Comparative Feeding Ecology of Cardinalfishes (Apogonidae) at Toliara Reef, Madagascar

Abstract

Bruno Frédérich, Loïc N. Michel, Esther Zaeytydt, Roger Lingofo Bolaya, Thierry Lavitra, Eric Parmentier, and Gilles Lepoint (2017) Despite their importance in coral reef ecosystem function and trophodynamics, the trophic ecology of nocturnal shes (e.g. Apogonidae, Holocentridae, Pempheridae) is by far less studied than diurnal ones. The Apogonidae (cardinal shes) include mostly carnivorous species and evidence of trophic niche partitioning among sympatric cardinal shes is still limited. The present study combines stomach contents and stable isotope analyses to investigate the feeding ecology of an assemblage of eight cardinal shes from the Great Reef of Toliara (SW Madagascar). δ13C and δ15N of shes ranged between -17.49‰ and -10.03‰ and between 6.28‰ and 10.74‰, respectively. Both stomach contents and stable isotopes showed that they feed on planktonic and benthic animal prey in various proportions. Previous studies were able to group apogonids in di erent trophic categories but such a discrimination is not obvious here. Large intra-speci c variation in the stomach contents and temporal variation in the relative contribution of prey to diet support that all apogonids should be considered as generalist, carnivorous shes. However the exploration of the isotopic space revealed a clear segregation of isotopic niches among species, suggesting a high level of resource partitioning within the assemblage. According to low inter-speci c variation in stomach content compositions, we argue that the di erences in isotopic niches could be driven by variation in foraging locations (i.e. microhabitat segregation) and physiology among species. Our temporal datasets demonstrate that the trophic niche partitioning among cardinal shes and the breadth of their isotopic niches are dynamic and change across time. Factors driving this temporal variation need to be investigated in further studies.

Keywords: Apogonids; Diet; Isotopic niche; Stable isotopes; Western Indian Ocean.

Fig. 1.

Fig. 1. (A) Mean values (± SD) of δ13C (‰) and δ15N (‰) of cardinal shes. (B) Isotopic niches of cardinal shes. Points are individual measurements, and solid lines represent the bivariate standard ellipses associated to each group Species and sampling years are represented by di erent symbols and colors, respectively.

Fig. 2.

Fig. 2. Boxplots of model-estimated bivariate standard ellipse area (SEAB). Dark, median and light grey boxes are respectively the 50%, 75% and 95% credibility intervals of the probability of density function distributions of the model solutions, and black dots are the modes of these distributions. Red dots represent the standard ellipse areas computed using a frequentist algorithm adapted for small sample sizes (SEAC).

Fig. 3.

Fig. 3. Relationship between body size (SL, mm) and isotopic values (A: δ13C; B: δ15N) in studied apogonids. Only significant relationships are illustrated.