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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.