Gandara-Martins, A.L.; Borzone, C.A.; Guilherme, P.D.B., and Vieira, J.V., 2015. Spatial effects of a washout on sandy beach macrofauna zonation and abundance.

Washouts have an important function in backshore zone drainage and remobilization of sediments for littoral transport. It is known that they can change beach morphology along its course, but their effects on the macrofauna community still represent a gap in knowledge of sandy beach ecology. Based on previous studies developed in larger systems, such as channels and estuaries, we aimed to assess how the macrofauna community responds to the presence of a permanent sandy beach washout. The study was carried out at an exposed sandy beach in southern Brazil, where six cross-cut transects 0, 3, 9, 27, 81, and 243 m in distance from the washout were defined. Biological and environmental samples were taken at nine levels along each transect. As expected, beach morphology and water table salinity were affected by the washout, resulting in changes in the macrofauna zonation pattern and community descriptors. The isopods Tholozodium rhombofrontalis and Excirolana armata were dominant at all levels close to the washout, where polychaetes, amphipods, and mollusks were almost absent. Macrofauna reached the typical zonation pattern for local, nearby beaches only at distant transects. A good correlation between biological and environmental variables was observed. These results indicate that washouts can modify the macrofauna community at a small spatial scale, and only species adapted to a high range of variation in salinity (euryhalines) with a high mobility can live in substantial numbers close to and within these freshwater streams.