盐度对太平洋牡蛎面盘幼虫垂直分布的影响

于1986年夏、秋两季在福建省惠安、罗源采集太平洋牡蛎,以人工授精法获取受精卵,在空调室内研究盐度变化对太平洋牡蛎面盘幼虫趋性行为的影响。结果表明,盐度的提高能促使牡蛎D形面盘幼虫从正趋地性转变为负趋地性,同时幼虫的正趋光性也得到加强。在D形面盘幼虫期,能引起趋光性加强的盐度增加阈值为2.9×10~(-12);在8日龄壳顶面盘幼虫,提高至5.0×10~(-12)以上。当D形面盘幼虫和壳顶面盘幼虫分别从25×10~(-12)移置于30×10~(-12)时,趋光水平能得到明显提高的时间阈值分别为4h和6h。据以上结果,作者认为该种幼虫在河口区有无阻留的主动性取决于该区环境的变化,同时也与幼虫不同发育时期有关。盐跃层的存在对牡蛎幼虫垂直分布的影响表明,只要盐跃层为2.5×10~(-12),即能抑制幼虫的向上游泳;一旦盐跃层增加,其阻抑作用仍维持接近低盐跃层水平。这说明盐跃层的存在对牡蛎幼虫的垂直迁移具有重要作用。

EFFECT OF SALINITY ON VERTICAL DISTRIBUTION OF LARVAE OF CRASSOSTREA GIGAS

Experimental material was collected in summer and autumn of 1986 in Huian County and Luoyuang County, Fujian Province, Fertilization of Crassostrea gigas eggs was achieved by artificial insemination.

The effects of salinity on the phototaxic and geotaxic response of C. gigas larvae have been studied in an air conditioned laboratory. The results indicated that a rise in salinity might promote positive photoresponse and change positive geotaxis into negative response. The threshold of salinity increase for strengthening significantly the photoresponse of veliger larvae was 2.9×10^-12, whereas in the veliconcha stage (8-day), this threshold increased to more than 5×10^-12. The time threshold for increasing obviously the photoresponse of veliger and veliconcha larvae were 4 h and 6 h, respectively, when they increased from 25×10^-12 to 30×10^-12. It is therefore suggested that the activeness of larvae staying in the estuary likely depends on the environmental variation in the estuary as well as on the larval stage. The haloclinic effects on the vertical distribution of C. gigas larvae have been determined. Larvae of C. gigas might reduce their upward movement greatly as soon as a halocline was constructed even if the magnitude were as small as 2.5×10^-12. Further increase in the halocline had nearly the same effect as that of a low halocline. This result suggests that the salinity stratification in nature is likely to inhibit the vertical migration of larvae in this species.