with grazing intensity on the Great Barrier Reef, being lowest within cages, 

 intermediate within damselfish territories, and greatest outside territories. 

 However, both Lobel (1980) and Hixon and Brostoff (in prep.), working in Hawaii, 

 found considerably more blue-green algae inside than outside territories. 

 These discrepancies suggest possible regional differences in local distributions 

 of blue-green algae. In any event, herbivorous fishes, especially territorial 

 damsel fishes, extensively affect reef algae in a variety of ways. 



SYNTHESIS 



Attempting to synthesize the above studies into a single conceptual framework 

 can be done only at the realized risk of over-generalization and over- 

 simplification. So be it. In general, fishes appear to strongly influence the 

 community structure of reef algae, much more so than that of corals. This 

 difference may be due to coral polyps and their surrounding calcareous skeletons 

 being less available, palatable, and productive than many algae. Indeed, 

 Randall (1974) has indicated that truly coral livorous fishes are among the most 

 highly evolved of fishes, suggesting that this form of predation has appeared 

 only recently in evolutionary time. However, many algae are inferior sources 

 of nutrition (e.g., Montgomery and Gerking 1980), and chemical defenses in 

 algae are being discovered at an increasingly rapid rate (e.g., Norris and 

 Fenical 1982, Paul and Fenical 1983). 



In any event, while transient grazing fishes certainly control the distribution 

 and abundance of many algae and some corals, the direct and indirect effects of 

 territorial damsel fishes appear to strongly alter a variety of components of 

 reef benthos. These fishes truly can be considered "keystone species" ( sensu 

 Paine 1969) where they are abundant (Williams 1980, Hixon and Brostoff 1983). 

 I thus submit Figure 1 as a flowchart summarizing the general scheme of fish- 

 benthos interactions on a "typical" coral reef where damsel fishes are common. 

 Some of these interactions are well documented; others are not. This "synthesis" 

 should therefore be considered a set of working hypotheses rather than a list 

 of facts. All that can be stated unequivocally is that, first, fishes do indeed 

 affect benthic community structure on tropical reefs, and second, more data on 

 this important topic clearly are needed. 



ACKNOWLEDGMENTS 



Many thanks to F. Lynn Carpenter for her eleventh-hour review and Pam McDonald 

 for her twelfth-hour typing of the manuscript. 



LITERATURE CITED 



Bak , R.P.M., & M.S. Engel . 1979. Distribution, abundance and survival of 



juvenile hermatypic corals (Scleractinia) and the importance of life history 



strategies in the parent coral community. Mar. Biol. 54:341-352. 

 Birkeland, C. 1977. The importance of rate of biomass accumulation in early 



successional stages of benthic communities 



Proc. 3rd Int. Coral Reef Symp. 1:15-21. 

 Birkeland, C. 1982. Terrestrial runoff as a 



planci (Echinodermata: Asteroidea). Mar. 

 Borowitzka, M.A. 1981. Algae and grazing in 



N.S. 5:99-106. 

 Brawley, S.H., & W.H. Adey. 1977. Territorial behavior of threespot damselfish 



(Eupomacentrus planifrons) increases reef algal biomass and productivity. 



Env. Biol. Fish. 2:45-51. 



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