Functional Pattern of Benthic Epifauna in the Chukchi Borderland, Arctic Deep Sea

Irina Zhulay,Katrin Iken,Paul E Renaud,Bodil A Bluhm,Renate Degen

doi:10.3389/fmars.2021.609956

Abstract

Assessment of Arctic deep-sea ecosystem functioning is currently an urgent task considering that ongoing sea-ice reduction opens opportunities for resource exploitation of yet understudied deep-sea regions. We used Biological Trait Analysis to evaluate ecosystem functioning and test if common paradigms for deep-sea fauna apply to benthic epifauna of the deep-sea Arctic Chukchi Borderland (CBL). We also investigated the influence of environmental factors on the functional structure of the epifauna. The analysis was performed for 106 taxa collected with a beam trawl and a Remotely Operated Vehicle from 486 to 2610 m depth. The most common trait modalities were small-medium size, mobile, benthic direct and lecithotrophic larval development, and predatory feeding, which mostly supports the current view of epifauna in the global deep sea. Functional composition of epifauna differed between two depth strata (486–1059 m and 1882–2610 m), with depth and sediment carbon content explaining most of the functional variability. Proportional abundances of the modalities free-living, swimming, suspension feeders, opportunists/scavengers, internal fertilization and globulose were higher at deep stations. Functional redundancy (FR) was also higher there compared to the mid-depth stations, suggesting adaptation of fauna to the more homogeneous deep environment by fewer and shared traits. Mid-depth stations represented higher functional variability in terms of both trait modality composition and functional diversity, indicating more variable resource use in the more heterogeneous habitat. Food input correlated positively with the proportional abundance of the modalities tube-dwelling, sessile and deposit feeding. Areas with drop stones were associated with higher proportional abundance of the modalities attached, upright, and predators. Comparatively low FR may render the heterogeneous mid-depth area of the CBL vulnerable to disturbance through the risk of loss of functions. Across the study area, high occurrence of taxa with low dispersal ability among adult and larval life stages may prevent rapid adaptation to changes, reduce ability to recolonize and escape perturbation.

Highlights

The deep ocean floor covers around 65% of the surface of the earth, yet it is the least explored ocean habitat
“crawlers” were dominant, though “sessile” was second most frequent and since this study focused on epifauna, “burrowers” were expectedly least frequent in the data set (Figure 2C)
Deep stations were characterized by significantly higher proportional abundance of the body form “globulose” (BF1), feeding habits “suspension feeder” (FH3) and “opportunist/scavenger” (FH4), reproduction “sexual-internal fertilization” (R3), and higher proportional abundance of “freeliving” (LH1), “highly mobile” (MO4), and “swimmer” (MV4) modalities (Kruskal–Wallis test; Table 4 and Figure 4)

Summary

Introduction

The deep ocean floor covers around 65% of the surface of the earth, yet it is the least explored ocean habitat. While we have begun to identify trends in deep-sea biodiversity patterns such as mid-depth peaks and latitudinal declines in diversity, and a generally higher level of rarity and endemism compared to shelf communities (Levin et al, 2001; Stuart et al, 2003; Renaud et al, 2006; Rex and Etter, 2010; Bluhm et al, 2011), still little is known about functional characteristics of deep-sea ecosystems This is a serious gap, because deep-sea regions experience increasing anthropogenic influences (e.g., deep-sea fisheries, oil and gas exploration, mining, marine debris), and are at the same time subjected to the influences of climate change, in particular in polar regions (Smith et al, 2008; Ramirez-Llodra et al, 2011; Levin and Le Bris, 2015; Tekman et al, 2017). These levels are considerably lower than other deep-sea areas, where pelagic primary production is highly variable, but often exceeds 20– 50 g C m−2 year−1 (Karl et al, 1996; Levin and Gooday, 2003; Emerson, 2014)

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Conclusion