Meeting Abstract

9.3  Monday, Jan. 4  Slow recovery or community shift? Assessing the long-term effects of kelp canopy removal in the rocky intertidal zone. BURNAFORD, J.L.; California State University Fullerton jburnaford@fullerton.edu

Saccharina sessile is a stipeless canopy-forming kelp that forms extensive beds in the low rocky intertidal zone of the Pacific Northwest. In 1998, to evaluate the effects of the S. sessile canopy on community structure, I removed all individuals from twenty 1m² plots at Pile Point, San Juan Island, WA. For the duration of this 2-year study, I continually removed S. sessile recruits in the plots. Community structure in treatment plots was compared with five 1m² control plots in which the S. sessile canopy was not manipulated. In 1998 before the start of the study, all plots had at least 70% canopy cover of S. sessile, with an average cover of 73%. Following termination of the experiment in 2000, no further manipulations were conducted in any of the 25 study plots. In 2008 and 2009, I re-surveyed plots to assess their recovery from this long-term canopy removal. In 2008, only one of twenty treatment plots had reached pre-removal S. sessile cover levels, and average cover in the treatment plots was 31%. Comparisons of community structure in treatment plots in 2008 and 1998 show substantial differences, including an increase in the abundance of the canopy-forming mid-intertidal alga Fucus distichus from an average of 0.1% cover in 1998 to an average of 12.1% cover in 2008. Across the treatment plots in 2008 and 2009, F. distichus cover was negatively correlated with S. sessile cover. Canopy dynamics also shifted in un-manipulated areas, with an average drop in canopy cover in control plots of more than 23% since 1998. Determining whether these changes represent natural fluctuations and slow recovery in the S. sessile population or a larger shift in community structure will be the topic of ongoing study.