Only a very limited number of animals feed on bryozoans, indicating that they possess an effective chemical defense system (Figure 6). This includes a variety of quinoline and pyrrole compounds (tambjamine C 31) and also purine derivatives (phidolopin 32), that are responsible for the powerful antifungal and antialgal activity of bryozoan extracts.
In addition, symbiotic bacteria that produce so-called bryostatins help to deter feeding animals. For instance, larvae of the marine bryozoan Bugula neritina are protected against predators by bryostatins such as bryostatin 20 33. Bryostatins exhibit ionophoric properties and efficiently inhibit cell growth.
The diterpenoids pukalide 28 and the related lophotoxin 29 are examples of furanocembranolides that are widespread among octocorals such as Leptogorgia virgulata. Furanocembranolides deter fishes by causing vomiting. In addition, they exhibit antimicrobial properties preventing biofouling. Lophotoxin 29 acts as neurotoxin-blocking acetylcholine receptors.
Antarctic octocorals are either protected by calcareous spicules apparently not relying on chemical defense compounds or are exclusively protected by chemical defense lacking mechanical armor. For example, Ainigmaptilon ant-arcticus produces the sesquiterpene ainigmaptilone A 27 which deters sea stars from feeding as well as inhibits the growth of bacteria and diatoms.
A different chemical defense strategy is observed by the octocoral Plexaura homomalla that produces an abnormally large amount of prostaglandin A2 30 (Figure 5). Usually prostaglandins serve in low amounts as mediators
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