ACANTHASTER (ECHINODERMATA, ASTEROIDEA) IN 



THE GULF OF CALIFORNIA 



Eric G. Barham,' Robert W. Gowdy,- and Fay H. Wolfson- 



ABSTRACT 



Possible invasion of the coral-rich Caribbean by eastern Pacific populations of Acanthaster, 

 which might follow on construction of a sea-level Central American canal, directed our 

 attention to Acanthaster in the Gulf of California. Based on the literature, field notes, and a 

 study of tagged specimens, the distribution, density, and behavior of this little known asteroid 

 are discussed. 



The population extends through some 300 miles of the southern half of the Gulf, mainly 

 along the western shore, and appears to be geographically isolated from eastern Pacific 

 Acanthaster populations known at lower latitudes. It is sparse and, even where common, 

 average density estimates are of the order of 1/200 m-. Through the northern part of its range, 

 the sea star feeds primarily on small encrusting growths of Porites caHfornica, but in the most 

 southerly regions, Pocillopora is a frequent prey. The change in prey preference appears 

 to be related to the distribution of the coral species and to changes in their dominant growth 

 forms. 



During a 48-h study of nine tagged specimens, 70% of the observed activity involved feed- 

 ing, 2Q% resting, and 10% traveling. There was no clear-cut diurnal behavior, and no tendency 

 to aggregate or to migrate as a population. 



Measurements and behavioral traits indicate that Acanthaster elUsii is a valid binomen 

 for the Gulf of California. We conclude that, if there is ground for concern over transoceanic 

 invasion, it should shift to the more southerly population. 



The alarm which followed early reports (Barnes, 

 1966; Endean, 1969; Chesher, 1969) of the dev- 

 astation of South Pacific coral reefs by the 

 crown-of-thorns sea star, Acanthaster plaiici, 

 appears to have subsided, although interpreta- 

 tion of the phenomenon is still being debated 

 (Dana, 1970; Newman, 1970; Vine, 1970; 

 Weber and Woodhead, 1970; Dana, Newman, 

 and Fager, 1972). However, the events have 

 served to highlight our ignorance of the eastern 

 tropical Pacific representatives of the genus. 

 Furthermore, the possible construction of a 

 Central American sea-level canal through which 

 eastern Pacific Acanthaster might gain access 



' Marine Environment Division, U.S. Naval Undersea 

 Research and Development Center, San Diego, Calif.; 

 present address: Southwest Fisheries Center, National 

 Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, 

 CA 92037. 



- Marine Environment Division, U.S. Naval Undersea 

 Research and Development Center, San Diego, CA 92152. 



to the coral-rich, but Aca}ithaster-free tropical 

 Atlantic, has raised the question of the preda- 

 tion-potential of the American population 

 (Newman and Dana, in press; David Pawson, 

 pers. comm.). 



The long-standing questions surrounding the 

 taxonomic status of Acaiithaster in the Gulf of 

 California and adjacent regions have been fur- 

 ther confused by the discovery of large numbers 

 in the Secas and Contreras Islands adjacent to 

 the Gulf of Panamjt (Glynn, 1970a, b; 1972), 

 and it is not at present clear whether any or all 

 of the American Acanthaster are assignable to 

 A. ellisii (Gray, 1840), to A. ellisii psendo- 

 planci Caso, 1962, or to A. planci (L., 1758). 

 However, we consider A. ellisii a valid binomen 

 for the populations we have observed in the 

 Gulf of California, and shall adhere to it for 

 purposes of this report. 



As recently as 1955, A. ellisii was known 

 from less than a dozen lots, mostly of single 



Manuscript accepted March 1973 

 FISHERY BUI LETIN: VOL. 71, NO. 4, 



1973 



927 



