Nutrients, phytoplankton and harmful algal blooms in shrimp ponds: a review with special reference to the situation in the Gulf of California

The present work is a first attempt to document the latest reports on the occurrence of algal blooms in shrimp farm ponds worldwide. Particular emphasis is placed on discussing the relation of algal blooms with nutrients, with special reference to the northwest of Mexico. Typically, shrimp pond waters are enriched with organic matter and nutrients whose concentrations depend mostly on the management (i.e. higher stocking densities, water use, food and fertilizers). Generally, more intensive culture systems produce higher loads of nutrients in their discharge (e.g. N and P). Nitrogen and P concentrations vary in pond waters; N/P ratio ranges from 1.1 to 67 with values being more frequently between 1.1 and 6.8. Such variations are closely related with the cycling and supply of nutrients in the ponds. In shrimp farms located in NW Mexico, phytoplankton abundance varies widely, having a higher abundance in advanced stages of the culture cycle. In the most common pond types (intensive and semi-intensive), Synechocystis diplococcus (cyanobacteria) was the dominant species (>88.9%), followed by Peridinium trochoideum (Scrippsiella trochoidea) and eventually Prorocentrum minimum and Gymnodinium spp. (dinoflagellates). The numerous occurrences of large blooms of dinoflagellates and other functional groups such as cyanobacteria, diatoms, chlorophytes and flagellates mean economic losses for farm industry on account of shrimp mortality or growth diminution due to poisoning, anoxic or mucus production effects, in which shrimp were mortality provoked in different regions: in China, the dinoflagellates Alexandrium tamarense (Gonyaulax tamarensis) and Gymnodinium; in Malaysia, the raphidophyte Hornellia (Chattonella) and the dinoflagellate Pyrodinium bahamense var. compressum; in Vietnam, the diatom Nitzchia navis-varingica; in Ecuador, the dinoflagellate Gyrodinium instriatum; and in NW Mexico the cyanobacteria S. diplococcus, Schizothrix calcicola, and the dinoflagellates P. minimum, and lastly Gymnodinium catenatum from supply waters.