Inertial bioluminescence rhythms at the Capo Passero (KM3NeT-Italia) site, Central Mediterranean Sea

J Aguzzi,A Schirone,T Ciuffardi,E Fanelli,J Craig

doi:10.1038/srep44938

Abstract

In the deep sea, the sense of time is dependent on geophysical fluctuations, such as internal tides and atmospheric-related inertial currents, rather than day-night rhythms. Deep-sea neutrino telescopes instrumented with light detecting Photo-Multiplier Tubes (PMT) can be used to describe the synchronization of bioluminescent activity of abyssopelagic organisms with hydrodynamic cycles. PMT readings at 8 different depths (from 3069 to 3349 m) of the NEMO Phase 2 prototype, deployed offshore Capo Passero (Sicily) at the KM3NeT-Italia site, were used to characterize rhythmic bioluminescence patterns in June 2013, in response to water mass movements. We found a significant (p < 0.05) 20.5 h periodicity in the bioluminescence signal, corresponding to inertial fluctuations. Waveform and Fourier analyses of PMT data and tower orientation were carried out to identify phases (i.e. the timing of peaks) by subdividing time series on the length of detected inertial periodicity. A phase overlap between rhythms and cycles suggests a mechanical stimulation of bioluminescence, as organisms carried by currents collide with the telescope infrastructure, resulting in the emission of light. A bathymetric shift in PMT phases indicated that organisms travelled in discontinuous deep-sea undular vortices consisting of chains of inertially pulsating mesoscale cyclones/anticyclones, which to date remain poorly known.

Highlights

Light as an evolutionary force shapes marine ecosystem functioning, regulating the biological clock of predator and prey species, which react by performing rhythmic displacements into photic and disphotic realms[1]
In the Mediterranean Sea, where tidal forces are very small[12], inertial currents dominate over internal tidal current periodicities, providing a natural laboratory to identify the importance of these motions on marine communities
In the present study, conducted in the deep central Mediterranean basin, inertial biological rhythms in bioluminescence appear as a response to inertial hydrodynamic cycles

Summary

Introduction

Light as an evolutionary force shapes marine ecosystem functioning, regulating the biological clock of predator and prey species, which react by performing rhythmic displacements into photic and disphotic realms[1]. Neutrino telescopes deployed in the deep sea, instrumented with light detecting photomultipliers (PMTs) as well as oceanographic and acoustic sensors, are providing data beyond their primary physical purpose and are being used to describe biological phenomena in poorly monitored deep-sea areas. Datasets generated from this technology are enabling new discoveries about life in the abyssopelagic environment[20,21,22,23] and PMT data are providing evidence of deep blooms in bioluminescence coupled to seasonal changes in passive carbon sinking, linking atmospheric-climatic and demersal components[24,25,26]

Methods

Results

Conclusion