Effects of proximity to stormwater on the sandy-beach macrofaunal assemblages of metropolitan Adelaide, South Australia

•The effects of stormwater run-off on sandy beaches are unknown.•The largest outlet studied had more taxa at the outlet than at the control site.•Small-scale effects from stormwater proximity were evident along a salinity gradient.•Stormwater at one site was having a positive effect on the benthic macrofauna.

Stormwater run-off often enters coastal zones but its effects on sandy beaches are unknown. This study aimed to investigate associations between macrofaunal assemblages and proximity to stormwater outlets along Adelaide's beaches, comparing semi-natural creeks with concrete drains. Five positions along an increasing-salinity gradient were sampled in the intertidal zone of six stormwater outlets and also at corresponding control sites. There was no significant difference between the two forms of stormwater (semi-natural creeks with concrete drains). Only the largest outlet (Torrens) had a significant difference in assemblage structure and taxon richness compared to its control. Total abundances at this outlet followed a convex pattern across the salinity gradient, so it appears that flow there may have a spatially-limited positive effect on the macrofauna in terms of increasing abundance and richness. Therefore, the hypothesised detrimental effects of stormwater have not been found to be evident and these observed patterns warrant further investigation.