The nature and ecological significance of epifaunal communities within marine ecosystems

Abstract

As the rate of global change increases, the structure and functioning of marine ecosystems, including the food webs that underpin them, will radically alter. Forecasting the consequences of these changes requires a sound understanding of the fundamental components of marine food webs: their community composition, baseline biomass and productivity. Epifauna, a term restricted here to small invertebrates (both mobile and sessile) that inhabit living and non-living surfaces within marine ecosystems, are a ubiquitous and pivotal component of marine food webs, supporting the flow of energy through marine ecosystems and providing a critical trophic link between benthic primary producers and higher-order consumers. Yet, despite their importance, epifauna are rarely studied compared to the more visible and gregarious components of marine ecosystems. They are also typically neglected in management strategies for the protection of marine habitats. In addition, the plethora of alternative terms used within this research field (macrobenthos, cryptofauna, epibiont, mesograzer) can be a barrier to understanding and assimilating existing research knowledge. This review provides an assessment of epifaunal communities studied within tropical, subtropical and temperate marine ecosystems globally. We first review alternative terms used to describe marine epifaunal communities, with the aim of offering a consensus-based definition of epifauna as an aid for unifying different research areas. We then review the primary literature on epifauna, including the scarce information on tropical marine habitats. We outline how a detailed understanding of epifaunal communities within individual habitats is needed to predict how benthic food webs will alter under global change. While epifauna can persist under degraded habitat conditions, changes to taxonomic composition can fundamentally affect secondary productivity, and impact higher-order consumers through changes in prey size-spectra and foraging habitats. Finally, we issue a "call-to-arms" for increased focus on the study of epifauna, given their potential to underpin critical aspects of marine ecosystem functioning. We highlight the potential for eDNA sampling, other new technologies, and monitoring by citizen scientists to facilitate the use of epifaunal community metrics, including incorporation into marine ecosystem planning.