The use of satellite remote sensing and a geographic information system (GIS) to characterize regions of persistent giant kelp (Macrocystis pyrifera) around Santa Catalina Island for designation as marine reserves

In order to identify habitat of sufficient size and complexity for designation as reserves to protect marine ecosystems, management techniques must be applied at larger spatial and temporal scales. This study utilized a geographic information system (GIS) to investigate the influence of island physiography on the distribution and persistence of giant kelp around an island off the southern California coast. Macrocystis pyrifera is an important algal species in the nearshore environment along temperate coasts, serving as structural habitat and food for many marine invertebrates and fishes. Santa Catalina Island's NW-to-SE orientation and highly dissected, 87-km coastline offers a wide range of microhabitats with respect to storm exposure, temperature, light regime and other factors.;GIS data layers included sea surface temperature (SST), a digital elevation model (DEM), a digital bathymetric model (DBM), submarine slope, submarine aspect, bottom relief at several spatial scales, and storm exposure (significant wave height). The physiographic data layers were used to generate a series of ocean surface insolation models incorporating the effect of terrestrial hillshading on nearshore waters. Insolation on the sea floor added light extinction through the water column utilizing depth and regional turbidity. Kelp distribution from surveys covering a period of 60 years were digitized from several sources. GIS overlay methods applied to the multi-temporal distribution maps generated a layer representing the spatial persistence of kelp.;Kelp distribution and persistence were evaluated by direct visualization of data layers, and statistically (univariate and multi-variate) relative to the coincident physical variables. Hypotheses tested focused on differences between the leeward and windward sides in disturbance (storm exposure and temperature) and nearshore light regimes. Definite patterns in distribution were observed relative to aspect, depth, slope, bottom relief, temperature, storm exposure, and insolation. Correlations with these environmental factors also exhibited inter-annual variability between survey years.;Correlations between persistence and the physical variables were used to characterize regions suitable for designation as marine reserves. The existing reserve system, located entirely on the leeward side, should be expanded to include sites on the windward side which differ in many physical factors and may harbor different kelp ecotypes.