pincushion urchin lifespan?
 

I'm heartbroken - I arrived home tonight to see Speedy, my much-loved pincushion urchin, shedding spines. He looks pretty much gone; I knew it was hopless when I saw the nassarius snails starting to move in :(

I've had Speedy about a year and a half now, and he's grown from 1.5" across to about 2.5" in that time (excluding spine length). Of course I have no way of knowing how old he was before he was captured, but I can't imagine an urchin only lasting a year and a half - he's got loads of coralline to eat, nori if he wants it (always there for the tang), turf and hair algae on the rocks, film algae on the glass and halimeda macroalgae grows all over the place. Nothing living in the tank is remotely interested in eating him, or attacking him, and none of the conditions have changed other than adding 8 drops of Kent Iron supplement (half the recommended daily dose) three days ago for the macroalgae.

Water: pH 8.0, 3.2meq/L KH, Ca 380ppm, Mg 1200ppm, SG 1.025, temp 78-80F, NO3 & PO4 undetectable.

Does anyone know how long urchins typically live in captivity? Was there something I should have been doing or something he needed in his diet I didn't provide? I feel terrible, I was very attached to the little guy.

Urchins are pretty long lived animals. There are some colder water species that are known to live for centuries, and it's very likely that their warmer water cousins live at least on the order of several decades if not a century. There's no reason they couldn't live just as long in captivity.

I don't see anything obviously wrong with the tank, though so I can't really recommend any action besides a waterchange. Does the iron supplement say what else it contains besides iron?

Thanks for the reply. The bottle says:
Soluble Potash (K20) 3%
Iron (Fe)(min) .24%
.24% chelated iron
Manganese (Mn)(min) .1%
Molybdenum (Mo)(min) .000005%
Zinc (Zn)(min) .00014%

The recommended dose is 5ml (1tsp) per 50g weekly or 8 drops per 50g daily.
My system contains about 100g of water, and I dosed 8 drops [I]once[/I] -- half the recommended 'everyday' dose -- three days before Speedy started to decline. Absolutely everything else in the tank looks just fine, really healthy even.

Just to update...

I hesitate to say anything, but I think Speedy might still be alive. I left him in the tank because I wasn't sure initially, and I did see nassarius moving toward and around him but didn't see them actually eating him... this morning he's moved and appears to be upright, attached to a rock (last night he was upside down on the sand). I'll be watching him through the day, but amazingly I think he might be recovering from whatever happened to him. He did drop a number of spines, but as of now hasn't lost any more and doesn't seem to be decomposing or anything. I really hope he's alright, he's become one of my favourite reef inhabitants.

Not sure if anyone's even reading this thread, but I'm going to update just in case ;)

I woke up this morning to find Speedy halfway up on the back glass -- positive confirmation that he is indeed still alive! His little suction-cup feet were out all over the place, he was definitely hanging on tight and looking for other footholds. He used to be white with purple-tipped spines, now he looks 'grubby', I don't know how else to describe it. He's lost a lot of spines, and seems darker in colour, but definitely alive. I hope to be able to update in a while and say he's fully recovered :D