Se. Stancyk et al., BORN TO LOSE .1. MEASURES OF TISSUE LOSS AND REGENERATION BY THE BRITTLESTAR MICROPHIOPHOLIS-GRACILLIMA (ECHINODERMATA, OPHIUROIDEA), Marine Biology, 118(3), 1994, pp. 451-462
To measure amounts of tissue lost in natural populations of the burrow
ing amphiurid ophiuroid Microphiopholis gracillima (Stimpson), individ
uals were collected from subtidal mud flats in North Inlet, South Caro
lina, USA, at monthly intervals between February 1985-February 1987 an
d December 1989-November 1990. Between 20 and 70% of all individuals w
ere regenerating the disc, and 85% of the 2045 arms examined had regen
eration scars; >50% had one scar and some arms had up to 4 scars. Fewe
r individuals were regenerating discs in warmer months, but there was
no seasonality in arm-loss frequency. To quantify rates of arm regener
ation in the field, individuals which had 1, 2, or 3 arms removed were
placed in mud-filled cores in the field in late July and November 198
8 and in March and May 1989, and recovered after periods of about one
month. Another set of cores was held in a running seawater laboratory
during the May 1989 experiment. No regeneration occurred during the co
oler times of year (November and March), and rates of regeneration wer
e slower in May (total: 0.13 mg/d; tissue: 0.03 mg/d) than July (total
: 0.17 mg/d; tissue: 0.05 mg/d). These rates indicate complete replace
ment of lost tissue in 100 to 120 d during the growth season. Within e
xperiments, per arm regeneration rates were similar regardless of the
number of arms removed. This finding is complicated by small sample si
ze, high variability and low statistical power, but in general individ
uals which lost 2 or 3 arms regenerated proportionally more tissue tha
n individuals which lost 1 arm. Individuals held in the laboratory reg
enerated the same amount of tissue but 30% less skeleton than individu
als in the field. Sublethal tissue loss is common in this population,
and M. gracillima is capable of regenerating at least 50% (each arm =
17% of total body weight x 3) of its standing crop in a single growing
season. Burrowing brittlestars probably constitute a significant rene
wable energy source for higher trophic levels in areas where they occu
r in dense populations.