Contaminant pathways in Port Curtis: Final report - OzCoasts

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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
Contaminant pathways in Port Curtis: Final report5: Metal bioaccumulation in food webcompared to the algae (1.1 ± 0.2‰) indicates a higher position in the food chainof approximately two trophic levels, considering fractionation of nitrogen of ~3‰per trophic level. This suggests the prawns were mainly feeding on primaryconsumers that may have been feeding directly on the algae. If the prawns areaccumulating toxins contained in the algae, then potentially these toxins may betransferred up the food chain. Should the toxin accumulate in the prawn muscletissue, this could also have human health ramifications for consumers of bananaprawns in Port Curtis.(Photograph courtesy of Leonie Andersen)Figure 5.4. Blue green algae (Lyngbya majuscula) demonstrating released pigment(arrowed) and the same pigment observed in the hepatopancreas (liver) of a bananaprawn from the same site (also arrowed)5.3.2 Metal distributions and relation to food web structureA summary of mean concentration data for each organism/metal is given inTable 5.2. Detailed statistical analyses of the data may be found in the report byAndersen et al. (2005). With the exception of aluminium and arsenic, there wereno noticeable between-site variations in tissue metal concentrations indicative of‘hotspots’ or gradients of metal bioaccumulation. On the whole, organisms fromthe inner harbour sites—Boat Creek (Site 1), Grahams Creek (Site 2) and BlackSwan (Site 3)—tended to have more elevated metal concentrations than thosefrom Yellow Patch (Site 4). Aluminium and arsenic data are summarised inFigures 5.5 and 5.6 respectively. Yellow Patch (reference site) organismstended to have the lowest aluminium accumulations compared to all the othersites but the highest arsenic concentrations. This does not necessarily implycontamination of arsenic at the reference site, but may reflect the complexinteractions (e.g. antagonistic effects of other metals/chemical species) affectingmetal bioaccumulation.60
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Contaminant pathways in Port Curtis: Final report - OzCoasts

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