Acropora Crab Question

landlubber · Apr 7, 2017

hello reefers!
my sps dominant system suffered an alkalinity related "mini-crash" recently and is in recovery mode now but i did lose 2 baseball sized colonies and 4 fragments. interestingly, i was watching the horror unfold on one of the small colonies and noticed an acropora crab jump ship on the coral that was RTN'ing and scoot over to a healthy, crab-less colony nearby.
now considering i've never seen any of my acro-dwelling crabs outside of the coral it resides in ever before it interested me. about 2 days later a similarly sized acropora started bleaching to the point where it was left colorless but didn't suffer and STN or RTN and the crab that it calls home has since stuck with the coral through the process. the coral is fairly white but algae has only collected on the tips and hasn't progressed which leads me to my question... is having a crab still calling that acropora home an indicator that the coral could possibly recover?
it's been a week and the crab is busy as ever inside and hasn't taken to any of the other, albeit smaller but crab-less corals in the area.

Ds04384 · Apr 7, 2017

landlubber said:
hello reefers!
my sps dominant system suffered an alkalinity related "mini-crash" recently and is in recovery mode now but i did lose 2 baseball sized colonies and 4 fragments. interestingly, i was watching the horror unfold on one of the small colonies and noticed an acropora crab jump ship on the coral that was RTN'ing and scoot over to a healthy, crab-less colony nearby.
now considering i've never seen any of my acro-dwelling crabs outside of the coral it resides in ever before it interested me. about 2 days later a similarly sized acropora started bleaching to the point where it was left colorless but didn't suffer and STN or RTN and the crab that it calls home has since stuck with the coral through the process. the coral is fairly white but algae has only collected on the tips and hasn't progressed which leads me to my question... is having a crab still calling that acropora home an indicator that the coral could possibly recover?
it's been a week and the crab is busy as ever inside and hasn't taken to any of the other, albeit smaller but crab-less corals in the area.

I've heard or stories where crabless colonies will die but colonies with crabs survive stressful events. Whether the crabs knew and went to/stayed on healthy colonies or if the crabs somehow helped the colony they were on survive was never clear. However, if a colony has a crab still I would definitely say it is a good sign.

landlubber · Apr 7, 2017

and that is kind of how i feel about it too.
as simple as i perceive a tiny crab to be it definitely appeared as if it had made an instinctual decision head to greener pastures when it felt the coral was past the point of recovery.
i guess time will tell if this other guy sticks with his home.

AcroNem · Apr 7, 2017

Ds0 explained that very well. I've had many colonies come in with crabs on them and I've always left them there. I've had colonies with or without crabs do better but usually find they will do better.

Salty1962 · Apr 7, 2017

The crab will stay as long as the coral is producing mucus which they primarily feed from.

landlubber · Apr 7, 2017

Salty1962 said:
The crab will stay as long as the coral is producing mucus which they primarily feed from.

ok well i guess the next question is how long will a dead coral produce enough mucus that the crab vacates? still interesting that a crab took the risk to abandon it's lifelong home the exact day that coral met it's demise and this one has opted to stay.
i just don't want to keep a coral in the system if it's decaying.

Salty1962 · Apr 7, 2017

landlubber said:
ok well i guess the next question is how long will a dead coral produce enough mucus that the crab vacates? still interesting that a crab took the risk to abandon it's lifelong home the exact day that coral met it's demise and this one has opted to stay.
i just don't want to keep a coral in the system if it's decaying.

I believe when you see the crab leaving the acro it's a good sign that things aren't going well. Mine have jumped ship once or twice before settling in. I have a large Purple Spotted Trapezia in my ReefGen Milka Stylo and he lets the fish know that it's his spot

They are pretty cool crabs, mine releases eggs every month. I don't know any other way of knowing when it loose it's soft tissue. Just keep an eye on it maybe frag it and keep your levels good. Good Luck with it.

landlubber · Apr 7, 2017

Salty1962 said:
I believe when you see the crab leaving the acro it's a good sign that things aren't going well. Mine have jumped ship once or twice before settling in. I have a large Purple Spotted Trapezia in my ReefGen Milka Stylo and he lets the fish know that it's his spot They are pretty cool crabs, mine releases eggs every month. I don't know any other way of knowing when it loose it's soft tissue. Just keep an eye on it maybe frag it and keep your levels good. Good Luck with it.

yea it's obviously an experiment i don't want to have to observe but i'll play with the cards i'm delt. thank you for your experience and advice and have a good weekend

Salty1962 · Apr 7, 2017

landlubber said:
yea it's obviously an experiment i don't want to have to observe but i'll play with the cards i'm delt. thank you for your experience and advice and have a good weekend

Thx, you too.