Upwelling and Lagoonal Ecosystems of the Dry Pacific Coast of Baja California
325
(mean 27 mg C m- 3 h- 1 , max. 44 mg C m- 3 h- 1 ) are among the highest reported for upwelling systems off Western Baja California (Lara-Lara et al.
1980). Although chlorophyll concentrations and surface primary productivity decrease from the mouth to the interior, mean assimilation ratios
(25 mg C mg- 1 Chl-a h- 1 ) do not vary significantly (Milhin-Nufiez et al.
1982). About 60% of the gross primary production in the Bahia San
Quintin system ( -38,380 tons C year- 1 ) depends on the phytoplankton
contribution while benthic primary producers contribute approximately
40%.
High primary productivity appears to support relatively large populations of consumers at higher trophic levels (Phleger and Ewing 1962) and
the coastal lagoons provide protection and feeding, nursery and acclimation areas for juveniles of several fish species. About 120 species of fishes,
the California halibut (Paralichthys californicus) and the spotfin croaker
(Roncador stearnsii) being the most abundant, occur in Bahia San Quintin.
Most fish ( 81 %) have northern affinity, about 6% are southern species and
only four species have wide distribution (Rosales-Casian 1997), while the
signal blenny (Emblemaria walkerii) is endemic to the bay (J. RosalesCasian, pers. comm.). More than 25,000 migratory shore birds spend the
winter in Bahia San Quintin, including 30-50% of Mexico's black brant
(Branta bernicla) population, as well as birds of prey like the American
peregrine falcon (Falco peregrinus anatum), the burrowing owl (Athene
cunicularia), and the short-eared owl (Asio Jlammeus). The area hosts the
largest reproductive populations of threatened or endangered bird species
and subspecies, like the yellow-footed clapper rail (Rallus longirostris
levipes), Belding's savannah sparrow (Passerculus sandwichensis beldingi),
California least tern (Sterna antillarum ), snowy plover ( Charadrius
alexandrinus), black rail (Laterallus jamaicensis), and California gnat catcher (Polioptila californica atwoodi; Massey and Palacios 1994). The bay is
the only nesting site for Foster's tern (Sterna forsteri) along the Mexican
Pacific coast.
21.4.1.3 Ecosystem Metabolism
The San Quintin coastal ecosystem is geographically isolated and comprised of a terrestrial compartment (San Quintin Valley) and a marine
compartment (Bahia San Quintin). A mass balance budget model (Gordon
et al. 1996) was used to estimate the net metabolism in Bahia San Quintin
(Camacho-Ibar et al. 1997). As a result of evaporation, the residual flow of
seawater and dissolved properties from the ocean into the bay exceeds
freshwater input from precipitation, runoff and groundwater flow. How-
325
(mean 27 mg C m- 3 h- 1 , max. 44 mg C m- 3 h- 1 ) are among the highest reported for upwelling systems off Western Baja California (Lara-Lara et al.
1980). Although chlorophyll concentrations and surface primary productivity decrease from the mouth to the interior, mean assimilation ratios
(25 mg C mg- 1 Chl-a h- 1 ) do not vary significantly (Milhin-Nufiez et al.
1982). About 60% of the gross primary production in the Bahia San
Quintin system ( -38,380 tons C year- 1 ) depends on the phytoplankton
contribution while benthic primary producers contribute approximately
40%.
High primary productivity appears to support relatively large populations of consumers at higher trophic levels (Phleger and Ewing 1962) and
the coastal lagoons provide protection and feeding, nursery and acclimation areas for juveniles of several fish species. About 120 species of fishes,
the California halibut (Paralichthys californicus) and the spotfin croaker
(Roncador stearnsii) being the most abundant, occur in Bahia San Quintin.
Most fish ( 81 %) have northern affinity, about 6% are southern species and
only four species have wide distribution (Rosales-Casian 1997), while the
signal blenny (Emblemaria walkerii) is endemic to the bay (J. RosalesCasian, pers. comm.). More than 25,000 migratory shore birds spend the
winter in Bahia San Quintin, including 30-50% of Mexico's black brant
(Branta bernicla) population, as well as birds of prey like the American
peregrine falcon (Falco peregrinus anatum), the burrowing owl (Athene
cunicularia), and the short-eared owl (Asio Jlammeus). The area hosts the
largest reproductive populations of threatened or endangered bird species
and subspecies, like the yellow-footed clapper rail (Rallus longirostris
levipes), Belding's savannah sparrow (Passerculus sandwichensis beldingi),
California least tern (Sterna antillarum ), snowy plover ( Charadrius
alexandrinus), black rail (Laterallus jamaicensis), and California gnat catcher (Polioptila californica atwoodi; Massey and Palacios 1994). The bay is
the only nesting site for Foster's tern (Sterna forsteri) along the Mexican
Pacific coast.
21.4.1.3 Ecosystem Metabolism
The San Quintin coastal ecosystem is geographically isolated and comprised of a terrestrial compartment (San Quintin Valley) and a marine
compartment (Bahia San Quintin). A mass balance budget model (Gordon
et al. 1996) was used to estimate the net metabolism in Bahia San Quintin
(Camacho-Ibar et al. 1997). As a result of evaporation, the residual flow of
seawater and dissolved properties from the ocean into the bay exceeds
freshwater input from precipitation, runoff and groundwater flow. How-