REPRODUCTION OF STYLOCHUS-ELLIPTICUS (PLATYHELMINTHES, POLYCLADIDA) IN RESPONSE TO TEMPERATURE, FOOD, AND PRESENCE OR ABSENCE OF A PARTNER

The common polyclad turbellarian Stylochus ellipticus is an important and abundant predator of young oysters, Crassostrea virginica, in Ches apeake Bay. Laboratory experiments revealed that higher temperature an d starvation negatively affected flatworm size. Egg production, adjust ed for flatworm area, was not significantly affected by flatworm size, nor by increasing number of egg batches produced. In addition, there was no significant statistical effect of higher temperature and starva tion on egg production, although there were some instances of diminish ed egg production under these conditions. Flatworms did react to highe r temperature and starvation by significantly decreasing the number of days that elapsed before egg laying began. Overall, more larvae would be produced at 21 degrees C than at 30 degrees C, by fed flatworms th an starved flatworms, and by solitary flatworms than paired flatworms. When isolated animals were alternately fed and starved for five-week periods over a 20-week experimental period at 21 degrees C, 56% of ind ividuals continued to deposit eggs, although the number of eggs laid a nd embryo hatching success declined with time. Stylochus ellipticus in dividuals can maintain a relatively high reproductive effort despite r eduction in available food. Thus, this species would appear to be a '' capital'' breeder, relying on stored energy to produce eggs.