Marine connectivity dynamics: clarifying cosmopolitan distributions of marine interstitial invertebrates and the meiofauna paradox

Abstract

Many interstitial species were first described as widely distributed, often cosmopolitan or amphi-oceanic, contrasting with descriptions of a sedentary life style and the general absence of pelagic dispersal stages. These inconsistencies became known as the "meiofauna paradox". In this review we present a literature review investigating these inconsistencies and address the assumptions of the meiofauna paradox. We break the paradox down to two aspects including species distribution and dispersal. Focusing on distribution, we demonstrate that wide distributions are seldom given and false records likely stem from biological phenomena like stasis or recent speciation. These phenomena account for morphological similarity, ultimately represented by the pronounced occurrence of cryptic species with restricted distribution ranges. Additionally, taxonomic artefacts such as the erroneous application of taxonomic keys contribute to the report of widely distributed species. Considering dispersal, we point out the mismatch between traditional assumptions of meiofaunal sedentarism and growing experimental and empirical evidences suggesting higher dispersal potential. These evidences include not only indications for dispersal by pelagic stages, but further consider ecological and life-history traits in shaping distribution ranges. We conclude that the meiofauna paradox sensu strictu most likely does not exist and provide a roadmap for future research, suggesting a focus on morphological similarity and marine connectivity. Meiofaunal research should concentrate on evolutionary factors resulting in morphological similarity, improving the taxonomic resolution of species complexes and conducting more sophisticated experimental experiments to meiofaunal dispersal. In all cases meiofaunal research will benefit from high-throughput sequencing such as genome scanning approaches, metagenomics or metatranscriptomics.

The ability to get everywhere: dispersal modes of free-living, aquatic nematodes

“…Since the survival rate (e.g., the avoidance of death by starvation, digestion) and recruitment from source habitats decline with increasing time and distance, most distribution probably takes place over smaller ranges, in line with the results of studies based on genetic approaches (Derycke et al, 2007;Bik et al, 2010;Derycke et al, 2013;Hauquier et al, 2017). However, according to the review of Cerca et al (2018), the presented studies suggests that the meiofauna paradox most likely does not exist because the dispersal of these small organisms is more diverse and effective than often assumed, but not entirely unrestricted (see next section). Finally, although the basic distribution pathways of nematodes have already been demonstrated, the picture is far from complete.…”

“…Studying the genetic diversity of certain nematode species (e.g., Derycke et al, 2013;Ristau et al, 2013;Schenk et al, 2016) can provide insights into the gene flow between species at different locations and thus the extent and range of their dispersal. Furthermore, ''sophisticated experimental experiments'' are another key for the detailed understanding of meiofauna dispersal processes (Cerca et al, 2018).…”

“…However, it is generally assumed that gene flow is mostly limited to distances \ 100 km (Derycke et al, 2008(Derycke et al, , 2013Hauquier et al, 2017). Cerca et al (2018) showed in their review that, based on molecular investigations, even amphi-oceanic distribution of marine meiofauna taxa seldom occurs.…”

“…Thus, in referring to this so-called meiofauna paradox, Giere (2009) rightly asked: How can we explain a wide distribution of animals with almost no dispersive capacity? In this context, Cerca et al (2018) already pointed out that the dispersal potential of meiobenthic organisms has been considerably underestimated in the past and the meiofauna paradox is rather to be regarded as a paradigm.…”

Does size really matter in biogeography? Patterns and drivers of global distribution of marine micro‐ and meiofauna

“…Many meiofaunal taxa, both marine and limnetic, are often reported from distant and isolated habitats and, therefore, are suspected of having wide or even cosmopolitan distribution (Chertoprud, Garlitska, & Azovsky, ; Giere, ), despite the limited potential for reproduction and dispersion (the so‐called ‘meiofauna paradox’, Giere, ). The mechanisms of dispersal underlying such distributional patterns are not conclusive and still remain debated (reviewed by Cerca, Purschke, & Struck, ). There are several studies on the large‐scale distribution of meiofaunal abundance and diversity (Chertoprud et al, ; Mokievsky, Udalov, & Azovsky, ), whereas the factors determining their taxonomic composition remain essentially unexplored.…”