| In order to understand the mechanism of settlement and metamorphosis in Styela canopus primarily, experiments observated the embryo stage of S.canopus and studied some chemical and biological factors which affect the settlement and metamorphosis of S.canopus larvae. The main results are as follows:1. Larvae of S.canopus were hatched at 9.5-11.0 hrs post-fertilization at 25?.5癈 andsalinity 27 ppt. Larvae of S.canopus develop competence to initiate settlement and metamorphosis at least 3 hrs after hatching. But if not any induction, S.canopus larvae can retain a stage of plankton at least 3-4 days.2. The seawater containing high concentration potassium ion or containing low concentration magnesium ion can induce the settlement and metamorphosis of S.canopus larvae. In natural seawater, the optimum K+ is +40mM TEA (Tetraethylammonium chloride) , a potassium channel blocker, cannot inhibit the S.canopus larval settlement and metamorphosis induced by K+-elevated seawater. This appears possible that potassium channels mediate the induction of settlement and metamorphosis by K+in S.canopus larvae, but that K+conductance through these channels is insensitive to external TEA. Increasing or decreasing calcium in artificial seawater cannot affect the settlement of S.canopus larvae, but elevating or reducing calcium concentration in artificial seawater will inhibit the metamorphosis of S.canopus larvae. 1 X 10 M L-DOPA can induce the settlement and metamorphosis of S.canopus larvae. But, adrenaline and noradrenaline don't show any significant effects on the settlement and metamorphosis of ascidian larvae. During experiment, acetylcholine shows significant inhibitory effects on the settlement and metamorphosis of ascidian larvae, but itsconcentration cannot lower 1 X 10-7mol/L. Similarly acetylcholine, y-aminobutyric (GABA ) and picrotoxin also can inhibit the settlement and metamorphosis of S.canopus larvae. Furthermore, L-Thyroxine don't show any effects on the settlement and metamorphosis of ascidian larvae.3. In the aspect of microfilms, we isolated four bacteria which can induce the settlement of S.canopus larvae. They are H-9 (Vibro), H-6 (Vibro), H-15(Achromobacter) H-13 (Achromobacter). H-4 (Vibro) can inhibit the settlement of larvae. H-13 (Achromobacter). can facilitate the metamorphosis of ascidian larvae. H-9 (Vibro), H-4 (Vibro) and H-7 (Lactobacillus) show inhibitory effects on the metamorphosis of larvae. Moreover, the films mixing 9 bacteria can facilitate the settlement and metamorphosis of S.canopus larvae. The effects of single-species' films may be the function of the character of the bacterium or the function of their exopolymers. Because we didn't study the effects of bacterial exopolymers on the settlement and metamorphosis of S.canopus larvae, we can't determine which is more important. The induction of the mixed films of 9 bacteria is like that in field.5. Through extracting the tunic of Styela plicata and S.canopus, we found their dissolvable extracts can induce the settlement and metamorphosis of S.canopus larvae. During the experiment, we found an interesting thing: high-density larvae can facilitate the settlement and metamorphosis of S.canopus larvae. So, we extracted the S.canopus larvae and found the crude extract can facilitate the settlement and metamorphosis of S.canopus larvae in some degree but the effect is not significant as that of the tunic of Styela plicata and S.canopus. We also found crude extracts of two sponges (Mycale sp.and Renieera spi) can inhibit the settlement and metamorphosis of ascidian larvae. The two extracts are all liposolube.S.canopus is one of common biofouling organisms in Xiamen harbor. Studying the mechanism of the settlement and metamorphosis in S.canopus is the key of controlling them. We study primarily the antifouling ability of some microfilms and some biological activated substance, which provide some scientific basis for inventing the non-toxic antifouling coating.
|
PDF Full Text Request