A modular unit intended for use as an artificial reef, marine habitat and/or
sea
wall which can be placed in stacked structures along the floor of an ocean, bay,
or other body of water comprises a top wall, bottom wall, opposed side walls and
opposed end walls which are interconnected to form a hollow interior. Each of the
walls is formed with one or more openings whose position and size is designed to
allow access of marine life into the interior of the units, permit the passage
of sunlight therein, direct the flow of sea water into and through the units in
a way which increases stability of the units when placed on the ocean floor, and
permit alignment of the holes of one unit with those of another when stacked together.
