Analyses/Maps

Environmental Variables

SUBSTRATE TYPES

About this map:
This map displays distribution of substrate types throughout the study area, from Pt. Arena to Pt. Sal California. The substrate is classified into 5 categories: mud, sand, pebbles/cobbles/gravel (pcg), rock, and mud/rock mix.

Data Sources:
California Continental Margin Geologic Map Series (Maps 4-6) (Greene and Kennedy, 1989). These maps were originally created with a 1:250,000 resolution and were used as the basemaps for recent revisions and incorporation of new high resolution multibeam data in small portions of the study area.

Download Substrate Shapefile

Methods:
Initially, seven maps were developed that displayed substrate type and geologic formations throughout California's coastal and marine environments. The original data were compiled by the California Division of Mines and Geology, USGS, and California Coastal Commission to produce paper maps. Geologists from California State University-Monterey Bay digitized these maps in 1999 and further interpreted these data to develop boundaries of substrate types (Greene et al., 1999). Three of the seven maps provide data for the study area and together provide the most comprehensive map of substrate type for the northern/central California marine and nearshore region. For a detailed description of the development of the original maps and classification scheme, refer to Greene et al., 1999 and Greene et al., 2002. Eight substrate types were classified, however, some were grouped together when the digital substrate shapefile was rasterized into 1 km2 grid cells to facilitate their use in the HSI model analyses (See Section 2.1.2). "Boulders" and "Hard/Anthropogenic" polygons were grouped within the "Rock" substrate type and "Grave"l was grouped with "Cobbles/Pebbles" because boulder and gravel polygons were limited in number and affinities to these were considered to be similar to the group it was reclassified with.

Results and Discussion:
The substrate map covers an area of approximately 44,000 km2, of which mud accounts for 86.4% (38,023 km2) of the total bottom area. Substrate containing pebble/cobble/gravel were the least abundant substrate types, only encompassing 100 km2 of the study area. Rock substrates were mostly patchy throughout the region, encompassing 1,561 km2. Mud and rock mixed substrate (1,706 km2) was almost exclusively distributed in the southern portion of the study area, with small localized areas near Monterey canyon. Sand (2,611 km2) is predominantly located nearshore with a large area located near and around Cordell Bank. Within sanctuary boundaries, soft sediments (mud, sand) account for almost 95% of the substrate. Rocky areas (including pebbles, cobbles, gravel) account for approximately 5%, while less than 1% consists of mud/rock mix. Within sanctuary boundaries, rocky substrates are distributed predominantly on the shelf, occurring in the areas near Cordell Bank, Farallone Islands, in many nearshore areas, and scattered within Monterey Bay. Outside sanctuary boundaries, several large areas of rock are found on the slope in depths greater than 1200 m. Mixed rock/mud substrate is scarce within the study area, with most occurring southwest of Monterey canyon. One large area of mixed rock/mud is present southwest of the southern Monterey Sanctuary boundary. Areas containing pebble, cobble, and gravel are found exclusively in Monterey's sanctuary and are generally found within depths of 100-200 m. The majority of sand substrate is found nearshore in the northernmost and southernmost portions of the study area, with significant coverage also occurring around Cordell Bank. Figure X displays the percent coverage of bottom types within each sanctuary. Other important substrate types exist within the study area, such as nearshore kelp beds, but were not included in the map based on their ephemeral distribution and the limitations associated with development of bathymetric SI's in nearshore areas.

Although the substrate map is a probabilistic map of substrate types, it reflects the most complete and current knowledge of benthic substrates for the northern/central California region. The map alone can be used to support investigations that require advanced knowledge of sea floor type. In addition, the maps are useful identifications of critical or important habitats for particular species or for determining essential fish habitat that can aid conservation and management plans for fisheries species. In this study, the map was primarily used as an environmental layer in GIS (in addition to bathymetry) to determine habitat suitability for groundfish species. This approach assumes that the underlying environmental GIS layers are an accurate representation of that particular variable, thus the model results are only as good as the underlying digital information. The substrate map is conservative, based on its original scale (1:250,000), and may have fine scale inaccuracies throughout the study area. Small localized areas of high resolution information (on the scale of 10's of meters) have been included in this map, however, these areas comprise a small percentage of the overall study area. More information is required to test the accuracy of the map; hence, thematic accuracy of substrate types is unknown.