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Changes in macrofaunal assemblage structure along a morphodynamic sandy beach gradient in the eastern tropical Pacific
Vanagt, T.; Steenhuyse, L.; Vincx, M.; Degraer, S. (2007). Changes in macrofaunal assemblage structure along a morphodynamic sandy beach gradient in the eastern tropical Pacific, in: Vanagt, T. De rol van swash in de ecologie van macrofauna op Ecuadoriaanse zandstranden, met speciale aandacht voor de surfende gastropode Olivella semistriata = The role of swash in the ecology of Ecuadorian sandy beach macrofauna, with special reference to the surfing gastropod Olivella semistriata. pp. 33-72
In: Vanagt, T. (2007). De rol van swash in de ecologie van macrofauna op Ecuadoriaanse zandstranden, met speciale aandacht voor de surfende gastropode Olivella semistriata = The role of swash in the ecology of Ecuadorian sandy beach macrofauna, with special reference to the surfing gastropod Olivella semistriata. PhD Thesis. Universiteit Gent. Faculteit Wetenschappen. Vakgroep Biologie: Gent. XVII, 289 pp., more

Available in Authors 
    VLIZ: Open Repository 125754 [ OMA ]

Keywords
    Beaches; Benthos; Ecological zonation; Surfing; Wave runup; IS, Eastern Tropical Pacific [Marine Regions]; Marine
Author keywords
    Morphodynamics; Morfodynamica

Authors  Top 
  • Vanagt, T., more
  • Steenhuyse, L.
  • Vincx, M., more
  • Degraer, S., more

Abstract
    The macrofauna of seven beaches along the coast of Ecuador, in the tropical part of the Eastern Pacific, was sampled along transects. The beaches covered the entire range of beach types that occur in this part of the continent. The aim of the study was to identify the relation between morphodynamic state of beaches and several biological characteristics of the macrofauna: biodiversity, density, abundance, biomass, zonation and trophic structure. The Ecuadorian beaches were characterized by a very diverse macrofaunal community; a total of 47 species were identified. This confirms the recent idea of a larger species pool existing in the tropics than in temperate regions. There was a very clear drop in species count when moving from the flat, dissipative beaches to the steep, reflective beaches. This was partly due to the absence of molluscs from the reflective beaches. Biomass and abundance (ind/m) likewise decreased towards reflective beach states, but not density (ind/m2), because reflective beaches harboured dense populations of interstitial polychaetes. Changes in biodiversity and, to a lesser extent, biomass could be linked to four environmental factors: sediment grain size, beach slope, number of effluent line crossings and swash width. The zonation patterns confirmed the current state of knowledge on the topic, with four distinct zones on dissipative and intermediate beaches and only three zones on reflective beaches. This seems to be caused by the relatively wide swash zone compared to the intertidal width, combined with the absence of a surf zone on reflective beaches. The major distinction between the two groups of beaches was based on the presence of a rich middle and lower beach species association on the dissipative / intermediate beaches and the abundant interstitial community on the reflective beaches; the upper beach association was very similar on all beaches. Six different feeding types were distinguished. Trophic diversity was markedly higher in the dissipative situation. Filter feeders were dominant on all beaches, followed by scavengers and carnivores. Deposit feeders peaked on the dissipative beaches; the reflective beaches were characterized by a high density of interstitial dwellers. In conclusion, the dissipative and intermediate beaches were very similar in species composition, density, abundance and trophic structure. The reflective beaches were clearly different in all these aspects. It seems that there is a gradual change from dissipative to intermediate beaches yet an abrupt change from intermediate to reflective beaches.

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