High congruence of isotope sewage signals in multiple marine taxa

- Sewage inputs are routinely mapped with stable isotopes (15N) in organisms.
- We tested whether choice of species influences spatial 15N distributions.
- Spatial gradients were consistent between algae, seagrasses, crabs, and fish.
- A match of sewage-N signals in multiple marine taxa has not been reported before.
- Spatially-coupled transfers in the food web produce the congruence of N imprints.

Assessments of sewage pollution routinely employ stable nitrogen isotope analysis (δ15N) in biota, but multiple taxa are rarely used. This single species focus leads to underreporting of whether derived spatial N patterns are consistent. Here we test the question of 'reproducibility', incorporating 'taxonomic replication' in the measurement of δ15N gradients in algae, seagrasses, crabs and fish with distance from a sewage outfall on the Adelaide coast (southern Australia). Isotopic sewage signals were equally strong in all taxa and declined at the same rate. This congruence amongst taxa has not been reported previously. It implies that sewage-N propagates to fish via a tight spatial coupling between production and consumption processes, resulting from limited animal movement that closely preserves the spatial pollution imprint. In situations such as this where consumers mirror pollution signals of primary producers, analyses of higher trophic levels will capture a broader ambit of ecological effects.