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Surfing on sandy beaches: an efficient strategy to flourish in a highly dynamic environment?
Vanagt, T.; Merckx, B.; Vincx, M.; Degraer, S. (2007). Surfing on sandy beaches: an efficient strategy to flourish in a highly dynamic environment?, 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. 151-183
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 125759 [ OMA ]

Keywords
    Beaches; Feeding behaviour; Surfing; Wave runup; Olivella semistriata (Gray, 1839) [WoRMS]; ISE, Ecuador [Marine Regions]; Marine

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Abstract
    The gastropod Olivella semistriata is a dominant surfer on exposed, intermediate beaches in the tropical part of the East-Pacific. The impact of the swash dynamics on the feeding behaviour of the species was studied in order to improve the understanding of the swash zonation pattern of O. semistriata, and its general success on beaches. The feeding activity of dense patch of Olivella semistriata was monitored for 5 to 15 min, while simultaneously noting the swash dynamics. Feeding time and feeding rate (both expressed per wave) were a function of three swash parameters: swash distance (i.e. swash run-up above the monitored patch), swash time (immersion time of the patch by a swash wave) and swash interval (time between two consecutive swash waves). The longer the swash time, the longer species could feed upon the backwash. Large waves were generally less favourable for feeding: the possibility of the next swash wave interrupting the backwash was very high. With the combination of the swash parameters (distance, time and interval), the feeding parameters could be modelled in terms of the swash position (i.e. the position relative to the swash boundaries). Both feeding time and feeding rate were found to follow a skewed unimodal curve within the swash zone, with highest feeding time and feeding rate in the upper half of the swash zone. Maximal feeding rate was modelled to be 32.25%. The feeding curves over the swash zone show remarkable similarities with the swash zonation of Olivella semistriata, suggesting that the zonation of the species is a result of the feeding opportunities. A migration model was built to calculate the total feeding time of Olivella semistriata per 6 hours as a function of distance travelled per surfing movement. The highest feeding time was found at 17 surfing movements per 6 hours, or 3.5 m per movement (on a beach of 60 m wide). Finally, using the migration model, a time budget for Olivella semistriata was calculated. With the optimal surfing distance of 3.5 m, just over 1% of the time has to be spent surfing (0.16% for emerging from the sediment, 0.47% for surfing itself and 0.73% for burrowing). This allows the species to feed during 30.26% of the time. Under the same conditions, a hypothetical non-migratory species would only be able to feed during 5.72% of the time. Thus, spending no more than 1% of the time or around 5% extra energy by surfing increases the feeding time by 529%, clearly demonstrating the benefits of this behaviour.

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