Changes in rocky intertidal floras along the Palos Verdes Peninsula (Los Angeles County) since E. Y. Dawson's surveys in the late 1950s

Changes in the rocky intertidal flora from 1950 to 2000 were studied at five Palos Verdes Peninsula sites (Los Angeles County, California). Of 74 conspicuous taxa, only 9 were found at all sites and 12 were warm-water species; 25 were classified as ephemeral and 49 as persistent members of the flora. Western-facing Peninsula sites were more diverse than southern-facing sites, averaging 44 versus 26 taxa. Cover averaged 69.8% for the five sites and was much greater for western-facing sites (109.3% versus 44.0%). Fleshy branched, turf-forming (FB-T), jointed calcareous (JC), and crustose (C) macrophytes accounted for 53.2% of the relative floral cover for the Peninsula; these groups made up 76.1% of floral cover at the southern-facing sites but only 39.7% at the western-facing sites. MDS and ANOSIM analyses, based on my data and results from earlier surveys, revealed significant differences in macrophyte community structures over the 50-year period. Increases in FB-T, JC, and C macrophytes have occurred on the Peninsula since the 1950s together with decreases in larger, fleshy algal species, including Silvetia compressa and several species of mid-sized, fleshy red algae. The red alga Caulacanthus ustulatus, possibly an introduced species, is recorded for the Peninsula for the first time.