Marine Meiofauna Diversity and Biogeography—Paradigms and Challenges

Scientists studying the biodiversity and biogeography of meiofauna encounter many uncertainties regarding the causes and consequences of natural and anthropogenic-driven changes in biodiversity patterns they observe worldwide. Recently developed novel analytical and computational technologies are facilitating more systematic and integrated approaches to the study of meiofauna biodiversity. In this chapter, we reflect on the state of the art in biodiversity and biogeography research with a focus on the most abundant and diverse meiofauna taxa including nematodes and copepods. Other occasionally abundant meiofauna taxa such as carbonate-shelled crustacean ostracods and protist foraminiferans, which are present in the fossil record, allow meiobenthologists to understand the links between shifts in biodiversity and major historical events in the marine environment. Sample-size dependency and the lack of standardization across benthic surveys currently hamper the integration of disparate meiofauna studies into wider research of seafloor biodiversity and biogeography. We discuss habitat-specific meiofauna biodiversity patterns that are observed at different scales and identify the main drivers of such patterns. Important factors include physical characteristics of the seafloor, biogeochemical processes, ecosystem productivity, geographical location, but also the interactions of meiofauna with other ecosystem components including their prey, their predators, competitors, and habitat facilitators. We discuss the importance of meiobenthic biodiversity for ecosystem functioning and touch on the biogeography of dominant meiofauna taxa by looking at what we know about the importance of endemism versus cosmopolitanism, the growing insights in population genetics and cryptic speciation, the phylogenic processes underpinning them, and critical gaps in our knowledge. We conclude by identifying some dynamic areas of research and inquiry for future generations of meiobenthologists studying the biodiversity and biogeography of meiofauna. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023.