Contaminant cocktails: Interactive effects of fertiliser and copper paint on marine invertebrate recruitment and mortality

•Copper paint and fertiliser affected community structure antagonistically.•Fertiliser increased recruitment and decreased mortality of ascidians and barnacles.•Copper paint decreased recruitment and increased mortality of some taxa.•In combination, fertiliser may mitigate adverse copper paint effects.

Understanding interactive effects of contaminants is critical to predict how human activities change ecosystem structure and function. We examined independent and interactive effects of two contaminants (fertiliser and copper paint) on the recruitment, mortality, and total abundance of developing invertebrate communities in the field, 2, 4, 6, and 8 weeks after substrate submersion. Contaminants affected community structure differently, and produced an intermediate community in combination. Fertiliser increased recruitment and decreased mortality of active filter feeders (ascidians and barnacles), while copper paint decreased recruitment and increased mortality of some taxa. Contaminants applied together affected some taxa (e.g. Didemnid ascidians) antagonistically, as fertiliser mitigated adverse effects of copper paint. Recruitment of active filter feeders appears to be indicative of nutrient enrichment, and their increased abundance may reduce elevated nutrients in modified waterways. This study demonstrates the need to consider both independent and interactive effects of contaminants on marine communities in the field.