PECHENIK, J. A.; PEARSE, J. S.; QIAN, P.-Y.; Tufts University, Medford, MA; Univ. of California, Santa Cruz; Hong Kong Univ. of Science and Tech., China: Effects of low salinity on spawning, fertilization, and early development in the externally fertilizing polychaete Hydroides elegans: development is more sensitive than fertilization.

Populations of Hydroides elegans in Hong Kong coastal waters experience drastic salinity reductions from heavy summer rains during their reproductive season. Little is known about the impact of such reduced salinity on spawning frequency or fertilization success of this species. We found that mature adults readily released gametes at salinities as low as 5 ppt. However, although many cleaving embryos were obtained at salinities of 22 ppt or greater, cleavage was low at 20 ppt and lower salinities tested. By combining eggs and sperm at full strength sea water for 5 min and then transferring them to a graded series of low salinities for further development, and vice versa, we determined that development was much more sensitive to low salinities than was fertilization. Consequently, reduced salinity appears to interfere with processes that occur immediately following fertilization rather than gamete viability or fusion.