner>
Lightfoot Crab Just a quick update--the sally lightfoot
crab that lost a claw and two right legs molted today and has all his
legs back! (Hmm, as I had told you... neat trick eh?) I had been
offering him frozen krill on the end of a skewer every other day or so
since the "accident" to ensure he was getting plenty to eat
and to speed up the growth/molting process. Looks like everything is
going to be fine on that front! (Ah good) I also caught a glimpse of
the peppermint shrimp last weekend--he's been hiding out in the
back of the tank, apparently, and has not become a lightfoot meal, yet.
(Also good news) The new tank is on order. I'm building the
sump/refugium (30 gal) this weekend. Everything else has been ordered
or has already arrived. I'm sure I'll have a question or two
once this whole process really starts cooking, but I've also found
a newsgroup with some pretty experienced reef keepers who have been
very helpful as well. (Ahh!) Take care. Chat again soon. --James D (Bob
Fenner, in Cabo San Lucas)
Question regarding Mithrax and Sally Lightfoot Crabs It
appears that either a newly added Mithrax or Sally Lightfoot Crab
killed two of the shrimp in my 60 gallon tank. My guess is the Mithrax
but I would appreciate your opinion. <Yes, this does happen with
both crab species... they are not "simple herbivores"... not
nearly as opportunistic as some crab species... but still...> Also
is there a way to catch the offending crab without dismantling the
tank. <You can try baiting, trapping... per "crustacean"
removal sections on our site: www.WetWebMedia.com> Thanks for your
input. Mark Hill <Good hunting my friend. Bob Fenner>
Sad crab just the other day my anemone crab started its
monthly molt. it usually takes about a day or so to complete the
process (most of it is at night). so anyways, this time was a total
bungle. this is the third day and its been having problems with the
molt. I feared it would suffocate on the first day so I -carefully-
aided in the removal of its top main shell (don't know the
technical term). I broke just enough off so that its gills weren't
covered and left the rest up to it. well the molt is pretty much over
with, but the crab had to ditch both of its main claws and about 50% of
its legs. it only has one of its 'filter' claws. as far as I
can tell both sets of oral pincers are ok, so it can eat. anyways id
rather write this one off and ditch it, but alas I've grow fond of
the little bugger. I placed him near an outcropping of rock so that it
has something to hold on to (otherwise its pretty much on its back or
drifting around). and I'm dropping some roe very close to him every
now and again. I know crabs can recover from loss of limbs, but this is
pretty bad. it definitely wouldn't last in the wild. got any
advice? <Don't help animals in ecdysis... they can/will molt in
due time... on their own... Keep track of alkalinity and biomineral
content with these animals and make available materials (rock,
substrate) that they can/will incorporate in their diet for purposes of
biomineralization. Provide plenty of cover of different size hiding
spaces...> thanks Jon Trowbridge ps. no other 'animals' in
there except some corals and a few urchins/snails. nobody will bug it.
perhaps there's a Ca problem? I'm using Kalk as well
(iodide/strontium/CoralVite/Coralaccel). <So... are these at
reasonable levels? Bob Fenner>
Legless Lightfoot One of my Sally Lightfoot crabs molted
yesterday. However, today he is missing one front claw and two of his
legs on the right side. Is it common for these crabs to lose legs in
connection with a molt? Or is something amiss here? <Hmm, sometimes
in ecdysis/molting some limbs are not formed due to nutritional
reasons... perhaps other factors... but in most cases like this,
"someone" was munching the inopportune animal during the
"hiding phase" of rehardening its new exoskeleton... it
can/will "re-make" these lost limbs next molt...> In case
you don't recall, one night I saw a different crab in the tank that
must have come in on the LR. The damaged lightfoot is now
"guarding" a hole in the LR, and I can see the two front
claws of the "mystery crab" at the entrance to the hole.
Occasionally the lightfoot will "pick" at the other
crab's claws. Are there any species of crabs that eat other crabs?
