Hidden Players—Meiofauna Mediate Ecosystem Effects of Anthropogenic Disturbances in the Ocean.

Humans have used, and had effects on, marine ecosystems throughout history. As the human population and its economic activities increase, these effects intensify. Yet, our awareness and understanding of the long‐term, pervasive effects of anthropogenic disturbances on the seafloor, and the resident meiofauna, is far from complete. This chapter summarises research on the responses of marine meiofauna to the most widespread anthropogenic disturbances, including bottom-fishing, pollution, introduction of invasive species, and climate change. Anthropogenic disturbance and natural environmental dynamics interact to cause changes in the response of meiofauna species, either in the short-term, through effects on growth and development, or in the long-term, through genetic selection. Species-specific sensitivity to disturbance can propagate to community-level responses, mediated by shifts in interspecific interactions. Meiofauna responses to anthropogenic disturbance are commonly nonlinear and depend on the environmental context in which the disturbance occurs, on the scales at which meiofauna responses are observed, and on the extent to which the disturbance creates novel environments that differ from those to which the resident meiofauna are adapted. Although responses of meiofauna assemblages to anthropogenic disturbance are complex, in general severe disturbance leads to dominance by opportunistic species. The widespread replacement of habitat-specific ecological specialists by broadly-adapted ecological generalists and opportunists often results in biotic and functional homogenisation of once disparate biotas. Their small size, their life history characteristics, and their phylogenetically and functionally diverse species pool, all suggest that meiofauna are resilient, and there is little evidence for the local extinction of meiofauna from anthropogenically disturbed seafloor habitats. It therefore seems likely that meiofauna have the ability to adapt, and thrive, in response to most environmental changes. New horizons for future meiofauna research pertain to the extent to which the resistance or resilience of meiofauna to anthropogenic disturbance buffers ecosystem functioning against further change.