Is the trophic diversity of marine benthic consumers decoupled from taxonomic and functional trait diversity? Isotopic niches of Arctic communities

Abstract

It is predicted that a diverse array of functional traits in species‐rich assemblages can lead to strong resource partitioning among coexisting species and moderate a wider spectrum of resource use. We compared two benthic communities in an Arctic fjord: a species‐rich community (in an outer basin) and an impoverished community (in a glacially impacted bay) and explored (1) if high species richness was translated into high functional trait richness and (2) if high taxonomic and functional diversity promoted high trophic diversity in terms of resource use (indicated by isotopic niche measures). We documented higher functional trait richness in the outer basin (computed based on traits describing feeding mode, mobility, food source, body size and life habit), but the area occupied by consumers in the δ15N vs. δ13C iso‐space (a proxy for total trophic resource use) did not differ between the two sites. A wide array of functional traits used to acquire food may extend the benthic community trophic niche spatially (where and how animals forage) without impacting the isotopic niche breadth (in this system, mostly reflecting “what animals feed on”) due to the relatively homogenous distribution of isotopic characteristics of detritus pool across vertical scales in marine sediments. Moreover, this trend could indicate that a species‐poor community tends to exploit all the available food items, possibly due to the low food availability for primary consumers in a glacially impacted environment. Communities in glacial bays could therefore be particularly sensitive to future changes in glacial inputs and associated organic matter fluxes.

Food source diversity, trophic plasticity, and omnivory enhance the stability of a shallow benthic food web from a high‐Arctic fjord exposed to freshwater inputs

“…Although the sampled stations in this study cover only a part of the fjord's length, significant gradients of salinity (Paulsen et al 2017; Sejr et al 2017), organic matter quality (Bridier et al 2019), and primary production (Meire et al 2017) have been reported between the same stations. In a similar spatial and salinity gradient of Hornsund (Svalbard), Włodarska‐Kowalczuk et al (2019) highlighted a clear δ 13 C shift between benthic food webs of inner and outer fjords, which they attributed to different relative contributions of various organic matter sources. The absence of such a trend in Young Sound may signify that the organic matter pool fueling inner and outer communities is minimally affected by environmental gradients.…”

“…The relatively low degradation of settled particles in polar ecosystems usually leads to the accumulation of a persistent sediment food bank of labile detritus (Smith et al 2006; Mincks et al 2008). The resuspension of these labile detritus (through bottom currents or bioturbation) has a considerable importance for arctic benthic food webs facing periods of low food availability by providing an alternative food source for suspension feeders (Smith et al 2006; Włodarska‐Kowalczuk et al 2019). We hypothesize that such resuspension events in Young Sound might thus partly increase the temporal stability and spatial homogeneity of the benthic food web in the face of strong spatiotemporal variations in primary production and organic matter quality (Meire et al 2017; Bridier et al 2019).…”

“…Surprisingly, impacts on benthic ecosystems have received less attention, with studies mainly focusing on the disturbance generated by high sedimentation close to marine glaciers (e.g., sediment instabilities, bivalve gill clogging, etc.) that may impoverish the specific and functional richness of benthic communities (Sejr et al 2010; Włodarska‐Kowalczuk et al 2019). Some food‐web studies have revealed significant contributions of terrestrial organic matter to the diet of benthic organisms, but they have mainly concerned large hydrological systems (e.g., Mackenzie River) over very large spatial scales (i.e., >100 s of km; Bell et al 2016).…”

“…Such advanced approaches have widely shown their ability to describe the functioning of benthic ecosystems exposed to high environmental pressures (e.g., flood events; Abrantes et al 2014) by tracking changes in organic matter pathways within communities over time and space. However, these methods are still rarely used in polar areas (but see Włodarska‐Kowalczuk et al 2019). Using community‐wide trophic niche metrics and stable isotope mixing/trophic position models, we investigated the small‐scale variability (i.e., inner vs. outer fjord communities) of benthic food‐web structures from a high‐Arctic fjord exposed to freshwater inputs.…”

Characterization of Trophic Structure of Fish Assemblages in the East and South Seas of Korea Based on C and N Stable Isotope Ratios

“…In our study, during both seasons, the TA and SEAc of fish assemblages in the South Sea exhibited wider ranges than those in the East Sea. Such spatial differences in the isotopic niche areas may mostly result from the different environmental conditions and/or species compositions that can alter the trophic relationships within the community [53,54]. Our results also suggest that the spatial differences in the TA and SEAc may be associated with the regional distinction in the fish community interacting with different environmental conditions.…”