The Extremes of Disturbance Reduce Functional Redundancy: Functional Trait Assessment of the Shallow Antarctic Benthos

Ben J O Robinson,David K A Barnes,Laura J Grange,Simon A Morley

doi:10.3389/fmars.2021.797112

Abstract

Climate-driven changes in disturbance are a major threat to ecosystem Functional diversity. The selective mechanisms underlying ecosystem response to disturbance are far from universal and remain the subject of scientific debate. Ice scouring of the shallow Antarctic benthos is one of the largest disturbance gradients in the natural environment and thus provides an opportunity to investigate how disturbance gradients influence functional structure of a biological assemblage. The Western Antarctic Peninsula, in particular, is a hotspot of climate-driven environmental change. Addressing how this system might respond to species loss is critical. Previous surveys across the shallowest 100 m of the seabed, detected unimodal changes in diversity and a shift in assemblage composition in response to disturbance gradients. This study investigated how functional traits and associated functional diversity change across the depth gradient. Our results revealed that selective mechanisms, such as disturbance filtering and inter-species competition, reduce functional redundancy at the extremes of the disturbance gradient. Our study highlights areas of potential vulnerability to future environmental change due to low functional redundancy. Threatening the important negative (mitigating) feedbacks on climate change, through blue carbon, currently provided by Antarctic continental shelf benthic assemblages.

Highlights

Disturbance in an assemblage, community or ecosystem is an abrupt change in conditions of at least one key resource, or controlling factor, for life
All taxa were recorded as Operational Taxonomic Units (OTUs), as not all specimens could be identified to species level
Community-Weighted Means (CWM) trophic groups indicated that the shallows were dominated by an abundance of grazers (Figure 2B) and autotrophs (Figure 2A), peaking between 10 and 20 m depth (0.63 and 0.30 CWM abundance, respectively), reaching a near 0 CWM abundance at 50 m and 80 m, respectively (Figure 2M)

Summary

Introduction

Disturbance in an assemblage, community or ecosystem is an abrupt change in conditions of at least one key resource, or controlling factor, for life (e.g., temperature, light, salinity, turbidity, availability of space, etc). Disturbance events occur in all natural ecosystems on varying time scales and magnitudes, and are key factors in controlling assemblage structure and function (Dell et al, 2019). Disturbance-diversity patterns and relationships are complex and often poorly understood, especially in the sea. These patterns are far from universal and some are under strong debate. Some studies have found unimodal relationships, which some researchers attribute to the Intermediate Disturbance Hypothesis (IDH) (Connell, 1978; Hughes et al, 2007; Huston, 2014).

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