DEEP-SEA ECOLOGY
The dark sea realm (below 200m depth) represents 80% of the oceanic volume on earth, being the largest habitat in the biosphere. The deep sea remains one of the least known and most poorly understood environments on our planet, characterized by a high pressure, low temperature and no light. Bioluminescence is the chemical reaction of living organisms to produce their own light. However, it is still poorly know what are the organisms involved in this emission of light and the role played by this ability in ecological relations. In my recent work, we first quantified that 76% of pelagic marine organisms are bioluminescent (Martini and Haddock, 2017) from the surface to the deep sea. Closer to the seafloor, about 30 - 40% of the benthic organisms were described as capable of bioluminescence (Martini et al., 2019). Because of its diversity of organisms, bioluminescence, used as a proxy, is also one way to access to biological information on the dynamic of populations.
OCEANOGRAPHY and BIOLOGICAL CARBON PUMP
The biological carbon pump is the transformation of carbon dioxide and nutrients into organic carbon, its sinking into the in the deep ocean, and finally, its decomposition at depth. In these ecosystems of complete darkness food sources and organic matter are scarce. The importance of luminescence in the fate of the biological carbon pump via visual detection, attraction or repulsion (for particles and preys) has been hypothesized for a long time but very few works investigated it. Multiple clues put forward this hypothesis. Sinking particles are colonized by microorganisms, and 70 to 98% of particles sampled at the surface have been found to be luminous. Bioluminescent emissions are thought to have two effects: glowing or distant sources attract predators, and rapid nearby flashes deter. While sinking into the deep, the glowing tags on these particles would lead to the detection, attraction, ingestion and decomposition of particles by larger organisms. Grazers would consume luminous matter at a higher rate than invisible particles and consequently will augment micro-organisms dispersion by faecal pellets excretion. There are two indirect impacts of these bioluminescent tags on particles. Bioluminescent sinking material accelerates the degradation of organic matter by attracting grazing organisms. First, due to aggregates fragmentation, fast-sinking particles are transformed into slowly-sinking particles. The second possibility is that the organic matter being ingested will be aggregated, and the excreted pellets of higher density, will be transformed into fast-sinking particles.
INSTRUMENTATION and TECHNOLOGICAL DEVELOPMENT
While bioluminescence has been well studied in the upper ocean, little is known about this phenomenon in the deep sea where bioluminescence is the only light source.
* MARS is a deep-sea observatory (MBARI, USA) about 900 meters deep, near the edge of Monterey Canyon. The photomultiplier deployed at this station in 2017-2018 were originally used by astronomers on the ANTARES neutrino observatory (http://antares.in2p3.fr/) deep in the Mediterranean Sea, detecting occasional bursts of Cherenkov radiation as cosmic neutrinos pass through seawater. In this experiment, they were adapted to measure the light from bioluminescent organisms.
* BathyBot is a benthic crawler robot “BathyBot” (funded by the FEDER project NuMerEnv). It has been delivered in September 2019 and will be deployed at the MEUST-NuMerEnv KM3NeT-EMSO site in March 2020 (postponed due to Covid-19) for several years. The robot is remotely operated and will be connected to a junction box linked to the shore providing real time data. BathyBot has multi-sensors implemented for environmental and biological surveys (temperature, oxygen concentration, CO2, current direction and speed, turbidity…). The robot will be the first deep-sea rover remotely controlled in Europe and the only one in the world equipped with low light cameras dedicated to bioluminescence observation.
* CENSOR is a project funded by the Centre National de la Recherche Scientifique (CNRS-France – PIs: Séverine Martini, /Christian Tamburini, Mediterranean Institute of Oceanography – CNRS, France) “Défi Instrumentation aux limites 2017” and aims at developing tags with a photon detector, high sensibility, associated with environmental and behavioral sensors (pressure, accelerometer, video camera). The goal of CENSOR is to develop these innovative bioluminescence sensors, increase the data acquisition of bioluminescence in the mesopelagic environment and to use this quantitative information to describe the distribution of bioluminescent organisms down to 2000m depth.
Follow these projects here
Most important related publications:
Martini S., Haddock S.H.D. 2017. Quantification of bioluminescence from the surface to the deep sea demonstrates its predominance as an ecological trait. Scientific Reports,7, 45750.
Martini S., Kuhnz L., Mallefet J., Haddock S.H.D., 2019. Distribution and quantification of bioluminescence as an ecological trait in the deep sea benthos, Scientific Reports. 9(1) 1-11.
Martini S., Al Ali B., Garel M., Nerini D., Grossi V., Pacton M., Casalot L., Cuny P., Tamburini C., 2013. Pressure effects on growth and luminescence of a moderatly piezophilic luminous bacterium Photobacterium phosphoreum ANT-2200. PLoS ONE 8 (6), e66580
Most important related publications:
Tanet L., Martini S., Casalot L., Tamburini C., "Bacterial bioluminescence: ecology and impact in the biological carbon pump" under review
Martini S., Michotey V., Casalot L., Bonin P., Guasco S., Garel M., Tamburini C., 2016. Bacteria as part of bioluminescence emission at the deep ANTARES station (North-Western Mediterranean Sea) during a one-year survey. Deep Sea Research Part I: Oceanographic Research Papers, 116, 33-40.
Martini S., Nerini D., Tamburini C. 2014. Relation between deep bioluminescence and oceanographic variables : a statistical analysis using time-frequency decomposition. Progress in Oceanography.
BathyBot. © DT-INSU CNRS
CENSOR tag.
Biological survey in relation to environmental variables in the deep sea using a cabled observatory (ANTARES)
PhD - thesis (2010-2013) - MIO laboratory
Bioluminescence is the emission of light by living organisms. In the bathypelagic waters, where darkness is one of the main characteristic, this phenomenon seems to play a major role for biological interactions and in the carbon cycle. This work aims to determine if bioluminescence can be considered as a proxy of biological activity in the deep sea. Two axes have been studied: (i) in the deep sea, we attempt to describe and explain the bioluminescence variability over time (ii) the part of bacterial bioluminescence is investigated in the light signal in situ. This multidisciplinary study develops both in situ and laboratory approaches.
The ANTARES telescope immersed in the Mediterranean Sea at 2,475 m depth has been used as an oceanographic observatory recording bioluminescence as well as environmental variables at high frequency. This time series analysis, defined as non linear and non stationary, highlighted two periods of high bioluminescence intensity in 2009 and 2010. These events have been explained by convection phenomena in the Gulf of Lion, indirectly impacting the bioluminescence sampled at this station. In the laboratory, bacterial bioluminescence has been described using a piezophilic bacterial model isolated during a high-bioluminescence-intensity event. Hydrostatic pressure linked to the in situ depth (22 MPa) induces a higher bioluminescence activity than under atmospheric pressure (0.1 MPa). Then, the survey of the deep prokaryotic communities has been done at the ANTARES station, over the year 2011. This survey shows the presence of about 0.1 to 1% of bioluminescent bacteria even during a low-bioluminescence-activity period. These cells were mainly actives.
