Contaminant pathways in Port Curtis: Final report - OzCoasts

Contaminant pathways in Port Curtis: Final report5: Metal bioaccumulation in food webadult prawns. The prawns in Port Curtis appear to be consumers of meiofauna(animals of microscopic size living in marine sediments), which in turn feed onbenthic algae.12108PrawnsMulletMud crabs6Mangrove snailsOystersEpiphytesDelta 15N (‰)42MacroalgaeGrapsidcrabsFiddler crabsSediment POMMud whelksSeagrassMangrove leavesFilamentous algae0-35 -30 -25 -20 -15 -10 -5-2Seston-4-6Delta 13C (‰)Figure 5.3. Relationship of δ 13 C and δ 15 N (mean ± 1 S.D.) of selected primary producersand consumers in a Port Curtis food webThere were no ecologically significant site or gender differences among male andfemale mud crabs in terms of their carbon and nitrogen signatures, indicatingcrabs from all four sites have similar diets and trophic positions. A previous study(Andersen & Norton 2001) determined there was a significant difference in thecarbon signatures of mud crabs from Port Curtis compared to those from thereference site in Ayr (North Queensland). The difference could have been due to anatural spatial variability in the same carbon source such as algae or alternativelythat the mud crabs from the two locations were consuming different foods. Thestudy also determined that there was a trend for a correlation betweenhepatopancreas copper concentrations and muscle δ 13 C, suggesting the dietsof mud crabs may be a major source of copper for mud crabs in Port Curtis.The δ 13 C of prawns (-19.3 ± 0.1‰) was similar to that of the filamentous algae(-17.8 ± 0.3‰), which were identified predominantly as Lyngbya majuscula(a blue-green algae) with some green algal filaments interspersed within. Visualconfirmation that the prawns were feeding on the algae directly or on smallerinvertebrates that had fed on the algae, were obtained when after 24 h,breakdown of the algae caused the release of purple pigments (most likelyphycoerythrin and phycocyanin). The same colouring was noted in the digestivetracts of the prawns (Figure 5.4). The higher δ 15 N of prawns (8.0 ± 0.3‰)59