Meeting Abstract

35.6  Sunday, Jan. 5 09:15  Two species of botryllid colonial ascidians show different responses to flow at early juvenile stages BELLON, AM*; SPAULDING, J; LEE, H; COHEN, S; Swarthmore College; Romberg Tiburon Center, San Francisco State Univ.; Swarthmore College; Romberg Tiburon Center, San Francisco State Univ. abellon1@swarthmore.edu

Viscosity of water poses an important challenge for small juvenile suspension feeders that may be particularly severe for internal filter-feeders, such as ascidians. Here, we take a comparative approach using colonial ascidians with similar filtration units, but early differences in size, to test the effect of flow differences on growth in field and flume environments. Botrylloides violaceus and Botryllus schlosseri were grown from settlement in a flume with flows of 0, 8, and 13 cm/s. B. violaceus was grown in the field at 0 and 5cm/s. In the flume measurements of colony area, number of buds and siphon diameter were taken every 3-4 days for up to 17 days. Siphon diameters were additionally measured from flume colonies grown at 0 and 13 cm/s. In the flume, B. violaceus showed significantly less growth at high compared to medium flow rates, while B. schlosseri showed no significant differences at any flow. However, growth rates of B. violaceus were not affected by flow rates in the field. Patterns of early development appear to differ between species. The larger propagule species, B. violaceus increased the number of zooids with little developmental change to the ozooid including a consistent siphon size. This strategy may be less flexible across habitats, as B. violaceus colonies showed lower success at the higher flow rates in lab. The smaller propagule species, B. schlosseri, showed variation in ozooid development including varying siphon sizes; growth rate decreased during addition of a new zooid and siphon growth slowed before budding and before the addition of a new zooid. B. schlosseri appears to have a flexible growth strategy showing allocation tradeoffs between siphon size and budding.