Beach and Faunal Response to the Construction of a Seawall in a Sandy Beach of South Central Chile

Abstract

The community structure and across shore zonation of the sandy beach macroinfauna has been found to be closely related to beach morphodynamics. Thus, any changes in beach morphodynamics may result in macroinfaunal changes. The construction during 1997 and 1998, of a concrete seawall at the northern and middle section of a beach in south central Chile (ca. 39° S) to protect the coast from erosion, provided the opportunity to look at the effects of changing morphodynamics on beach fauna. To do that, we used physical and biological data collected at both sides of the beach, before and after the seawall was constructed. Sediment samples (0.03m², 30cm deep) were collected at ten equally spaced levels along three replicated transects extending from above the drift line to the swash zone. The sediment was sieved through a 1 mm mesh and the organisms collected were stored in 5% formalin until sorting and measuring. Physical measurements included width of the intertidal, height and period of waves, sand fall velocity and Dean's parameter. Values of this parameter showed that both sides had reflective to low intermediate features. The results of ANOVA indicate that no significant differences (p>0.05) were found between before and after or control and impact sites. BACI analyses were carried out with physical characteristics, i.e. the means of differences between both sides of the beach were similar. We found no significant differences when similar BACI analyses were carried out with macroinfaunal community characteristics such as species richness, macroinfaunal abundances and body sizes of the most common species (the cirolanid isopod Excirolana hirsuticauda Menzies and the anomuran decapod Emerita analoga (Stimpson)). Thus, it is concluded that during the study period the presence of the seawall has not influenced the physical and macroinfaunal characteristics at the beach studied.