Short‐Term Effects on Artemia salina of Aponin and Gomphosphaeria aponina in Unialgal Cultures and in Mixed Cultures with Gymnodinium breve

Abstract

Previous investigations showed that the natural marine substance aponin, produced by the blue‐green algaGomphosphaeria aponina, was cytolytic toward 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 ofArtemia salinawere investigated. Two contrasting effects were observed in mixed cultures: survival ofA. salinawas promoted in lowG. aponinapopulations, while enhanced toxicity ofG. brevetoA. salinaoccurred at higher culture populations. UnialgalG. aponinacultures exerted no adverse effects onA. salina. The apparent protective effect is thought to result from the observed change inG. brevemorphology (motile to sessile); toxicity was the result of enhanced toxin release by cytolyzedG. brevecells. In dose‐response studies, aponin exhibited no adverse effect onA. salinaat concentrations (1 unit) that were deleterious toG. breve. However, at higher applied levels (4‐6 units), mortality was substantial (> 70%) after 48hr of incubation. Probit analysis yielded an apparent LD50of 2.3 units, where 1 unit was that amount required to cytolyze 50% of theG. brevecells (2000 cells/ml) after 20hr of incubation.