Honduras on Media Luna and Becerro reefs. On the overfished reefs, the rate of
T. testudinum removal increased significantly with depth, urchin densities were
high, and urchin grazing was equal to, or greater than, fish grazing in shallow
habitats. At the overfished reefs (Haiti, Saint Croix and Saint Thomas) the percent
of T. testdinum eaten per hour by sea urchins was between 0 and 10.8 % with a
D. antillarum density range between 5-20 ind m
-2
. At the less fished reefs
(Honduras and Belize) it was between 0 and 1 % with D. antillarum densities
of \ 1 ind m
-2 for the Honduras sites and around 0.2 and 8 ind m
-2 for the Belize
sites. He concluded that on the reef unaffected by humans, the overall impact of
urchins on macrophytes was minor relative to the impact of grazing fishes.
The combined effects of a reduction in herbivory due to D. antillarum mass
mortality in 1983–1984 (Lessios et al. 1984) and the increase in vacant substratum
because of coral death (Aronson et al. 2000) have caused dramatic changes in the
Caribbean. This has led to several attempts to understand the ecosystem dynamics
after these events. McClanahan (1999) examined the ecology of a grazer living
sympatrically with D. antillarum and Echinometra viridis. He assessed the role
that finfish and invertebrate predators play in controlling the distribution of
E. viridis as well the ability of E. viridis to control exposed fleshy algae on patch
reefs on the Glovers Reef Atoll lagoon. McClanahan’s (1999) results showed that
the abundance of E. viridis is constrained by predation, which restricts E. viridis to
cryptic locations. He proposed that this sea urchin is unable to control exposed
erect fleshy algae as well as D. antillarum (McClanahan 1999).
In despite of McClanahan’s (1999) results, Aronson et al. (2002a) reported that
high densities of the sea urchin E. viridis kept the cover of fleshy and filamentous
macroalgae to low levels. They concluded that herbivorous activity of E. viridis
could help re-establishment of the coral Agaricia tenuifolia. This trend has been
observed by Aronson and his colleagues throughout the Caribbean as well in
Belizean reefs (Aronson 2002b; Aronson et al. 2005). Carpenter and Edmunds
(2006) reported that dense populations of Diadema now occur over a multikilometer-wide scale across the entire Caribbean. They conclude that population
recovery of D. antillarum is occurring at both local and regional scales and that
grazing by this echinoid is creating conditions that favor the recruitment of corals
(Carpenter and Edmunds 2006).
Brown-Saracino et al. (2007) examined urchin population characteristics,
bioerosion rates, their fish predators, and potential competitors on three unprotected reefs and one reef within Hol Chan Marine Reserve in the lagoonal regions
of the reef system off Belize. Their report presents densities of Balistidae and
Labridae (as predator fish of urchins) and Labridae (potential competitors of
urchins). Population data on coral reefs and algae were collected. They recorded
urchin wet weight and test diameter. They also analyzed gut contents to estimate
yearly bioerosion rates per square meter of reefs. Six species of sea urchin were
found at the study sites, D. antillarum, E. lucunter, E. viridis, E. tribuloides,
L. variegatus and L. williamsi. Echinometra viridis was the dominant species at all
but one of the patch reef sites surveyed. Furthermore, D. antillarum was found in
3 Central America Echinoderms: Diversity, Ecology and Future Perspectives
87
T. testudinum removal increased significantly with depth, urchin densities were
high, and urchin grazing was equal to, or greater than, fish grazing in shallow
habitats. At the overfished reefs (Haiti, Saint Croix and Saint Thomas) the percent
of T. testdinum eaten per hour by sea urchins was between 0 and 10.8 % with a
D. antillarum density range between 5-20 ind m
-2
. At the less fished reefs
(Honduras and Belize) it was between 0 and 1 % with D. antillarum densities
of \ 1 ind m
-2 for the Honduras sites and around 0.2 and 8 ind m
-2 for the Belize
sites. He concluded that on the reef unaffected by humans, the overall impact of
urchins on macrophytes was minor relative to the impact of grazing fishes.
The combined effects of a reduction in herbivory due to D. antillarum mass
mortality in 1983–1984 (Lessios et al. 1984) and the increase in vacant substratum
because of coral death (Aronson et al. 2000) have caused dramatic changes in the
Caribbean. This has led to several attempts to understand the ecosystem dynamics
after these events. McClanahan (1999) examined the ecology of a grazer living
sympatrically with D. antillarum and Echinometra viridis. He assessed the role
that finfish and invertebrate predators play in controlling the distribution of
E. viridis as well the ability of E. viridis to control exposed fleshy algae on patch
reefs on the Glovers Reef Atoll lagoon. McClanahan’s (1999) results showed that
the abundance of E. viridis is constrained by predation, which restricts E. viridis to
cryptic locations. He proposed that this sea urchin is unable to control exposed
erect fleshy algae as well as D. antillarum (McClanahan 1999).
In despite of McClanahan’s (1999) results, Aronson et al. (2002a) reported that
high densities of the sea urchin E. viridis kept the cover of fleshy and filamentous
macroalgae to low levels. They concluded that herbivorous activity of E. viridis
could help re-establishment of the coral Agaricia tenuifolia. This trend has been
observed by Aronson and his colleagues throughout the Caribbean as well in
Belizean reefs (Aronson 2002b; Aronson et al. 2005). Carpenter and Edmunds
(2006) reported that dense populations of Diadema now occur over a multikilometer-wide scale across the entire Caribbean. They conclude that population
recovery of D. antillarum is occurring at both local and regional scales and that
grazing by this echinoid is creating conditions that favor the recruitment of corals
(Carpenter and Edmunds 2006).
Brown-Saracino et al. (2007) examined urchin population characteristics,
bioerosion rates, their fish predators, and potential competitors on three unprotected reefs and one reef within Hol Chan Marine Reserve in the lagoonal regions
of the reef system off Belize. Their report presents densities of Balistidae and
Labridae (as predator fish of urchins) and Labridae (potential competitors of
urchins). Population data on coral reefs and algae were collected. They recorded
urchin wet weight and test diameter. They also analyzed gut contents to estimate
yearly bioerosion rates per square meter of reefs. Six species of sea urchin were
found at the study sites, D. antillarum, E. lucunter, E. viridis, E. tribuloides,
L. variegatus and L. williamsi. Echinometra viridis was the dominant species at all
but one of the patch reef sites surveyed. Furthermore, D. antillarum was found in
3 Central America Echinoderms: Diversity, Ecology and Future Perspectives
87