Marine benthic habitat mapping of the Channel Islands National Park: a characterization of monitored sites using high-resolution bathymetric analysis

Kelp forest ecosystems are sensitive to changing global environmental conditions and unsustainable fishing practices (Tegner and Dayton 2000). Natural resource managers have implemented marine protected areas (MPAs) to mitigate ecosystem collapse and conserve fisheries stocks around the globe (Castilla and Moreno 1982). In California, MPAs have been primarily established as a way to mitigate unsustainable fishing practices of the past, while insuring a future for marine resources (Airamé et al. 2003). The establishment and implementation of MPAs has proven an effective conservation tool, but further research is needed to better understand the habitat selection process (Young et al. 2010). This study examined nearshore benthic habitat associations between select species in kelp forest ecosystems of the northern Channel Islands within the Channel Islands National Park, with the intended purpose of identifying specific habitat characteristics for a suite of selected species. Important habitat associations help inform continued and adaptive management efforts and guide the establishment of new MPAs in kelp forest ecosystems. Mapping efforts to help characterize habitat were focused on long-term biological monitoring sites that are part of the Channel Islands National Park Kelp Forest Management (KFM) program (Kushner et al. 2018). Side scan and multibeam sonar technologies were used to map previously uncharted areas of the rocky reef and seafloor of nearshore environments of Anacapa and Santa Cruz Islands at a fine scale resolution of 10-15 cm and data was summarized to characterize habitat at the two-meter^2 and 10m^2 (two and ten-meter) scales. Physical habitat parameters of interest included bathymetry (average depth from sea surface), rugosity (a ratio that measures the topographic complexity of the seafloor), and slope (gradient or steepness of elevation change within a defined area). Eleven sites were sampled for physical variables and species encounters recorded between 2005 and 2013 provided the data to analyze associations between the physical setting and habitat use. Five of the eleven sampled areas in my study were found within MPAs including State Marine Reserves (SMRs) and State Marine Conservation Areas (SMCAs). Six of the eleven sites were located on Santa Cruz Island and five were on Anacapa Island. Selection of target species was derived from a preexisting list of monitored kelp forest inhabitants. Target species were selected with the help of Channel Islands National Park KFM biologists to represent the broadest spectrum of benthic microhabitat users in the kelp forest community. The eight species selected for my study at the two-meter scale have well documented ecological roles within the Channel Island National Park. Two of these species, giant kelp and giant spined sea star, were also observed and analyzed at a larger ten-meter scale. A backwards eliminating stepwise regression (BESR) model for habitat characterization between seafloor statistics (bathymetry, rugosity, and slope) and select kelp forest species was implemented to identify habitat associ ations. In addition, protection status and island were included in the analysis. Results showed that species indicative of healthy kelp forest ecosystems were found in greater numbers inside the MPA boundaries, while the inverse was true for species that represent disturbed systems. In addition, the ten-meter sampling scale was found to be a more accurate predictor of species encounters for the two target species. My study also identified fine scale habitat preference varied among several target species (i.e., purple sea urchin encounters were highly dependent on bathymetry). The results of this research are important to natural resource managers and are intended to help inform decision makers responsible for kelp forest ecosystems and the establishment and implementation of MPAs.