Changes in macrofaunal assemblage structure along a morphodynamic sandy beach gradient in the eastern tropical Pacific

The macrofauna of seven beaches along the coast of Ecuador, in the tropical part of the Eastern Pacific, was sampled along transects. The beaches covered the entire range of beach types that occur in this part of the continent. The aim of the study was to identify the relation between morphodynamic state of beaches and several biological characteristics of the macrofauna: biodiversity, density, abundance, biomass, zonation and trophic structure. The Ecuadorian beaches were characterized by a very diverse macrofaunal community; a total of 47 species were identified. This confirms the recent idea of a larger species pool existing in the tropics than in temperate regions. There was a very clear drop in species count when moving from the flat, dissipative beaches to the steep, reflective beaches. This was partly due to the absence of molluscs from the reflective beaches. Biomass and abundance (ind/m) likewise decreased towards reflective beach states, but not density (ind/m2), because reflective beaches harboured dense populations of interstitial polychaetes. Changes in biodiversity and, to a lesser extent, biomass could be linked to four environmental factors: sediment grain size, beach slope, number of effluent line crossings and swash width. The zonation patterns confirmed the current state of knowledge on the topic, with four distinct zones on dissipative and intermediate beaches and only three zones on reflective beaches. This seems to be caused by the relatively wide swash zone compared to the intertidal width, combined with the absence of a surf zone on reflective beaches. The major distinction between the two groups of beaches was based on the presence of a rich middle and lower beach species association on the dissipative / intermediate beaches and the abundant interstitial community on the reflective beaches; the upper beach association was very similar on all beaches. Six different feeding types were distinguished. Trophic diversity was markedly higher in the dissipative situation. Filter feeders were dominant on all beaches, followed by scavengers and carnivores. Deposit feeders peaked on the dissipative beaches; the reflective beaches were characterized by a high density of interstitial dwellers. In conclusion, the dissipative and intermediate beaches were very similar in species composition, density, abundance and trophic structure. The reflective beaches were clearly different in all these aspects. It seems that there is a gradual change from dissipative to intermediate beaches yet an abrupt change from intermediate to reflective beaches

Swash zonation patterns of two surfers on exposed tropical sandy beaches

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

Les fouilles récentes du Pech de L\u27Azé IV (Dordogne)

The Mousterian site of Pech de l\u27Azé IV is located in Carsac (Dordogne) in the Perigord region of southwest of France, very near the town of Sarlat. The site was excavated during the 1970s by F. Bordes but it was never well published. In 2000 we published a study of the lithics from Bordes\u27 excavations. From 2000 to 2003 we conducted new work at the site to re-study the stratigraphy in order, to better understand the site\u27s formation processes, and to obtain dates from the sequence. We present here some initial results on the geology, a description of the stone tool industries, and some initial ESR dates (the dating program is still in progress).A detailed micro- and macroscopic study of the eight main stratigraphic levels shows that the sandy deposits come from a vast cave system that likely includes all the sites of Pech de l\u27Azé (I, II, and IV). The lowest level, which is characterized by dark, organic sediments,is particularly interesting. It includes within it multiple combustion zones that show evidence of having been subsequently trampled and perhaps emptied. Though the deposits come from a temperate climate, the sediments of anthropogenic origin are nevertheless well conserved. Macroscopically, there are traces of solifluction in the sequence, but the micromorphological analysis shows practically no evidence of a cold climate. As for the lithic industries, the new collection is in general comparable to that of Bordes. Nevertheless, there are some new elements including the presence of Quina technology in the upper part of the sequence