Shallow-water diving in marine ecology

[First paragraph(s)...]
Since there are a number of popular books covering the more spectacular aspect, of submarine life, this paper will be confined to some of the less obvious details. I will try to present the aqualung diver as the counterpart of the terrestrial ecologist with his notebook, camera, and sampling techniques.
Equipment: The aqualung, which is air-breathing apparatus, is the most generally useful type of equipment. It has a safe depth range of about 100 ft. without encountering special physiological difficulties, though greater depths are possible if extra precautions are taken. Recent American models have a full-face mask which leaves the mouth free to use a micro-phone An Australian worker has recently designed an apparatus which allows "wire-less" conversation with the surface or another diver. Oxygeen-breathing equipment has a greater duration and leaves no bubbles, but is not safe below 33 ft.