See complete methodolgy in:
Pernet, B., et al. 2016. Establishment of the reef-forming tubeworm Ficopomatus enigmaticus (Fauvel, 1923) (Annelida: Serpulidae) in southern California. BioInvasions Records, Volume 5, Issue 1: 13–19. doi:10.3391/bir.2016.5.1.03.

In brief (extracted from above):
54 intertidal sites were surveyed in Los Angeles and Orange Counties from August-October 2015.All sites were relatively wave-protected, and all had hard substrate that seemed likely to be suitable for colonization by Ficopomatus enigmaticus. Surveys were carried out at or near the time of predicted low tide. At each site, we characterized substrate type, measured water temperature (with an alcohol or digital thermometer) and salinity (with a calibrated refractometer), and searched the area for ~5 min for the presence of serpulids. The tubes of F. enigmaticus are very distinctive and were easily identifiable in the field. We characterized populations of F. enigmaticus at each site as "sparse" when primarily isolated individuals were identified, and "abundant" when worms were found in large aggregations. Samples of F. enigmaticus were collected from some sites and either fixed in 5% formalin in seawater and then preserved in 70% ethanol, or preserved directly in 95% ethanol. All samples were deposited in the polychaete collection of the Natural History Museum of Los Angeles County.