HORN ABUNDANCE AND DIVERSITY OF MORRO BAY FISHES 



the diversity and similarity pattern for Mugu La- 

 goon is close to that for Morro Bay as would be 

 expected for an unspoiled habitat. Data obtained 

 during quarterly periods (February-November 

 19781 from bag seine collections of 23 species in 

 upper Newport Bay (Horn and Allen in press) re- 

 sulted in a total H' value of 0.66 and PS indices 

 ranging from 13 to dWc (Table 5). Quarterly bag 

 seine data (February-November 1973) for 16 

 species in Colorado Lagoon (Allen and Horn 1975) 

 produced a total //' value of 0.75 andPS measures 

 ranging from 2 to 57Vr (Table 5). According to the 

 Haedrich (1975) model, the relatively low diver- 

 sity values for upper Newport Bay and Colorado 

 Lagoon should be accompanied by high similarity 

 values and dominance of the community by one or 

 a few species. However, a combination not 

 explicitly recognized by Haedrich, that of low di- 

 versity and wide ranging seasonal similarity, is 

 evident in these two habitats. Low//' values com- 

 bined with variable PS values indicate a high 

 seasonal abundance of one or a few species. This 

 condition is realized in that in each case there was 

 an extreme summer abundance of only one 

 species — A. affinis in upper Newport Bay and £. 

 mordax in Colorado Lagoon. In the most highly 

 stressed habitat, low diversity, and a high relative 

 abundance of a single species over the entire year 

 (i.e., high seasonal similarity) would be predicted 

 by the model. Thus, upper Newport Bay and Col- 

 orado Lagoon would be rated as intermediate in 

 environmental quality. In general, Colorado La- 

 goon could be considered as the more highly per- 

 turbated of the two habitats (Table 5). The heavy 

 rainfall of 1978, the year in which the upper New- 

 port Bay data were collected, probably was a 

 primary factor in producing the low diversity and 

 divergent similarity values (Horn and Allen in 

 press). 



The use of the two indices in combination ap- 

 pears to have greater resolution and predictive 

 strength than the use of only species diversity as 

 an indicator of pollution, as has been proposed by 

 Bechtel and Copeland (1970). Diversity H' pro- 

 vides information on species richness and 

 equitability but not on species composition. The 

 absolute replacement of one species by another, 

 possibly a result of environmental alteration. 



^Millicent L. Quammen, graduate student, Department of 

 Biological Science, University of California, Santa Barbara, CA 

 93106, pers. commun. August 1979. 



would not be detected by a diversity measure nor 

 would the seasonal succession of individual 

 species. An index of similarity provides an indica- 

 tion of the magnitude and direction of seasonal 

 dynamics. 



The diversity-similarity approach holds prom- 

 ise as one of the procedures for distinguishing the 

 relative quality of bay-estuarine habitats and de- 

 serves to be tested in additional localities. The 

 results for Morro Bay also underscore the need for 

 a more thorough knowledge of its fish com- 

 munities since it is a relatively pristine habitat 

 that may be subject to a number of alterations in 

 the future (Gerdes et al. 1974). 



ACKNOWLEDGMENTS 



I especially thank S. Marie Harvey who contrib- 

 uted significantly to the completion of this study. 

 She ably assisted in the field work, meticulously 

 recorded and compiled the data, and carefully 

 drafted the figures. I greatly appreciate the efforts 

 of Larry Allen, Gregory Smith, and Wayne White 

 who showed unwavering support of the project 

 throughout its duration. They, along with James 

 Knost, Linda Sims, Robert Sims, and John Tiede- 

 man, performed tirelessly and enthusiastically 

 during the long hours of field work. I am grateful 

 to the numerous other people who assisted with 

 the data collection, including David Chapman, 

 Myra Chapman, Gary Devian, Richard Dumke, 

 Wanda Halbakken, Kathryn Heath, Kheryn 

 Klubnikin, Lee Lorenzen, Margaret Neighbors, 

 Sarah Swank, Denise White, and Robert White. I 

 extend sincere thanks to Millicent Quammen who 

 kindly made available to me her unpublished data 

 on Mugu Lagoon fishes. Financial assistance and 

 material support were provided by the De- 

 partment of Biology, California State University, 

 Fullerton. 



LITERATURE CITED 



Allen, L. G. 



1976. Abundance, diversity, seasonality and community 

 structure of the fish populations of Newport Bay, Califor- 

 nia. M.A. Thesis, Calif. State Univ., Fullerton, 108 p. 

 Allen, L. G., and M. H. Horn. 



1975. Abundance, diversity and seasonality of fishes in 

 Colorado Lagoon, Alamitos Bay, California. Estuarine 

 Coastal Mar. Sci. 3:371-380. 



Bane, G., and M. Robin.son. 



1970. Studieson i\\e shiner Y)erch,Cymatogasteraggregata 

 Gibbons, in upper Newport Bay, California. Wasmann J. 

 Biol. 28:259-268. 



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