Growth of a Sea Urchin, Allocentrotus fragilis, off the Oregon Coast

摘要

Allocentrotus fragilis (Jackson) was obtained from six stations atdepths of 100 to 1,260 m on the continental shelf and upper slope off Newport,Oregon.Ages and growth rates of A. fragilis were determined by two methods: (1) fromsize-frequency distributions of trawl collections from 200 m, and (2) from growthzones on skeletal test plates. Collections from other depths were not adequate forsize-frequency analyses. Gonad indices of A. fragilis from 200 m were used todetermine spawning periodicity and frequency. A semiannual frequency was suggested,with spawning occurring in early spring and early autumn. No individualscollected below 400 m were reproductively mature. A procedure was developed tomake growth zones of the skeletal test plates visible. Dark growth zones arethought to correspond to semiannual periods of growth, one-half the number ofdark growth zones indicating the urchin's age.The growth curve of A. fragilis from 200 m, which was plotted from the meantest diameter of age groups defined by test plate growth zones, shows a good least-squaresfit to von Bertalanffy's growth equation. Growth rates determined from plategrowth zones appeared to be similar for A.fragilis from 100 to 600 m, but decreasedfor specimens from 800 to 1,260 m. The asymptotic size decreased with increasingdepth below 200 m.