|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|
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.
Population characteristics > Population density
Water waves > Surface water waves > Breaking waves > Surf
Olivella semistriata (Gray, 1839) [WoRMS]
ISE, Ecuador [Marine Regions]
During this thesis, we investigated different aspects of the ecology of macrofauna on Ecuadorian sandy beaches. The ultimate goal was to improve our knowledge about the functioning of sandy beach macrofauna in the tropical part of the East Pacific Ocean. Prior to the start of this project this region had not seen any major research on sandy beach ecology, despite the great importance of beaches in both the local marine ecosystem and the local economy. As in other regions, the Ecuadorian sandy beaches attract most of the coastal tourism. Additionally, sandy beaches are thought to play a vital role in the life cycle of the shrimp Litopenaeus vannamei, Ecuador’s most important aquaculture species and the countries second most important export product. In three pilot studies, reported in the addenda, some basic features of Ecuadorian sandy beach fauna were investigated. Moreover, these pilot studies provided useful feedback concerning the sampling strategy that should be applied for further investigations. Addendum 1 lists a description of the zonation of macrofauna in the bay of Valdivia. One of the beaches in this bay, the intermediate beach of San Pedro, was used as model beach throughout this thesis. Addendum 1 provides an interesting overview of the macrofaunal diversity and density distribution in different intertidal zones. The gastropod Olivella semistriata proved to be the most dominant and conspicuous species. This small snail (shell length around 1 cm) was found in incredibly large numbers in the swash zone, the zone with wave run-up and run-off. This study also learned us, however, that the sampling strategy, which was based on previous research along the Belgian coast, is not suitable for the very exposed Ecuadorian beaches. Hence, a different approach was used in further studies. In Addendum 2, the spatial and temporal variability of the macrofauna from the sublittoral fringe was studied, in combination with the surf zone hyper- and epibenthos. Therefore, nine different beaches were sampled at four occasions during one year. The macrofaunal assemblage was clearly different between different beach types, whereas hyperbenthos varied primarily on a temporal scale. Moreover, the temporal variation in endobenthos was not uniform over the different beach types, making generalizations very difficult. In Addendum 3, several hypotheses about the impact of the climate phenomenon El Niño Southern Oscillation (ENSO) on Ecuadorian sandy beach macrofauna are discussed. During the cold La Niña phase we noted a much lower density in molluscs and crustaceans compared to the normal situation. The first hypothesis states that these low numbers were caused by the very strong preceding El Niño. Unfortunately, no data preceding, or during, this El Niño are available. The alternative hypothesis, however, explains the observed patterns as a direct cause of the La Niña itself, in which the fauna of a tropical ecosystem - like the Ecuadorian coast - is severely affected by low temperatures. The information retrieved from the pilot studies was used as an outline for this thesis. The idea was to start by constructing a detailed image of the spatial distribution of sandy beach macrofauna over a continuum of beach types - from flat, dissipative to steep reflective beaches, as well as looking at distribution patterns within one beach (Chapter 1). Subsequently, a comprehensive study of the ecology of the dominant gastropod Olivella semistriata was be performed (Chapters 2 to 6). The first three chapters, bundled in Part II, deal with the impact of swash and other morphodynamic beach factors on the distribution of macrofauna in general and O. semistriata in specific. The last three chapters (Part III) report some aspects of the biology of O. semistriata: feeding, migrating and burrowing. In accordance with many other papers from various locations, macrofaunal diversity, and to a lesser extent abundance (ind/m) and