The formation of the Isthmus of Panama united South and North America, and
gave rise to the great biological interchange of terrestrial faunae and floras, but
cutting the seaway between the Atlantic and the Pacific (O’Dea et al. 2007). This
process was the result of two geologic processes: plate tectonics and volcanisms
(Coates and Obando 1996). Twenty million years ago (m.y.a.; Miocene), Central
and South America were separated by a wide and deep seaway. This seaway
became narrower due to the movement of the South American plate to the
Northwest until the arc of Panama collided with South America 10 m.y.a. Subsequently, it began to rise and produced the emergence of land around 5 m.y.a.,
causing a final closure of the isthmus between 3.5 and 2.5 m.y.a. (Coates and
Obando 1996; O’Dea et al. 2007).
The Pacific coast is characterized by extensive mangrove systems; sandy beaches, rocky points, cobbles beaches, deltas, and isolated coral reefs of limited
development (Cortés 2007). This coast experiences seasonal upwelling of cold,
nutrient-rich waters from December to April, and produces an increase of the
plankton productivity (D’Croz and Robertson 1997; Fiedler 2002; Amador et al.
2006). This elevated productivity caused by upwelling adds to the high production
from river run-off caused by high precipitation, and increases the nutrients contribution of terrestrial origin (O’Dea et al. 2007). This coast is under the influence
of the Intertropical Convergence Zone (ITCZ), characterized by high irradiance,
variable winds and high precipitation (Amador et al. 2006). The depth of the
mixing layer is shallow (30–40 m) with a permanent thermocline (Longhurst 1998),
and localized near the surface (25 m depth) (Brenes et al. 1990). Productivity is
considered as moderate to high, due to the presence of upwelling areas such as the
Costa Rica Thermal Dome (Fiedler 2002) and seasonal upwelling in the Gulfs of
Tehuantepec, Papagayo and Panama (Bakun et al. 1999). The Pacific coast has six
mayor gulfs: (1) The Gulf of Fonseca (shared by El Salvador, Honduras and
Nicaragua), (2) the Gulf of Papagayo, (3) the Gulf of Nicoya and (4) the Golfo
Dulce (2, 3 and 4 in Costa Rica), and the Gulfs of (5) Chiriquí and (6) Panama
(in Panama) (Cortés 2007). Golfo Dulce is one of four fjord-like gulfs in the tropics
with anoxic conditions at the bottom (Quesada-Alpízar and Cortés 2006).
The Pacific side of CA also has an oceanic island, Cocos Island (Isla del Coco), of
volcanic origin, and located approximately 500 km Southwest of Costa Rica and
630 km Northeast of the Galápagos Islands (Fig. 3.1). Cocos Island is the only
subaereally exposed portion of the aseismic Cocos Ridge. Its volcanic origin is
associated with the Galápagos hot spot (Castillo et al. 1988). This oceanic ridge is
more than 1,000 km long and approximately 200 km wide with depths of 2,000 m
(Harpp et al. 2005; Marcaillou et al. 2006). Moreover, the middle America Trench,
in front of the Pacific coast of CA extends from Mexico to Costa Rica with a maximum depth of 6,669 km (Astiz et al. 1987). Hydrothermal and cold seeps and oxygen
minimum zones have been reported in the continental shelf (Bohrmann et al. 2002;
Helly and Levin 2004, respectively).
The currents on the Pacific side of CA (Fig. 3.1) are under the influence of the
North Equatorial Countercurrent (NECC), and are responsible for the heat transport from the Tropical Pacific to CA. A portion of the water is first carried out to
68
J. J. Alvarado et al.
gave rise to the great biological interchange of terrestrial faunae and floras, but
cutting the seaway between the Atlantic and the Pacific (O’Dea et al. 2007). This
process was the result of two geologic processes: plate tectonics and volcanisms
(Coates and Obando 1996). Twenty million years ago (m.y.a.; Miocene), Central
and South America were separated by a wide and deep seaway. This seaway
became narrower due to the movement of the South American plate to the
Northwest until the arc of Panama collided with South America 10 m.y.a. Subsequently, it began to rise and produced the emergence of land around 5 m.y.a.,
causing a final closure of the isthmus between 3.5 and 2.5 m.y.a. (Coates and
Obando 1996; O’Dea et al. 2007).
The Pacific coast is characterized by extensive mangrove systems; sandy beaches, rocky points, cobbles beaches, deltas, and isolated coral reefs of limited
development (Cortés 2007). This coast experiences seasonal upwelling of cold,
nutrient-rich waters from December to April, and produces an increase of the
plankton productivity (D’Croz and Robertson 1997; Fiedler 2002; Amador et al.
2006). This elevated productivity caused by upwelling adds to the high production
from river run-off caused by high precipitation, and increases the nutrients contribution of terrestrial origin (O’Dea et al. 2007). This coast is under the influence
of the Intertropical Convergence Zone (ITCZ), characterized by high irradiance,
variable winds and high precipitation (Amador et al. 2006). The depth of the
mixing layer is shallow (30–40 m) with a permanent thermocline (Longhurst 1998),
and localized near the surface (25 m depth) (Brenes et al. 1990). Productivity is
considered as moderate to high, due to the presence of upwelling areas such as the
Costa Rica Thermal Dome (Fiedler 2002) and seasonal upwelling in the Gulfs of
Tehuantepec, Papagayo and Panama (Bakun et al. 1999). The Pacific coast has six
mayor gulfs: (1) The Gulf of Fonseca (shared by El Salvador, Honduras and
Nicaragua), (2) the Gulf of Papagayo, (3) the Gulf of Nicoya and (4) the Golfo
Dulce (2, 3 and 4 in Costa Rica), and the Gulfs of (5) Chiriquí and (6) Panama
(in Panama) (Cortés 2007). Golfo Dulce is one of four fjord-like gulfs in the tropics
with anoxic conditions at the bottom (Quesada-Alpízar and Cortés 2006).
The Pacific side of CA also has an oceanic island, Cocos Island (Isla del Coco), of
volcanic origin, and located approximately 500 km Southwest of Costa Rica and
630 km Northeast of the Galápagos Islands (Fig. 3.1). Cocos Island is the only
subaereally exposed portion of the aseismic Cocos Ridge. Its volcanic origin is
associated with the Galápagos hot spot (Castillo et al. 1988). This oceanic ridge is
more than 1,000 km long and approximately 200 km wide with depths of 2,000 m
(Harpp et al. 2005; Marcaillou et al. 2006). Moreover, the middle America Trench,
in front of the Pacific coast of CA extends from Mexico to Costa Rica with a maximum depth of 6,669 km (Astiz et al. 1987). Hydrothermal and cold seeps and oxygen
minimum zones have been reported in the continental shelf (Bohrmann et al. 2002;
Helly and Levin 2004, respectively).
The currents on the Pacific side of CA (Fig. 3.1) are under the influence of the
North Equatorial Countercurrent (NECC), and are responsible for the heat transport from the Tropical Pacific to CA. A portion of the water is first carried out to
68
J. J. Alvarado et al.