DAHLBERG and CONYERS: ECOLOGICAL STUDY OF GOBIOSOMA 



Table 3. — Monthly length frequencies of Gobiosoma ginsburgi, from the Georgia coast, April 1967-June 1970. 

 M - male, F - female, U - unidentifiable sex (including juveniles), I - incubation of eggs or larvae, G - gravid female. 



and 25 females in February collections from the 

 tidal creek. March collections of G. ginsburgi 

 from burrows in an eroding clay outcrop at Sa- 

 pelo Beach included 59 males and 54 females. 

 This even sex ratio also occurs in G. robustum 

 (Springer and McErlean, 1961). 



NESTING BEHAVIOR 



G. bosci and G. ginsburgi apparently have 

 evolved an instinctive ability to select nesting 

 sites that will allow successful reproduction. 

 They lay adhesive eggs inside dead, gaping, 

 hinged oyster shells, which provide a clean stable 

 substrate and protection from predators. The 

 size of the aperture of the oyster shell, its sub- 

 mergence throughout the tidal cycle, and the 

 amount of water circulation provided by tidal 

 currents seem to be important criteria for se- 

 lection of nesting sites in reef areas. Though 

 nests were most commonly found in oyster shells, 

 we collected one male G. bosci with eggs from 

 a hinged quahog (Mercenaria mercenaria) shell. 

 Nelson (1928) also reported G. bosci nesting in 

 "clam" shells, and Breder (1942) found nests 

 of the reproductively similar G. robustum in 

 sponges and scallop shells. 



We noted during our collection of nesting 

 shells that all nests were below mean low tide, 

 and none were found emerged during the ex- 

 tremely low spring tides. The gape of each nest- 

 ing shell was just large enough to allow the goby 

 to enter. This characteristic gape facilitated 

 our recognition and collection of nests. Closing 



the shells before extracting them from the reef 

 prevented escape of the parent gobies. 



Nests seemed to be located where the tidal 

 current restricted siltation and stagnation at low 

 tide. Masses of developing eggs and larvae 

 probably require a continuous flow of water to 

 provide oxygen and remove metabolic waste 

 products. In aquarium observations, male gobies 

 provided additional circulation by fanning the 

 egg masses with slow undulations of the caudal 

 fin. They apparently display this behavior in 

 nature because all egg masses examined were 

 free of silt. 



Male G. bosci and G. ginsburgi guard and ag- 

 gressively defend the nest until the eggs hatch 

 and larvae become free-swimming. In labora- 

 tory observations males even attacked inanimate 

 objects such as pipettes which were inserted into 

 the nest. In defensive display, the dorsal fin and 

 pelvic disc were erected, the mouth was opened 

 broadly, and the body color was darkened. The 

 erected pelvic disc elevated the body and may 

 function to make the goby appear larger. 



Male G. bosci were observed to successfully 

 defend their nests against other male G. bosci 

 introduced in the vicinity of the nest. Attached 

 eggs of G. ginsburgi placed with male G. bosci 

 were promptly eaten, even when the males were 

 guarding their own eggs. Furthermore, male 

 G. bosci were cannibalistic when presented with 

 unfamiliar unhatched eggs while guarding their 

 own nests. Both species may be important 

 predators on eggs of their own species and other 

 species nesting in oyster reefs. Since we saw 



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