Plant detritus is selectively consumed by estuarine copepods and can augment their survival

Jennifer Harfmann,Tomofumi Kurobe,Swee Teh,Brian Bergamaschi,Peter Hernes

doi:10.1038/s41598-019-45503-6

Jennifer Harfmann, Tomofumi Kurobe + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-45503-6

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Abstract

Particulate material comprising the detrital remains of terrestrial plants and macrophytes is a substantial source of organic matter to estuaries and therefore has the potential to support the energy demands of the pelagic aquatic food web. Despite the prevalence of macrophytic or terrestrial particulate organic carbon (tPOC), phytoplankton are nutritionally superior and are thought to be the primary food resource for zooplankton. However, estuarine phytoplankton primary productivity abundances can wax and wane, and often production cannot meet heterotrophic energy needs. In this study, we examined how tPOC (detritus of macrophytes and grasses) may affect survival of a calanoid copepod (Eurytemora affinis) common in the San Francisco Estuary (SFE), an estuary with relatively low phytoplankton primary productivity. Using chemical biomarkers and a targeted DNA metagenomic methodology, we show that E. affinis consumed tPOC (dominated by Schoenoplectus sp., or tule) even when phytoplankton were abundant and tPOC was scarce. Furthermore, we found that a mixed diet of phytoplankton and terrestrial material (1:3 carbon ratio) enhanced the survival of E. affinis over a diet of phytoplankton alone. These data show that tPOC can be a vital supplementary food source for zooplankton, perhaps extending survival during low phytoplankton periods, and may help explain elevated zooplankton abundances in tidal wetlands and other detrital-dominated regions.

Highlights

In most estuarine systems worldwide, phytoplankton primary production is perceived as the major food source for zooplankton, effectively fueling higher trophic level energy needs[1,2,3]
Lignin in copepods themselves increased during the experiment from 0.038 ng copepod−1 to 1.9 ng copepod−1, indicating uptake of terrestrial particulate organic carbon (tPOC)
Macrophyte- and terrestrial-derived detritus is a major contributor to the organic matter (OM) pool in estuaries, and plays a vital role in the lower aquatic food web mediated by active uptake by zooplankton, even when algae is accessible

Summary

Introduction

In most estuarine systems worldwide, phytoplankton primary production is perceived as the major food source for zooplankton, effectively fueling higher trophic level energy needs[1,2,3]. The toolkit for detecting zooplankton consumption of tPOC is diverse and well-developed and outdated It includes a host of chemical biomarkers such as gut carbohydrate, lipid, and protein composition[14] or stable isotopes[21] to track plant material. Lignin is another chemical tool for this purpose, as it is unique to vascular plants and can provide source information (e.g. gymnosperm or angiosperm, woody or non-woody tissues). While such techniques have been suitable for detecting tPOC to-date, recent advancements in the field of metagenomics provide an opportunity to perform diet analysis with higher specificity and sensitivity. Adding DNA metagenomic techniques to the tPOC toolkit can provide higher sensitivity zooplankton diet analyses than can be obtained by chemical analyses alone

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