Abstract: A modular apparatus for cultivating marine animals caged within rearing units submerged in a body of water of the natural environment of the animals includes a row and column structure that floats at the water surface. The apparatus is moored by anchors deployed at the column ends and at position intermediate the column ends. The members of the rows, and optionally the columns, are constructed from substantially rigid tubes, especially plastic, corrugated wall, culvert pipe, filled with a substantially incompressible foam. The row members are releasably attached between adjacent columns in perpendicular orientation to the longitudinal axes of the columns.Each rearing unit is a perforated wall container suspended from a row member by a suspension assembly so as to hang above the water floor. Multiple rearing units can be suspended from each row member. The rearing units contain vertically oriented panels of substrate material, especially sheets of cementitious backer unit.