Surface temperature within the BMLC is consistently greater than that of adjacent ocean waters and is spatially and temporally variable.
Hydrologic conditions in the BMLC are hypersaline throughout the year as a result of low precipitation, the typical absence of fresh water input, and a high rate of evaporation.
The BMLC region is part of the Sonoran Desert, and the climate characteristically varies from temperate to hot and is very dry (Garcia 1973; MacMahon 1997).
Most of these authors, however, consider the BMLC to representa transition zone between warm-temperate and tropical species (e.g., Hubbs 1960; Briggs 1974; Brusca 1980; Allen and Robertston 1994).
Many tropical species extend north of the BMLC for a considerable distance, inhabiting shallow, protected bays and inlets, whereas warm temperate species are found in nearshore coastal regions and cool temperate species are associated with upwelling areas (Garth 1960; Hubbs 1960).
White (Laguncularia racemosa), red (Rhizophora mangle), and black (Avicennia germinans) mangrove species are present throughout the BMLC (Nienhuis and Guerrero-Caballero 1985; Garate-Lizarraga and Siqueiros-Beltrones 1998; pers.
More than 130 species of macroalgae have been recorded from the BMLC (Sanchez-Rodriguez et al.
The BMLC is a region of high primary productivity throughout the year, with maximum reported microphytoplankton densities of 1,500,000 cells/liter and maximum reported nanoplankton densities of 791,760 cells/liter (Alvarez-Borrego et al.
These inconsistent results are probably a consequence of the extremely high temporal and spatial variability in BMLC hydrological parameters.
At least 87 genera and 277 taxa of phytoplankton have been reported from the BMLC (Garate-Lizarraga and Sisqueiros-Beltrones 1998; Garate-Lizarraga and Verdugo-Diaz 2001).
The BMLC zooplankton assemblage is dominated by copepods, which comprise 50-90% of total zooplankton biomass throughout the year (Palomares-Garcia 1992; Palomares-Garcia and Gomez-Gutierrez 1996).
There is a well-defined seasonal pattern of copepod diversity and species succession in the BMLC that is closely related to changes in hydrology, especially the direction and intensity of the California Current.