Trophic structure of vermetid reef community: high trophic diversity at small spatial scales

Abstract

Stable isotopes were used to investigate contributions of autochthonous (i.e. benthic: epilithon and macroalgae) and allochthonous (i.e. pelagic: phytoplankton) organic matter sources to the diet of suspension-feeders, grazers and predators associated to small reef-pools (cuvettes) created by the reef-building species Dendropoma petraeum in the north-western coast of Sicily (Italy). Contributions of potential food sources were calculated using Bayesian mixing-models and integrated to a multivariate approach to highlight the diversity of C and N pathways within Dendropoma cuvettes. Both pelagic and benthic organicmatter sources were exploited by benthic consumers, although clear differenceswere revealed in the various species depending on their feeding strategy. Three different trophic pathwayswere identified: one basedmainly on phytoplankton, one basedmainly on macroalgae and a third one mainly on epilithon. Suspension-feeders seemed to rely mainly on allochthonous organic matter sources, while grazers showed a wider diet spectrum. Predators revealed a high specialization in each of the three food chains and showed a distinct reliance on organicmatter originated frombenthic or pelagic sources. Stable isotopes evidenced here a marked differentiation of the trophic niche within the cuvetteassociated community, which allows minimizing competition in very space-limited conditions.