Variation in rocky shore assemblages and abundances of key taxa along gradients of stormwater input

• Taxon richness and algal cover on rocky shores increased between 10 and 60 m from three stormwater outfalls.
• In most cases there was a step up in diversity after 20 m.
• Assemblage structure at or near stormwater sites differed from that at sites 100 m away.

Stormwater brings freshwater and terrestrially derived contaminants into coastal systems and is predicted to increase with climate change. This study aimed to characterise variation in rocky shore assemblages in relation to stormwater pollution. Intertidal assemblages were sampled in similar habitats at a range of distances (0 m, 10 m, 20 m, 60 m, and 100 m) from stormwater outfalls on three rocky shores north of Dublin. In general, taxon richness and algal cover increased after 20 m from a stormwater outfall. Limpet population structure and condition index showed no consistent patterns among shores. Assemblage structure at or near stormwater sites differed from that at sites 100 m away. These findings, ideally supplemented by experimental research, may be used to inform stormwater management and remediation approaches.