Feeding Preferences of Abyssal Macrofauna Inferred from In Situ Pulse Chase Experiments

Rachel M Jeffreys,Ciara Burke,Ursula Witte,Kenneth L Smith,Henry A Ruhl,Alan J Jamieson,Bhavani E Narayanaswamy

doi:10.1371/journal.pone.0080510

Abstract

Climatic fluctuations may significantly alter the taxonomic and biochemical composition of phytoplankton blooms and subsequently phytodetritus, the food source for the majority of deep-sea communities. To examine the response of abyssal benthic communities to different food resources we simulated a food sedimentation event containing diatoms and coccolithophorids at Station M in the NE Pacific. In one set of experiments we measured incorporation of diatomC and coccoN into the macrofauna using isotopically enriched 13C-diatoms and 15N-coccolithophores. In a second experiment we measured incorporation of C and N from dual-labelled (13C and 15N) diatoms. The second experiment was repeated 2 months later to assess the effect of seasonality. The simulated food pulses represented additions of 650 – 800 mg C m−2 and 120 mg N m−2 to the seafloor. In all cases rapid incorporation of tracer was observed within 4 days, with between 20% and 52% of the macrofauna displaying evidence of enrichment. However, incorporation levels of both diatomC and coccoN were low (<0.05% and 0.005% of the added C and N). Incorporation of labelled diatoms was similar during both June and September suggesting that the community was not food limited during either period. We found no evidence for selective ingestion of the different food types in the metazoan fauna suggesting that macrofauna do not have strong preferences for diatom vs. coccolithophore dominated phytodetrital pulses. C∶N ratios from both experiments suggest that the metazoan macrofauna community appear to have higher C demands and/or assimilation efficiencies compared to N. Concomitantly, the foraminifera preferentially selected for diatomN over coccoN, and we suggest that this may be related to foraminiferal requirements for intracellular nitrate. These experiments provide evidence that abyssal faunal feeding strategies are in part driven by an organism's internal stoichiometric budgets and biochemical requirements.

Highlights

IntroductionAbyssal communities are energy limited and rely on the input of particulate organic matter (POM) produced through photosynthesis in the surface waters for food [2,3]
The abyssal seafloor is a vast ecosystem covering,54% of the Earth’s surface [1]
There was no significant difference in the macrofaunal density, biomass dry weight or biomass C normalised to m2 between background cores and the experimental cores from each spreader (Table 2)

Summary

Introduction

Abyssal communities are energy limited and rely on the input of particulate organic matter (POM) produced through photosynthesis in the surface waters for food [2,3]. Energy limitation at abyssal depths (.4000 m) has led to a reduced standing stock of macrofaunal organisms when compared to smaller size classes i.e. bacteria and meiofauna [12]. In spite of this the macrofauna are an important facet of abyssal communities. More recently macrofaunal activity (e.g. grazing and microhabitat destruction) has been linked to lower incorporation of labelled carbon by bacteria [18,19]

Objectives

Methods

Results

Conclusion