Population Characteristics and Food Resource Utilization of Conus in the Galapagos Islands!

Two large collections of Conus from the Galapagos Islands permitted the analysis of size, sex ratio, and food of 4 of the estimated 13 species of Conus present in the islands. The species investigated were C. diadema, C. lucidus, C. tiaratus, and C. nux. Significantly unequal sex ratios were found in the samples of C. diadema, C. lucidus, and C. tiaratus, but there was no indication of sexual dimorphism in shell sizes. Conus diadema was found to have the most catholic diet of the species, consuming mainly polychaetes of the family Terebellidae, but also sipunculids, mollusks, and eight other polychaete families. Very few food items were recovered from the guts of C. lucidus and most were polychaetes of the families Sabellariidae and Capitellidae. Conus tiaratus and C. nux were both found to feed primarily on polychaetes of the families Nereidae and Eunicidae. In both cases, the dominant species was Nereis jacksoni. Comparison of diets between cognate species in the Galapagos and the Indo-West Pacific indicated the Galapagos species consumed somewhat different prey species. Although there are significantly fewer Conus speCies peihabitafiri the Galapagos than in the Indo-West Pacific, fhere were no significant differences with respect to number of prey species consumed or prey species diversity between the areas. Thus, there was no evidence of decreased dietary specialization in the presence of fewer competing congeners. THE GALAPAGOS ISLANDS and their fauna have elicited considerable interest from biologists since the famous visit of Darwin in 1835. However, most of this interest has been directed at the terrestrial fauna and to the unique assemblage ofmarine vertebrates such as penguins, cormorants, and lizards. Relatively little attention has been paid to the marine invertebrate fauna. Most studies on the marine invertebrate fauna of the islands have been taxonomic or zoogeographic (Bowman 1966) and have generally shown that the marine invertebrate fauna is most closely related to that of the East Pacific and Caribbean (Abbott 1966) rather than the richer Indo-West Pacific. The Galapagos, together with Clipperton and Isla Rivelligegados, represent the most I Manuscript accepted 3 April 1978. 2 Central California State University and Colleges, Moss Landing Marine Laboratories, Moss Landing, California 95039. isolated outposts of the East Pacific Conus species. They are further of interest in that the marine environment is considered to be warm temperate (Abbott 1966) rather than tropical, which is the climate most other Conus assemblages exist under in the East Pacific area. It is thus of some interest to compare the ecology of Conus species assemblages on these islands with similar sets from tropical regions to see if the lack of tropical conditions and the isolated nature of the islands have affected the ecological characteristics of the assemblages. It is the purpose of this paper to begin such an ecological analysis by considering the food and population characteristics of the more common Galapagos species. The specimens upon which this paper is based were collected by J. J. Von Mol of the University of Brussels, Belgium, in 1970 and by G. M. Wellington of the University of California at Santa Barbara in 1973 and 1974. I am greatly indebted to them for placing this material at my disposal.