Patterns of polychaete recolonization in Queensland subtropical estuaries following severe flooding

Quantitative sampling of macrobenthos and fouling organisms in the estuarine reaches of the Calliope River and Auckland Creek, Gladstone, Australia has been conducted since November 1974, and includes the recovery period (1974-1981) following severe flooding (and flood-induced scouring) in December 1973/January 1974. Changes in numbers of the 18 most abundant species of benthic polychaetes and one encrusting serpulid (Ficopomatus uschakovi) are examined. Numbers of F. uschakovi settling on fouling panels showed a regular seasonal pattern, with a late summer maximum and a winter minimum throughout this period. The total numbers of individuals for all taxa in benthic samples followed a clear colonization pattern, with super-imposed seasonality; plateau densities were reached five years after flooding. Total numbers of the 18 most abundant polychaetes showed a similar recolonizational pattern including the seasonal variation. Generally, those species of polychaetes with similar trophic strategies displayed similar patterns of abundance throughout the period: (i) The suspended detritus feeders (F. uschakovi, Branchiomma sp., Lysilla pacifica, Amaena trilobata and Terebellides stroemi) formed a constant proportion of the population; (ii) Mobile surface detrital feeders (Glycera americana, Nephtys mesobranchia, Lumbrineris sp., Sthenolepis sp. and Poecilochaetus serpens) initially formed a high proportion of the population which diminished with time; (iii) The stationary surface detrital feeders (Magelona dakini, Paraprionospio sp., Isolda pulchella and Pseudopolydora kempi) initially formed a low proportion which increased to a maximum four to five years after flooding and subsequently declined; (iv) The sole surface deposit feeder examined (Leitoscoloplos normalis) had two peaks - in early 1975 and 1978; (v) The subsurface deposit feeders (Cossura sp., Sternaspis scutata, Euclymene sp. and Mediomastus sp.) initially formed a small proportion increasing continuously to become the most abundant group at the end of the period. It is suggested that these changes reflect changes with time in the substrate since theflood-induced scouring of these estuaries, particularly the gradual accumulation of detrital material, and the changing availability of food for the different trophic groups.