Deep Ocean Benthic Observatory (DOBO)
The Deep Ocean Benthic Observatory (DOBO) is a titanium lander capable of long term (10 month) deployments. The DOBO has undergone three consecutive six-month deployments at a depth of 2500m in the Goban Spur region of the Porcupine Seabight, carrying small cetacean carcasses as bait.
It has also undergone shorter deployments to abyssal depths on the Mid Atlantic Ridge and Porcupine Abyssal Plain, fitted with a multiple bait release system.
The DOBO is equipped with an acoustic Doppler current profiler (ADCP) (a), 35 mm stills camera in time-lapse mode (capacity 1400 frames) (b), battery (c), controller (d), flash system (e), FSI current meter (f) and bait system (not shown).
The upward looking ADCP records current velocity and direction in 3m depth cells above the lander (g). The camera photographs the bait system arranged at the base of the lander (h).
Porpoise Food Falls
The DOBO has been used to carry out observations of consumption processes of 3 large food falls (porpoise and dolphin carcasses) placed at slope depth (2500 - 2700m) in the Porcupine Seabight (PSB), Northeast Atlantic. Deep water currents were recorded and the data analysed for cyclic periodicity using Maximum Entropy Spectral Analysis. The fauna present at the baited lander where photographed at high frequency for periods of up to 6 months.
To date high frequency observations of experimental food falls using baited camera systems have been limited in duration to 1 – 2 weeks. Longer term studies have used repeat visits by remotely operated vehicles and manned submersibles. The DOBO experiments are the first large food falls to be monitored continuously over a six-month period, and the first observations of a large food fall at bathyal depth in the north-east Atlantic.
Below is a sequence of time lapse images illustrating the rapid consumption of a porpoise carcass (Phocena phocena) at 2700m, PSB. These images were taken at 3 hourly intervals over a period of 6 months. The abyssal grenadier Coryphaenoides armatus and the cusk eel Spectrunculus grandis dominate the scavenging fauna in the initial stages and the bulk of the flesh is removed by day 15. The blue hake Antimora rostrata also appears infrequently. After removal of the flesh the main visitor to the carcass is the squat lobster Munidopsis crassa, and a benthoctopus makes several fleeting appearances.
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For a larger version of the video please contact Kirsty Kemp
Periodic Bait Release
The lander has since been refitted with a periodic bait release system better suited to the analysis of faunal behaviour in the context of constantly changing ocean currents. These experiments were designed to investigate the species and size composition of fish attracted to the bait over time, and to identify possible biological responses to physical time signals. The lander has been deployed in this mode to abyssal depths on the Mid Atlantic Ridge and Porcupine Abyssal Plain.
Initially a solution of amino acids was formulated to mimic a fish bait and pumped into a sponge to create an odour plume in the water column. This design side-stepped the complicating influence of a deteriorating large bait when investigating changes in the frequency, behaviour, size and number of fish visitors to the bait over the winter and spring months. This system has recently been replaced with a series of cylinders containing single mackerel carcasses in a sterile salt solution. Mackerel are exposed at two week intervals and the response of the scavenging fauna photographed at regular intervals.
Kirsty Kemp, PhD Student
Telephone: +44 (0)1224 274425