Ice algae versus phytoplankton: resource utilization by Arctic deep sea macroinfauna revealed through isotope labelling experiments

Leichter

et al. 2018

Global Change Biology

Organic matter produced by the sea ice microbial community (SIMCo) is an important link between sea ice dynamics and secondary production in near-shore food webs of Antarctica. Sea ice conditions in McMurdo Sound were quantified from time series of MODIS satellite images for Sept. 1 through Feb. 28 of 2007-2015. A predictable sea ice persistence gradient along the length of the Sound and evidence for a distinct change in sea ice dynamics in 2011 were observed. We used stable isotope analysis (δ C and δ N) of SIMCo, suspended particulate organic matter (SPOM) and shallow water (10-20 m) macroinvertebrates to reveal patterns in trophic structure of, and incorporation of organic matter from SIMCo into, benthic communities at eight sites distributed along the sea ice persistence gradient. Mass-balance analysis revealed distinct trophic architecture among communities and large fluxes of SIMCo into the near-shore food web, with the estimates ranging from 2 to 84% of organic matter derived from SIMCo for individual species. Analysis of patterns in density, and biomass of macroinvertebrate communities among sites allowed us to model net incorporation of organic matter from SIMCo, in terms of biomass per unit area (g/m ), into benthic communities. Here, organic matter derived from SIMCo supported 39 to 71 per cent of total biomass. Furthermore, for six species, we observed declines in contribution of SIMCo between years with persistent sea ice (2008-2009) and years with extensive sea ice breakout (2012-2015). Our data demonstrate the vital role of SIMCo in ecosystem function in Antarctica and strong linkages between sea ice dynamics and near-shore secondary productivity. These results have important implications for our understanding of how benthic communities will respond to changes in sea ice dynamics associated with climate change and highlight the important role of shallow water macroinvertebrate communities as sentinels of change for the Antarctic marine ecosystem.

Section: Introductionmentioning

confidence: 99%

Contribution of sea ice microbial production to Antarctic benthic communities is driven by sea ice dynamics and composition of functional guilds

Leichter

et al. 2018

Global Change Biology

“…To date, only a few studies have investigated the responses of benthos to ice algae and phytoplankton, and the consequent impacts on C cycling processes. While certain bivalves and deposit feeding taxa preferentially consume ice algae over phytoplankton in shallow subtidal sites in Alaska andSvalbard (McMahon et al 2006, Sun et al 2009), other faunal communities efficiently assimilate both ice algal and phytoplankton C, with no taxa in the Canadian Arctic deep sea exclusively preferring ice algae (Mäkelä et al 2017a). Macrofaunal uptake, however, is usually a minor pathway in the total POC processing at the seafloor (Heip et al 2001, Hunter et al 2012, Findlay et al 2015.…”

Section: Introductionmentioning

confidence: 99%

Short-term processing of ice algal- and phytoplankton-derived carbon by Arctic benthic communities revealed through isotope labelling experiments

Mäkelä¹,

Witte²,

Archambault³

2018

Mar. Ecol. Prog. Ser.

Self Cite

Benthic ecosystems play a significant role in the carbon (C) cycle through remineralization of organic matter reaching the seafloor. Ice algae and phytoplankton are major C sources for Arctic benthic consumers, but climate change-mediated loss of summer sea ice is predicted to change Arctic marine primary production by increasing phytoplankton and reducing ice algal contributions. To investigate the impact of changing algal C sources on benthic C processing, 2 isotope tracing experiments on 13 C-labelled ice algae and phytoplankton were conducted in the North Water Polynya (NOW; 709 m depth) and Lancaster Sound (LS; 794 m) in the Canadian Arctic, during which the fate of ice algal (C IA) and phytoplankton (C PP) C added to sediment cores was traced over 4 d. No difference in sediment community oxygen consumption (SCOC, indicative of total C turnover) between the background measurements and ice algal or phytoplankton cores was found at either site. Most of the processed algal C was respired, with significantly more C PP than C IA being released as dissolved inorganic C at both sites. Macroinfaunal uptake of algal C was minor, but bacterial assimilation accounted for 33−44% of total algal C processing, with no differences in bacterial uptake of C PP and C IA found at either site. Overall, the total processing (i.e. assimilation and respiration) of C PP was 33 and 37% higher than processing of C IA in NOW and in LS, respectively, suggesting that the future changes in quality of organic matter sinking to the seafloor could impact the C residence time at the seafloor.

“…However, most studies target assimilation by specific size classes of organisms, e.g. macrofauna, or specific taxonomic groups such as Foraminifera (Enge et Experimental food web studies in the Arctic deep-sea with labelled food sources are scarce and have focussed on uptake of DOC, bacteria or diatom detritus by nematodes (Guilini et al, 2010;Ingels et al, 2010) or phytoplankton and ice algae by macrofauna (Mäkelä et al, 2017). The latter studies are ship-based experiments, an approach 70 which can involve decompression of the samples and is therefore prone to introducing biases, e.g.…”

mentioning

confidence: 99%

“…by changing the activity of the benthic biota. This type of studies shows that infauna selects its food sources specifically or is indifferent: macrofauna seems to have a preference for ice algae over phytoplankton in shallower Arctic water (McMahon et al, 2006;Sun et al, 2007) but displays a dietary plasticity in Arctic deep-sea sediments, assimilating both ice algae and phytoplankton efficiently (Mäkelä et al, 2017). Also in the abyssal Pacific, macrofauna did not 75 show preference for any type of food source when phytodetritus was readily available, whereas foraminifera selected coccolithophore nitrogen over diatom nitrogen (Jeffreys et al, 2013).…”

mentioning

confidence: 99%

“…In this study, we compare the in situ mineralization pathways of phytodetritus of a traditionally prevailing primary producer with a food source that will possibly dominate in the near future as a consequence of global change effects on phytoplankton communities. Such a shift may entail significant effects on the ecosystem since the 80 availability and degradation patterns of different food sources might differ (Mäkelä et al, 2017;Ruhl and Smith, 2004;Smith et al, 2013). The previously dominant diatom Thalassiosira, for example, is protected by a silica wall which can be easily dissolved by bacteria (Bidle and Azam, 1999).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Carbon and nitrogen turnover in the Arctic deep sea: in situ benthic community response to diatom and coccolithophorid phytodetritus

Braeckman¹,

Janßen²,

Lavik³

et al. 2018

Preprint

Abstract. In the Arctic Ocean, increased sea surface temperature and sea ice retreat have triggered shifts in phytoplankton communities. In Fram Strait, coccolithophorids have been occasionally observed to replace diatoms as the dominating taxon of spring blooms. Deep-sea benthic communities depend strongly on such blooms but with a change in quality and quantity of primarily produced organic matter [OM] input, this may likely have implications for deep-sea life. We compared the in situ responses of Arctic deep-sea benthos to input of phytodetritus from a diatom (Thalassiosira sp.) and a coccolithophorid (Emiliania huxleyi) species. We traced the fate of 13C and 15N labelled phytodetritus into respiration, assimilation by bacteria and infauna in a 4 d and 14 d experiment. Bacteria were key assimilators in the Thalassiosira OM degradation whereas Foraminifera and other infauna were at least as important as bacteria in the Emiliania OM assimilation. After 14 d, 5 times less carbon and 3.8 times less nitrogen of the Emiliania detritus was recycled compared to Thalassiosira detritus. This implies that the utilization of Emiliania OM may be less efficient than for Thalassiosira OM. Our results indicate that a shift from diatom-dominated input to a coccolithophorid-dominated pulse could entail a delay in OM cycling, which may affect bentho-pelagic coupling.