The climatic regime of the islands is characterized by the predominance of
trade winds from the northeast that affects the islands when they are under the
influence of the Azores anticyclone. These winds have an average speed of 20–22
km h
-1 . They are not constant throughout the year, undergoing major seasonal
variations. In summer they reach their maximum frequency, occurring around
90–95 % of the days. In fall the Azores anticyclone gets weaker, producing
periods of calm. However, it is in winter and spring when there are minimum
levels of trade winds, with an incidence of less than 50 % of the days. During this
period low pressures from the Atlantic Ocean are frequent, producing winds from
the northwest, southwest or southeast, as well as warm and dry invasions of
Saharan weather conditions towards the east and southeast (Marzol 1988).
The tidal regime of islands is semidiurnal as in the rest of the Atlantic region,
with two high tides and two low tides each day. Usually two consecutive high tides
and two low tides have the same amplitude, experiencing a change during the year.
The maximum tidal amplitude occurs during the spring and fall equinoxes,
reaching about 2.5 m, whereas minimum values are recorded during the summer
and winter solstices, not exceeding 0.7 m of amplitude. During the rest of the year
the average tidal amplitude usually ranges between 1.2 and 1.3 m, but local
variations may occur due to the morphology of the coast, the depth, or to particular
climatic conditions of winds and waves in favor or against tidal waves (Braun and
Molina 1988; Yanes 1990).
15.1.3 General Characteristics of Communities and Ecosystems
The seabed of the Canary Islands is morphologically highly complex with a rich
and diverse biota. The presence of certain biological populations and their structure are determined by the interplay of five factors: insularity, topography of the
bottoms, great length of coastline, oceanographic conditions and geographical
location. Since the Canary Islands originated from the seabed, isolated from other
regions, its biota necessarily came from nearby continents or islands. One could
expect to find in the islands the same patterns of communities and ecosystems
structures as in nearby regions. However, despite the great dispersal ability of
marine species, many species fail to cross ocean barriers. Therefore a biased
representation of the biota appears in the archipelago. The volcanic nature of the
islands determines the pronounced slope of the bottoms and the small extent of
sublittoral platforms that abruptly terminates onto the islands’ slopes. This implies
that the extension on which benthic communities can develop is spatially very
limited. However, the long coastline, along with the rich and diverse coastal
morphology, allows the occurrence and development of numerous different habitats and ecosystems. On the other hand, the waters surrounding the islands are
oligotrophic that limits production in the environment (Braun and Molina 1988).
From a biogeographic point of view, the geographical location of the archipelago has resulted in the coexistence of both temperate and tropical species (Brito
15 Echinoderms of the Canary Islands, Spain
477
trade winds from the northeast that affects the islands when they are under the
influence of the Azores anticyclone. These winds have an average speed of 20–22
km h
-1 . They are not constant throughout the year, undergoing major seasonal
variations. In summer they reach their maximum frequency, occurring around
90–95 % of the days. In fall the Azores anticyclone gets weaker, producing
periods of calm. However, it is in winter and spring when there are minimum
levels of trade winds, with an incidence of less than 50 % of the days. During this
period low pressures from the Atlantic Ocean are frequent, producing winds from
the northwest, southwest or southeast, as well as warm and dry invasions of
Saharan weather conditions towards the east and southeast (Marzol 1988).
The tidal regime of islands is semidiurnal as in the rest of the Atlantic region,
with two high tides and two low tides each day. Usually two consecutive high tides
and two low tides have the same amplitude, experiencing a change during the year.
The maximum tidal amplitude occurs during the spring and fall equinoxes,
reaching about 2.5 m, whereas minimum values are recorded during the summer
and winter solstices, not exceeding 0.7 m of amplitude. During the rest of the year
the average tidal amplitude usually ranges between 1.2 and 1.3 m, but local
variations may occur due to the morphology of the coast, the depth, or to particular
climatic conditions of winds and waves in favor or against tidal waves (Braun and
Molina 1988; Yanes 1990).
15.1.3 General Characteristics of Communities and Ecosystems
The seabed of the Canary Islands is morphologically highly complex with a rich
and diverse biota. The presence of certain biological populations and their structure are determined by the interplay of five factors: insularity, topography of the
bottoms, great length of coastline, oceanographic conditions and geographical
location. Since the Canary Islands originated from the seabed, isolated from other
regions, its biota necessarily came from nearby continents or islands. One could
expect to find in the islands the same patterns of communities and ecosystems
structures as in nearby regions. However, despite the great dispersal ability of
marine species, many species fail to cross ocean barriers. Therefore a biased
representation of the biota appears in the archipelago. The volcanic nature of the
islands determines the pronounced slope of the bottoms and the small extent of
sublittoral platforms that abruptly terminates onto the islands’ slopes. This implies
that the extension on which benthic communities can develop is spatially very
limited. However, the long coastline, along with the rich and diverse coastal
morphology, allows the occurrence and development of numerous different habitats and ecosystems. On the other hand, the waters surrounding the islands are
oligotrophic that limits production in the environment (Braun and Molina 1988).
From a biogeographic point of view, the geographical location of the archipelago has resulted in the coexistence of both temperate and tropical species (Brito
15 Echinoderms of the Canary Islands, Spain
477