How does tidal submersion time affect macroinvertebrate community patterns on a temperate sheltered sandflat

A general model of vertical zonation has been a fruitful foundation of rocky shore ecology, but no analogous model is widely accepted for intertidal soft sediments. Various local proxies have been used for shore height or tidal submersion time, although objective measurements are rare in the literature. In this study, temperature loggers identified submersion period (SP) in a sheltered temperate New Zealand inlet at discrete distances along transect vertical profiles associated with macrofaunal community differences. Our aim was to evaluate this submersion quantification method and determine whether SP described macrofaunal patterns. Despite the patchy presence of engineering species Zostera muelleri and Callianassa filholi, the method was effective in quantifying SP in an inlet with asymmetric tides and SP described spatial macroinvertebrate patterns well. Macrofaunal assemblages corresponded with shore height differences of ~100 mm and SP differences of ~10%. Observations distinguished assemblages submerged less than 30% of the time from those submerged >50% of the time with a continuous community gradient between. We suggest that future intertidal soft-sediment investigations should directly measure SP to: (1) adequately control for this influence when studying more obvious processes with subtle impacts; and (2) further a generic model of soft-sediment zonation.