Origin of Carbon and Essential Fatty Acids in Higher Trophic Level Fish in Headwater Stream Food Webs.

Megumu Fujibayashi,Takashi Sakamaki,Reina Suganuma,Naoyuki Miyata,Yoshie Miura,So Kazama,Shinji Takahashi

doi:10.3390/biom9090487

Megumu Fujibayashi, Takashi Sakamaki + Show 5 more

Open Access

https://doi.org/10.3390/biom9090487

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Abstract

Dietary carbon sources in headwater stream food webs are divided into allochthonous and autochthonous organic matters. We hypothesized that: 1) the dietary allochthonous contribution for fish in headwater stream food webs positively relate with canopy cover; and 2) essential fatty acids originate from autochthonous organic matter regardless of canopy covers, because essential fatty acids, such as 20:5ω3 and 22:6ω3, are normally absent in allochthonous organic matters. We investigated predatory fish Salvelinus leucomaenis stomach contents in four headwater stream systems, which are located in subarctic region in northern Japan. In addition, stable carbon and nitrogen isotope ratios, fatty acid profile, and stable carbon isotope ratios of essential fatty acids were analyzed. Bulk stable carbon analysis showed the major contribution of autochthonous sources to assimilated carbon in S. leucomaenis. Surface baits in the stomach had intermediate stable carbon isotope ratios between autochthonous and allochthonous organic matter, indicating aquatic carbon was partly assimilated by surface baits. Stable carbon isotope ratios of essential fatty acids showed a positive relationship between autochthonous sources and S. leucomaenis across four study sites. This study demonstrated that the main supplier of dietary carbon and essential fatty acids was autochthonous organic matter even in headwater stream ecosystems under high canopy cover.

Highlights

IntroductionAquatic animals are supported by two basal organic carbon sources, autochthonous (aquatic primary producers) and allochthonous sources (fallen leaf litter and insects from surrounding terrestrial ecosystems) [1]
Aquatic animals are supported by two basal organic carbon sources, autochthonous and allochthonous sources [1]
This implies that autochthonous organic carbon may be the main essential fatty acid source for consumers, other carbon components are derived from allochthonous inputs in headwater streams

Summary

Introduction

Aquatic animals are supported by two basal organic carbon sources, autochthonous (aquatic primary producers) and allochthonous sources (fallen leaf litter and insects from surrounding terrestrial ecosystems) [1]. Contributions of these basal organic carbon sources to aquatic food webs depend on the proportion of microalgal and phytoplankton productivity, and the number of terrestrial subsidies [2]. 20:5ω3 is present at high levels in diatoms [19], which are sometimes the dominant algae attached to the surface of substrates in headstream ecosystems [20] This implies that autochthonous organic carbon (i.e., attached algae) may be the main essential fatty acid source for consumers, other carbon components are derived from allochthonous inputs in headwater streams

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Discussion

Conclusion