early morning following very low levels (4.6 mg./L) to which

it falls at night. The nighttime depletion of dissolved

oxygen is extremely rapid, due most likely to the respiratory

demands of the bottom fauna. It should also be remembered

that the water is very shallow here (average O.Sm.) and so

the volume overlying a given area of bottom and the total

amounted oxygen it carried is not great. The result is that

the small oxygen reserve produced during daylight is rapidly

used up at night. The dominant benthic organism here is

dense Thalassia, so that the aereal potential for oxygen

production is great and once production commences the con-

centration raises quickly to high levels (7.8 to 8.0 mg./L).

However, because of the shallow water column and the generally

higher temperatures and salinity, there is little storage

capacity for oxygen and on both occasions levels fell rapidly

after about 3 p.m. Recovery from nocturnal low begins only

after an early morning lag, but is relatively rapid.


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