Simulation of oscillating water movement in the laboratory for cultivation of shallow water sedentary organisms
- A. Svoboda1
© Biologischen Anstalt Helgoland 1970
1. Experiments in the natural habitat and under laboratory conditions have been conducted to analyse the factors responsible for the orientation of the fans of the colonial hydroidAglaophenia pluma. These experiments indicate that the prevailing direction of water movement significantly affects fan positioning.
2. Field experiments reveal thatAglaophenia pluma growing onCystoseira sp. orientates the dorsal side of its fans towards the base of this algae. After detaching and turning of substrate piecesA. pluma colonies lose their fans and re-orientate the regenerating fans prevailing to water current.
3. Laboratory experiments in running water onAglaophenia pluma var.teissieri show, as in the field, dorsal fan orientation perpendicular to the water current; however, rate of up growth is much slower than in the field.
4. Simulation of oscillating water movement, characteristic of the natural habitats of the species investigated, was possible via a special, newly designed pump system. The new system is described.
5. TheAglaophenia pluma var.teissieri fans were fixed with their rocky substrate on a turntable and exposed to the oscillating water movement in a current canal. After the fans have been cast off, the oscillating water movement induces a much higher rate of growth than the running water only. The orientation of the fans was strictly perpendicular to the current.
6. On the margins of the substrate exposed to the current, the fans were orientated with their dorsal surface toward the margin; in the centre of the rock fragments the fans are also strictly orientated perpendicular to the current with their dorsal sides showing in either direction.
7. A close study of the flow of current at the edges of the substrate showed that the whirls may diminish or even reverse the current coming from the substrate side. The orientation of the fans with their dorsal side outwards shows that they orientate themselves to the strongest current.
8. The orientation of a developing fan is basically determined by the first polyp. However, by slow, step by step turning of the upgrowing fan, a helically twisted fan could be obtained, indicating that secondary directioning is possible during growth. Twisted fans can also be found occasionally in the field; presumably they grew up under alternating current directions.Aglaophenia pluma var.teissieri exposed to permanent rotation give rise to regenerating fans which are orientated in the same way as the previous set of fans (preceding cast off).