The role of sediment type on the vertical distribution of meiofauna at two Galician rias (NW Iberian Peninsula)

Meiofauna vertical distribution knowledge is important to improve the ecological understanding of meiobenthic communities. However, most works are usually limited to single taxa or to a sedimentary type or environment. In this work total meiofauna and main taxa vertical distribution were studied considering two depth scales: 5 cm intervals up to 20 cm depth and 1 cm intervals up to 10 cm depth. These samples were collected at three sedimentary types: medium sands, fine sands and muddy sands; from two Galician rias (NW Iberian Peninsula). Results pointed out a general trend, with maximum densities within the first 5 cm then declining with depth but sediment grain size seriously influenced vertical distribution, showing a drop in density at finer sediments. Moreover, copepods and ostracodes were more restricted to the sand surface than nematodes, gastrotrichs and turbellarians probably due to the different sensitivity to low oxygen levels. Vertical distribution within the first 10 cm, considering 1 cm horizons, showed that both total meiofauna and main taxa reached the highest densities in the first centimetre then declining with depth into the sediment, except for gastrotrichs and turbellarians.