Sandy beach ⁄ surf-zone ecosystems are unique environments that, despite the harsh and highly variable hydrodynamic conditions, present a diverse and heterogeneous fauna. However, the dynamics of these ecosystems are currently poorly understood. In this study we tested the hypothesis that surf-zone assemblages vary with temporal factors such as time of day, tide and tidal height. To test this hypothesis, the surf-zone community of Bastendorff, a Southern Oregon sandy beach was sampled during the summer of 2006. Samples were collected to (i) describe the smaller, benthic and larger swimming assemblages, (ii) determine whether assemblage compositions, densities, species richness and diversity vary with time of day, tide and tidal height, (iii) explore potential reasons for the variation by correlating environmental factors to the assemblages, and (iv) identify particular species that most strongly exhibit these variations. A hyperbenthic sledge, a sediment corer and a beach seine were used to collect the smaller swimming, benthic and larger swimming fauna, respectively. Sampling occurred during day and night, spring and neap tide, and high, mid and low tide. A total of 76,743 individuals belonging to 105 species were collected. Ninety-one invertebrate (72,904 individuals), 15 invertebrates (2234 individuals), and 19 invertebrate and vertebrate species (1605 individuals) were collected with the sledge, corer and seine, respectively. Nine species of fish were caught, 98% of which were juveniles. The smaller and larger swimming assemblages varied most strongly with the time of day, suggesting certain species will actively move to the shallow surf-zone at night. The three assemblages also varied with the tide, potentially due to the larger waves and higher abundance of detached macrophytes observed during spring tides when compared to neap tides, which could push individuals into the surf zone. The benthic assemblage most strongly varied with tidal height and sand grain size, confirming the presence of different faunal zones within Oregon sandy beaches. Finally, several variables of the swimming assemblages varied with temperature and salinity, suggesting that downwelling favorable conditions may have transported species close to shore. Bastendorff presents a complex and diverse surf-zone community that appears to be influenced by diel species movements, environmental variables such as wave height and abundance of detached macrophytes, and regional oceanographic conditions. Marine Ecology. ISSN 0173-9565 232 Marine Ecology 32 (2011) 232-242 ª
Temperate and subtropical sandy beach surf zones present diverse and abundant fauna that are important in local food webs. However, dynamics of these fauna have been poorly studied in tropical areas. The aims of the present study were to describe the small swimming surf-zone fauna (~1–5mm in length) of two Ecuadorian sandy beaches, determine whether this fauna varies with beach, season or tide, and explore the environmental factors correlated with faunal variability. Beaches were sampled in wet and dry seasons during high, mid- and low tide (2001–2002) by using a hyperbenthic sledge. Beaches were inhabited by an abundant and diverse fauna (>1200 individuals per 100m2 and >30 taxa), where most individuals were in their early life stages (65%), and the dominant taxa included mysid shrimp (>40% of individuals) and fish and crab larvae (>25 taxa). Composition of groups that are present during their entire life or only early life stages varied most strongly between beaches, potentially because of differences in wave exposure and the influence of an adjacent river, and between seasons with changes in coastal oceanic currents. These results suggest that despite the environmental stability often portrayed for tropical environments, Ecuadorian surf-zone fauna are spatially and temporally variable.
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