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ORIGINAL ARTICLES

Allochthonous versus autochthonous organic matter sustaining macroconsumers in a subtropical sandy beach revealed by stable isotopes

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Pages 241-258 | Received 01 Oct 2018, Accepted 24 May 2019, Published online: 08 Jul 2019
 

ABSTRACT

Exchange of matter and energy between ecosystems has been an important topic in ecology. In this work, we estimated the relative assimilation and seasonality of autochthonous versus allochthonous organic matter by macrofauna and fishes of a subtropical sandy beach. Sampling of consumers and autotrophic food sources (particulate organic matter in suspension-POM and in sediment-SOM) were obtained seasonally at the sandy beach for carbon (δ13C) and nitrogen (δ15N) stable isotope analysis. The range in isotopic values of POM was nearly two-fold higher in winter than in other seasons, which coincided with similar decrease in δ13C values of several consumers. Such decreasing patterns in δ13C were associated with high rainfall and freshwater discharge during winter, which exported 13C-depleted continental POM to the sandy beach. The continental allochthonous matter assimilated by marine organisms originated from the drainage of wetlands by innumerous coastal streams spread along the coast and by a larger estuarine system. Bayesian isotope mixing models revealed a slightly higher average assimilation of organic matter of the coastal streams (24%) than the estuary (18%). The assimilation of allochthonous matter was higher in filter feeders bivalves and detritivore fish and lower in carnivorous guilds (e.g. zoobenthivores, zooplanktivores, carnivorous and scavengers).

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Acknowledgements

We are thankful for the help in field collections and sample processing by colleagues from the Ichthyology Lab. We are also thankful to Alexandro M. Tozetti, Paulo C. Abreu and Tommaso Giarrizzo for their comments on an earlier draft of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

AMG acknowledges fellowship support from the Brazilian National Institute of Science and Technology [310141/2015-0] and MCLMO from the INCT-Mar COI, respectively; Conselho Nacional de Desenvolvimento Científico e Tecnológico.

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