Ecology of the Epiphytic Potentially Harmful Dinoflagellate Ostreopsis cf. ovata (Fukuyo) from Coastal Waters off Alexandria Egypt

Despite macroalgae epiphytes play an important role in algal habitats, available information from Alexandria coastal waters is scarce. To evaluate the role of environmental factors on the inventory of the ephyphytic Ostreopsis c.f ovata cells, its abundance on the thalli of 14 different macroalgae collected from two sites at Abou Qir rocky area was done on the basis of sampling carried out for one year. The annual maximum Ostreopsis cf. ovata cell abundance was observed in May (late-spring), reaching the maximum on the green macroalgae Ulva linza in July (mid- summer). Analysis of variance showed significant difference of abundance between seasons and hosts. Water temperature and NO2, NO3 and PO4 seem the major factor affecting on abundance of Ostreopsis c.f ovata. The present study documented the significant importance of Ulva sp. as the suitable host of O. ovata in Alexandria waters, in contrasting with others in the Mediterranean Sea that show O. ovata most often found on Phaeophyta and Rhodophyta.