Rocky intertidal community monitoring at Channel Islands National Park: 2016–17 annual report

Whitaker, Stephen

Channel Islands National Park includes the five northern islands off the coast of southern California and the surrounding waters out one nautical mile. There are approximately 176 miles of coastline around the islands, about 80% of which is composed of rock. The diversity and undisturbed nature of the tidepools of this rocky coastline were recognized as special features of the islands in the enabling legislation. To conserve these communities unimpaired for future generations, the NPS has been monitoring the rocky intertidal communities at the islands since 1982. Sites were established between 1982 and 1998. Site selection considered visitation, accessibility, presence of representative organisms, wildlife disturbance, and safety. This report summarizes the 2016–17 sampling year efforts (from November 2016 to April 2017) and findings of the Channel Islands National Park (CHIS) Rocky Intertidal Community Monitoring Program. Specific monitoring objectives are 1) to determine the long-term trends in percent cover of key sessile organisms in the rocky intertidal ecosystem (Table 1), and 2) to determine population dynamics of Haliotis cracherodii, Lottia gigantea, and Pisaster ochraceus. Objectives were met by monitoring percent cover of core species in target intertidal zones using photo-plots and transects, and measuring size frequency and abundance of black abalone, owl limpets, and sea stars using fixed plots or timed searches. Thirteen key species or assemblages have been monitored twice per year at 21 sites on the five park islands (Figure 1) as part of the Rocky Intertidal Community Monitoring Program. Fixed photo-plots were used to monitor the percent cover of thatched and acorn barnacles (Tetraclita rubescens, Balanus glandula/Chthamalus spp., respectively), mussels (Mytilus californianus), rockweeds (Silvetia compressa, and Hesperophycus californicus), turfweed (Endocladia muricata), red algal turf (Pterocladiella spp. and Gelidium spp.), goose barnacles (Pollicipes polymerus) and tar. Point-intercept transects were used to determine the percent cover of surfgrass (Phyllospadix spp.). Information about size distribution (i.e. “size-frequency” data) was collected for owl limpets (Lottia gigantea) in circular plots. Size distribution and relative abundance of black abalone (Haliotis cracherodii) and ochre sea stars (Pisaster ochraceus) were determined using timed searches. The maximum number of shorebirds and pinnipeds seen at one time were counted at each site. The number of concession boat visitors to the Anacapa tidepools was collected and reported. All sites were sampled during the 2016–17 monitoring season. In 2015–16, we officially reduced our sampling interval from twice per year (spring and fall) to once in the fall to streamline the program and allow for the implementation of additional protocols. Weather conditions during the site-visits were satisfactory, but high wind coupled with strong swell and surge limited or prevented the completion of some of the abalone and sea star searches.

Rocky intertidal community monitoring at Channel Islands National Park: 2016–17 annual report

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