From obligate to opportunistic ectoparasites: unlikely heroes of environmental monitoring.

Ectoparasites and opportunistic protists exhibit species-, toxicant-, and environment-specific responses to different pollutants. This review summarises the effects of organic, inorganic, and emerging pollutants on ectoparasites and opportunistic protists, and their applicability in environmental monitoring. From an indicator context, most studies have focused on endoparasites, largely because they fulfil key criteria used to assess the general suitability of parasites as indicators. Fewer studies have assessed effects of pollution on ectoparasites and protists despite being exposed for their entire life cycles. Their sensitivity to environmental changes, host-related factors, and macroenvironment interactions position them as promising tools for ecosystem assessment. However, the complexity of multi-stressor and species-specific dynamics necessitates novel approaches to their use as bioindicators.