Disentangling settlement responses to nutrient-rich contaminants: Elevated nutrients impact marine invertebrate recruitment via water-borne and substrate-bound cues

Abstract

Anthropogenic contaminants, including nutrient enrichment, frequently alter environmental conditions in marine systems and affect the development of communities on hard-substrata. Biofilms can influence the settlement of marine invertebrates and hence impact on the structure of fouling communities. Few studies have examined bacteria, invertebrates and nutrient-rich contaminants in concert, with none yet to examine the effects of nutrient-rich contaminants on both biofilms and the recruitment of sessile invertebrate communities in-situ to ascertain the mechanistic basis behind observed impacts. Biofilm treatments were allowed to develop under manipulated environmental conditions of either ambient or enriched nutrient levels. Enrichment conditions were elevated via slow-release fertiliser and invertebrate recruitment was prevented during initial biofilm development. Biofilm treatments (including a no film control) were then subject to either ambient or enriched water-borne nutrients (in a fully-factorial design) during a period of invertebrate colonisation in the field. Effects of nutrient-rich contaminants on invertebrate recruitment were observed as changes to community composition and the abundances of taxonomic groups. Communities on no biofilm control treatments differed from those with pre-developed biofilms. Naturally developed biofilms promoted recruitment by all organisms, except barnacles, which preferred nutrient-enriched biofilms. Water-borne nutrients increased the recruitment of ascidians and barnacles, but suppressed bryozoan, serpulid polychaete and sponge recruitment. The direct and indirect impacts observed on biofilm and invertebrate communities suggest that increasing nutrient levels via nutrient-rich contaminants will result in structural community shifts that may ultimately impact ecosystem functioning within estuaries.