Vulnerability of macronutrients to the concurrent effects of enhanced temperature and atmospheric pCO2 in representative shelf sea sediment habitats

Abstract

Fundamental changes in seawater carbonate chemistry and sea surface temperatures associated with the ocean uptake of anthropogenic CO 2 are accelerating, but investigations of the susceptibility of biogeochemical processes to the simultaneous occurrence of multiple components of climate change are uncommon. Here, we quantify how concurrent changes in enhanced temperature and atmospheric pCO 2 , coupled with an associated shift in macrofaunal community structure and behavior (sediment particle reworking and bioirrigation), modify net carbon and nutrient concentrations (NH 4 -N, NO x -N, PO 4 -P) in representative shelf sea sediment habitats (mud, sandy-mud, muddy-sand and sand) of the Celtic Sea. We show that net concentrations of organic carbon, nitrogen and phosphate are, irrespective of sediment type, largely unaffected by a simultaneous increase in temperature and atmospheric pCO 2 . However, our analyses also reveal that a reduction in macrofaunal species richness and total abundance occurs under future environmental conditions, varies across a gradient of cohesive to non-cohesive sediments, and negatively moderates biogeochemical processes, in particular nitrification. Our findings indicate that future environmental conditions are unlikely to have strong direct effects on biogeochemical processes but, particularly in muddy sands, the abundance, activity, composition and functional role of invertebrate communities are likely to be altered in ways that will be sufficient to regulate the function of the microbial community and the availability of nutrients in shelf sea waters.

Benthic estuarine communities' contribution to bioturbation under the experimental effect of marine heatwaves

“…Regarding nitrates, results suggest a delay in response to the warming, with an increasing nitrate release 1-week after the heatwave occurrence. However, we could not relate it with the bioturbation, nor with the specific functional behaviour of the species that compose the benthic community, as in 35 . We would need to extend the experiment to conclude some warming effect, as the impact of warming in species' bioturbation and nutrient generation may only manifest for prolonged periods 34 .…”

“…Bioturbation mediated by macrofauna generally increases sediments' oxygenation and may be an essential trigger for nutrient release 35 , 39 , 48 , 49 . However, the variation trends in the nutrient release data in this study were not directly correlated with macrofauna's bioturbation, as also concluded by 33 , 40 .…”

“…Most experimental studies testing temperature impact have focused on particular species or communities with different species compositions to define species thermal tolerances and limits 14 or unravel potential effects on specific aspects of ecosystem functioning 26 , 34 , 35 . Existing experimental works studying the effects of temperature extremes oscillations (by simulating heatwaves) have detected different, often contrasting, biological responses, ranging from a lack of effect, negative or positive effect depending on species tolerance, species interactions, and local context 19 , 36 , 37 .…”

Global Carbon Cycling on a Heterogeneous Seafloor

“…However, evidence suggests that variation in the functional attributes of communities [37][38][39] can affect carbon-and nutrient-cycling processes more than species diversity can [40]. Anticipated changes in the abundance, distribution, and behavior of functionally important species in response to global environmental change [2,41,42] raise concerns about significant alteration of ecosystem function and services, given the strong interlinkages among seabed functioning [43] and ocean productivity. Local-regional-level studies that consider faunal mediation of carbon cycling from shallow to deep seafloor ecosystems highlight the potential importance of including organisms in global carbon models and considering the contributions of different seabed environments [44].…”

Interregional comparison of benthic ecosystem functioning: Community bioturbation potential in four regions along the NE Atlantic shelf

“…It is important to account for differences in sediment habitat when assessing biogeographic patterns, as for example much of the functioning is undertaken by physical processes rather than biological processes in sand habitats, whilst the reverse is true in muddy sediments (Sciberras et al 2017;Hale et al 2017;Godbold et al 2017). Accounting for spatial differences even at smaller scale of distinct seafloor morphologies was found crucial for improving management of goods and services delivered by marine ecosystems (Zeppilli et al, 2016).…”