of 3.2 ind m
-2 . They also pointed out that it was abundant in the islands of Rábida
and Santiago with average densities of 5.0 ind m
-2 . The lowest densities occurred
in the northern islands of Darwin and Wolf with average densities of 2.1 ind m
-2 .
Irving and Witman (2009) carried out experiments and density surveys of E.
galapagensis in different habitats in Academy Bay, Santa Cruz Island. They found
maximum densities of 28 ind m
-2 in algal turfs, and only 6 ind m
-2 in barren
habitats. Sonnenholzner et al. (2009) studied the density of E. galapagensis in 20
shallow rocky reefs in the southeastern biogeographic region of the Galápagos
Marine Reserve (off Santiago, Santa Cruz, Baltra and Seymour Islands), specifically in sites open and closed to fishing. Eucidaris galapagensis densities (±SE)
were higher in open than in closed sites to fishing (4.5 ± 1.55 vs.
2.2 ± 1.55 ind m
-2 , respectively). More recently, Paredes (2010) conducted
population surveys of E. galapagensis at four sites in San Cristóbal Island between
August 2009 and March 2010. The highest densities were in Punta Carola and
Playa Mann (1.3 ind m
-2 ) followed by La Lobería (1.1 ind m
-2 ) and Tijeretas
(0.9 ind m
-2 ).
Size Structure and Gonad Production
Brandt and Guarderas (2002) indicated that the mean test diameter of E. galapagensis was 5.12 ± 0.01 cm around the archipelago. The test diameter ranged
from 1 to 9 cm and varied between regions/islands (H = 1462.162, p \ 0.0001,
df = 6), with the largest test diameters occurring in Floreana and the southeastern
islands.
During the Base Line survey collections between September 2000 and April
2001 Francisco and Smith (unpublished data) estimated morphometric relationships and gonad index of the most common sea urchins. Twenty individuals of
each species (E. galapagensis, Lytechinus semituberculatus and Tripneustes depressus) were collected haphazardly at a depth of approximately 6 m at 12 sites on
seven islands. Individuals were dissected and gonad index (GI) was calculated by
dividing the drained gonad weight by the total body weight, multiplied by 100.
The mean GI (±SE) for E. galapagensis was 2.98 ± 0.11 (Francisco and Smith,
unpublished data).
Diet and Feeding Habits
Eucidaris galapagensis feeds on encrusting algae (Wellington 1975; Hickman
1998), live hermatypic polyps, dead corals and barnacle plates (Glynn et al. 1979).
It contributes to the production of sediment in the subtidal community of the
Galápagos (Wellington 1975). It also has the ability to bore deeply into the substrate to create crevices, which reduces its risk of dislodgement from hydrodynamic forces (Witman and Dayton 2001).
6 Echinoderms of Ecuador
201
-2 . They also pointed out that it was abundant in the islands of Rábida
and Santiago with average densities of 5.0 ind m
-2 . The lowest densities occurred
in the northern islands of Darwin and Wolf with average densities of 2.1 ind m
-2 .
Irving and Witman (2009) carried out experiments and density surveys of E.
galapagensis in different habitats in Academy Bay, Santa Cruz Island. They found
maximum densities of 28 ind m
-2 in algal turfs, and only 6 ind m
-2 in barren
habitats. Sonnenholzner et al. (2009) studied the density of E. galapagensis in 20
shallow rocky reefs in the southeastern biogeographic region of the Galápagos
Marine Reserve (off Santiago, Santa Cruz, Baltra and Seymour Islands), specifically in sites open and closed to fishing. Eucidaris galapagensis densities (±SE)
were higher in open than in closed sites to fishing (4.5 ± 1.55 vs.
2.2 ± 1.55 ind m
-2 , respectively). More recently, Paredes (2010) conducted
population surveys of E. galapagensis at four sites in San Cristóbal Island between
August 2009 and March 2010. The highest densities were in Punta Carola and
Playa Mann (1.3 ind m
-2 ) followed by La Lobería (1.1 ind m
-2 ) and Tijeretas
(0.9 ind m
-2 ).
Size Structure and Gonad Production
Brandt and Guarderas (2002) indicated that the mean test diameter of E. galapagensis was 5.12 ± 0.01 cm around the archipelago. The test diameter ranged
from 1 to 9 cm and varied between regions/islands (H = 1462.162, p \ 0.0001,
df = 6), with the largest test diameters occurring in Floreana and the southeastern
islands.
During the Base Line survey collections between September 2000 and April
2001 Francisco and Smith (unpublished data) estimated morphometric relationships and gonad index of the most common sea urchins. Twenty individuals of
each species (E. galapagensis, Lytechinus semituberculatus and Tripneustes depressus) were collected haphazardly at a depth of approximately 6 m at 12 sites on
seven islands. Individuals were dissected and gonad index (GI) was calculated by
dividing the drained gonad weight by the total body weight, multiplied by 100.
The mean GI (±SE) for E. galapagensis was 2.98 ± 0.11 (Francisco and Smith,
unpublished data).
Diet and Feeding Habits
Eucidaris galapagensis feeds on encrusting algae (Wellington 1975; Hickman
1998), live hermatypic polyps, dead corals and barnacle plates (Glynn et al. 1979).
It contributes to the production of sediment in the subtidal community of the
Galápagos (Wellington 1975). It also has the ability to bore deeply into the substrate to create crevices, which reduces its risk of dislodgement from hydrodynamic forces (Witman and Dayton 2001).
6 Echinoderms of Ecuador
201