Zonation of macrofauna across sandy beaches and surf zones along the Dutch coast

On nine beaches and two transects in the surf zone along the Dutch coast the presence of benthic macrofauna was studied in relation to basic abiotic characteristics. According to Short’s classification system, Dutch beaches are mesotidal and dissipative (Ω = 8.6), and the RTR is low (1.52–1.27), which means that they are not tide-dominated. BSI ranged from 1.4 to 1.1 for the northern and western Dutch coasts respectively and had an overall value of 1.2. The rates of exposure of the beaches varied between 8 and 12, and are therefore regarded as sheltered to moderately exposed. The Dutch beaches display a geographical trend in beach types. Those of the Wadden Sea islands in the northern part of the Netherlands are dissipative, flat, fine-grained, and host high densities of many species of benthic macrofauna. The beaches along the western Dutch coast are less dissipative, steeper, with a higher mean grain size; the species diversity and abundance there are lower. Species diversity and abundance on the beaches increase from the high- to the low-water line. The maximum number of species was found between 0 and –1 m relative to the mean tidal level. The abundance peaks just above the mean tidal level, while the biomass reaches a maximum at the mean tidal level. Species diversity and abundance are low in the surf zone, but increase towards deeper water. Species numbers are high and the abundance is very high in the trough between the two bars. The relation between the diversity and abundance of macrobenthic species on the one hand, and the sediment composition, water column depth, and position between the bars on the other show a clear pattern of zonation for the beach, surf zone and near-shore: (1) a supralittoral zone with insects and air-breathing crustaceans, (2) a midshore zone, with intertidal species, (3) a lower shore zone, whose species extend into the shallow surf zone, and (4) a zone of sublittoral fauna in the trough between the two breaker bars within the surf zone.