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The trophic significance of the invasive seaweed Sargassum muticum in sandy beaches
Rossi, F.; Olabarria, C.; Incera, M.; Garrido, J. (2010). The trophic significance of the invasive seaweed Sargassum muticum in sandy beaches. J. Sea Res. 63(1): 52-61. dx.doi.org/10.1016/j.seares.2009.09.005
In: Journal of Sea Research. Elsevier/Netherlands Institute for Sea Research: Amsterdam. ISSN 1385-1101, more
Peer reviewed article

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Keywords
    Benthos; Food webs; Introduced species; Sandy beaches; Sargassum (Bactrophycus) muticum (Yendo) Fensholt, 1955 [WoRMS]; ANE, Spain, Galicia [gazetteer]; Marine

Authors  Top 
  • Rossi, F., more
  • Olabarria, C.
  • Incera, M., more
  • Garrido, J.

Abstract
    Native and exotic seaweeds frequently lie on the beach and sustain part of the benthic food web. However, the role of exotic seaweeds as food sources for beach consumers has been poorly studied. We studied the temporal and spatial variability in the trophic significance of the invasive brown seaweed Sargassum muticum on sandy beaches. We measured the stable isotopes (δ13C and δ15N) in the tissues of S. muticum and of invertebrate consumers and estimated the dietary biomass proportion of S. muticum during four sampling dates at two beaches and heights on the shore. Samples were collected from eight pitfall traps placed at a distance of 2 m from each other. Detrital macroalgae and seagrasses were also collected by hand within an area of 30 cm around each pitfall trap. We measured the spatial and temporal variability in the isotope composition of the beach consumers and of S. muticum using different models of analyses of variance. We then calculated the biomass proportion of S. muticum to the animal diet with a two-isotopic mixing model. The invasive alga S. muticum seemed to be one of the main food sources for the amphipod Talitrus saltator and, to a less extent, for the isopod Tylos europaeus. The importance of S. muticum was however temporally variable and decreased during spring (in March and May), probably due to the availability of native macrophytes. The supply of invasive wrack to beach food webs thus deserves more attention if we want to understand their role in influencing food web dynamics.

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