The data represent counts 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 2018. There were six sites, each of which had five 20 square meter band transects. The sites were usually monitored twice per year, most often in October and April. The species list is as follows: Stephanocystis osmundacea (formerly Cystoseira osmundacea), Laminaria spp., Eisenia arborea, Pterygophora californica, Macrocystis pyrifera greater than 1 m tall, Macrocystis pyrifera less than 1 m tall, Juvenile Laminariales (genus uncertain), Mesocentrotus franciscanus (formerly Strongylocentrotus franciscanus), Strongylocentrotus purpuratus, Patiria miniata, Dermasterias imbricata, Pisaster giganteus, Pycnopodia helianthoides, Megastraea undosa.