The Tropical Pacific Coast of Mexico
309
70 o/o of the shallower Huizache-Caimanero lagoon ( 17.5 km 2 ) dries up
during the dry season. The exposed bottom substrate cracks, increasing
nutrient release during flooding in summer (Arenas and de la Lanza 1981).
High concentrations of nutrients favor elevated biomass (> 1 kg dry
wt. m- 2 ) of the sea grass Ruppia maritima (de la Lanza and Garda-Calderon 1991). The Estero de Urias lagoon permanently exchanges water with
the ocean. However, the lagoon receives urban wastewater, cooling water
from a thermoelectric plant, effluents from the fishing industry, and
elevated nutrient discharge from shrimp ponds (Paez-Osuna et al. 1997a),
leading to eutrophication which is often associated with excessive growth
of the alga Ulva lactuca.
Coastal lagoon systems of the humid Chiapas coast are characterized by
high water temperatures (29-35.5 oC) and salinity varies between 0-34.5
psu (Chantuto-Panzacola), 0-22.7 psu (Carretas-Pereyra, 3.7km 2 ), and
12-39 psu (La Joya-Buenavista, 62km 2 ) during the rainy (September) and
dry season (April), respectively. Reduced water exchange with the ocean
(La Joya-Buenavista) and elevated phosphorus input from rivers (Carretas-Pereyra and Chantuto-Panzacola) tend to cause high total phosphorus
concentrations (up to 42jlg 1- 1 ) compared to those of nitrite/nitrate
(0.5-2.9jlg l- 1 ), thus favoring elevated chlorophyll-a levels (55-80 mg m- 3 ).
High ammonia concentrations ( Carretas-Pereyra, 34jlg 1- 1 ) are likely to be
due to large quantities of mangrove detritus (Flores-Verdugo et al. 1992;
Contreras-Espinosa 1993). Hypersaline (salinity up to 55 psu) conditions
are common in the Superior, Inferior, and Mar Muerto lagoons (about
1,400km 2 ) in Oaxaca State.
Coastal lagoons assume an important function in the life cycles of
marine fishes, and commercial species, such as mullet (Mugil), snapper
(Lutjanus), and snook (Centropomus), are abundant in both lagoons and
adjacent marine waters. In general, the abundance and distribution of the
ichthyofauna is controlled by seasonal changes in precipitation (YafiezArancibia 1978).
20.3.2 Mangroves and freshwater wetlands
Although mangrove distribution is discontinuous, extensive forests are
common in southern Sinaloa and Nayarit (Teacapan-Agua Brava and San
Bias) and Chiapas (Chantuto-Panzacola-El Huayate). The structure of
mangrove forests increases with higher rainfall and freshwater runoff
towards the south (Flores-Verdugo et al. 1992). Mangrove forests are dominated by red (Rhizophora mangle), white (Laguncularia racemosa), black
(Avicennia germinans), and button mangrove ( Conocarpus erectus). Rhizo-
309
70 o/o of the shallower Huizache-Caimanero lagoon ( 17.5 km 2 ) dries up
during the dry season. The exposed bottom substrate cracks, increasing
nutrient release during flooding in summer (Arenas and de la Lanza 1981).
High concentrations of nutrients favor elevated biomass (> 1 kg dry
wt. m- 2 ) of the sea grass Ruppia maritima (de la Lanza and Garda-Calderon 1991). The Estero de Urias lagoon permanently exchanges water with
the ocean. However, the lagoon receives urban wastewater, cooling water
from a thermoelectric plant, effluents from the fishing industry, and
elevated nutrient discharge from shrimp ponds (Paez-Osuna et al. 1997a),
leading to eutrophication which is often associated with excessive growth
of the alga Ulva lactuca.
Coastal lagoon systems of the humid Chiapas coast are characterized by
high water temperatures (29-35.5 oC) and salinity varies between 0-34.5
psu (Chantuto-Panzacola), 0-22.7 psu (Carretas-Pereyra, 3.7km 2 ), and
12-39 psu (La Joya-Buenavista, 62km 2 ) during the rainy (September) and
dry season (April), respectively. Reduced water exchange with the ocean
(La Joya-Buenavista) and elevated phosphorus input from rivers (Carretas-Pereyra and Chantuto-Panzacola) tend to cause high total phosphorus
concentrations (up to 42jlg 1- 1 ) compared to those of nitrite/nitrate
(0.5-2.9jlg l- 1 ), thus favoring elevated chlorophyll-a levels (55-80 mg m- 3 ).
High ammonia concentrations ( Carretas-Pereyra, 34jlg 1- 1 ) are likely to be
due to large quantities of mangrove detritus (Flores-Verdugo et al. 1992;
Contreras-Espinosa 1993). Hypersaline (salinity up to 55 psu) conditions
are common in the Superior, Inferior, and Mar Muerto lagoons (about
1,400km 2 ) in Oaxaca State.
Coastal lagoons assume an important function in the life cycles of
marine fishes, and commercial species, such as mullet (Mugil), snapper
(Lutjanus), and snook (Centropomus), are abundant in both lagoons and
adjacent marine waters. In general, the abundance and distribution of the
ichthyofauna is controlled by seasonal changes in precipitation (YafiezArancibia 1978).
20.3.2 Mangroves and freshwater wetlands
Although mangrove distribution is discontinuous, extensive forests are
common in southern Sinaloa and Nayarit (Teacapan-Agua Brava and San
Bias) and Chiapas (Chantuto-Panzacola-El Huayate). The structure of
mangrove forests increases with higher rainfall and freshwater runoff
towards the south (Flores-Verdugo et al. 1992). Mangrove forests are dominated by red (Rhizophora mangle), white (Laguncularia racemosa), black
(Avicennia germinans), and button mangrove ( Conocarpus erectus). Rhizo-