<Many> This "mystery crab" was pretty small before, but
is it possible that as he's getting bigger he's munching on the
Lightfoots? Or is this loss of legs just something that sometimes
happens when they molt? <More likely the former. Bob
Fenner>
Black Crab Dear Sir, I have a 55 gal reef tank approx. 7
mos. old. I was feeding my fish one evening and noticed a couple of
hairy legs beneath my chubby plate coral. wait till lights out and came
back in the room after lights out. The thing I was a crab sort of looks
like a sally light foot but smaller but its coal black very shiny and
has hairy legs with white spots. I did not buy it so I think it came in
with my rock. But it has been staying under my chubby until it died and
I wondered if that crab anything to do with it. <Doubtful>
I've talk to aquarium shop but they can't help me. I just
wanted to know this this species eats corals and leathers if so I, I
need to get it removed!! Thank you, Gary! <Good question, but I too
cannot identify this crustacean from your description. Perhaps by
chance you might find something similar in books concerning these
decapods at a large local library? Bob Fenner, who would just remove it
"on general principles" if it were more than a couple of
inches in diameter.>
Can an arrow crab live without claws? Hello Mr. Fenner!
First of all, thanks for offering your services! (I really appreciate
your expertise.) <Glad to be here, help> I bought a large arrow
crab a few months ago and it only had one claw. (Since I have a set-up
that makes it easy for him/her to obtain food, I thought it
wouldn't be a problem.) <Likely not> However, last night, he
lost his other claw. I couldn't find it anywhere and was wondering
if you could tell me if he'll a.) be able to survive? b.) How it
might have happened? <b. a tussle of some sort, a. likely yes> I
have a 60-gallon hex. with live rock and all I have are 5 small green
Chromis and 1 yellow damsel. I also have 4 hermits and some Astreas.
This past weekend, I purchased a Sally Lightfoot as it was recommended
to me as a good and harmless algae grazer. Might it have been that?
(Could a Sally Lightfoot take on a large one-clawed arrow crab? Would
it?) <Yes...> Thanks for any insight you could provide me with.
<Next molt your Stenorhynchus will likely have something in the way
of claws back... and then next... a bit more> PS - Two weeks ago, I
noticed one of his legs on the tank bottom. (I suspect he was molting
since he still had 6 legs.) <Sounds like a miniature crustacean
version of "Clash of the Titans"... I would separate these
two if you have the facilities> Best, Declan Procaccini <Be
chatting, Bob Fenner>
Arrow crabs Mr. Fenner I placed an arrow crab in my
aquarium in hopes that it would rid my live rock of bristle worms. but
recently, if been reading that these crabs could attack fish or even
other crustaceans or invertebrates. is this possible? <Yes,
unfortunately... for their size these oddities can/do become predaceous
toward fishes, other invertebrates> the crab we have doesn't
seem to bother anyone. should I remove it, or just keep a cautious eye
on it. <The latter IMO. You will likely see signs (scraped fishes,
stalking behavior) before outright missing livestock. Bob Fenner>
thank you
Lightfoots OK--now you'll really know what a
greenhorn I am. When I got home this evening, I pulled another
"dead" sally lightfoot crab out of the bottom of the tank.
