HOBSON: FEEDING RELATIONSHIPS OF FISHES 



Table 59. — Food of Gomphosus varius. 



CONCLUSION. — Gomphosus varius is a diur- 

 nal predator that takes relatively large crusta- 

 ceans from reef crevices. 



General Remarks on Wrasses 



Kona reefs, like tropical reefs the world over, 

 are populated by a diverse array of wrasses, most 

 of them with strong pharyngeal teeth adapted to 

 crush hard-bodied prey. Macropharyngodon geof- 

 froy, for example, preys on more heavily armored 

 prey — in this case mollusks and foramini- 

 ferans. Others, like Anampses cuvier, have the 

 pharyngeal teeth less developed and prey mostly 

 on tiny crustaceans. Some of the wrasses, espe- 

 cially Thalassoma duperrey, are highly oppor- 

 tunistic, and these tend to be the most widespread 

 and have the most varied diets. 



It is well known that wrasses are active only 

 during the day; at night they rest in reef crevices 

 and under the sand (Longley and Hildebrand, 

 1941; Goshne and Brock, 1960; Hobson, 1965, 

 1968a, 1972; Starck and Davis, 1966; Collette and 

 Talbot, 1972). They are among the first diurnal 

 fishes on the reef to seek cover at day's end, and 

 among the last to leave cover in the morning ( Hob- 

 son, 1965, 1968a, 1972; Collette and Talbot, 1972). 



Family Scaridae: parrotfishes 



Scarus sordidus Forskal — uhu 



This is one of the more numerous parrotfishes in 

 Kona, especially over coral-rich reefs. During the 

 day, it swims actively close to the substratum, 

 often in groups. With its parrotlike beak, it 

 scrapes away the fine filamentous algae that 

 grows over the surface of dead coral, especially 

 Pontes. Although frequently it scrapes up to the 

 edge of living coral, it stops there (Figure 34). 

 During twilight, this species migrates in schools 

 from one part of the reef to another, but the mi- 

 gratory pattern remains unclear (Hobson, 1972). 



At night S. sordidus rests solitarily in reef crev- 

 ices. Because some parrotfishes are known to se- 

 crete a mucous envelope around themselves at 

 night (Winn, 1955), during a series of night obser- 

 vations over 3 mo I estimated the standard length 

 of each resting parrotfish, and noted whether or 

 not it was encased in mucus. During these obser- 

 vations, 20 individuals of this species were seen, 

 estimated to be between 150 and 350 mm long. All 

 eight that appeared to be shorter than 300 mm 

 were in mucous envelopes, whereas all six without 

 envelopes were judged to be longer than 300 mm. 

 The other six, all estimated to exceed about 300 

 mm long, were in envelopes. Thus, all the smaller 

 individuals, but only some of the larger ones, were 

 in envelopes. 



The guts of all seven S. sordidus (195: 150-213 

 mm) that were speared during midday were full of 

 bits of algae, mixed with calcareous powder, or- 

 ganic slurry, and sand (proportions undeter- 

 mined, but the algae constituted less than 207f ). 

 No evidence was found in these specimens of coral 

 tissues or mucus (the latter is prominent in the gut 

 contents of fishes known to feed on coral), even 

 though Hiatt and Strasburg (1960) reported that 

 coral polyps constituted the major food of this 

 parrotfish in the Marshall Islands. These authors 

 stated (p. 103): "Scraping living coral heads seems 

 to be its predominant mode of feeding." This ob- 

 servation contrasts with mine in Kona, where S. 

 sordidus avoids the living coral when feeding. 



CONCLUSION. — Scarus sordidus is a diurnal 

 herbivore that feeds mostly by scraping fine 

 benthic algae that have overgrown the surface of 

 dead coral. 



Scarus taeniurus Valenciennes — uhu 



My observations of their social interactions ren- 

 der it clear that the two forms Schultz (1969) 

 distinguished in Hawaii as S. taeniurus and S. 

 forsteri are conspecific and that his "S. forsteri" 

 represents the large male of the species. 



995 



