Food webs supporting fisheries production in estuaries with expanding coastal urbanisation

Abstract

The prospects that coastal urbanisation propagates in more fish production remains untested and thereby a fundamental question for managers challenged with approving urban expansion while also protecting and conserving habitat resources important for fish production. We tested this by collecting giant mud crabs (Scylla serrata) from highly urbanised waterways in south-east Queensland, Australia, and report that this crab not only occupy urban coastal waterways, but using a Bayesian stable isotope mixing model (MixSIAR) of the potential individual autotrophic sources, the range of feasible contributions for autotrophs was very broad, limiting the conclusions that could be made directly from the modelling. Patterns of contributions from pooled categories of autotrophs were clearer; at the site closest to seagrass, the pooled enriched autotroph sources contributed 69 to 87% of crab isotope signatures, while at all other sites (beyond approximately 500 m distance) it appears that crabs utilise a generalised pool of sources, either local or perhaps a mix of local transported sources. Using spatial analysis we reveal that the crab isotope values were not significantly related to the distance from any of the vegetated habitats (mangroves, seagrass and saltmarsh). The exception was two sites very close to seagrass (< 500 m distance), and not saltmarsh grass which has been reported elsewhere, where crabs had the most enriched C value. At all other sites (beyond approximately 500 m distance) it appears crabs utilise a generalised organic producer pool, either local or perhaps a mix of transported sources. Overall, this study provides evidence that in an era of coastal urbanisation expansion and loss of natural coastal vegetated areas, some fisheries species may have remarkable trophic plasticity to the new, engineered, habitat settings.