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Swash zonation patterns of two surfers on exposed tropical sandy beaches
Vanagt, T.; Dewinter, P.; Steenhuyse, L.; Vincx, M.; Degraer, S. (2007). Swash zonation patterns of two surfers on exposed tropical sandy beaches, 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. 73-94
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 125755 [ OMA ]

Keywords
    Beaches; Competition; Ecological zonation; Wave runup; Emerita Scopoli, 1777 [WoRMS]; Olivella semistriata (Gray, 1839) [WoRMS]; ISE, Ecuador [Marine Regions]; Marine

Authors  Top 
  • Vanagt, T., more
  • Dewinter, P.
  • Steenhuyse, L.

Abstract
    Macrofaunal species that show surfing behaviour on tidal sandy beaches use the swash to migrate up and down the beach. When studying the zonation of these surfers, some complications arise which do not occur for sessile organisms or organisms that remain burrowed for some time during the tidal cycle. In this paper, a new approach for sampling mobile swash fauna is proposed. The described method deals with two problems innate to investigating swash zonation of surfing species: setting a reference point independent of the tidal state and taking all the samples of a transect without having migration in due course. The upper swash limit, defined as the highest swash wave during 10 minutes of observation, was chosen as reference point. By placing wooden boxes at every sampling spot prior to sampling, migration while taking the samples was prevented. This allowed us to sample transects in the swash zone, producing swash zonation data for two surfing species on Ecuadorian sandy beaches: the gastropod Olivella semistriata and the mole crab Emerita rathbunae. Both species showed a symmetric to negatively skewed unimodal swash distribution curve, independent of the tidal state or sampling location. Peak densities were typically found around 15-60 % of the upper swash limit, with O. semistriata living higher and E. rathbunae living lower in the swash. It is hypothesized that this zonation is a result of a gradient in feeding time, with optimal feeding conditions around the middle of the swash zone. The different position of peak densities is thought to be caused by differences in morphology and behaviour. The mole crab is a much faster swimmer and burrower than the snail, and its feeding structures seem more robust. This idea is supported by distribution data for both species from beaches with different morphodynamics: where O. semistriata is restricted to relatively flat beaches with fine sediment and gentle swash conditions, E. rathbunae is mostly present on reflective beaches with coarse sediment and vigorous swash action.

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