Spatial pa tterns of nematode community structure from two geographically spaced intermediate, microtidal beaches (i.e. Mediterranean and Baltic) were investigated. Differences in the nematode assemblages were found to be significantly different and related to the morphodynamic characteristics of the studied zones (upper beach, swash/breaker and subtidal). Highest nematode densities and species diversities were recorded on the coarse-grained, more physically controlled, Italian beach in contrast to the more chemically controlled Polish beach. This is in contrast to the worldwide pa tterns of macrofaunal communities. As demonstrated by higher taxonomic distinctness measurements, upper beaches were found to harbour species from both the marine and terrestrial ecosystem and are considered to be impo rtant ecotones between these adjacent systems. The swash/breaker zones are characterised by the loss of distinctive species caused by the high water percolation in these zones. The concept of parallel ecological communities 'isocommunities' is only supported for the upper beach zones.KEYWORDS: free-living nematodes, diversity, taxonomic relatedness, isocommunities, sandy beach morphodynamics, Mediterranean, Baltic CHAPTER III: Nematodes from wave-dominated sandy beaches
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INTRODUCTIONSandy beaches are examples of simple ecosystems, driven principally by the interacting physical forces of waves, tides and sediment movements. Wave dominance varies from total on sandy, tide-less shores, decreasing as other processes, especially tides, increase their influence on the shore face topography.Microtidal (wave-dominated) sandy beaches represent widely fluctuating environments which have been classified into three distinctive types (reflective, intermediate and dissipative) according to the modal breaker height, modal wave period and sediment fall velocity, which are all combined in the dimensionless fall velocity or Dean's parameter (S2) (Sho rt 1999).These sandy sediments offer a considerable range and diversity of biotic habitats: horizontally, the sub-aerial (dunes and upper beach), the inte rt idal (swash zone/shoreline) and the subtidal (surfzone and near-shore) while vertically there are pelagic, benthic and interstitial environments. As the beach is the dynamic inte rface between the terrestrial and marine ecosystem several biotic and abiotic gradients characterize this interface.Due to these steep gradients (e.g. in oxygen, temperature, organic material, etc.) and the sediment heterogeneity, zones with specific physico-chemical properties can develop, harbouring, as a consequence, a different benthic fauna (Wieser el al. 1974). Most of the faunal research on sandy beaches has been concentrated mainly on macrofauna (>1 mm) (McLachlan and Jaramillo 1995 and references therein) and more recently also birds (e.g. Cornelius el al. 2001). In contrast, sandy beach meiofauna (all metazoans between 1 mm and 38 pm) have received considerably less a ttention notwithstanding their high diversity (even at taxon level) and de...