02424nas a2200229   4500008004100000245007300041210006900114260006600183300001200249490000800261520164200269653001401911653001701925653001801942653001401960653002201974653002601996100002302022700002202045700002002067856010702087       2007                        eng d00aThree-dimensional spatial structure: nematodes in a sandy tidal flat0 aThreedimensional spatial structure nematodes in a sandy tidal fl  aNORDBUNTE 23, D-21385 OLDENDORF LUHE, GERMANYbINTER-RESEARCH  a177-1860 v3363 aBenthic infauna live in a three-dimensional world, and patterns of horizontal distribution may vary with depth in the sediment, as may the mechanisms that determine those patterns. This study examines how horizontal spatial structure varies with depth in a semi-exposed coarse-sand flat adjacent to St Martin's, one of the Isles of Scilly, UK. Nematode samples were collected from 3 sediment depth horizons (0 to 5, 5 to 10 and 10 to 15 cm) in a nested hierarchical design, with samples 0.1, 1 and 10 m apart. Results show that spatial patterns are strongest amongst samples of intermediate depth (5 to 11) cm), and generally insignificant amongst samples collected from 10 to 15 cm. There is short-order spatial autocorrelation in surface (0 to 5 cm) samples, with samples collected 10 cm apart being significantly more alike than samples collected further apart. We postulate that this is because spatial structure of nematodes in surface sediments is determined by patchiness induced by interactions between the water column and the physical structure of the surface layers of the sediment, which are constantly reworked by wind and tides. The deeper layers, 10 to 15 cm below the surface, are constantly reworked by a dense population of heart urchins Echinocardium cordatum. It is only in the intermediate horizon that relatively stable conditions allow nematode assemblages to establish spatial structure over a range of scales. It is concluded that the interaction between sediment permeability, and therefore interfacial advection, and bioturbation in controlling infaunal diversity and spatial patterns is potentially important.10aadvection10abioturbation10aEchinocardium10anematodes10aspatial structure10avertical distribution1 aSomerfield, P., J.1 aDashfield, S., L.1 aWarwick, R., M.  uhttps://nematoda.myspecies.info/content/three-dimensional-spatial-structure-nematodes-sandy-tidal-flat