Three recently recorded Ostreopsis spp. (Dinophyceae) in New Zealand: temporal and regional distribution in the upper North Island from 1995 to 1997

Three species of epiphytic dinoflagellates-Ostreopsis siamensis, O. lenticu laris, and O. ovara have recently been found on both the east and west coas ts of the upper North Island, New Zealand. The morphological differences of all three Ostreopsis spp. have been studied with both light and scanning e lectron microscopes. Detailed studies of the inner face of the thecal wall of Ostreopsis siamensis revealed two types of trichocyst pores: small, simp le pores and large multipore structures. The multipore structures apparentl y have not been previously reported. Surveys conducted during the period fr om November 1995 to April 1997 showed that all three Ostreopsis spp, were f airly widespread in northern New Zealand, and all three species were found to occur south of 35 degrees S latitude. Cell concentrations of Ostreopsis spp. in summer were substantially higher than in early spring. There was al so a clear regional difference in distribution; cell concentrations of the dominant species, O. siamensis, were greatest in Rarawa and Tokerau on the north-east coast. Other less abundant epiphytic species recorded during the same period included Prorocentrum lima, P. compressum, and Coolia monotis. These species were generally more sporadic in distribution than Ostreopsis spp.