University of Tasmania
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Functional traits explain trophic allometries of cephalopods

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journal contribution
posted on 2023-05-20, 22:40 authored by Kieran MurphyKieran Murphy, Gretta PeclGretta Pecl, Shane RichardsShane Richards, Jayson SemmensJayson Semmens, Revill, AT, Suthers, IM, Everett, JD, Rowan TrebilcoRowan Trebilco, Julia BlanchardJulia Blanchard
  1. Individual body size strongly influences the trophic role of marine organisms and the structure and function of marine ecosystems. Quantifying trophic position–individual body size relationships (trophic allometries) underpins the development of size‐structured ecosystem models to predict abundance and the transfer of energy through ecosystems. Trophic allometries are well studied for fishes but remain relatively unexplored for cephalopods.
  2. Cephalopods are important components of coastal, oceanic and deep‐sea ecosystems, and they play a key role in the transfer of biomass from low trophic positions to higher predators. It is therefore important to resolve cephalopod trophic allometries to accurately represent them within size‐structured ecosystem models.
  3. We assessed the trophic positions of cephalopods in an oceanic pelagic (0–500 m) community (sampled by trawling in a cold‐core eddy in the western Tasman Sea), comprising 22 species from 12 families, using bulk tissue stable isotope analysis and amino acid compound‐specific stable isotope analysis. We assessed whether ontogenetic trophic position shifts were evident at the species‐level and tested for the best predictor of community‐level trophic allometry among body size, taxonomy and functional grouping (informed by fin and mantle morphology).
  4. Individuals in this cephalopod community spanned two trophic positions and fell into three functional groups on an activity level gradient: low, medium and high. The relationship between trophic position and ontogeny varied among species, with the most marked differences evident between species from different functional groups. Activity‐level‐based functional group and individual body size are best explained by cephalopod trophic positions (marginal R2 = 0.43).
  5. Our results suggest that the morphological traits used to infer activity level, such as fin‐to‐mantle length ratio, fin musculature and mantle musculature are strong predictors of cephalopod trophic allometries. Contrary to established theory, not all cephalopods are voracious predators. Low activity level cephalopods have a distinct feeding mode, with low trophic positions and little‐to‐no ontogenetic increases. Given the important role of cephalopods in marine ecosystems, distinct feeding modes could have important consequences for energy pathways and ecosystem structure and function. These findings will facilitate trait‐based and other model estimates of cephalopod abundance in the changing global ocean.


Australian Research Council


Publication title

Journal of Animal Ecology










Institute for Marine and Antarctic Studies


Blackwell Publishing Ltd

Place of publication

9600 Garsington Rd, Oxford, England, Oxon, Ox4 2Dg

Rights statement

© 2020 British Ecological Society. This is the pre-peer reviewed version of the following article: Murphy, KJ, Pecl, GT, Richards, SA, et al. Functional traits explain trophic allometries of cephalopods. J Anim Ecol. 2020; 89: 2692– 2703, which has been published in final form at This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

Repository Status

  • Open

Socio-economic Objectives

Assessment and management of pelagic marine ecosystems