Intra- and inter-spatial variability of meiofauna in hadal trenches is linked to microbial activity and food availability

Abstract

Hadal trenches are depocenters for organic material, and host intensified benthic microbial activity. The enhanced deposition is presumed to be reflected in elevated meiofaunal standing-stock, but available studies are ambiguous. Here, we investigate the distribution of meiofauna along the Atacama Trench axis and adjacent abyssal and bathyal settings in order to relate the meiofauna densities to proxies for food availability. Meiofauna densities peaked at the sediment surface and attenuated steeply with increasing sediment depth. The distribution mirrored the vertical profile of the microbial-driven oxygen consumption rate demonstrating a close linkage between microbial activity and meiofauna density. Meiofaunal standing-stock along the trench axis varied by a factor of two, but were markedly higher than values from the abyssal site at the oceanic plate. Overall, meiofaunal densities poorly correlated with common proxies for food availability such as total organic carbon and phytopigments, but strongly correlated with the microbial benthic O₂ consumption rate. We argue that microbial biomass likely represents an important meiofaunal food source for hadal meiofauna. Observations from three trench systems underlying surface water of highly different productivity confirmed elevated meiofaunal densities at the trench axis as compared to abyssal sites on oceanic plates. Food availability appear to drive elevated abundance and variations in meiofauna densities in hadal sediments.

Figure 1

Locations of multi-corer deployments on trench axis (A2–A6 & A10), on the bathyal (A1) and abyssal (A9) sites on the continental margin, and on the oceanward abyssal plain (A7). White square Danovaro et al. hadal site; black squares Danovaro et al. bathyal sites.

Figure 2

Vertical distribution of meiofauna density (A, C, E, G) and meiofauna respiration, O₂ micro-profiles and volume specific O₂ consumption (B, D, F, H) of four selected sites. For figures on right side: blue line bars – volume specific O₂ consumption; grey bars – meiofauna respiration with standard errors; red dots – O₂ micro-profiles. Values of meiofauna respiration was multiplied by 5 for better representation. Values of the volume specific O₂ consumption is a subset of data presented in Glud et al..

Figure 3

Total meiofauna density (A) and biomass (B) of integrated sediment column up to 5 cm depth. Light blue – bathyal depth; blue – abyssal depths; dark blue – hadal depths. One-way ANOVA, density – F: 9.8, p < 0.001, df.: 8. One-way ANOVA, biomass – F:7.0, p < 0.001, df.: 8. Lowercase letter above each box are results from Tukey pairwise test.

Figure 4

Regressions of meiofauna density/biomass against diffusive oxygen uptake (DOU) (A, B) and total organic carbon (C, D). Light blue triangle – bathyal depth; blue circles – abyssal depths; dark blue squares – hadal depths. Data of DOU is a subset of data presented in Glud et al..

Figure 5

Comparison of trench axis and adjacent abyssal plain of Atacama, Japan, Kuril-Kamchatka and Tonga trenches. * this study. ** data compiled from Schimdt & Arbizu, Schmidt et al., and Itoh et al. comprising: 8 abyssal plain and 7 trench axis sites. *** data compiled from Leduc et al. comprising: 1 abyssal plain and trench axis site each. All data compiled in this figure is up to 5 cm sediment depth and abyssal plain sites are on the oceanic plate. Net primary production (NPP) values was derived using Behrenfeld & Falkovski model and remote sensing data from the period 2009–2018 and previous presented in: #—Glud et al.; §—Oguri et al. (in prep).