Dataset: Percent coverage along a transect or subsample of each of four substrate types recorded during emergent and rapid emergent surveys conducted in the subtidal zone of northern California, Sonoma and Mendocino counties, from 1999 to 2023

All surveys were done using SCUBA along 30x2 meter (m) transects (60 square meters total area) randomly placed in the subtidal zone in rocky habitats dominated by bull kelp (Nereocystis luetkeana) forests. These randomly placed band transect surveys were stratified by depth (A=0-15, B=16-30, C=31-45, D=46-60 ft) as we know sea urchin and abalone populations differ by depth. Two divers (a dive team) work together to count and measure organisms.

Divers were deployed as teams to randomly-selected GPS waypoints within designated depth strata (A, B, C, D). Divers typically complete multiple transects within each of the four depth strata ranging from 0 to 60 feet at each site. Divers swim along transect tapes measuring 30 x 2m in area across the rocky reef. All transect surveys were in habitat dominated (>70% rock) by rocky reef.

Emergent Surveys:
Emergent sampling focused on emergent, exposed, or cryptic animals in rock crevices or under rock ledges but visible without turning rocks or the use of a flashlight. Data collected on the transects include depth of transect, dive number, the number of each species of abalone and sizes of Haliotis rufescens, pinto abalone (H. kamtschatkana), flat abalone (H. walallensis), number of sea urchins (red, Mesocentrotus franciscanus, or purple, Strongylocentrotus purpuratus) and size as time allowed, number of associated species and predators, substrate, algal type percent cover. Where needed divers mark abalone shells with yellow forestry crayons to avoid duplicate counts and measures. Data from each dive were recorded on waterproof datasheets which the divers fill out along the transect. Upon return to the boat, data sheets were checked by the lead diver to ensure accuracy and readability for the first field site quality control check.

Rapid Emergent Surveys:
In response to the extreme purple sea urchin population increase and abalone mortality event in 2016-18, survey methodology changed somewhat with fewer transects per site (approx. 12 per site). Divers conducted a rapid assessment sampling technique: Rapid Emergent Abalone Surveys were similar to standard emergent surveys (see above) but focused on purple sea urchin and red abalone counts of live and dead abalone and sea stars. Divers conduct two to four rapid emergent transects per dive.

Primary data collected on each rapid transect are number of live, dying, and dead red sea urchins, purple sea urchins, red abalone, pinto abalone, and flat abalone, as well as empty abalone shells. Additional data collected (if bottom time and/or air allowed): red abalone size, number of associated species and predators, algal habitat coverage, substrate type, and presence of bull kelp. Abalone that were measured were marked with yellow forestry crayons to avoid duplicate counts and measures. As with the emergent surveys, the divers fill out data on waterproof datasheets along the transect. Upon return to the boat data sheets are checked by the lead diver to ensure accuracy and readability for the first field site quality control check.

The data specific to this dataset are the percentages of four different substrate types: reef, boulder, cobble, and sand. Data on the substrate types differed depending on the year and the focus of the studies in response to ecosystem conditions. Note that some transects were subsampled. "L" is left side, "R" is right side, "LR" is the entire 30m x 2m transect, both sides. Not all transects were subsampled due to time constraints.

In some rare cases, substrate can range from 95-105 for a subsample, and from 190-210 for both sides of the full transect, so they should be rounded off to 100 or 200%.