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

These data represent sizes of individuals of the sea urchin species Strongylocentrotus franciscanus (also known as Mesocentrotus franciscanus) and Strongylocentrotus purpuratus on permanent subtidal monitoring sites around San Nicolas Island between 2014 and 2019. The sites usually have been monitored twice per year, most often in October and April. Divers measured in situ urchin test diameters in millimeters. Approximately 200 individuals of each of the two species was measured at each supersite (pair of adjacent sites) during a sampling period.

The monitoring program at San Nicolas Island (SNI) was conceived in anticipation of the potential reintroduction of southern sea otters to the island. Subtidal monitoring was initiated in autumn of 1980 at six sampling sites positioned around the island to sample communities exposed to a range of wave exposures and other oceanographic conditions. Three additional sites were subsequently added. Following their reintroduction in 1987, the sea otter population at the island remained low for several years but 154 were counted there in 2019. There are nine permanent sites that are monitored on rocky reefs around San Nicolas Island. Six of these (Nav Fac, West End Urchin, West End Kelp, West Dutch Harbor, East Dutch Harbor, and Daytona) were installed and first sampled in 1980. The two West End sites are physically joined, with the end bolt of the main 50 m transect of the Urchin site being also the beginning of the Kelp site’s main transect. The Dutch Harbor sites are not contiguous but are on adjacent rock reefs separated by approximately 140 m of sand. A seventh site, Sandy Cove, was added in 1986. Data collected from the project’s inception in October 1980 to October 2011 were published in Kenner et al. (2013). In fall 2014, two additional sites were added that are contiguous with two of the original sites. North Nav Fac was installed with the end of its main transect line sharing the beginning of the Nav Fac site and South Daytona was added in a similar relation to the Daytona Site. This yielded eight paired sites or four “supersites” in addition to Sandy Cove. Most of the data is collected separately on the individual sites but can be pooled at the larger supersite level. The original sites consisted of a 50-m main transect with five 10-m x 2-m benthic band transects (swaths), ten 1-m2 random point contact (RPC) quadrats and five 50-m fish transects. The two new sites do not have fish transects associated with them but are otherwise identical. Temperature data and sea urchin and other invertebrate size data are collected at the supersite level. Sites have usually been sampled twice a year, in spring and fall since their installation but have been missed several times due to weather, budgetary constraints, or mechanical issues with boats. References: Kenner, M.C., Estes, J.A., Tinker, M.T., Bodkin, J.L., Cowen, R.K., Harrold, C., Hatfield, B.B., Novak, M., Rassweiler, A. and Reed, D.C., 2013. A multi-decade time series of kelp forest community structure at San Nicolas Island, California. Ecological Archives E, 94(11), p.244. https://doi.org/10.1890/13-0561R.1

These data represent holdfast diameters of giant kelp (Macrocystis pyrifera) that were greater than one meter tall and were on fixed 10-meter by 2-meter benthic transects on permanent subtidal monitoring sites around San Nicolas Island between 1980 and 2019. The number of stipes counted on the plants is also listed if recorded. Holdfast diameters give an indication of the M. pyrifera age structure because the holdfast continues to grow throughout the life of the alga. Stipe counts are more variable with age but give an indication of algal biomass. Stipe counts were made on some transects beginning in 1997 and on all plants beginning in 2014. Between 1980 and 2006, 3694 of the plants were tagged and followed over time. Tagged plants have been assigned unique identifier numbers so they can be tracked over multiple sampling periods. 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 Benthic Marine Communities Monitoring Protocol is implemented in four parks in the Pacific and addresses two monitoring questions: What are the changes over time in the composition (e.g., species or assemblage) and physical structure (rugosity) of the coral reef benthos? And what are the changes over time in settlement, growth, survival, and health of targe coral assemblages, species, or individuals? Note: Growth and survival data has not been collected due to lack of resources to do so. The Marine Fish Monitoring Protocol is conducted in the same parks and sampling location sites, and addresses one monitoring question: What are the long-term trends in the numerical density, biomass, and size of reef fishes? Sampling location sites were randomly selected on hard substrata in an isobath between the 10- and 20-meter depths. This data package contains data collected for these two protocols.

These data represent counts of fin fish made by divers on fixed transects on permanent subtidal monitoring sites around San Nicolas Island between 1981 and 2019. Beginning in 2014, total length was estimated for most individual fish or size ranges were estimated for fish in schools. Fish were counted on seven sites, each of which had five midwater and five benthic fish transects. Six of the sites were first sampled in 1980, one additional was added in 1987. The sites have usually been monitored twice per year, most often in October and April. The midwater and bottom portions of each transect were sampled separately. Midwater transects were 5 m wide and encompassed the entire water column except the bottom 2 m. Bottom transects were 2 m wide and included only the bottom 2 m of the water column. The list of species counted was expanded over time as new species were encountered and the data here include all 66 species counted.

Stationary Point Counts at 4 stations at each survey site were surveyed as part of Rapid Ecological Assessments conducted at 3 sites at Laysan Island in September,2004 from the NOAA vessel Hi'ialakai (HI04-01). Raw survey data included species level abundance estimates.

The Benthic Marine Communities Monitoring Protocol is implemented in four parks in the Pacific and addresses two monitoring questions: What are the changes over time in the composition (e.g., species or assemblage) and physical structure (rugosity) of the coral reef benthos? And what are the changes over time in settlement, growth, survival, and health of targe coral assemblages, species, or individuals? Note: Growth and survival data has not been collected due to lack of resources to do so. The Marine Fish Monitoring Protocol is conducted in the same parks and sampling location sites, and addresses one monitoring question: What are the long-term trends in the numerical density, biomass, and size of reef fishes? Sampling location sites were randomly selected on hard substrata in an isobath between the 10- and 20-meter depths. This data package contains data collected for these two protocols.

The Benthic Marine Communities Monitoring Protocol is implemented in four parks in the Pacific and addresses two monitoring questions: What are the changes over time in the composition (e.g., species or assemblage) and physical structure (rugosity) of the coral reef benthos? And what are the changes over time in settlement, growth, survival, and health of targe coral assemblages, species, or individuals? Note: Growth and survival data has not been collected due to lack of resources to do so. The Marine Fish Monitoring Protocol is conducted in the same parks and sampling location sites, and addresses one monitoring question: What are the long-term trends in the numerical density, biomass, and size of reef fishes? Sampling location sites were randomly selected on hard substrata in an isobath between the 10- and 20-meter depths. This data package contains data collected for these two protocols.