August 1, 2011.
Colonial botryllid tunicates, such as Botrylloides violaceus, brood large, non-feeding offspring with extremely limited larval life spans of minutes to perhaps one day. Despite the importance of this transitory life history stage, there is little information on how environmental factors such as ambient water flow affect larval size among invertebrates. Since adult tunicates feed by filtering particles from the water flowing around the siphons, we reasoned that colonies of B. violaceus in high water flow may produce larger offspring due to greater food availability. We tested to see whether there was a relationship between larval size and water motion in low and high flow environments. We collected colonies from Pillar Point Harbor in Half Moon Bay, CA from random locations, conducted flow measurements, and measured larvae released naturally in the lab from each colony. Contrary to our expectation, results showed a statistically significant inverse correlation between larval size and flow rate. Bigger larvae were produced by colonies located in slower flows, while smaller larvae were found in colonies from across the full spectrum of flow rates measured. Perhaps, low flow environments are actually high food environments allowing these colonies to have a dual reproductive strategy where they produce both large and small larvae as a bet-hedging strategy. Whereas, high flow, lower food environments may constrain reproductive options.
Terrestrial and Aquatic Ecology
Dr. Sarah Cohen
Romberg Tiburon Center for Environmental Studies (RTC)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation.