Preventing ascidian fouling in aquaculture: screening selected allelochemicals for anti-metamorphic properties in ascidian larvae

Fouling by ascidians causes major stock losses and disrupts production in marine aquaculture, especially bivalve aquaculture. Currently, no cost effective solution exists despite the testing of many prospective control techniques. This study examined a range of allelochemicals suspected to inhibit metamorphosis in marine larvae. Five allelochemicals were screened in a larval metamorphosis bioassay using Ciona savignyi Herdman to determine their potential as a remedy for ascidian fouling in bivalve aquaculture. Three of the compounds tested inhibited ascidian larval metamorphosis and increased mortality at low concentrations. These were radicicol (99% inhibition of metamorphosis [IC99], 0.8 mu g ml(-1); 99% lethal concentration [LC99], 2.5 mu g ml(-1); 99% lethal time [LT99], 7.0 days), polygodial (IC99, 0.003 mu g ml(-1); LC99, 0.9 mu g ml(-1); LT99, 6.4 days), and ubiquinone-10 (IC99, 3.2 mu g cm(-2); LC99, 14.5 mu g cm(-2); LT99, 5.6 days; expressed as mu g cm(-2) due to insolubility in water and ethanol). While spermidine significantly affected metamorphosis and mortality of C. savignyi, the effect was insufficient to achieve inhibition in 99% of larvae over the 7-day timeframe of the assay. Muscimol did not affect metamorphosis or mortality at the concentrations tested. The present study demonstrates that radicicol, polygodial and ubiquinone-10 have potential for future development in antifoulant formulations targeted towards the inhibition of metamorphosis in ascidian larvae, while spermidine and muscimol appear unsuitable.