Slow arm regeneration in the Antarctic brittle star Ophiur crassa (Echinodermata, Ophiuroidea)

Regeneration of arms in brittle stars is thought to proceed slowly in low temperature environments. Here a survey of natural arm damage and arm regeneration rates is documented in the Antarctic brittle star Ophiura crassa. This relatively small ophiuroid, a detritivore found amongst red macroalgae, displays high levels of natural arm damage and repair. This is largely thought to be due to ice damage in the shallow waters it inhabits. The time scale of arm regeneration was measured in an aquarium-based 10 mo experiment. There was a delayed regeneration phase of 7 mo before arm growth was detectable in this species. This is 2 mo longer than the longest time previously described, which was in another Antarctic ophiuroid, Ophionotus victoriae. The subsequent regeneration of arms in O. crassa occurred at a rate of approximately 0.16 mm mo−1. To date, this is the slowest regeneration rate known of any ophiuroid. The confirmation that such a long delay before arm regeneration occurs in a second Antarctic species provides strong evidence that this phenomenon is yet another characteristic feature of Southern Ocean species, along with deferred maturity, slowed growth and development rates. It is unclear whether delayed initial regeneration phases are adaptations to, or limitations of, low temperature environments.