SEASONAL CYCLES OF ACTIVITY AND INACTIVITY IN SOME HYDROIDS FROM VIRGINIA AND SOUTH-CAROLINA, USA

Of 20 species studied in Virginia, 14 were active only during warmer months and 6 only during colder months of the year. Seven of the 18 species examined in South Carolina were active all year, whereas 9 were active only in warmer months and 2 only during colder months. Warm-water species commenced activity in late winter or spring at higher temperatures than those coinciding with hydranth regression in autumn or early winter. Activity in cold-water species began at lower temperatures than those observed at regression in spring. Correlations were apparent in the seasonality, water temperature tolerances, and latitudinal distribution of most species. A number of species survived unfavourable periods as dormant coenosarc in stems and stolons. With the return of favourable conditions, new growth began and hydranths were regenerated from dormant tissue. -from Author