Before I ran a barrage of water tests, however, I counted them--and
there were three crabs on the rocks--and we started with three. Now I
know what an empty exoskeleton looks like after a crab molts. I guess
they're happy and growing. . . <No worries... glad to read,
know... and do leave these cast off exoskeletons in the tank for a week
or two... sometimes consumed, incorporated by the shedding animals to
augment their new ones> On another note--I guess I need to build a
calcium reactor, and soon. Tonight I dosed the aquarium with the Tropic
Marin Bio-Calcium. It's a powder product, if you're not
familiar with it, and the instructions say to just put the powder in
the tank by sprinkling it on top of the water. <Very familiar
with the product and company... both are excellent> The hammer
coral, moon coral and finger leather were unaffected--in fact, all
three of them seemed to love the Ca boost and extended their polyps
even further. The moon extended its tentacles about an inch, and some
of the hammer polyps were an inch long as well. However, the pagoda got
what looked like "blisters" all over it and the flesh looked
very irritated, and the bubble and Goniopora (I know--bad choice. . .),
and toadstool leather all retracted completely. Is a sudden increase in
Ca likely to cause such a reaction in these species? <Yes... a
few things at play here... like you state, sudden increase in calcium,
but also pH (locally), and physical irritation (irrespective of how
well the product appears to dissolve... Best to pre-dissolve, introduce
the new material by way of a filter, sump... and slowly (perhaps rig up
a drip bottle or siphon of airline tubing...> (Based on the label
instructions, Ca was increased roughly 35 ppm by the dose.) Any
permanent damage? <Not likely, unless the animals health was
impugned before use... but more nicks toward the negative...> (They
all seem okay now, after several hours--but no reason to put them
through any stress if I can dose the Ca gradually, on a daily basis,
and by first dissolving the Ca in the top-off water--or better yet, by
building a reactor.) <Ah yes... the process continues.> Thanks
once again for your thoughts. <You're welcome my friend. Bob
Fenner>
Cleaners The cleaner shrimp are doing fine. However,
when I got home yesterday, my smallest sally lightfoot crab was
decimated at the bottom of the tank, missing several legs. Is it likely
the Lysmata are the culprits? From reading about these shrimp on the
site, my guess would be that they got hungry and decided to snack on
the crab. <Very unlikely... crustaceans know who to avoid... and
Lysmata are pathetically slow compared to this genus of crabs... You
may have a Stomatopod... Alpheid... hungrier fish... or just a
sick/dead Sally...> Hope you're doing well--got your book on
Monday and it's been a great reference--very informational and easy
to read. Thanks for your contributions--and for the section describing
the terrible use of cyanide to collect fishes. I'll certainly ask
about the origin of every specimen I buy in the future. <Ahh, deeply
gratifying. Thank you. Bob Fenner> Talk again soon! James A.
Deets
Percnon gibbesi Hi Bob - I recently walked into the LFS
and, as described in your chapter on crustaceans, scurrying around
inside a display tank were a half dozen Percnon gibbesi with an
accompanying "Sally Lightfoot Crabs" I.D. sign. The Nimbles
really do deserve their correct common name and fascinated ... I bought
one. Nimble Sally has been in QT for two weeks and I'm getting
ready to move it into my display. The only behavior that I've found
curious has been the specimen rubbing its legs together; occasionally
"wiping" it's face with legs or claws; and rubbing /
"scratching" its back on the piece of rock I keep in non-fish
QT. Are these unusual habits for Ms. Nimble? <Not at all...
general cleaning> Recently, I found a discarded exoskeleton ... does
the itchy behavior precede a molting event? <Perhaps ecdysis
(fancy schmancy term) is related... but maybe not> Should the
abandoned shell be regarded as a decay/ammonia threat and removed from
the tank? <I'd leave in for a few days... little ammonia/protein
in it... and like many crustaceans your Percnon may consume it for
mineral et al. content to build new exoskeleton> Finally, should
crabs receive the "freshwater dip" treatment prescribed for
fish? <Not most, and not this one> Thanks for your help - Tom
<Thank you for your input and asking. Bob Fenner>
Have you ever heard of this happening? Hello Bob,
I've written in the past to ask questions about the upkeep of my
nano reef, but this time I have more of an anecdote to relate. Night
before last, I spotted my happy, well-fed and well-adjusted ocellaris
clownfish, which was about 1.5" long, apparently 'wedged'
between two rocks. Thinking (naively) that he had swum into a spot from
which he could not escape, I tried to use a feeding prong to ease him
