New Horizons in Meiobenthos Research: Profiles, Patterns and Potentials
Jyotsna Sharma
Abstract
The word “interdependent” is particularly relevant when studying a diverse group of ubiquitous microscopic organisms that comprise over 25 phyla, the meiobenthos. The 11 chapters of New Horizons in Meiobenthos Research: Profiles, Patterns and Potentials (Olav Giere, Michaela Schratzberger Editors, Springer Verlag, 407 p.) are a collection of reviews of topics covering the ecosystems and habitats meiofauna occupy and their role within each. Though early meiobenthic studies were from Western Europe, the international team of 33 authors, specialists in their field, gives the research presented here global coverage. The meiobenthos, generally defined to be organisms ranging in size from 63 μm to 1.0 mm, can also include microalgae but it is often used interchangeably with meiofauna. Since the last comprehensive review of meiobenthos by Giere (2009), the availability of new microscopic, molecular, genomic, analytical, and computational technologies has increased in addition to access to previously inaccessible habitats with oceangoing ships equipped with up-to-date labs to conduct onboard experiments. Several new approaches and methods are now available to examine the interaction of meiofauna with other benthic organisms and the physical and chemical environment they inhabit. The emphasis on community is notable as the index does not include individual meiobenthic taxa; the only place they are identified is in a compilation of scanning electron photographs of the dominant meiofauna taxa. Instead, the book examines the role of the meiobenthos within ecosystems and should encourage ecologists who may have been intimidated by the daunting task of meiofauna taxonomy that is facilitated by Schmidt-Rhaesa (2020). This shift was seen in presentations at the International Association of Meiobenthologists (yes there is such a group, though small) meetings from emphasis on taxonomy and systematics to ecosystems processes. The diverse meiobenthic taxa have uncertain evolutionary origins yet share the common feature of miniaturization with many convergent morphological features as an adaptation to their interstitial habitat. Their small size and soft bodies leave scarce paleontological information; thus, to understand their evolution, morphological, and molecular evidence is linked to genomic and phenotypic organization. The high-population density and diversity of meiofauna have significant effects on bioturbation and interactions with macro- and microbenthos. Biochemical profiles in sediments show interactions of biological activity with bioturbation and biogeochemical processes and are discussed with graphs and integration of significant chemical cycles such as nitrogen and sulfur. The occurrence of “extremophiles” among the meiobenthic taxa has led to findings of mutualistic symbioses with microbes that allow them to live in hot deep-sea vents and subglacial sediments. Though meiobenthic studies have often been focused on marine habitats, the review of freshwater meiofauna notes that as these habitats are often disconnected and ephemeral, the animals found here are helped in their dispersal by wind, rain, drift, and migrating animals. Studies of cave meiofauna show high endemicity in inland freshwater caves. As with other studies, knowledge of cave meiofauna has many gaps particularly due to access. Though meiofauna occupy all trophic guilds, anthropogenic disturbances allow opportunist taxa to dominate. With increasing pollution from industry, exploitation of the deep seas for mineral resources, coastal development, and climate change, the authors are optimistic: “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. Therefore, it seems likely that meiofauna have the ability to adapt, and thrive, in response to most environmental changes” (p. 176). Past studies identified the feeding preferences of meiofauna by their buccal morphology, but “Results from stable-isotope tracer experiments suggested that different meiofauna can feed selectively on the different food sources available, and that their trophic plasticity allows them to exploit high Particulate Organic Carbon (POC) fluxes.” enabling adaptation to alternate food sources in a changing environment (p. 295). The thorough review of each topic by authors experienced in the subject coupled with a comprehensive reference list should encourage a student or a researcher beginning a study of meiobenthos to go beyond the identification of individual taxa and study the community as a whole. It is also a recognition of the importance of the meiobenthos in regulating ecological processes and should be ample justification for their inclusion in research of ecosystems. Though they are invisible to the naked eye, they should not be overlooked in favor of charismatic macrobenthos. In a changing world subject to climate and human influences, integration of technological advances and a multidisciplinary approach will “determine the limits and potential of the benthic realm” (p. 402).