east, while the oldest islands are San Cristóbal and Española (Cox 1983; Geist
1996). The total land area of the archipelago is about 8,000 km
2 . It is surrounded
by a Marine Reserve that covers an area of 137,975 km
2 , with a total of 1,800 km
of coastline (Snell et al. 1995; Toropova et al. 2010) making it the ninth largest
marine protected area in the world. Outside the Marine Reserve, national waters
extend 200 nautical milles from the island baseline. Climatologically, these islands
are not a uniform group, as they extend both north and south of the equator and are
influenced by different oceanographic conditions (Abbott 1966). More than 90 %
of their surface area is located south of the equator. In spite of their equatorial
position, a rather temperate climate (with an annual mean temperature of *24 °C)
prevails because the islands are located in a climatic transition zone between the
west coast of South America and the dry zone of the Central Pacific Ocean. These
islands are influenced by both warm and cold currents (Figs. 6.1, 6.2) which meet
in the Galápagos region. Most climate data available come from the arid coastal
zone where the year is divided into a dry season (June–October) and a rainy season
(December–April). During the dry season, upwelling cold oceanic water (19 °C)
flows along the southern part of the archipelago. The extreme temperatures in the
‘‘arid zone’’ are rarely below 13 °C or above 23 °C, which are cool for this latitude.
There is occasional or intermittent drizzle in the coastal zone but almost continuous
drizzle in the higher zones of the islands. This kind of rainfall, locally called
‘‘garua’’, is also typical of all South American coasts influenced by the Humboldt
Current (Chile, Perú, and southern Ecuador). In the arid zone, the monthly rainfall
from May to October never exceeds 25 mm. During the rainy season, the dominant
wind changes from south-southeast to east, with light winds in the lower regions.
Upwelling of cold oceanic water stops during this period and genuine tropical
conditions prevail. The heaviest rainfall is on the southern slopes of the large
islands above 250 m altitude. There is almost no rainfall on the leeward side of the
coastal region (northern side).
Oceanography
Several marine currents converge at the Galápagos Islands (Fig. 6.2). This
determines the great ecological uniqueness of these marine ecosystems. Seven
ocean currents have been identified. Three of these are the most decisive currents
that determine the seasonal periods of the islands, in terms of intensity, direction
and temperatures: (1) the South Equatorial Current (SEC); (2) the warm Panamá
Current; and (3) the deep cold Cromwell Current (Chávez and Brusca 1991;
Banks 1999).
South Equatorial Current (SEC)
The SEC is the main surface current that flows westward. It is a product of the
confluence of two currents with different direction and intensity throughout the
6 Echinoderms of Ecuador
187
1996). The total land area of the archipelago is about 8,000 km
2 . It is surrounded
by a Marine Reserve that covers an area of 137,975 km
2 , with a total of 1,800 km
of coastline (Snell et al. 1995; Toropova et al. 2010) making it the ninth largest
marine protected area in the world. Outside the Marine Reserve, national waters
extend 200 nautical milles from the island baseline. Climatologically, these islands
are not a uniform group, as they extend both north and south of the equator and are
influenced by different oceanographic conditions (Abbott 1966). More than 90 %
of their surface area is located south of the equator. In spite of their equatorial
position, a rather temperate climate (with an annual mean temperature of *24 °C)
prevails because the islands are located in a climatic transition zone between the
west coast of South America and the dry zone of the Central Pacific Ocean. These
islands are influenced by both warm and cold currents (Figs. 6.1, 6.2) which meet
in the Galápagos region. Most climate data available come from the arid coastal
zone where the year is divided into a dry season (June–October) and a rainy season
(December–April). During the dry season, upwelling cold oceanic water (19 °C)
flows along the southern part of the archipelago. The extreme temperatures in the
‘‘arid zone’’ are rarely below 13 °C or above 23 °C, which are cool for this latitude.
There is occasional or intermittent drizzle in the coastal zone but almost continuous
drizzle in the higher zones of the islands. This kind of rainfall, locally called
‘‘garua’’, is also typical of all South American coasts influenced by the Humboldt
Current (Chile, Perú, and southern Ecuador). In the arid zone, the monthly rainfall
from May to October never exceeds 25 mm. During the rainy season, the dominant
wind changes from south-southeast to east, with light winds in the lower regions.
Upwelling of cold oceanic water stops during this period and genuine tropical
conditions prevail. The heaviest rainfall is on the southern slopes of the large
islands above 250 m altitude. There is almost no rainfall on the leeward side of the
coastal region (northern side).
Oceanography
Several marine currents converge at the Galápagos Islands (Fig. 6.2). This
determines the great ecological uniqueness of these marine ecosystems. Seven
ocean currents have been identified. Three of these are the most decisive currents
that determine the seasonal periods of the islands, in terms of intensity, direction
and temperatures: (1) the South Equatorial Current (SEC); (2) the warm Panamá
Current; and (3) the deep cold Cromwell Current (Chávez and Brusca 1991;
Banks 1999).
South Equatorial Current (SEC)
The SEC is the main surface current that flows westward. It is a product of the
confluence of two currents with different direction and intensity throughout the
6 Echinoderms of Ecuador
187