Hydrobiology of a salt pan from the Peninsula of Baja California, Mexico

The study site, a salt pan in the northwest of Baja California, Mexico,has a surface area of 33.2 ha and water capacity of 216,072m³. It is intermittently isolated from the adjacent ocean by asand bar, so that flooding via the coastal plain is a low frequency eventassociated with extreme storm conditions. Temporal changes in water volumewere represented by a particular expression of the mass conservationequation having as variables the volumetric capacity of the system, waterinputs by pluvial precipitation, runoff and infiltration, and water loss byevaporation; the numerical model explained over 80 per cent of observedfluctuations. The hydrobiological study covered a three-year period and twohydrological cycles; the first one was of mixed marine and pluvial origin,and the second, continental. Throughout the first cycle, phosphate andnitrate concentrations were up to one order of magnitude higher as weretotal particulate protein, chlorophyll a and phytoplankton abundance. Ingeneral, nannoplankton abundance was up to three orders of magnitude greaterthan the microphlanktonic fraction. In the former, 29 different cell formswere observed; two halophytic bacteria constituted 60–80 per cent ofthat fraction. In the microplankton, there were 27 different forms; mostwere benthic diatoms. The zooplanktonic assemblages of the first cycle hadmarine and continental elements; at 141 per mille, Artemia sp. firstappeared; at 240 per mille, it was the only faunistic element in the system.During the second cycle, Artemia was always present, co-existing with othercontinental species up to a salinity of 99 per mille. The morphology andmorphometry of Artemia were similar to those of Artemia franciscana.