Physiological ecology and possible control strategy of a toxic marine dinoflagellate, Amphidinium sp., from the benthos of a mariculture pond

Some species of Amphidinium are known to have produced toxins. When a species of Amphidinium bloomed in a mariculture sediment pond fed by effluent water from semi-intensive fishponds, it was isolated and its physiological ecology was investigated to find its tolerances and optima for population growth (temperature, salinity, pH, nitrate/ammonia, phosphorus, and vitamin B₁₂). In a preliminary test, an ether-soluble extract was toxic to mice. The Amphidinium sp. was eurytrophic, with a great facility for luxury consumption and the ability to store nitrate and phosphate for several generations. It needs vitamin B₁₂ and formed cysts when exposed to high levels of ammonium. Its maximum growth rate was 1 division/day, and it grew well between 20 and 33°C. It was tolerant of a wide range of pH (6.5-9.5; optima 6.5-8.6) and salinities (20-50 ‰; optima 22-32 ‰). The Amphidinium was outcompeted by diatoms if the Si/N ratio was kept at 1:1 or greater, suggesting that this factor could control its growth in sedimentation ponds used in integrated systems to grow mollusks. Eurytrophic organisms are difficult to control by environmental methods, thus, vigilance is required to ensure that bivalves fed from sediment ponds are not contaminated with toxins from this or any other dinoflagellate.