The Santa Barbara Channel MBON tracks long-term patterns in species abundance and diversity. This dataset contains counts of algae and invertebrates (both sessile and mobile) by integrating data from four contributing projects working in the kelp forests of the Santa Barbara Channel, USA. This dataset includes three entities, two data tables and R code. The main data table number of organisms and the area over which that number was counted for calculation of areal abundance. Data were collected by human observation (divers using SCUBA) during regular surveys. The column labeled “count” records the number of organisms found at a given timestamp. The algae and invertebrate counts record the number of taxa found in each plot, including quad (small square plots such as 1 or 2 m2) and swath (large linear plots such as 60 m2). See Methods for information on integration and data processing. A second data table contains place names and geolocation for sampling sites. Information is sufficient for the calculation of density, which is left to the user. Sample R-code is included (third entity) to illustrate generation of a basic table of areal density by taxa and sampling site. See Methods for information on integration and data processing The four contributing projects are two research projects: the Santa Barbara Coastal LTER (SBC LTER) and the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO), and the kelp forest monitoring program of the Santa Barbara Channel National Park, and the San Nicolas Island monitoring program supported by USGS. Together, these projects have recorded data for more than 200 species at approximately 100 sites on both the mainland coast and on the Santa Barbara Channel Islands. Sampling began in 1982 and is ongoing.