Abstract
The stability of the ecosystems depends on the dynamics of the prey community, but changes in the composition and abundance of prey species are poorly understood, especially in open ocean ecosystems. We used neon flying squid Ommastrephes bartramii, an active top predator, as a biological sampler to investigate the dynamics of the prey community in the southwestern part of the Western Subarctic Gyre in the northwestern Pacific Ocean. Squid were collected monthly from July to November 2016. There were no significant differences among months in stable isotopes (δ13C and δ15N) in the digestive gland, a fast turnover organ reflecting recent dietary information. Similar findings were obtained from analyses of isotopic niche width and fatty acid profiles. The potential influence of the environment (monthly mean sea surface temperature, SST, and chlorophyll-a, Chl-a) on the prey community was examined with SST and Chl-a both varying significantly among sampling months. We found little evidence for significant effects of SST and Chl-a on the isotopic values, nor on the fatty acid profiles except for 20:4n6 and 24:1n9. These lines of evidence indicate that the prey community in the southwestern part of the gyre remains stable, with little evidence for systematic changes at the community level. This study provides a novel understanding of the dynamics of the prey community and highlights the use of top predators to study the trophic dynamics of an oceanic system where a long-term scientific survey is unavailable.
Highlights
Concern about ecosystem functioning [1,2,3] highlights the need for a better understanding of how the composition and abundance of species in natural communities respond to environmental change
Our work indicates that neon flying squid, O. bartramii, can provide information about the prey community in the southwestern part of the Western Subarctic Gyre in the northwest Pacific Ocean
We demonstrate that stable isotopes and fatty acid composition data from the digestive gland of Ommatrephes bartramii, an opportunistic top predator, varies little from July to November in the southwestern part of the Western Subarctic Gyre of the northwest Pacific Ocean
Summary
Concern about ecosystem functioning [1,2,3] highlights the need for a better understanding of how the composition and abundance of species in natural communities respond to environmental change. Predatory animals are susceptible to reduction or extirpation of available prey due to environmental processes, which undermines the stability of ecosystems and the services they provide [3, 4]. Stability is central to ecosystem functioning, which includes the ecological processes controlling the fluxes of energy, nutrients and organic matter. Top predator reveals the stability of prey community
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