CHRISTENSEN: TROPHIC RELATIONSHIPS OF SPARID FISHES 



Phoxostoma sp. (amphipod), and Corallina sp. 

 (rhodophytan alga). 



Sarpa salpa 



The percentage composition of the diet of Sarpa 

 salpa is illustrated in Figure 9 and Table 4. The 

 food habits of this species changed from being 

 primarily a carnivore as a juvenile to a herbivore 

 as a subadult. 



Juveniles in the 10- to 25-mm size classes fed 

 mainly on harpacticoid copepods. In the next size 



100- 



Figure 9. — Changes in diet with length of Sarpa salpa, as 

 shown by the comparative feeding index. Food items included in 

 Others are: bryozoans, cirripede nauplii , crab zoaea, fish muscle, 

 insects, isopods, leptostracans, mysidaceans, ostracods, 

 pMjlychaetes, rhaciglossid molluscs, and tanaidaceans. 



class (25-35 mm), however, the total animal con- 

 tribution is only 15.1%, diatoms and rhodophytan 

 algae being most important. Diatoms are taken in 

 decreasing amounts from then on and those fish 

 >75 mm SL fed predominantly on chlorophytan 

 and rhodophytan algae. 



Identity of Food 



Chlorophytan algae: eight species — Bryopsis 

 sp., Caulerpa filiformis, Chaemaedoris delphini, 

 Cladophora spip.,Enteromorpha sp.,Rhizoclonium 

 sp., and Ulua sp. 



Rhodophytan algae: Ceramium sp., Champia 

 compressa, Hypnea spicifera, Polysiphonia sp., 

 and Tayloriella sp. commonly taken as well as Ac- 

 rosorium sp., Arthrocardia sp., Centroceras sp., 

 Corallina spp., Polyzonia elegans, and Ptero- 

 siphonia cloiophylla. 



Chrysophytan algae: three species of 

 diatoms — Isthmia enervis, Licmophora ehrenber- 

 gii, and L. pfannkucheae . 



Hydrozoans: Gattya humilis commonly ingested 

 by the 75- to 100-mm size class, whereas Ser- 

 tularella sp. and Thecocarpus formosus were un- 

 common. 



Polychaetes: only two species of Nereis. 



Isopods: uncommon, but six species were 

 found — Dynamenella huttoni, D. macrocephala, 

 Gnathia sp., Janiropsis sp., Panathura sp., and 

 Stenetrium sp. 



Table 4. — Changes in the percentage composition of the food of Sarpa salpa with length, as assessed by the comparative 

 feeding index (CFI) and occurrence (Occ.) methods. In the case of the latter, all values exceeding 30% have been italicized in 

 order to emphasize those food items which contribute maximally to the diet ( — = absent). 



Size classes (mm) 

 10-15 15-25 25-35 35-50 50-75 75-100 125-150 



Taxon CFI Oca ^R Oca "CFJ Oca CFI Occ. CFI Occ. CFI Occ. CFI Occ. 



Chlorophyta 0.3 8 7 — — 9 313 37.2 92 34.0 917 30 6 100.0 48.3 100.0 



Rhodophyla — — 0.4 9.1 21.3 62.5 323 76.0 28.6 66.7 45.9 83.3 50.7 100,0 



Chrysophyta 0.2 87 9.3 24,2 62,7 1000 32 4 68,0 33.4 66.7 _ _ _ — 



Hydrozoa _______ — 0,1 16.7 20.5 50.0 0.8 50.0 



Polychaeta 5.1 17.4 2.6 30,3 _ _ _ _ 0.4 8,3 0,1 167 — — 



Crustacea 



Isopoda 17 17.4 9 30.3 0,1 6 3 — — — — — — — — 



Amphipoda 73 30,4 17,8 63,6 4,2 50 0.9 16.0 0.1 16.7 0.3 33.3 0.8 50 



Ostracoda 67 26 1 14 36 4 01 63 01 12 ______ 



Harpacticoid copepoda 77.0 87,0 64 5 72 7 0,5 18 8 1,4 24 ______ 



Cirnpedia (nauplii) 5,5 22,0 2 1 18,2 _____ — _ — — — 



Brachyura (zoaea) — — 0,1 3,0 0,1 12.5 ________ 



Leptostraca 1 4 4 — — — — — — — — — — — — 



Insecta 0,1 4 4 0,2 3.0 0.1 12.5 — — — — — — — — 



Bryozoa ________ — — 01 16 7 — — 



Mollusca __________ 0.1 16,7 — — 



Pisces ____ 0,2 6,3 — — — — — — — — 



Unidentified fragments 



and sand 2.0 26.1 0.7 24.2 9.8 31.3 1.7 32.0 3.4 41.7 2.4 50.0 — — 



No, of fisfi examined 23 33 16 25 12 6 2 

 Average no of points 



allotted per stomach 7.8 9.5 13.8 15.7 16.5 15.5 28.0 



397 



