Short-term effects on Artemia salina of aponin and Gomphosphaeria aponina in unialgal cultures and in mixed cultures with gymnodinium breve.

Previous investigations showed that the natural marine substance aponin, produced by the blue-gree alga Gomphosphaeria sponina, was cytolytic towards Florida's red tide organism, Gymnodinium breve. As part of a study of the aponin-alga biological interactions, the effects of unialgal (G. aponina) and mixed cultures (G. aponina + G. breve) on the viability of artemia salina were investigated. Two contrasting effects were observed in mixed cultures: survival of A. salina was promoted in low G. aponina populations, while enhanced toxicity of G. breve to A. salina occurred at higher culture populations. Unialgal G. aponina cultures exerted no adverse effects on A. salina. The apparent protective effect is thought to result from the observed change in G. breve morphology (motile to sessile); toxicity was the result of enhanced toxin release by cytolyzed G. breve cells. In dose-response studies, aponin exhibited no adverse effect on A. salina at concentrations (1 unit) that were deleterious to G. breve. However, at higher applied levels (4--6 units), mortality was substantial (greater than 70%) after 48 hr of incubation. Probit analysis yielded an apparent LD50 of 2.3 units, where 1 unit was that amount required to cytolyze 50% of the G. breve cells (2000 cells/ml) after 20 hr of incubation.