Effects of El Nino y La Nina over marine microphytoplankton behavior and physical-chemical variables during the 2008-2010 period in the Gulf of Nicoya, Costa Rica

The 2009 El Nino phenomenon was responsible for a rainy season of low intensity as well as higher annual average water temperatures, total solids, salinity and dissolved oxygen. Average densities of diatoms and dinoflagellates decreased during 2009, while average densities of cyanobacteria and silicoflagellates were similar in the 2008 and 2010 La Nina phenomena. In the Gulf of Nicoya, this phenomenon caused significant changes in abundance and/or presence-absence of different species comprising the microphytoplankton community based on: (1) Decreased density of dinoflagellates: G. catenatum, A. fraterculus, A. monilatum, D. caudata, N. scintillans, C. furca, Type 1 C. fusus, P. conicum, G. verior, C. tripos, L. polyedrum, C. lineatum, G. polygramma, and diatom S. costatum; (2) Increased density of dinoflagellates: C. macroceros, P. kofoidii, P. micans, C. furca, and cianobacteria T. erythraeum and M. elegans; (3) Exclusive presence of dinoflagellates: G. instriatum, Ceratocorys sp., P. bipes, C. massiliense, G. instriatum, P. balticum, and diatom Aulacodiscus sp.; and (4) Absence of C. lineatum, C. trichoceros, O. steinii, Alexamdrium sp., and C. macroceros. The exclusive presence of some microalgae and the microphytoplankton community composition are considered potential marine biological indicators of El Nino and La Nina in the Gulf of Nicoya. Further studies of the hydrographic conditions and the phytoplankton composition are recommended, with special focus on those species considered as biological indicators and main nutrients.