sediments layers on sandy shallow beaches along the entire circumference of the
island. Mellita lata was extremely numerous along the north-northeast coast
(Luquillo, San Juan, Guayama) and northwest and west coast (Aguadilla, Añasco,
Mayagüez). The moves by rhythmical movements of the long spines of the body,
marginal spines, interambulacra spines 1, 2, 3, and 4, and posterior lunule spines.
Kenk (1944) recorded about 35 strokes of the spines per minute at 26.5 °C. Other
members of order Clypeasteroida and family Mellitidae include Mellita quinquiesperforata (Leske) and Leodia sexiesperforata. Both are also commonly found
partially buried under sediments on sandy beaches, but particularly on bottoms
with high abundance of organic material (e.g., Naguabo, Humacao, Yabucoa).
Diadema antillarum Distribution
Before the mass mortality D. antillarum densities were high at many locations
around Puerto Rico, San Juan 13.8 ind m
-2 (Bauer 1980), La Parguera 12.7 ind
m
-2 (Craft 1975), Guayanilla 3.0 ind m
-2 (Vicente and Goenaga 1984), and Jobos
Bay 2.6 ind m
-2 (Rivera and Vicente 1976). Lugo (2004) measured the density
and size structure of D. antillarum at five reefs in La Parguera: Turrumote, Mata la
Gata, Cayo Enrique, Laurel, and Media Luna. The median density for all locations
was 0.08 ind m
-2 . The highest mean urchin density (0.13 ind m
-2 ) was at Mata La
Gata, followed by Laurel (0.30 ind m
-2 ) and Media Luna (0.15 ind m
-2 ). No adult
D. antillarum were found at Turromote. The highest mean densities of D. antillarum were in the shallow fore-reef zone (depth from 0 to 3 m). He found that the
average size (± SD) for all sites was 6.71 cm (± 0.25). The size varied with
depth: 6.95 cm in shallower areas, 6.48 at intermediate depths, and 3.37 cm at
deeper reefs.
Shortly after Lugo (2004), Weil et al. (2005) described the decrease in the
population of D. antillarum from 1984 until 2001 and the population status
(abundances, distribution and size structure) after 17 years after the mass mortality
in La Parguera. They also found that overall the D. antillarum populations were
unevenly distributed and low across all sites (0.83–1.55 ind m
-2 ) compared to premortality densities. They also observed more urchins in shallow water areas
(depth \ 3 m). Urchins were significantly higher in shallow reef platforms
(0.89–1.98 ind m
-2 ) (depths from 0 to 3 m), and the upper fore-reef (0.56–2.33 ind
m
-2 ) habitats (depths from 3 to 7 m), compared to deeper (depths [ 7 m) habitats
(0.01–0.88 ind m
-2 ). In contrast, El Atravesado reef had higher urchin densities at
the deeper (depths from 8 to 10 m) habitats, along with high abundance of juveniles. A number of factors such as, planktonic settlement, differential morality of
juveniles, higher spatial heterogeneity, and presence of refuges could influence
D. antillarum distribution. Populations in the sea grass mounds were dominated by
midsize (6 cm) to large individuals (9 cm). Within reefs, the average size was
medium to large. Small sized individuals were more common in shallow reef
waters than on the Thalassia mounds. They observed a high abundance of juveniles in protected, back reef and lagoonal reef habitats. Higher number of
458
S. M. Williams et al.
island. Mellita lata was extremely numerous along the north-northeast coast
(Luquillo, San Juan, Guayama) and northwest and west coast (Aguadilla, Añasco,
Mayagüez). The moves by rhythmical movements of the long spines of the body,
marginal spines, interambulacra spines 1, 2, 3, and 4, and posterior lunule spines.
Kenk (1944) recorded about 35 strokes of the spines per minute at 26.5 °C. Other
members of order Clypeasteroida and family Mellitidae include Mellita quinquiesperforata (Leske) and Leodia sexiesperforata. Both are also commonly found
partially buried under sediments on sandy beaches, but particularly on bottoms
with high abundance of organic material (e.g., Naguabo, Humacao, Yabucoa).
Diadema antillarum Distribution
Before the mass mortality D. antillarum densities were high at many locations
around Puerto Rico, San Juan 13.8 ind m
-2 (Bauer 1980), La Parguera 12.7 ind
m
-2 (Craft 1975), Guayanilla 3.0 ind m
-2 (Vicente and Goenaga 1984), and Jobos
Bay 2.6 ind m
-2 (Rivera and Vicente 1976). Lugo (2004) measured the density
and size structure of D. antillarum at five reefs in La Parguera: Turrumote, Mata la
Gata, Cayo Enrique, Laurel, and Media Luna. The median density for all locations
was 0.08 ind m
-2 . The highest mean urchin density (0.13 ind m
-2 ) was at Mata La
Gata, followed by Laurel (0.30 ind m
-2 ) and Media Luna (0.15 ind m
-2 ). No adult
D. antillarum were found at Turromote. The highest mean densities of D. antillarum were in the shallow fore-reef zone (depth from 0 to 3 m). He found that the
average size (± SD) for all sites was 6.71 cm (± 0.25). The size varied with
depth: 6.95 cm in shallower areas, 6.48 at intermediate depths, and 3.37 cm at
deeper reefs.
Shortly after Lugo (2004), Weil et al. (2005) described the decrease in the
population of D. antillarum from 1984 until 2001 and the population status
(abundances, distribution and size structure) after 17 years after the mass mortality
in La Parguera. They also found that overall the D. antillarum populations were
unevenly distributed and low across all sites (0.83–1.55 ind m
-2 ) compared to premortality densities. They also observed more urchins in shallow water areas
(depth \ 3 m). Urchins were significantly higher in shallow reef platforms
(0.89–1.98 ind m
-2 ) (depths from 0 to 3 m), and the upper fore-reef (0.56–2.33 ind
m
-2 ) habitats (depths from 3 to 7 m), compared to deeper (depths [ 7 m) habitats
(0.01–0.88 ind m
-2 ). In contrast, El Atravesado reef had higher urchin densities at
the deeper (depths from 8 to 10 m) habitats, along with high abundance of juveniles. A number of factors such as, planktonic settlement, differential morality of
juveniles, higher spatial heterogeneity, and presence of refuges could influence
D. antillarum distribution. Populations in the sea grass mounds were dominated by
midsize (6 cm) to large individuals (9 cm). Within reefs, the average size was
medium to large. Small sized individuals were more common in shallow reef
waters than on the Thalassia mounds. They observed a high abundance of juveniles in protected, back reef and lagoonal reef habitats. Higher number of
458
S. M. Williams et al.