free. After several minutes of prying, I almost had him free, when a
frustrated green Mithrax crab reached out of his crevice and pulled him
back in! It appears my emerald crab had caught and killed the
clownfish, and was in the very early stages of consuming him. I know I
caught him right after the fact, since the fish's eyes were clear,
his color was good, but his gills were still when I finally freed him
from the tank. Have you ever heard of such a thing happening? Thanks
for your time. Josh <Yes. Unfortunately, Mithrax/Emerald Green Crabs
are not entirely the benign, strictly algae-eating creatures some folks
make them out to be... They will indeed eat fishes when they are large,
hungry enough to catch them. Only small crabs of this genus are to be
tried, trusted. Bob Fenner>
Arrow Crab Hi Bob, Thank you for your previous advice,
and your current work to help us becoming a "conscientious marine
aquarist" (loved your book!). I am currently in the process of
ordering your new book---although an on-line form would be more
convenient :-). <Thank you times three... Agreed... wish we did have
the capability... but then, it would take away the fun and good I can
do answering queries, maintaining and building the site... maybe some
day soon, or better, hopeful that the pet-fish publishing world (it is
small!) will "wake up, smell the java", and get more of my
works (and several friends) into print, distribution, sales... In the
meanwhile, nothing really wrong with snail-mail... Will get you the
book in, um, maybe a week total transit time from you sending order to
receiving it.> I wanted to have your expert opinion on the arrow
crab (Stenorhynchus sp.). I just completed the initial phase (cycling)
for a 90 gal. reef system. I envisioned to have mushrooms, star polyps,
soft corals, cleaner shrimps, scarlet hermit crabs, and a few fish
(orchid Dottyback, flame angel, and yellow or Kole tang). My questions
are as follows: 1) Is it safe to add an arrow crab in my system I
envisioned? <Maybe... depends on what you're going to put in
with it... and thanks for prompting me... have my "crab"
slides and reference works, old articles, on the tables here... re-did
the shrimp, cleaner shrimp, fw shrimp... and lobster sections of WWM
the last few days... and am on to the crabs today....!> 2) Does the
arrow crab have a history of surviving/thrive in a captive environment?
<Yes, but...> 3) What is a typical diet for an arrow crab?
<Most anything it can get its claws on... which is considerable as
this animal gets bigger. Have seen them eat Butterflyfishes in
captivity...> 4) Where can I find more information regarding the
arrow crab? <Take a look at the www.WetWebMedia.com site in a couple
of days... for the references listed there... I'll be looking
through the bibliographic tools at my disposal (online), and be adding
the "pet-fish" references there as well> As always, any
information will be greatly appreciated. Thanks, Dan <Chat with you
soon my friend. Bob Fenner>
Mystic Mithrax Dear Bob: I have a 155 gal tank started
in Oct. 99. I have lots of live rock and also the live sand. I really
haven't had much growth on it except some brown grass and my
Mithrax crabs ate that. I think they are eating so much that nothing is
growing. I got 10 of them. I have feather dusters, two anemones, some
different corals(7) arrow crab, a clam, two metal halide lamps,
skimmer, 350 magnum pump with charcoal, temp. 80%, water tests good,
but: I just lost a large coral (star coral) that had been doing really
good, before that a carnation coral, before that an elegance (2). It
seems that the inhabitants I have now do well but new ones slowly die.
I just purchased some plants from ff. and I'm hoping this will
help. I also really like them. Can you help? I lovvvvvvvvvvvvvvvvve
this hobby. Temp. 78 - 80 Brenda (thanks and I really appreciate your
diary.) >> Yikes, ten Mithrax Crabs? You really should try to
remove all but a couple or three of these... more are too many... a
tough job I know. Is the Magnum (canister filter) all your filtration?
Not sufficient for a 155 gallon system... Hopefully you have left off
some gear, circulation mention. And the Carnation and Elegance choices
were poor... they generally don't live... New animals slowly dying
is a bad sign... Poor water quality, some sort of poisoning from inside
(dead, dying organisms) or outside (supplements... what is your history
here?)... The macro-algae ("live plants") you mention getting
a step in the right direction... but do read over the Marine set-up and
maintenance pieces stored at my site: www.wetwebmedia.com for insights
into what's been done so far that is the cause of your losses. Once
we get your system set-up and running properly, it will be far more fun
and easier to maintain. Bob Fenner
Sally light foot Hey Bob I have a Sally light foot crab.
