The Panamá Current (PC)
Every year a body of surface water (warm and low in salinity and nutrients) that
flows from Panamá (Fig. 6.2) reaches Galápagos in January. At this time of year,
the SE winds decrease in intensity and the currents flowing westward also weaken.
This allows the ITCZ warm water masses to invade from the north. This mass of
warm water flows southward along the NW coast of South America. When the PC
penetrates to the south and lasts long enough, the event known as El Niño occurs.
This has devastating impacts on the marine ecosystems of the region (Jiménez
1987).
The Subsurface Equatorial Current (or Cromwell Current)
The Cromwell Current directly or indirectly generates a series of unusual effects.
These include cool surface water temperatures on the equator (17 °C on average)
and a large amount of plankton that is responsible for the richness of fauna in the
archipelago. It has a thickness of 300 m and a width of 400 km. It is normally
positioned at a depth of about 100 m, well below the euphotic zone. Upwelling
occurs when it hits the Galápagos platform (Fig. 6.2) bringing nutrient rich, cold
waters to the surface (Wyrtki 1985). This current produces persistent upwelling
zones enriched with nutrients in the western coasts of most islands and consistently
colder water masses. This allows the occurrence and persistence of temperate
species in Galápagos, which is an equatorial zone (Feldman 1985). The branches
of this water mass come together again in one undercurrent about 100 km east of
the archipelago (Banks 1999). Based on analysis of satellite remote sensing data
(SeaWiFS), Banks (2002) identified regions where annual primary production is
consistently high, in particular to the west of Isabela, known for its high productivity and fishing intensity, but also at some easterly points of Isabela and SE
Santa Cruz, which may be due to local patterns of currents and seamounts. It has
been suggested that an elevated productivity (10–30 mg Chl a m
-3 ) occurs in
sporadic but intense events of short duration, while occasional, spatially large but
moderately intense (0.5–1.0 mg Chl a m
-3 ) productivity occurs throughout the
archipelago. This is possibly due to a mixing of points of freshwater runoff and
nutrient enrichment from the coast, surface advection from other islands, and
retention effects of nutrients from areas with high sediment content and mangrove
bays (Wellington 1984; James 1991).
6.2 Diversity of Echinoderms and Distribution
Explorations of echinoderms in Ecuador have been intensive, particularly around
the Galápagos Islands, where several expeditions made collections over the past
100 years. These include the Albatross in 1894, 1898, 1899, 1905; the Eagle and
6 Echinoderms of Ecuador
189
Every year a body of surface water (warm and low in salinity and nutrients) that
flows from Panamá (Fig. 6.2) reaches Galápagos in January. At this time of year,
the SE winds decrease in intensity and the currents flowing westward also weaken.
This allows the ITCZ warm water masses to invade from the north. This mass of
warm water flows southward along the NW coast of South America. When the PC
penetrates to the south and lasts long enough, the event known as El Niño occurs.
This has devastating impacts on the marine ecosystems of the region (Jiménez
1987).
The Subsurface Equatorial Current (or Cromwell Current)
The Cromwell Current directly or indirectly generates a series of unusual effects.
These include cool surface water temperatures on the equator (17 °C on average)
and a large amount of plankton that is responsible for the richness of fauna in the
archipelago. It has a thickness of 300 m and a width of 400 km. It is normally
positioned at a depth of about 100 m, well below the euphotic zone. Upwelling
occurs when it hits the Galápagos platform (Fig. 6.2) bringing nutrient rich, cold
waters to the surface (Wyrtki 1985). This current produces persistent upwelling
zones enriched with nutrients in the western coasts of most islands and consistently
colder water masses. This allows the occurrence and persistence of temperate
species in Galápagos, which is an equatorial zone (Feldman 1985). The branches
of this water mass come together again in one undercurrent about 100 km east of
the archipelago (Banks 1999). Based on analysis of satellite remote sensing data
(SeaWiFS), Banks (2002) identified regions where annual primary production is
consistently high, in particular to the west of Isabela, known for its high productivity and fishing intensity, but also at some easterly points of Isabela and SE
Santa Cruz, which may be due to local patterns of currents and seamounts. It has
been suggested that an elevated productivity (10–30 mg Chl a m
-3 ) occurs in
sporadic but intense events of short duration, while occasional, spatially large but
moderately intense (0.5–1.0 mg Chl a m
-3 ) productivity occurs throughout the
archipelago. This is possibly due to a mixing of points of freshwater runoff and
nutrient enrichment from the coast, surface advection from other islands, and
retention effects of nutrients from areas with high sediment content and mangrove
bays (Wellington 1984; James 1991).
6.2 Diversity of Echinoderms and Distribution
Explorations of echinoderms in Ecuador have been intensive, particularly around
the Galápagos Islands, where several expeditions made collections over the past
100 years. These include the Albatross in 1894, 1898, 1899, 1905; the Eagle and
6 Echinoderms of Ecuador
189