Bioluminescence bathyphotometer

A few words should be said about the existence of PMT-based instruments that are developed to solve specific problems in chemi- or bioluminescence. For instance, marine laboratories have developed and improved over time a range of so-called bathyphotometers for hydrobiophysical measurements (microalgae, zooplankton in the surface waters of the sea) [7]. 

Our primary measurement technique was to pull seawater through a 25-mL volume chamber with a pump. The organisms emit light when stimulated by the tur-bulently flowing seawater. This light is viewed by a photomultiplier tube (PMT). Two in situ measurement systems were used on surface ships. The on-board bioluminescence detector pulls seawater from below the ship s hull for continuous realtime measurements of surface bioluminescence a bathyphotometer was used on station to depths of 100 m. An additional laboratory system was used to measure bioluminescence flashes from individual plankters isolated from plankton tows and pumped collections. 

Figure 2, Submersible bathyphotometer used for vertical profiling of bioluminescence. (Reproduced with permission from Ref. 20.)...

Other Parameters Measured Simultaneously with Bioluminescence. Measurements of several other parameters were obtained from the seawater after it had traversed the bioluminescence detector. When working on station with the bathy-photometer, which was equipped with a pressure transducer, temperature and beam transmittance were measured at depth while seawater was pumped by the submersible pump at depth to shipboard with 110 m of 2.54-cm ID hose. Sea surface temperature was obtained continuously from a probe at the intake near the sea chest. The seawater, obtained from either the sea chest or the bathyphotometer, was pumped through a Turner Designs fluorometer to measure chlorophyll fluorescence, and past a pH probe (31) and a conductivity cell when available. Samples of seawater were frozen for subsequent nutrient analysis (NO , NH4OH, P04 , and NO2). Plankton filtrates from 20 to 100 L (depending on plankton abundance) of seawater were collected from a 100-L effluent tank fitted with plankton net collection cups of 20-fxm mesh porosity. The filtrate was split, filtered onto Whatman GF/C 4.25-cm filter discs, and frozen for subsequent carbon and nitrogen determinations. The other half of the sample was preserved in 5% buffered formaldehyde solution for taxonomic analysis. 

Data obtained from the pumped (closed) deep bathyphotometer and the open bathyphotometer mounted on the Alvin submersible show that skylight penetrates to 200 m on a moonless night and to 500-700 m in daylight conditions. Therefore, bioluminescent measurements at depths to about 200 m at night and 500 m in the daylight can reasonably be done only with a closed system. (These depths can vary considerably with the turbidity of the seawater.)... 

The measurement of bioluminescence potential with a pump-through bathyphotometer presents several problems (11). The first problem is... 

Third, in both pump-through and towed bathyphotometers, the distance between the bioluminescing organism and the photomultipier varies to some extent. This variation makes the true intensity of the bioluminescence difficult to determine. 

Fourth, no ideal way to calibrate the photometers has been found. Seliger et al. (25) calibrated their pump-through bathyphotometer with dilute solutions of luminous marine bacteria. They assumed that the average spatial distribution of stimulated bioluminescence inside the impeller housing of their bathyphotometer was the same as that of the continuously luminous bacteria. They noted... 

Seventh, if the rare but comparatively bright organisms are important, large volumes should be sampled to obtain statistically significant estimates of bioluminescent potential. Most current bathyphotometers do not pump large volumes of water. Thase factors suggest that more bioluminescence potential is in the sea than is currently measured with pump-through bathyphotometers. 

Note To determine the photon yield of their bioluminescence, batches of 10 P. noctiluca cells were stimulated mechanically to exhaustion in a laboratory photometer. The batches of P. noctiluca cells were pumped through the bathyphotometer, and the values given assume that the cells were stimulated to exhaustion in the photometer. The mean for all values, stations, and datas is given with its 95% confidence limit. 

Iselin cruise. On all cruises, cells for calibration were collected in nearsurface waters so that cells would have high levels of bioluminescence (34). The dinoflagellates were collected late in the afternoon by net tows, isolated by pipette into filtered seawater, collected from the same depth, and held in 10-mL pipettes with enlarged tips. After several hours in the dark, and at the time of natural darkness, they were gently introduced a few at a time into the sample chamber intake of the bathyphotometer with the pump running. Batches of the same cells were assayed in the laboratory photometer after being isolated into 3 mL of filtered seawater, held several hours in darkness, and stimulated mechanically to exhaustion. 

A similar N-S trend in the estimated value of the total stimulated bioluminescence per square meter was recorded by the bathyphotometer... 

Figure 6. Bathyphotometer profiles of the concentration of bioluminescent organisms and the hioluminescence they produced at Stations 1 and 3. Organisms producing less light than P. noctiluca (—A—) produce most of the total flashes (O) at any depffi, hut the organisms producing dim flashes (a) do not contribute much to the total bioluminescence ( ). The profile of the chlorophyll peak is shown for comparison (—A—).

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