. Bulletin. Science; Natural history; Natural history. 100 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. lU^' >'>'''^<'":^€^<^€'''^ e^"-' ipf \)^ ^oiJ"-' Fig. 3. Macrophyte cover on emergent substrata plotted over three tidal inten^als before (shaded histograms in rear) and after the flash flood. From left to right (and front to back), the first third of each histogram indicates the mean for mean-lower-low-water fMLLW) to m. the middle third = ^ to m, and the last third = to m. March 1977 and May 1977 (Fig. 5) showed some important differences. Mac
. Bulletin. Science; Natural history; Natural history. 100 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. lU^' >'>'''^<'":^€^<^€'''^ e^"-' ipf \)^ ^oiJ"-' Fig. 3. Macrophyte cover on emergent substrata plotted over three tidal inten^als before (shaded histograms in rear) and after the flash flood. From left to right (and front to back), the first third of each histogram indicates the mean for mean-lower-low-water fMLLW) to m. the middle third = ^ to m, and the last third = to m. March 1977 and May 1977 (Fig. 5) showed some important differences. Mac- romvertebrates that increased in numbers (significant at P < ANOVA) throughout all ;als were the mobile species: CoUisella limatula (mean increase of 27-m"-). Pagurus samueUs (increase of 22-m"-). C conns C. scabra (increase of 49-m"-). and the sessile barnacle Tetraclita rubescens (mcrease of 1500-m~-); the last clearly related to recruitment of juveniles on the upper shoreline. The two species showing pronounced decreases (significant at P < ANO\'A) m terms of both cover and density (cf Figs. 4 and 5) were Eupomarus (Hydroides) gracilis (Bush) (mean decrease of 74-m"-) and Strongylocentrotus purpuratus (decrease of 60-m"-) in the intenv'al from MLLW to — m. The most dramatic effects over relatively broad areas of the intertidal (Fig. 5) were revealed by the density counts of Strongylocentrotus purpuratus immediately following the storm. Our belt transects documented an average of °o mortality (19 recently killed out of 21 urchins), whereas a census of the total area between the two permanent transect lines revealed of the S. purpuratus to be dead (52 dead out of 54 urchins). An equal area just beyond the region flooded (20 m north of the north transect line) contained only °o dead S. purpuratus (6 dead out of 539 urchins). As mentioned, there were several hundreds of S. purpuratus tests cast in w
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