. Bulletin. Science; Natural history; Natural history. 102 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES f^^' K' iM^' rLi5 ^<. /^^'^x^>%^,,,'^> ^o^':;^^s^'^^-^"^''^^"^ ^^ fS' U5 «* ^e^'^ 5^'^ ^i>^ f^ Fig. 5. Macroinvertebrate densities (features same as Fig. 3). and Littler 1984), the thin sheet-like and microfilamentous algae, mainly Ulva/ Enteromorpha and Ectocarpaceae, appeared abundantly in former sea urchin territories following the mass mortality of Strongy'locentrotus purpuratus. Such algal forms have been shown (Sousa et al. 1981) to be maintained in low abun- dances by
. Bulletin. Science; Natural history; Natural history. 102 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES f^^' K' iM^' rLi5 ^<. /^^'^x^>%^,,,'^> ^o^':;^^s^'^^-^"^''^^"^ ^^ fS' U5 «* ^e^'^ 5^'^ ^i>^ f^ Fig. 5. Macroinvertebrate densities (features same as Fig. 3). and Littler 1984), the thin sheet-like and microfilamentous algae, mainly Ulva/ Enteromorpha and Ectocarpaceae, appeared abundantly in former sea urchin territories following the mass mortality of Strongy'locentrotus purpuratus. Such algal forms have been shown (Sousa et al. 1981) to be maintained in low abun- dances by S. purpuratus when populations of the herbivore remain at high levels. From early Februar\- to late May 1977, 5. purpuratus populations were assessed (Murray and Littler 1984 at a comparable intertidal study site just 40 km to the north. Fig. 1) by the identical methods used here and showed very little variability ( cover and 16-m"- density in Februan,' versus cover and 13-m"^ density in late May, not significant, P > , ANOVA). The sheet form Ulva californica was uncommon at Whites Point and increased only slightly (from ), whereas Ectocarpaceae and Entero- morpha sp. consistently remained at only trace levels. The three persistent pe- rennial taxa Hydrolithon decipiens, blue-green crust, and Gelidium coidteri/pusil- lum that decreased slightly at Corona del Mar, underwent a combined relative increase of one third during the same period at Whites Point ( to , to , and to absolute cover, respectively). Dawson (1959, 1965) analyzed groups of intertidal organisms and reported a decline in leafy red algal forms and increased growth of jointed calcareous cor- allines in Southern California near sites of sewage discharge. Since then, changes in terms of gross morphological groupings of algal taxa have been evaluated (Widdowson 1971; Thorn and Widdowson 1978: Sousa et al. 1981; Murray and Littler 1984) subsequently for the same
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