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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Isotopic Ratios Reveal Mixed Seasonal Variation Among Fishes from Two Subtropical Estuarine Systems
Auteurs :	Jill A. Olin, Auteur ; Scott A. Rush, Auteur ; M. Aaron MacNeil, Auteur ; Aaron T. Fisk, Auteur
Type de document :	Article
Dans :	Estuaries and Coasts (35(3) MAY 2012)
Article en page(s) :	811-820
Résumé :	Characterizing dietary resources and species interactions in estuaries is challenging, particularly when considering the dynamic nature of these ecosystems, the ranges in body sizes of species, and the potential for trophic roles to vary with ontogeny. We examined the influence of season and location on relationships between body size and delta(15)N, delta(13)C, and delta(34)S values across a range of fishes from two subtropical estuaries. The results suggest that isotopic values of estuarine fishes are independent of body size. However, seasonal variation propagated throughout the assemblage as the majority of fishes integrated different delta(15)N, delta(13)C, or delta(34)S values. The absence of delta(15)N-, delta(13)C-, and delta(34)S-body size relationships suggests that either (1) dietary preference of these fishes do not shift within the range of body sizes sampled, (2) these fishes shift to an alternate diet that is not isotopically distinct, or (3) that spatial and temporal variation in isotopic signatures of prey negate any size-based relationships. Seasonal variability in the isotopic values of these fishes suggests either movement to an alternative habitat or a shift in organic matter source associated with the transition of dry to wet seasons. Moreover, variance distributions of the best-fit models indicate that seasonal dietary preferences of conspecifics do not vary over moderate spatial scales. Seasonal variability among fishes in these estuaries suggests plasticity in feeding strategies that may afford greater adaptive flexibility to these species in response to changes in food availability resulting from variable environmental conditions.

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