Recurrent blooms of Heterosigma akashiwo (Raphidophyceae) in the Piraquê Channel, Rodrigo de Freitas Lagoon, southeast Brazil

Florações recorrentes de Heterosigma akashiwo (Raphydophyceae) no Canal do Piraquê, Lagoa Rodrigo de Freitas, sudeste do Brasil

Six blooms of Heterosigma akashiwo(Raphidophyceae) were observed from March 2007 through March 2008 in the Rodrigo de Freitas Lagoon, a semi-confined eutrophic system located in Rio de Janeiro state, southeast Brazil. Vegetative cells of H. akashiwo analysed by optical and electron microscopy showed morphology as described in the literature. The blooms (2.8 × 10⁴ to 4 × 10⁸ cell.L^–1) were restricted to the middle section of the Piraquê Channel, which is situated in the northeastern part of the lagoon and receives freshwater inflow. The salinity of subsurface water and the channel depth showed significant negative correlations with H. akashiwo abundances, and appeared to restrict the blooms to this compartment of the lagoon. No fish mortality was associated with the H. akashiwo blooms, nor were brevetoxins detected in a cell extract obtained from the bloom observed on 19 March 2007.

morphology; taxonomy; blooms; urban coastal lagoon; Rio de Janeiro