AN ECOLOGICAL STUDY OF GOBIOSOMA BOSCl AND G. GINSBURGI 

 (PISCES, GOBIIDAE) ON THE GEORGIA COAST' 



Michael D. Dahlberg- and James C. Conyers' 



ABSTRACT 



The ecology of two species of "scaleless" gobies, Gobiosoma bosci and G. ginsburgi, from 

 estuarine and beach waters around Sapelo Island, Ga., is compared. Small patches of 

 oysters, in addition to oyster reefs, are important nesting areas for both species. Nu- 

 merous invertebrates and five other fishes are characteristic of the oyster patches. Habi- 

 tats common to both species include reefs and patches of oysters, bottoms of estuarine 

 rivers of moderate to high salinity, and burrows in an eroding clay deposit off Sapelo 

 Beach. In contrast to G. bosci, G. ginsburgi ranges offshore, is thought to spawn in deep 

 water, and is not found in fouling communities, marsh pools, and low salinities. 



These gobies are sexually dimorphic in genital papilla, body size, and color. They nest 

 in oyster shell. Males incubating and guarding their own eggs are cannibalistic on eggs 

 of other individuals, apparently having the ability to distinguish their own nests or eggs 

 from those of other individuals. Higher egg counts in nests than in ovaries prove that 

 G. bosci is polygamous. 



The spawning seasons of G. bosci and G. ginsburgi are apparently similar. The season 

 of G. bosci is protracted to the south and correlates with water temperature. 



Our study of the reproduction and ecology of the 

 two species of "scaleless" gobies, the naked goby 

 {Gobiosoma bosci) and seaboard goby (G. gins- 

 burgi), was initiated when they were discovered 

 incubating eggs in oyster shells at Sapelo Island, 

 Ga. This provided the opportunity to compare 

 certain aspects of the life history of these two 

 secretive species and analyze their ecological re- 

 lationship to oyster communities. There are 

 some published ecological information on these 

 two species (Dawson, 1966, 1969, and referen- 

 ces therein) and some scattered reports on re- 

 production that are partially summarized by 

 Breder and Rosen (1966). 



Since most species of Gobiosoma are tropical 

 (Bohlke and Robins, 1968), the genus probably 



^ This work was done at the University of Georgia 

 Marine Institute, Sapelo Island, Ga. 



- Virginia Institute for Scientific Research, 6800 River 

 Road, Richmond, VA 23229; present address: Cyrus 

 Wm. Rice Division, NUS Corporation, Manor Oak Two, 

 1910 Cochran Road, Pittsburgh, PA 15220. 



^ Virginia Institute for Scientific Research, 6300 River 

 Road, Richmond, VA 23229. 



Manuscript accepted May 1972. 



FISHERY BULLETIN; VOL. 71, NO. 1, 1973. 



originated in the tropics. However, the low 

 spawning threshold of G. bosci, about 20 °C (Nel- 

 son, 1928), suggests a temperate-water origin 

 for this species. G. bosci ranges from Connecti- 

 cut (Pearcy and Richards, 1962) and Long 

 Island Sound to Campeche, Mexico (Dawson, 

 1969). G. ginsburgi ranges from the Wareham 

 River and Woods Hole, Mass. (Ginsburg, 1933; 

 Lux and Nichy, 1971), to Jekyll Island, Ga. 

 (Dawson, 1966). G. robnstnm ranges from the 

 Gulf of Mexico to the St. Johns River, Fla. 

 (Tagatz, 1968) , and has been found in Maryland 

 (Schwartz, 1971). G. longipala, the Gulf cog- 

 nate of G. ginsburgi, is considered a distinct spe- 

 cies (Dawson, 1966). The similarity of these 

 two species, however, leaves little doubt that they 

 are derived from a common ancestor whose dis- 

 tribution was split by the emerged Florida pla- 

 teau, which now functions as an ecological and/ 

 or physical barrier. In contrast, Atlantic and 

 Gulf populations of G. bosci have not diverged 

 recognizably. 



G. bosci and G. ginsburgi are easily distin- 

 guished. G. ginsburgi has two ctenoid scales 



279 



