Isotopic niche variability in macroconsumers of the East Scotia Ridge (Southern Ocean) hydrothermal vents: What more can we learn from an ellipse?

Wdk Reid,Nvc Polunin,Cj Sweeting,Rar Mcgill,Bd Wigham

doi:10.3354/meps11571

Abstract

Aspects of between-individual trophic niche width can be explored through the iso- topic niche concept. In many cases isotopic variability can be influenced by the scale of sampling and biological characteristics including body size or sex. Sample size-corrected (SEAc) and Bayesian (SEAb) standard ellipse areas and generalised least squares (GLS) models were used to explore the spatial variability of δ 13 C and δ 15 N in Kiwa tyleri (decapod), Gigantopelta chessoia (peltospirid gastropod) and Vulcanolepas scotiaensis (stalked barnacle) collected from 3 hydrothermal vent field sites (E2, E9N and E9S) on the East Scotia Ridge (ESR), Southern Ocean. SEAb only revealed spatial differences in isotopic niche area in male K. tyleri. However, the parameters used to draw the SEAc, eccentricity (E) and angle of the major SEAc axis to the x-axis (θ), indicated spatial differences in the relationships between δ 13 C and δ 15 N in all 3 species. The GLS models indicated that there were spatial differences in isotopelength trends, which were related to E and θ of the SEAc. This indicated that E and θ were potentially driven by underlying trophic and biological processes that varied with body size. Examination of the isotopic niches using standard ellipse areas and their parameters in conjunction with length-based analyses pro- vided a means by which a proportion of the isotopic variability within each species could be described. We suggest that the parameters E and θ offer additional ecological insight that has so far been overlooked in isotopic niche studies.

Highlights

Hutchinson’s definition of the ecological niche as a ‘n-dimensional hypervolume’ encompassing all the environmental factors that allow a species to inhabit a given area (Hutchinson 1957) encapsulates a huge amount of ecological complexity that is challenging to parameterise
We address the question: What more can we learn from an ellipse? The focus here is expanding the potential of standard ellipse area (SEA) by incorporating E and θ into an assessment of isotopic variability using fauna collected from deep-sea hydrothermal vents
Muscle was removed from the chelipeds of K. tyleri, whole V. scotiaensis were removed from their shells and the foot was dissected from G. chessoia

Summary

Introduction

Hutchinson’s definition of the ecological niche as a ‘n-dimensional hypervolume’ encompassing all the environmental factors that allow a species to inhabit a given area (Hutchinson 1957) encapsulates a huge amount of ecological complexity that is challenging to parameterise. Stable isotope analysis is a tool for investigating intraspecific trophic niche variation (Bolnick et al 2003, Bearhop et al 2004, Sweeting et al 2005) that has advantages over conventional techniques such as stomach content analysis and behavioural observations. Carbon (13C:12C expressed as δ13C) and nitrogen (15N:14N expressed as δ15N) stable isotope data provide a time-integrated signal of the materials assimilated from an individual’s diet (Hesslein et al 1993, Martinez del Rio et al 2009) rather than providing a snap-shot of what an individual has consumed (Pinnegar & Polunin 1999). Δ13C and δ15N values often provide spatial-integrated signals when consumers move amongst habitats with different isotopic baselines (McMahon et al 2013)

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