Benthic-pelagic trophic coupling in an Arctic marine food web along vertical water mass and organic matter gradients

Source at: http://doi.org/10.3354/meps12582Understanding drivers of benthic-pelagic coupling in Arctic marine ecosystems is key to identifying benthic areas that may be sensitive to climate-driven changes in hydrography and surface production. We coupled algal biomass and sedimentary characteristics with stable isotope data for 113 fishes and invertebrates in the Canadian Beaufort Sea and Amundsen Gulf to examine how trophic structure was influenced by the vertical water mass structure and organic matter input regimes, from 20 to 1000 m depths. Indices of community-level trophic diversity (isotopic niche size, 13C enrichment relative to a pelagic baseline, and δ13C isotopic range) increased from west to east, coincident with the use of more diverse dietary carbon sources among benthic functional groups. Data suggested benthic-pelagic trophic coupling was strongest in the western study region where pelagic sinking flux is relatively high, intermediate in the central region dominated by riverine inputs of terrestrial organic matter, and weakest in the east where strong pelagic grazing is known to limit sinking flux. Differences in δ13C between pelagic and benthic functional groups (up to 5.7 ‰) increased from west to east, and from the nearshore shelf to the upper slope. On the upper slope, much of the sinking organic matter may be intercepted in the water column, and dynamic hydrography likely diversifies available food sources. In waters > 750 m, there were no clear trends in benthic-pelagic coupling or community-level trophic diversity. This study represents the first description of fish and invertebrate food web structure > 200 m in the Canadian Beaufort Sea

Relationships between depth and δ15N of Arctic benthos vary among regions and trophic functional groups

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.dsr.2018.03.010 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Stable isotope ratios of nitrogen (δ15N) of benthic primary consumers are often significantly related to water depth. This relationship is commonly attributed to preferential uptake of 14N from sinking particulate organic matter (POM) by microbes, and suggests that relationships between δ15N and water depth may be affected by local POM sources and flux dynamics. We examined the relationships between δ15N and water depth (20–500 m) for six trophic functional groups using a mixed effects modelling approach, and compared relationships between two contiguous Arctic marine ecosystems with different POM sources and sinking export dynamics: the Canadian Beaufort Sea and Amundsen Gulf. We demonstrate for the first time in the Arctic that δ15N values of mobile epifaunal carnivores increased as a function of depth when considered separately from benthopelagic and infaunal carnivores, which contrarily did not exhibit increasing δ15N with depth. The δ15N of suspension/filter feeders, infaunal deposit feeders and bulk sediment also increased with water depth, and the slopes of the relationships were steeper in the Amundsen Gulf than in the Beaufort Sea. We propose that regional differences in slopes reflect differences in POM sources exported to the benthos. In the Beaufort Sea, terrestrial POM discharged from the Mackenzie River quantitatively dominates the sedimentary organic matter across the continental shelf and slope, dampening change in δ15N of benthic POM with depth. In the Amundsen Gulf, we attribute a faster rate of change in δ15N of POM with increasing depth to larger contributions of marine-derived POM to the benthic sedimentary pool, which had likely undergone extensive biological transformation in the productive offshore pelagic zone. Differences in POM input regimes among regions should be considered when comparing food webs using stable isotopes, as such differences may impact the rate at which consumer δ15N changes with depth.Funding was provided by the Fisheries Joint Management Committee (Inuvik, NWT), Aboriginal Affairs and Northern Development Canada (BREA), Natural Resources Canada (Environmental Research Fund, Program of Energy Research and Development), internal Fisheries, National Sciences and Engineering Research Council (NSERC) grants to MP and HS, NSERC Alexander Graham Bell CGS D and NSERC Michael Smith Foreign Study Supplement scholarships awarded to AS, and internal support from UiT – The Arctic University of Norway to B

The role of water clarity in structuring niche dimensions and overlap between smallmouth bass and walleye

Smallmouth bass (Micropterus dolomieu) have experienced substantial range expansions in northern Ontario over the past century, with adverse consequences for native salmonid predators. It is unclear how climate-induced water clarity shifts will affect interactions between native dark-adapted walleye (Sander virteus) and invading smallmouth bass in northern Ontario. This study used stable isotopes of nitrogen (15N/14N) and carbon (13C/12C) in fish muscle tissue to investigate how resource partitioning between walleye and smallmouth bass is related to water clarity in 34 small (100-200 ha) Boreal Shield lakes (ranging from 1 to 8.5 m Secchi depth, and from 3.2 to 13.1 mg/L DOC). Quantitative metrics of trophic niche dimensions (based on the size, position, and dispersion of multivariate ellipses drawn around sampled individuals in δ15N vs. δ13C biplot space) were calculated for each individual population and used to determine trophic interactions and niche overlap between sympatric walleye and smallmouth bass. Linear and multiple regressions were then used to explore potential relationships between trophic interactions and water clarity. Available habitat and fish assemblage data was also explored for potential influences on isotopic niche dimensions and trophic interactions of walleye and smallmouth bass. Total occupied niche space decreased significantly with increasing water clarity for smallmouth bass as populations occupied a narrower range of trophic levels and made greater use of pelagic resources. In contrast, walleye trophic niche dimensions did not respond significantly to water clarity. Isotopic niche overlap ranged from 0 to 65%, but no metric of trophic overlap was significantly related to water clarity. Other abiotic and biotic variables, however, did have a significant influence on the similarity between some aspects of walleye and smallmouth iv bass isotopic niche dimensions (but not interaction). Both species fed on more isotopically similar carbon sources as lakes became shallower, which may be a result of a lack of distinct littoral and limnetic habitats. Walleye and smallmouth bass niche size also became more similar with increasing DOC but this may be a result of lower prey diversity. Both species also occupied more similar average food web positions as yellow perch relative abundance increased, indicating that the exploitation of yellow perch by both species increased with perch abundance. Together with other studies that have found little evidence for an impact of smallmouth bass on walleye fitness and abundance, this research suggests that, unlike salmonid and cyprinid species, walleye may be resilient against smallmouth bass invasions regardless of water clarity conditions in oligotrophic boreal lakes.Master of Science (M.Sc.) in Biolog

Plenty of room at the bottom: Niche variation and segregation in large-bodied benthivores of boreal lakes

Realized trophic niches of aquatic consumers are expected to reflect the particular abiotic and biotic conditions of the ecosystems they occupy. We examined patterns in the position, size, and shape of trophic niches of two common benthivorous fishes, white sucker (Catostomus commersoni) and lake whitefish (Coregonus clupeaformis), across boreal lakes using a stable isotope approach. In sympatry, white sucker niche positions reflected greater benthic reliance (higher δThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Appendix A. Computation of niche regions.

Computation of niche regions

Appendix D. A comparison of overlap at different α.

A comparison of overlap at different α

Supplement 1. Raw data and source R code for all calculations, figures, and tables.

<h2>File List</h2><div> <p><a href="nichefishdata.csv">nichefishdata.csv</a> (MD5: b621543c218974dce68c8c2dd17c21f3)</p> <p><a href="SourceCode_nicheROVER.R">SourceCode_nicheROVER.R</a> (MD5: e911a75dbaa59412366ba9406c4baf97)</p> </div><h2>Description</h2><div> <p>The supplements allow the reader to implement the methods using commented source code in R (SourceCode_nicheROVER.R). The raw data are also provided (nichefishdata.csv).</p> </div