These data represent density per square meter of individuals of a suite of kelp and macroinvertebrate species on fixed 10-meter by 2-meter benthic transects on permanent subtidal monitoring sites around San Nicolas Island between 1980 and 2019. There are a total of nine sites, each of which has five 20 square meter band transects. Six of the sites were first sampled in 1980, one additional was added in 1987, and the other two were added in 2014. The sites have usually been monitored twice per year, most often in October and April. The target species list is as follows: Strongylocentrotus franciscanus (also known as Mesocentrotus franciscanus) Strongylocentrotus purpuratus Apostichopus parvimensis Pycnopodia helianthoides Patiria miniata Pisaster giganteus Astrometis sertulifera Dermasterias imbricata Haliotis corrugata Haliotis rufescens Megathura crenulata Megastraea undosa Cystoseira osmundacea (also known as Stephanocystis osmundacea) Eisenia arborea Laminaria spp. Macrocystis pyrifera <1 m tall Macrocystis pyrifera >1 m tall Pterygophora californica Young Laminariales (species uncertain) In fall 2014, the following additional organisms were added to the target list: Lytechinus anamesus Kelletia kelletii Crassadoma gigantea Aplysia californica Tealia lofotensis (also known as Urticina eques) Tethya aurantia (also known as Tethya aurantium) Sargassum horneri