The black dbalone Hal~otls cracherodil was once abundant in many lntert~dal habitats in southern Callforn~a USA Beginning In 1985 however, black abalone In southern California suffered mass moltal~ties attributed to a condltton telmed lvlthenng syndrome The mass mortalities and w~therlng hyndrome were confined to southern Califoinla except for Dlablo Cove, 70 kin no1 th of Polnt Conception, where mortalities were limlted to the immediate vlcinity of a watm-water dtscharge Beylnnlng In 1992 we monltoied 5 locations along the mainland coast ot central California to detelmine whether mass mortal~ties of black abalone would occur there Abalone numbers decreased at the 3 southern sltes but not at the 2 northern sltes The decline was greatest at the southernmost site Government P o~n t (near Point Concept~on), where there was a 97% reduction in numbers between 1992 and 1995 The 2 sltes ~mmedlately upcoast of Government Polnt, Boathouse and Polnt Arguello, expenenced a 39 to 4Got, decllne ivh~le the 2 northernmost s~t e s (Stalrs and P u n s~m a ) expenenced a s l~g h t increase In abalone All abalone size classes d e c l~n e d at Government Polnt, Boathouse and Point Arguello lndicatlng the decllne was not caused by overharvesting Symptoms of w~therlng syndrome assessed by p u l l~n g on indlv~duals were noted at Boathouse and Polnt Arguello Witheling syndrome was also detected in the flnal survey at Stairs, as lvas a sllght dechne In abalone abundance, suggestlng that mass mortal~ties may be beginning there Our observations demonstrate that w~d e s p r e a d mass mortal~ty assoc~ated w~t h w~t h e l~n g syndlome has reached central Cal~fornia and is progressing northward from Point Conceptlon

Octopus bimaculatus, a common member of subtidal and intertidal communities of southern California (USA), 1s found in a wide range of habitats at Santa Catalina Island, where it is equally abundant in holes, under rocks, and in crevices. Although shelters may b e scarce in some areas, it appears that shelters generally do not limit the size of 0. bi~naculatus populations Shelters suitable for habitation by adult and juvenile 0. birnaculatus were always in excess during this study. Nearly half of the population studied inhabited their shelter for more than a month, and a few octopuses occupied the same shelter for at least 5 months. O n e fourth of the population spent less than a week in the same shelter, and many of these may have changed shelters every day. However, nearly all octopuses remained in the same area. The nontransient behavior of 0. bimaculatusmay have important implications for resource utilization, mating and agonistic behavlor

Octopus birnaculatus, a common member of intertidal and subtidal communities in southern California, consumes many motile benthic invertebrate species, including snails, chitons, h p e t s , bivalves, and crustaceans. An analysis of octopus d d holes in empty snail shells indicates that 0. bimaculatus is a major s n d predator in the community. The addition of marked snails to a natural reef with unmanipulated octopus densities demonstrated that octopuses can quickly reduce s n d abundances, consuming 24 % of the available snails within 24 d. During 5 yr at 1 site, octopus abundance declined from 40 to 8 octopuses, while total prey abundance increased from 16 to 80 ind m-'. A second site experienced a similar drop in octopus density and increase in prey density over 3 yr. At both sites, snails and hermit crabs showed the greatest increases. Sedentary grazers, bivalves, and crabs and shrimps occurred at low densities throughout, possibly because the abundances of these preferred prey were depressed by octopus predation even during years of low octopus density. In splte of the strong negative association at the 2 sltes between octopus and prey over time, for a single time penod at 15 different s~t e s prey densities were not negatively correlated w t h the densities of their predators. However, octopus densities were much higher when they appeared to reduce the abundances of their prey than when the 15 different sites were sampled. I conclude that octopus predation can dramatically reduce prey densities when octopuses are unusually common, but that in most years the abundance of octopuses 1s too low to disrupt the basic patterns of prey abundance that result from other processes. The hghest prey species richness and diversity at the 2 study sites occurred during years of lowest octopus densities. Species richness, chversity and evenness of the prey assemblage were not correlated with octopus, lobster or predatory gastropod abundances at the 15 different locations; when the effects of habitat structure were held constant by partial correlation, seastar abundance was negatively correlated with species nchness and diversity. The relation between predation and species chversity suggests that, when predation is effective in this assemblage, it decreases diversity.