distributions extend to the south of Ecuador. The colder water species (surface
temperature can drop to 14 °C in August and December) include Astrometis
sertulifera, Luidia bellonae (Fig. 6.4f), and Linckia columbiae (Fig. 6.4g).
Echinometra vanbrunti is a rare species in this region, despite being common in
almost all the islands. It is presumed that the Peruvian species occur here due to
the environmental conditions that include colder temperatures and more productive waters, similar to the conditions prevailing along the coast of South
America where these species initially evolved. This is also the case of the sea
urchin Caenocentrotus gibbosus (Fig. 6.4h), an immigrant from the temperate
region of the Peruvian-Chilean banks, which is dominant in the lower areas of
the western coast of Isabela and Fernandina Islands.
3. The Central/Eastern/Southern bioregions contain a combination of species from
various regions. Widely distributed in shallow waters are the sea urchins Eucidaris galapagensis (Fig. 6.3b), Tripneustes depressus (Fig. 6.3d), Diadema
mexicanum (Fig. 6.3e), Toxopneustes roseus (Fig. 6.3f) and Centrostephanus
coronatus. Lytechinus semituberculatus is native to the Galápagos, and replaces
the ubiquitous L. pictus of the Eastern Pacific. On sandy and rocky bottoms, the
most frequent sand dollars species are Clypeaster elongatus, C. europacificus
and C. rotundus.
Edgar et al. (2004) emphasized that the variation in the abundance of echinoderms around individual islands was high, often greater than the variation between
islands, thereby significantly lowering the density of certain species of sea stars.
For example, Heliaster cumingi (Gray, 1840) was not found during baseline surveys despite being previously abundant, occurring in densities greater than 2–
3 ind m
-2 in the intertidal (Wellington 1975). Nevertheless, it has been recently
found in Pinzón Island (see Fig. 6.4d). On the other hand, densities of some other
species seem to be increasing, for example the sea urchin Tripneustes depressus. It
appears that its abundance has increased at least an order of magnitude since the
1970s. This species was recorded in just one of ten sites investigated by Strickland
(1968), Wellington (1975), and Glynn (Edgar et al. 2002b). However, it is also
known that its populations greatly fluctuate through time, absent during some
periods, but very abundant during others (Brandt and Guarderas 2002).
Lawrence and Sonnenholzner (2004) documented the occurrence of the most
conspicuous echinoderms at seven sites with distinct habitats in central Galápagos
(i.e. sites were considered upon spatial gradients, from north to south, on hydrodynamics, wave energy, and sloping). Eighteen species (eight species of echinoids,
five species of holothurians, and five species of asteroids) were recorded. Of the
echinoids, Eucidaris galapagensis occurred in most of the sites ([90 % of the
quadrats at every site except one), and reached the highest densities (between
10.1 ± 4.8 and 15.6 ± 6.1 ind m
-2 ). Lytechinus semituberculatus was found in
[90 % of the quadrats at two sites. Other echinoderms present in more than 35 %
of the intervals along transects at a site), were the echinoids Tripneustes depressus,
Diadema mexicanum, Toxopnesutes roseus and Caenocentrotus gibbosus, the
asteroid Pentaceraster cumingi and the holothuroid Holothuria atra. Diversity was
6 Echinoderms of Ecuador
195
temperature can drop to 14 °C in August and December) include Astrometis
sertulifera, Luidia bellonae (Fig. 6.4f), and Linckia columbiae (Fig. 6.4g).
Echinometra vanbrunti is a rare species in this region, despite being common in
almost all the islands. It is presumed that the Peruvian species occur here due to
the environmental conditions that include colder temperatures and more productive waters, similar to the conditions prevailing along the coast of South
America where these species initially evolved. This is also the case of the sea
urchin Caenocentrotus gibbosus (Fig. 6.4h), an immigrant from the temperate
region of the Peruvian-Chilean banks, which is dominant in the lower areas of
the western coast of Isabela and Fernandina Islands.
3. The Central/Eastern/Southern bioregions contain a combination of species from
various regions. Widely distributed in shallow waters are the sea urchins Eucidaris galapagensis (Fig. 6.3b), Tripneustes depressus (Fig. 6.3d), Diadema
mexicanum (Fig. 6.3e), Toxopneustes roseus (Fig. 6.3f) and Centrostephanus
coronatus. Lytechinus semituberculatus is native to the Galápagos, and replaces
the ubiquitous L. pictus of the Eastern Pacific. On sandy and rocky bottoms, the
most frequent sand dollars species are Clypeaster elongatus, C. europacificus
and C. rotundus.
Edgar et al. (2004) emphasized that the variation in the abundance of echinoderms around individual islands was high, often greater than the variation between
islands, thereby significantly lowering the density of certain species of sea stars.
For example, Heliaster cumingi (Gray, 1840) was not found during baseline surveys despite being previously abundant, occurring in densities greater than 2–
3 ind m
-2 in the intertidal (Wellington 1975). Nevertheless, it has been recently
found in Pinzón Island (see Fig. 6.4d). On the other hand, densities of some other
species seem to be increasing, for example the sea urchin Tripneustes depressus. It
appears that its abundance has increased at least an order of magnitude since the
1970s. This species was recorded in just one of ten sites investigated by Strickland
(1968), Wellington (1975), and Glynn (Edgar et al. 2002b). However, it is also
known that its populations greatly fluctuate through time, absent during some
periods, but very abundant during others (Brandt and Guarderas 2002).
Lawrence and Sonnenholzner (2004) documented the occurrence of the most
conspicuous echinoderms at seven sites with distinct habitats in central Galápagos
(i.e. sites were considered upon spatial gradients, from north to south, on hydrodynamics, wave energy, and sloping). Eighteen species (eight species of echinoids,
five species of holothurians, and five species of asteroids) were recorded. Of the
echinoids, Eucidaris galapagensis occurred in most of the sites ([90 % of the
quadrats at every site except one), and reached the highest densities (between
10.1 ± 4.8 and 15.6 ± 6.1 ind m
-2 ). Lytechinus semituberculatus was found in
[90 % of the quadrats at two sites. Other echinoderms present in more than 35 %
of the intervals along transects at a site), were the echinoids Tripneustes depressus,
Diadema mexicanum, Toxopnesutes roseus and Caenocentrotus gibbosus, the
asteroid Pentaceraster cumingi and the holothuroid Holothuria atra. Diversity was
6 Echinoderms of Ecuador
195