Diel Feeding Features of Juveniles of Two Sparids in the Stagnone di Marsala Coastal Sound (Western Sicily, Italy)

Abstract

Diet composition, feeding rhythms, gastric evacuation rates, daily rations of Diplodus puntazzo (Gmelin 1789) and Sarpa salpa (Linneo 1758) juveniles were studied in order to investigate their trophic ecology, niche breadth and overlap. These Sparids were collected in the Stagnone di Marsala (Western Sicily), in April 1997, in a 24 hour sampling period. Gastric content of 86 specimens of D. puntazzo (standard length = 31.9 ± 6.6 mm; body wet weight = 1.0 Ī 0.5 g) and of 100 specimens of S. salpa (standard length = 32.3 ± 2.9 mm; body wet weight = 0.6 Ī 0.2 g) were examined. Amphipoda and Tanaidacea were the most frequent prey items in stomach content of D. puntozzo, while Hydrozoa, Bryozoa and Rhodophycaea were the most frequent prey items in that of S. salpa. Both species displayed high frequency of occurrence (% Fr) of Copepoda and Ascidiacea larvae. A unimodal trend of daily rhythm of food consumption was deduced for both species. Gastric evacuation of juvenile D. puntazzo was best described by a square root model, with a gastric evacuation rate R= 0.011 ± 0.001 (r = 0.84; n = 28; P < 0.001). Similarly, gastric evacuation of S. salpa followed a square root model, with a gastric evacuation rate R=0.014 ± 0.001 (r = 0.90; n = 42; P < 0.001). The amount of food consumed daily, calculated according to Pennington’s model, was 0.0133 g dry weight g−1 body dry weight for D. puntazzo and 0.0159 g dry weight g−1 body dry weight for S. salpa, equal to 1.3% and 1.6% of the average body dry weight, respectively. Standardised Levins’ index (BA), calculated on percent volume (% V), suggested that juveniles of D. puntazzo have a niche breadth (mean standardised Levins’ index = 0.2 ± 0.02) larger than the one of S. salpa (mean standardised Levins’ index = 0.1 ± 0.01) at most sampling times. Juvenile specimens of these two Sparids presented a niche overlap at 4 pm, in correspondence with their feeding peak (Simplified Morisita’s index C H = 0.9). Feeding habits of D. puntazzo and S. salpa and their niche overlap are discussed in comparison with literature available on the same field.