RELEARNING THE ABC - TAXONOMIC CHANGES AND ABUNDANCE BIOMASS RELATIONSHIPS IN DISTURBED BENTHIC COMMUNITIES

For marine macrobenthic communities, a shift from higher biomass domin ance with increasing levels of disturbance can be determined by the ab undance/biomass comparison (ABC) method. This response results from (i ) a shift in the proportions of different phyla present in communities , some phyla having larger-bodied species than others, and (ii) a shif t in the relative distributions of abundance and biomass among species within the Annelida (specifically Polychaeta) but not within any of t he other major phyla (Mollusca, Crustacea, Echinodermata). The shift w ithin polychaetes reflects the substitution of larger-bodied by smalle r-bodied species, and not a change in the average size of individuals within a species. In most instances the phyletic changes reinforce the trend in species substitutions within the polychaetes, to produce the overall ABC response, but in some cases they may work against each ot her. Indications of pollution or disturbance detected by this method s hould be viewed with caution if the species responsible for the pollut ed configurations are not polychaetes. These observations provide an a id to interpretation of the ABC plots, especially in some situations w here they have been deemed to give a false impression of the disturban ce status of a community.