péridinine effectuées sur une radiale proche de Belle-Île indiquent une
bonne corrélation entre les distributions verticales de la bioluminescence et de ce pigment, marqueur de dinoflagellés.
La zone sud du golfe de Gascogne est plus riche en bioluminescence
que la zone nord, avec d’importantes variations nycthémérales. Ceci
suggère la présence d’organismes photo-inhibés le jour, comme les dinoflagellés hétérotrophes.
Introduction
Bioluminescence, a photon emission provoked by a chemical reaction,
is vety common throughout the marine environment (Herring, 1978). In
epipelagic waters, a wide variety of planktonic organisms are able to emit
light. Dinoflagellates are the only phytoplankton species to possess such a
function. Among zooplankton organisms, copepods have a major role
together with other groups such as tunicates and radiolarians. Bioluminescence is mechanically stimulated by water turbulences; short flashes of
various intensities are emitted in the blue green spectrum, betwœn 450
and 520 nm, wave lenghts that are best transmitted in seawater.
In situ measurements of bioluminescence, started in the sixties, have allowed
analy ses of bioluminescence and other physical and biological components
of the water (Batchelder et ai, 1990; Sullivan & Swift, 1994; Piontkovski et
ai, 1997). Although some studies have locally demonstrated relationships
between bioluminescence and other parameters, bioluminescence determinism remains rather unknown. In this context, measuring bioluminescence emissions in coastal waters, characterized by strong physical and
biological gradients, is a good approach to study bioluminescence distribution in space and time, in relation with other environmental parameters.
Material and methods
Bioluminescence is measured in situ by a bathyphotometer designed
and built at the Naval Academy (Geistdoerfer & Vincendeau-Croci,
1999). It is composed of a dark chamber separated by a glass window from a photomultiplier tube, which can detect light intensities
from 10
4 to 10 -9 µW.cm -2 .
A pump with a constant flow rate (0.4 1/s) ensures the incoming flow’ of
seawater in the dark chamber. A grid at the entrance of the chamber restrict the admittance of organisms smaller than two millimetres and induce a turbulent flow which lead to mechanical and synchrone stimulation of the organisms entering the dark chamber. The bathyphotometer is
coupled to a CTD probe, providing vertical profiles of temperature, salinity, fluorescence and bioluminescence. Bioluminescence is obtained in
volt and converted in µW.m -2 .
The Modycot cruise in April 1999 allowed the sampling of 35 stations
from the north to the south of the bay, between the coast and about 80
miles offshore (fig. 1).
141
bonne corrélation entre les distributions verticales de la bioluminescence et de ce pigment, marqueur de dinoflagellés.
La zone sud du golfe de Gascogne est plus riche en bioluminescence
que la zone nord, avec d’importantes variations nycthémérales. Ceci
suggère la présence d’organismes photo-inhibés le jour, comme les dinoflagellés hétérotrophes.
Introduction
Bioluminescence, a photon emission provoked by a chemical reaction,
is vety common throughout the marine environment (Herring, 1978). In
epipelagic waters, a wide variety of planktonic organisms are able to emit
light. Dinoflagellates are the only phytoplankton species to possess such a
function. Among zooplankton organisms, copepods have a major role
together with other groups such as tunicates and radiolarians. Bioluminescence is mechanically stimulated by water turbulences; short flashes of
various intensities are emitted in the blue green spectrum, betwœn 450
and 520 nm, wave lenghts that are best transmitted in seawater.
In situ measurements of bioluminescence, started in the sixties, have allowed
analy ses of bioluminescence and other physical and biological components
of the water (Batchelder et ai, 1990; Sullivan & Swift, 1994; Piontkovski et
ai, 1997). Although some studies have locally demonstrated relationships
between bioluminescence and other parameters, bioluminescence determinism remains rather unknown. In this context, measuring bioluminescence emissions in coastal waters, characterized by strong physical and
biological gradients, is a good approach to study bioluminescence distribution in space and time, in relation with other environmental parameters.
Material and methods
Bioluminescence is measured in situ by a bathyphotometer designed
and built at the Naval Academy (Geistdoerfer & Vincendeau-Croci,
1999). It is composed of a dark chamber separated by a glass window from a photomultiplier tube, which can detect light intensities
from 10
4 to 10 -9 µW.cm -2 .
A pump with a constant flow rate (0.4 1/s) ensures the incoming flow’ of
seawater in the dark chamber. A grid at the entrance of the chamber restrict the admittance of organisms smaller than two millimetres and induce a turbulent flow which lead to mechanical and synchrone stimulation of the organisms entering the dark chamber. The bathyphotometer is
coupled to a CTD probe, providing vertical profiles of temperature, salinity, fluorescence and bioluminescence. Bioluminescence is obtained in
volt and converted in µW.m -2 .
The Modycot cruise in April 1999 allowed the sampling of 35 stations
from the north to the south of the bay, between the coast and about 80
miles offshore (fig. 1).
141