GROWTH AND BURROWING RATES OF JUVENILE GEODUCKS PANOPEA GENEROSA AND PANOPEA GLOBOSA UNDER LABORATORY CONDITIONS

摘要

The burrowing behavior, growth, and size-dependent burrowing rates of two geoduck species-Panopea globosa and Panopea generosa-from the Mexican coast were assessed during early juvenile development (6-7 mo) using 30-L aquariums with a muddy or sandy sediment substrate. Preburial response time, digging rates, and growth were recorded monthly for organisms with an initial shell length of 5 mm (P. globosa) or 10 mm (P. generosa), and continued for 6 or 7 mo. Organisms were fed Isochrysis sp. (clone T-ISO) at libitum on a daily basis during the experimental period. Digging behaviors included the inflation of the geoduck siphon, followed by expulsion of a water jet through the pedal orifice, in conjunction with coordinated muscular contractions of the foot. Both species exhibited a lag in their burial response time that was related linearly to shell length, with rates of 4.5 min/mm (P. globosa) and 3.4 min/mm (P. generosa). Burrowing rates were independent of shell length and were similar in both species (similar to 0.9-1.4 mm/min) for a size range of 7-36 mm, but were slower in 5-mm seed (0.4 mm/min). Shell growth rate increased linearly with time and was faster in P. globosa (162 mu m/day) than P. generosa (61 mu m/day). These results suggest that short-term temporary enclosures may be useful for restocking natural populations of geoducks with laboratory-produced seed, at a size as small as 7 mm.