Rev. biol. mar. oceanogr. 47(3): 527-535



Phytoplankton photosynthetic parameters from the Gulf of California southern region

Gerardo Verdugo-Díaz1, Aída Martínez-López1, Gilberto Gaxiola-Castro2 & José Eduardo Valdez-Holguín3

1Departamento de Plancton y Ecología Marina, Centro Interdisciplinario de Ciencias Marinas, (CICIMAR-I.P.N), Apdo. Postal 592, Av. Instituto Politécnico Nacional S/N Col. Playa Palo de Santa Rita, La Paz, BCS, México, CP 23096
2División de Oceanología, Centro de Investigación Científica y de Educación Superior de Ensenada, Apdo. Postal 2732, Carretera Ensenada-Tijuana No 3918, Zona Playitas, CP 22860, Ensenada BC, México
3Departamento de Investigaciones Científicas y Tecnológicas, Universidad de Sonora, Luis Donaldo Colosio S/N, entre Sahuaripa y Reforma Col. Centro, Hermosillo, Sonora, CP 83000, México

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Phytoplankton physiologic response in the euphotic zone was determined by photosynthesis-irradiance experiments carried out between June 2000 and June 2001 at Bahia de La Paz, Gulf of California, Mexico. A stratified water column was present, from June to September (stratification index > 200 J m-3), with the assimilation number (Pm) represented by an average of 3.7 mg C m-3 h-1, while for the period from November through February, the water column was homogeneous (stratification index = 0 J m-3) and the average was 9.2 mg C m-3 h-1. The maximum photosynthetic efficiency at low irradiances (a) of 0.017 mg C m-3 h-1 (µmol quanta m-2 s-1)-1 was the representative average for the stratified period, while 0.063 mg C m-3 h-1 (µmol quanta m-2 s-1)-1 was the corresponding value for the homogeneous period. The photosynthetic parameters (Pm and a) had an increase during mixing conditions, as result of phytoplankton photoacclimation to average irradiance in the euphotic zone. Diatom abundance (Pseudo-nitzschia delicatissima, Chaetoceros compressus and Coscinodiscus perforatus) were related with higher values of Pm, while lowest values of this parameter are associated with the dinoflagellate group. Average values estimated for the light saturation parameter (Ek) were 334, 173 and 91 µmol quanta m-2 s-1 for the surface, 10 and 1% of the euphotic zone, respectively. In general, nanophytoplankton (2-20 µm) dominated the phytoplanktonic community during the period studied.

Key words:  Photosynthetic parameters, euphotic zone, Gulf of California