. Bulletin. Science. 50 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 120 100- 60 40- 20. 100% sw 75% SW 50% SW 25% SW 0 Days of hyposaline treatment Fig. 5. Percent of initial numbers of zooxanthellae remaining following 4 days of treatments in which anemones were held in 100% seawater except for one 3 h pulse of hyposalinity per day (100% = 32 ppt, 75% = 24 ppt, 50% = 16 ppt, and 25% = 8 ppt). Shown are means ± standard errors. Over the summer of 1995 we observed freshwater runoff from the arroyo on several occasions, covering a much greater area of the expanse of rocky intertidal habitat than the
. Bulletin. Science. 50 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 120 100- 60 40- 20. 100% sw 75% SW 50% SW 25% SW 0 Days of hyposaline treatment Fig. 5. Percent of initial numbers of zooxanthellae remaining following 4 days of treatments in which anemones were held in 100% seawater except for one 3 h pulse of hyposalinity per day (100% = 32 ppt, 75% = 24 ppt, 50% = 16 ppt, and 25% = 8 ppt). Shown are means ± standard errors. Over the summer of 1995 we observed freshwater runoff from the arroyo on several occasions, covering a much greater area of the expanse of rocky intertidal habitat than the natural runoff channel. Heavy equipment had been used to bulldoze sand in order to direct the storm water runoff much more broadly, rather than allowing it to continue to run in its natural, narrow channel. In addition, fresh water seeped farther across the beach by flow under the sand when the water was deep in the arroyo channel. From these studies it is not clear whether some other factors, such as pollutants, could also have contributed to the bleaching seen in the field. However, in the laboratory distilled water was used for all dilutions of artificial seawater in the experiments, and no contaminants were present. The hyposaline dilution alone is sufficient to cause the bleaching. The increased area of LCSB containing bleached anemones in 1995 is cause for concern. Freshwater inundation is episodic but frequent at this site, and it is channeled artificially in a manner that causes direct effects in this near-shore marine environment. Particularly during low and minus tides, seawater dilution of storm water runoff does not occur. We measured salinity in the field as low as 0 ppt, or freshwater, in the intertidal zone during a minus tide that occurred a few hours after a light rainfall. We are concerned that efforts to increase the speed and efficiency of storm water runoff have taken precedence over efforts to preserve an important biological habitat that educates and is
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