ИСТИНА

As with all hexacorallians, the study of the transport system in Acropora is complicated by the presence of a calcareous skeleton. Acropora form radially symmetrical branches. The axial canal of the apical corallite runs along the axis of each branch, with axial canals of numerous radial corallites stemming from it. These canals are, in turn, surrounded by several layers of porous skeletal tissue. Soft coral tissue lines skeletal partitions, thus following their architectonics. The skeleton-facing epidermal cells secrete CaCO3, while gastrodermal cells facing the gastric cavity are covered with cilia that serve to pump the endocavitary fluid (hydroplasm). Pronounced radial structure of Acropora corals seemed to suggest that their transport system should also be radially symmetrical. However, this assumption was not upheld by our research. The hydroplasm flows at constant speed towards the apex (distally) along the upper side of the branch (facing the water surface) and towards the base of the branch (proximally) along its underside (facing the seabed). This can be established by applying vital stains to the chipped tip of a branch. Staining occurs only in the lower half of the chipped surface, which absorbs the surrounding water, whereas the upper (non-stained) half of the stem is where the hydroplasm is ejected. A change in the position of the branch over a few days does not affect the pattern of hydroplasmic flow. The study was supported by RFBR grant No. 11-04-00994-a.