To what extent are the characteristics of nematode assemblages in nearshore sediments on the west Australian coast related to habitat type, season and zone?

This study has determined the ways in which the characteristics of the nematode assemblages in nearshore marine waters along the microtidal lower west coast of Australia are influenced by habitat type, time of year and shore-perpendicular zones. The habitat types (1, 2 and 6), which had previously been identified on the basis of a suite of enduring environmental characteristics, could be broadly described as highly sheltered from wave activity and containing dense seagrass (1), moderately sheltered from wave activity with sparse seagrass (2) and relatively exposed to wave activity with no seagrass (6). Sampling in five consecutive seasons yielded 15 751 nematodes representing 75 species, of which, at present, only three can be referred to described species. The number of species and densities in habitat type 1, and particularly those in its subtidal zone (C), were far greater than those in the other two habitat types. Both of these biotic variables underwent marked seasonal changes, declining to low levels during winter. The compositions of the assemblages differed significantly among the three habitat types, with the differences between habitat types 1 and 6 being particularly marked. Species of Paracomesoma, Dichromadora, Marylynnia, and Pomponema, which are assumed to feed primarily on benthic diatoms, were particularly abundant at the most sheltered habitat type, whereas those of Gonionchus, Theristus and Bathylaimus, which are assumed to be deposit feeders, were relatively abundant at the most highly exposed habitat type. The compositions of the assemblages differed among seasons and were most discrete in spring, due to marked increases in the densities of certain species. However, differences in the compositions in the different zones of each habitat type were relatively small, presumably reflecting the presence of only a small tide in the region.