Constantly busy eating algae etc. Also constantly shedding it's exo
and growing. JUST HOW BIG IS THAT THING GONNA GET? It is already more
than 9" from one leg tip to another. Do I have any thing to worry
about its size and becoming a clumsy nuisance? I really like him or
her, well it anyway. Kevin Johnson <Wowzah! this is a very large
Sally Lightfoot Crab (Grapsus grapsus)... the biggest one I know of was
(collected with difficulty in the wild) about ten centimeters/4"
across its carapace (upper shell)... This is a very big crab for a reef
tank... and though they mainly eat algae, this species has been
recorded eating invertebrates... even capturing small land mammals...
Bob Fenner>
Re: Sally light foot I am sorry I must have said it
wrong. The crab is about 9" from the very tip end of one leg
across to the very tip end of another. The body of it is about
1.25" across. Is it going to get much bigger. I don't want it
eating my invertebrates. Right now it is very content on eating algae.
Do I need to take this one to a pet store soon? Kevin Johnson <I
understood the end to end part... those are some long legs! And I
wouldn't trade this crab in if it was doing a good job, and leaving
your other livestock alone. Bob Fenner>
Stowaway Crab I ordered some fish and corals from you a
couple of weeks ago and everything is great. However, one of the
things I ordered, a Pink Stylophora, had a stowaway. When I took
it out of the bag, I saw a small crab hiding in the branches of
the coral which looks like a Mithrax crab, except that it was red. I
left the crab alone until I noticed that it appeared to be feeding on
the polyps of the Stylophora at night. At that point I removed it
from the Stylophora by blowing a powerhead on it. However, at that
point, it looked like many of the polyps at the base of the coral
had been picked at or eaten. What is this crab? Should I get rid of it
from the tank altogether? <Hmm, sorry, but not surprised to hear of
such stowaways... I would give it the heave ho... Doesn't sound
like a commensal... probably more trouble as time goes by. Bob
Fenner>
WHAT TO FEED A DECORATOR CRAB... I BOUGHT A DECORATOR
CRAB TWO WEEKS AGO AND HAVE JUST BEEN LETTING HIM FEED ON HIS OWN. I
CAN NOT FIND ANY INFORMATION ON THEM THAT TELLS OF THERE DIETARY
HABITS. HE IS IN A FISH ONLY TANK, DOES HE NEED LIVE ROCK TO USE FOR
HIMSELF AND WILL HE EAT BROWN ALGAE. >> These animals are feeders
on other invertebrates: worms, shrimp and other crustaceans... and a
minimal amount of greenery... They can live pretty well on newer live
rock inhabitants, in addition to meaty scraps from feeding your fishes
and other invertebrates. Bob Fenner
Decorating by eating others I bought a decorator crab a
few days ago, and this morning it looked like he was trying to eat one
of snails. Will the decorators eat the snails or any of my other
livestock? (I have 3 tangs, a clown, 2 damsels, mushrooms, button
polyps, daisy polyps, and anemones) <Yes, most crabs will gladly
consume most anything in the way of food... live or otherwise... Do you
know which species this is? Time to do some investigating... Bob
Fenner>
Crab cleaner ups or eater ups? Hi Bob, I ordered one of
the large clean-up crew packages from FFExpress and the crabs ate all
of the snails within a couple of days. I have never experienced or
heard of this happening before and was just wondering if you would have
any comments?? Thanks, Diane. <I do... my standard spiel re Decapod
crustaceans... I don't trust any crab around anything it can get
its greedy pincers around... They are almost all opportunistic
omnivores.... eating most everything that can't get away if they
get hungry... Bob Fenner>
To Mithrax or no Bob, Thanks for all your past help.
I've read your book, (loved it) and have all your FFE Q/A in one
doc for easy searching. Here's my questions. I have a 75 with
4x96 CF Bulbs (2 6700, 2 7100) bulbs. I run them 14 hours a day.
I've read different things on CF, what is your opinion on how
frequently they should be changed? I've seen you recommend Mithrax
crabs for reef tanks, and also seen the following quoted from Julian
Sprung: Avoid Mithrax crabs. They may do a good job when real small but
they grow real fast and cause damage .
http://www.athiel.com/lib5/macna2.htm What problems could they cause?
