GROWTH AND SURVIVAL OF ATLANTIC SURFCLAM, SPISULA-SOLIDISSIMA, LARVAEAND JUVENILES FED VARIOUS MICROALGA DIETS

This study examined the effects of various algal diets upon the growth and survival of both larvae and juveniles of the Atlantic surfclam, S pisula solidissima. Larvae of the Atlantic surfclam were reared on six diets: a control of no food, Tahitian strain Isochrysis sp (TISO), Ch aetoceros muelleri (CHAET), Thalassiosira pseudonana (3H), plus the eq ual combined concentrations by cell numbers of TISO and CHAET and TISO and 3H. Juvenile clams ((x) over bar = 5.8 mm shell length) were rear ed on a 5% diet (gram dry weight of algae to gram wet weight of clams) of TISO, CHAET, or a mixture of TISO and CHAET. No larvae survived pa st Day 15 when fed the control or 3H diets. After 19 days, significant ly greater survival (p < 0.0001) of larvae occurred in the TISO diet t reatment (46.3%) over ether treatments. Larvae-fed CHAET had 23.3% sur vival, which was not significantly different from larvae fed the TISO plus 3H diet (10.1%), but had higher survival than larvae fed the TISO plus CHAET diet (8.4%). No significant differences in survival occurr ed for larvae fed the two mixed diets. Larval shell length was signifi cantly greater (p < 0.0001) for larvae fed TISO ((x) over bar = 215.3 +/- 5.7SE mu m)> TISO plus 3H ((x) over bar = 182.7 +/- 6.1 mu m)> TIS O plus CHAET((x) over bar = 147.3 +/- 5.4 mu m) > CHAET((x) over bar = 119.1 +/- 3.3 mu m). In the juvenile feeding trial, no clam mortaliti es were observed. After 21 days, no significant differences (p = 0.367 1) in clam size occurred among treatments (means ranged from 14.1 mm f or TISO to 14.4 mm for CHAET); however, clams fed the mixed diet had a significantly (p < 0.0001) higher mean biomass (67.2 +/- 0.9 g wet we ight) than those fed TISO (60.4 +/- 0.5 g) and CHAET (59.6 +/- 0.9 g), which were not significantly different from each other. The results s how that TISO is the superior food for larval surfclam growth and surv ival, whereas juveniles fed a mixed diet of TISO and CHAET grow to a g reater biomass.