Barriers to restoration: Pollution alters nurse effects for an ecosystem engineer

Nurse plants modify the environment to facilitate the recruitment of propagules, and are potentially valuable tools for ecological restoration. Yet empirical tests, particularly in polluted environments, remain rare. The few studies that have examined nurse-effects in polluted environments report exclusively positive effects, but most tests have focused on pollution-tolerant species in metal contaminated environments. Biotic interactions are highly context-dependent, however, such that extrapolations to other suites of species and pollutant types appear premature. We examined changes in intraspecific nurse-effects across pollution regimes for a pollution-sensitive, macroalgal ecosystem engineer that is a target for intertidal restoration. In a manipulative field experiment, we out-planted propagules in the presence and absence of conspecific canopies at (i) unpolluted control shores and (ii) shores that received a partially-remediated (low toxicity) sewage effluent, and monitored the pe...