Tuesday, August 7, 2007 - 3:50 PM

COS 44-7: Effects of commercial collection on growth and reproductive output of Postelsia palmaeformis

Sarah Ann Thompson1, Karina J. Nielsen1, Carol A. Blanchette2, Brennan Brockbank1, and Heather R. Knoll1. (1) Sonoma State University, (2) University of California, Santa Barbara

The Sea Palm Postelsia palmaeformis is an iconic rocky intertidal species endemic to the West Coast of North America and an increasingly popular commercial product.  However, little is known about the impact of commercial collecting on Postelsia populations.  Commercial collecting regulations for edible seaweeds do not require species or location specific information on landing reports, and do not take a precautionary approach to exploitation.  Postelsia is especially vulnerable to over-exploitation because of its annual life history and limited dispersal.  Commercial collecting techniques vary but many collectors claim their methods are sustainable.  There is no scientific evidence, however, to support these claims.  We studied the effects of commercial collection practices by mimicking these methods in a controlled experiment at two California sites representing central and southern range limit populations.  Here we report the results from this experiment concerning the popular collection technique of clipping fronds below the meristem on the metrics of growth and reproductive output.  Frond regrowth after clipping depended on season and number of times clipped.  Sorus area was reduced in response to clipping but varied in magnitude with season, number of times clipped and site.  Reproductive output and germination success of spores were both strongly impacted by clipping, but there was variation in these responses associated with both site and season.  Changes in timing of reproduction and reproductive output may have important consequences for local population dynamics.  Commercial regulations should reflect our best scientific understanding of these impacts, and incorporate regional variation in responses to collecting.