Lytechinus semituberculatus
Distribution and Density
The green sea urchin Lytechinus semituberculatus (Fig. 6.3c) has been reported as
the second most abundant sea urchin species (1.2 ind m
-2 ) of the Galápagos’
rocky reefs (Brandt and Guarderas 2002). L. semituberculatus was widely distributed in islands with colder and higher productivity water regimes, particularly
on Isabela Island (2.7 ind m
-2 ). The lowest densities were in the northern islands
(0.1 ind m
-2 ), and on Santa Cruz island (0.2 ind m
-2 ). L. semituberculatus shows
a significant density pattern associated with depth, suggesting it prefers shallow
habitats (\10 m) (Brandt and Guarderas 2002). Edgar et al. (2010) documented
changes in its density before and after El Niño 1982/1983. They found a decrease
from 0.52 ind m
-2 in 1982 to 0 individuals in 1984. In another study, L. semituberculatus had higher densities in barren grounds (51 ind m
-2
) than in turf
habitats (1.6 ind m
-2 ) (Irving and Witman 2009). Finally, Paredes (2010) conducted population surveys at four sites in San Cristóbal Island between August
2009 and March 2010. Density data showed that Bahía Tijeretas had higher
densities of L. semituberculatus than the other surveyed sites. The highest density
was 4.8 ind m
-2 , followed by La Lobería (1.6 ind m
-2 ), Playa Mann
(0.9 ind m
-2 ) and Punta Carola (0.6 ind m
-2 ).
Size Structure, Allometric Scaling and Gonad Production
Brandt and Guarderas (2002) reported a mean test diameter (±SE) for L. semituberculatus in the whole archipelago of 4.3 ± 0.02 cm, with a range of 1–7 cm.
There were significant differences in test diameters among islands (H = 691.363,
p \ 0.0001, df = 6). Populations at Floreana and Santa Cruz islands had the
highest mean test diameters (Brandt and Guarderas 2002). In relation to gonad
production, Francisco and Smith (unpublished data) found a mean gonad index
(±SE) was 7.36 ± 0.43.
In general, body size affects most aspects of an organism’s biology (Calder
1984), and scaling of structure and function to body size can be considered in
terms of ontogeny and phylogeny. Lawrence et al. (2010) studied the ontogenetic
and phylogenetic scaling of lantern components (weight of demipyramid, rotula
and epiphysis of the lantern and test diameter) of L. semituberculatus from the
Galápagos Islands versus three other species of Lytechinus (L. variegatus from
west coast of Florida, U.S.A. and San Blas Islands, Panamá; L. williamsi from San
Blas Islands, Panamá; and L. pictus, northern Baja California, México) and one
species of Tripneustes (T. gratilla from Okinawa, Japan). Results showed that all
components were largest in the smallest species (L. williamsi), and smallest in the
largest species (T. gratilla), suggesting a genetic basis and interrelated scaling. All
components are larger in L. variegatus from Panamá than those from Florida,
which could have a genetic and/or environmental basis. These results are very
important, since the arguments proposed by Ebert (1980) suggested that large
202
J. Sonnenholzner et al.
Distribution and Density
The green sea urchin Lytechinus semituberculatus (Fig. 6.3c) has been reported as
the second most abundant sea urchin species (1.2 ind m
-2 ) of the Galápagos’
rocky reefs (Brandt and Guarderas 2002). L. semituberculatus was widely distributed in islands with colder and higher productivity water regimes, particularly
on Isabela Island (2.7 ind m
-2 ). The lowest densities were in the northern islands
(0.1 ind m
-2 ), and on Santa Cruz island (0.2 ind m
-2 ). L. semituberculatus shows
a significant density pattern associated with depth, suggesting it prefers shallow
habitats (\10 m) (Brandt and Guarderas 2002). Edgar et al. (2010) documented
changes in its density before and after El Niño 1982/1983. They found a decrease
from 0.52 ind m
-2 in 1982 to 0 individuals in 1984. In another study, L. semituberculatus had higher densities in barren grounds (51 ind m
-2
) than in turf
habitats (1.6 ind m
-2 ) (Irving and Witman 2009). Finally, Paredes (2010) conducted population surveys at four sites in San Cristóbal Island between August
2009 and March 2010. Density data showed that Bahía Tijeretas had higher
densities of L. semituberculatus than the other surveyed sites. The highest density
was 4.8 ind m
-2 , followed by La Lobería (1.6 ind m
-2 ), Playa Mann
(0.9 ind m
-2 ) and Punta Carola (0.6 ind m
-2 ).
Size Structure, Allometric Scaling and Gonad Production
Brandt and Guarderas (2002) reported a mean test diameter (±SE) for L. semituberculatus in the whole archipelago of 4.3 ± 0.02 cm, with a range of 1–7 cm.
There were significant differences in test diameters among islands (H = 691.363,
p \ 0.0001, df = 6). Populations at Floreana and Santa Cruz islands had the
highest mean test diameters (Brandt and Guarderas 2002). In relation to gonad
production, Francisco and Smith (unpublished data) found a mean gonad index
(±SE) was 7.36 ± 0.43.
In general, body size affects most aspects of an organism’s biology (Calder
1984), and scaling of structure and function to body size can be considered in
terms of ontogeny and phylogeny. Lawrence et al. (2010) studied the ontogenetic
and phylogenetic scaling of lantern components (weight of demipyramid, rotula
and epiphysis of the lantern and test diameter) of L. semituberculatus from the
Galápagos Islands versus three other species of Lytechinus (L. variegatus from
west coast of Florida, U.S.A. and San Blas Islands, Panamá; L. williamsi from San
Blas Islands, Panamá; and L. pictus, northern Baja California, México) and one
species of Tripneustes (T. gratilla from Okinawa, Japan). Results showed that all
components were largest in the smallest species (L. williamsi), and smallest in the
largest species (T. gratilla), suggesting a genetic basis and interrelated scaling. All
components are larger in L. variegatus from Panamá than those from Florida,
which could have a genetic and/or environmental basis. These results are very
important, since the arguments proposed by Ebert (1980) suggested that large
202
J. Sonnenholzner et al.