Meiofauna as sentinels of beach ecosystems: A quantitative review of gaps and opportunities in beach meiofauna research

Meiofauna are the most abundant and diverse animal group on beaches, encompassing 20 metazoan phyla and contributing to taxonomic, functional, and phylogenetic diversity of beach ecosystems. Meiofauna react fast to environmental change and disturbance, and therefore, might represent a good sentinel to efficiently anticipate human-driven perturbations and the global ecological crisis in globally threatened beach ecosystems. We review the state of meiofauna research on beach ecosystems and to what extent meiofauna are included in ecological studies and ecosystem assessments of beaches. We reviewed 14,644 studies focusing on beaches available in the Web of Science, covering 58 years, and our analysis reveals that only 312 of these references addressed meiofauna in beaches. The majority of these 312 studies are from Brazil, India and the USA, and primarily focus on taxonomy or specific meiofaunal groups, with very few addressing processes such as erosion, and impacts such as microplastics pollution, nourishment, or management—topics frequently highlighted in wider beach science research. Notably, only 70 out of 312 studies (22%) mentioning meiofauna also discuss beach ecosystem threats and services. Although molecular approaches have the potential to enhance the use of meiofauna in addressing these issues, only seven meiofaunal studies have incorporated such methods, and approximately half of the meiofaunal genera cited in our dataset have been DNA barcoded. Our findings suggest that research on the ecology of beach meiofauna is still in its early stages, and we propose a series of short- and long-term actions to address the gaps preventing the integration of meiofauna into ecological research and beach monitoring programs. • Studies on meiofauna in beach ecosystems are still in their infancy compared to those dealing with other animal groups. • Most beach meiofauna papers appear to be descriptive and focused on biodiversity, rather than addressing processes such as erosion, pollutants or management. • The potential of meiofauna as indicators of natural and anthropogenic impacts on beach ecosystems appears to be underexplored. • Only 7 out of 312 beach meiofauna papers addressed molecular methods—and only 5 focused on metabarcoding.