What should I NOT have them with? I am looking for a good sand stirrer.
I had some white burrowing starfish, but they got eaten by my pacific
or fire cleaner shrimp? Thanks! Marty < Good questions... ones that
are tough to answer... Regarding the CF lamps, you'll have to check
with your supplier...some have "effective lifetimes" about
the same as (T-12) regular/old-fashioned fluorescents... on the order
of 7,500 to 10,000 hours... and others up to 20,000 hours... And
really, the only way to tell, irrespective of "doing the
math" on how many hours you're running yours... that they need
replacing is to use a PAR or lumen meter... IMO they should be replaced
either at 80% of their calculated "effective lifetime" or at
80% of their output... The latter, the better judge.> "Avoid
Mithrax crabs. They may do a good job when real small but they grow
real fast and cause damage", this bit lifted from the URL you
posted. But also see: From 'The Reef Aquarium, Vol. 1', Sprung
and Delbeek, p279: Mithrax crabs are good herbivores for large
aquariums. Mithrax sculptus only grows to about 6.3 cm (2.5
inches), but is capable of capturing small fish. Some Mithrax
species grow very large, and are therefore unsuitable for most
Aquariums. Some species have been reported to eat Valonia. This
crab is from the Caribbean. < So... I think these statements
are confluent... that in the former Jules was referring to little reefs
(ten gallons, like his), and in the book version of his opinions,
larger systems. Some aquarists have reported that Mithrax crabs will
eat polyps if hungry enough. I recommend that you start with only one
and keep your eye on it to make sure it does no harm. Bob
Fenner >
Lightfoot, light some legs I have a sally lightfoot crab
and he/she has lost 4 legs in three days, also all 4 legs fell off
on one side. I have two emerald crabs, 1 three striped damsel,
three blue damsels, 1 clown, hermit crabs, snails, . do I have the
right fish combo or is my crab sick. please help!!! < Yikes... very
unlikely that the legs have "just" fallen off. More likely
pulled off... I'd guess by the other crabs (real: emeralds, and
false: hermits)... or a more remote possibility that the animal has an
internal problem (e.g. an infectious or parasitic disease). In any
case, the prognosis is bleak to bleakest if you do nothing... if you
can't move the Sally Lightfoot, do place it in a separate
chemically inert container (outside power filter box?, plastic breeding
net-trap?...) away from your other crustaceans... Bob
Fenner>
Mithrax, reef safe? I noticed that the Mithrax Crab will
eat bubble algae. Are they safe for a reef tank and how many is
necessary for a 90 gal tank with 90 lb. of live rock?
Thanks.........Lin Smith < Of all crabs, this genus is amongst the
best for reef use, though not totally "safe" (they can eat
coralline/red algae, might try your other animals if hungry), but do
often consume Valonia/bubble/pearl algae as well. I'd only use a
couple... easier to remove a few if they've got to go than many.
Bob Fenner>
Mean Crab disease I have recently started a reef tank 44
gal, pentagon, with some live rock and a few anemones. With the live
rock I got a really mean crab that has now grown to almost 1.1/2"
in diameter, and ate both the gobies I had in the tank, and I think
some of the anemones. I don't really want to get rid of him (my 3
year old thinks he's "cool"), so I bought a dwarf lion,
that is right now my only fish in the tank. Last night I noticed that
the lion had little air bubbles all over him. When he was chasing his
dinner a lot of the bubbles blew off, but then a few hours later they
seemed to return. Is this a problem? < Hmm, might be, and may be
related to the Crab that ate Cincinnati... Are there bubbles from air
or water pumps just kind of floating around in the system? Lionfishes
are quite slimy and these bubbles might be adhering to it from these
sources... on the other hand maybe Mr. Crab is chasing/pinching the
lion about at night, causing it to jet up to the surface... If it were
me, I'd A) give that crab the heave-ho, B) Get less pinchable
fishes to keep with it, C) A combo. of both... Bob Fenner>