ASSESSMENT OF FIELD FERTILIZATION SUCCESS IN THE INFAUNAL POLYCHAETE ARENICOLA-MARINA (L)

Previous studies on the fertilization rates in externally fertilizing marine invertebrates have been concerned principally with free spawnin g epifaunal organisms (e.g., Babcock et al., 1992). A technique has be en developed to investigate fertilization success in the intertidal in faunal polychaete Arenicola marina. The spawning period at the East Sa nds, St Andrews, is predictable from previous data, and this facilitat es the study of spawning behaviour. Female worms spawn within their bu rrows, where the eggs may remain for several days. Male worms release sperm puddles on to the surface of the sediment at low water. The sper m is carried on the incoming tide over the surface of the sediment whe re it is actively drawn into female burrows by pumping. The decrease i n sperm concentration as the tide comes in has bean measured, and it i s estimated that there are typically about 10(6) sperm.ml(-1) in the w ater column and available to the female at 1 min after covering by the incoming tide. By placing the worms into artificial plastic burrows w ith removable stoppers, they can be transplanted into the field prior to spawning, and removed afterwards whilst retaining all the contents of the tube (worms, gametes, sediment and water). Preliminary data on the fertilization success suggests that it is highly variable (between 0% and 90%), with typical values of 40-60% for Arenicola marina. Labo ratory assays investigating fertilization rate with varying sperm conc entration have shown that there is a marked increase in success at 10( 4) and 10(5) sperm per ml, with values of 30-70%. The field data there fore appear to be consistent with laboratory studies.