THE DISTRIBUTION AND ABUNDANCE OF DEEPWATER MACROALGAE IN CENTRAL CALIFORNIA

Abstract

Deepwater macroalgal assemblages (DWAAS) were sampled from 30m to their lower depth limits at 4 locations in central California using enriched air Nitrox and the ROV Ventana. The lowest observed depth limits were 78 m for nongeniculate (encrusting) coralline algae, 58 m for non‐calcified red algae (i.e. Maripelta rotata), 40 m for foliose brown algae (i.e. Desmarestia tabacoides), and 37 m for kelps (i.e. Pleurophycus gardneri). Green algae, such as Derbesia marina and an undescribed deep water species of Codium, were observed at 30m, while large patches of an unknown green or blue‐green algal film of coccoid cells were found from 45 to 48 m. DWAAS zonation was generally similar to that in southern California, with subtle differences in the zonation of foliose red algae and the occurrence of an unknown Chlorophyta or Cyanophyta from 45–49m. Twenty four species of algae (13 Rhodophyta, 11 Phaeophyta) were sampled during the percent cover analysis at 30 m. Nongeniculate corallines varied from 53% to 91% cover depending on location, while geniculate corallines (i.e. Bossiella schmittii) averaged ca. 25% cover. Pleurophycus gardneri, a stipitate kelp previously described as “rare” in central California, was the most abundant brown alga, averaging from 2.68 to 4.8 individuals m−2. Algal abundance (percent cover and density), zonation, and light levels at the lower algal depth limits were similar between sites and locations, suggesting that the environment of deep water algal populations in this region is less variable than that of the shallow water kelp forest communities above them.