Limited congruence across micro, meio and macrofaunal benthic assemblages in a heterogeneous coastal environment. Limited congruence across micro, meio and macrofaunal benthic assemblages in a heterogeneous coastal environment

The ecology of spatially complex environments is frequently summarised using a restricted group of species present, such as the use of macrofauna to investigate marine sediments. Inferences from such an approach rely on similarities between sampled and unsampled taxon responses. The assumptions of similarity in response imply that (1) unsampled taxa respond to the same gradients as the sampled taxa and that (2) spatial differences among sites are similar for different groups (congruent). These assumptions were tested across five benthic taxon groups (Archaea, Bacteria, Protista, meiofauna and macrofauna) for Plymouth Sound, a harbour with many independent, spatially separated pollution sources. Sediment samples varied in grain size, hydrocarbon and trace metal concentrations. Following variable reduction into broad categories (i.e. granulometry, hydrocarbon content, ‘environmental’ including metals and nutrients and macrofaunal bioturbation), canonical correspondence analysis did not identify any associations between sediment characteristics and assemblage composition of marcofauna or Archaea. In contrast, variation in Bacteria was associated with granulometry, trace metal variations and bioturbation (e.g. community bioturbation potential). Protista varied with granulometry, hydrocarbon and trace metal predictors, with meiofaunal variation associated with hydrocarbon and bioturbation variables. Taxon turnover between sites varied, with only 3 out of 10 group pairs showing congruence (meiofauna-Protista, meiofauna-macrofauna and Protista-macrofauna). While the results support using certain taxon groups as proxies for each other, in general the lack of congruence suggests caution should be applied to inferring wider indicator or functional interpretations from studies of a single taxon group.