FISHERY BULLETIN: VOL. 76, NO. 2 



green algae. The overlap on amphipods by the 

 latter two species may be partially compensated 

 for by behavioral separation. Diplodus cervinus is 

 a secretive substrate feeder whereas Z). sargus is a 

 more open water fish tending to feed on vertical 

 rock surfaces away from the bottom. The fact that 

 neither species was very common intertidally in 

 these size classes may also contribute towards a 

 reduction in competition. 



The diet of large juvenile S. salpa is unusual in 

 that it consists mainly of diatoms and epiphytic 

 rhodophytan algae which occur commonly on 

 corallines, Hypnea spicifera and Tayloriella spp. 

 (M. H. Giffen, pers. commun.). The fish must, 

 therefore, selectively separate these food items as 

 few fragments of the algae on which they grow 

 were found in the stomach contents. This is in 

 contrast to Rhabdosargus holubi, also a sparid, 

 which ingests algae for their epiphytic diatoms 

 rather than separating them, even though the 

 algae are not digested (Blaber 1974). The situation 

 may be similar to this in larger S. salpa as the 

 rectal contents appeared to be relatively undi- 

 gested and fewer diatoms were observed on the 

 algae (Figure 12). 



Temporal separation of juveniles to reduce com- 

 petition has not been reported previously for tide 

 pool fish species as far as I am aware, although it 

 has been observed in two pelagic plankton feeders 

 from the Adriatic, the anchovy and sardine ( Vuce- 



tic 1975). Large dietary overlaps have been noted 

 in several intertidal fish, including blennies, 

 clinids, gobies, and labrids (Gibson 1968, 1972). 

 These fed predominantly on crustaceans and it is 

 possible that similar mechanisms reduce competi- 

 tive pressure amongst them, although this was not 

 determined as samples were only taken for 2 mo. 



The data presented indicates that/), cervinus is 

 a carnivore, D. sargus is an omnivore, and S. salpa 

 an omnivore when juvenile and a herbivore when 

 adult. Similar feeding habits were found for adults 

 of the same three species in the Klein River es- 

 tuary (Talbot 1954). The dentition and gross gut 

 morphology changed with size and this was most 

 marked in S. salpa, corresponding with the ob- 

 served diet. Comparable transformations have 

 been reported for other fish species (Nikolsky 

 1963). 



Two other sparids, Sparodon durbanensis and 

 R. holubi, cohabit with those studied in the littoral 

 zone. The few specimens examined had fed mainly 

 on harpacticoid copepods as small juveniles, with a 

 resultant overlap with D. sargus as all three oc- 

 curred in the research area in November- 

 December. Large specimens were not examined, 

 but R. holubi appears to be an omnivore as a 

 juvenile in estuaries and a carnivore feeding on 

 molluscs as an adult (Talbot 1954; Blaber 1974). 

 Adult S. durbanensis are carnivores feeding on 

 small fish, molluscs, and crustaceans (Biden 



Figure 12.— Scanning electron micrograph of the surface of a chlorophytan alga, Ulva sp., removed from the gut ofSarpa salpa (147 

 mm SL) to show the disappearance of diatoms. A. Oesophageal sample. B. Rectal sample. 



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