D. antillarum on the algal biomass in damselfish territories, this damselfish species
was found to rarely defend its feeding areas against D. antillarum and therefore
had little effect on its distribution.
On the Pacific coast of Panama grazing by D. mexicanum results in the
bioerosion of the predominantly Pocillopora spp. coral reefs (Glynn 1988).
This species contributes 78 % of the overall bioerosion 13 kg m
-2 y
-1 produced
by benthic eroders (Glynn 1988; Eakin 1991). Analysis of faecal pellets has
revealed that the diet of D. mexicanum consists of 75.2 ± 11.03 % coral and
only 23.0 ± 11.4 % of crustose coralline algae (CCA). In contrast the diet of
Toxopneustes roseus (A. Agassiz, 1863) is composed of approximately 20 %
coral and 80 % of CCA (Glynn 1988). This highlights the potential damage
D. mexicanum poses to reef structures, particularly when present in large numbers.
Such a threat was realised following the 1982–83 El Niño Southern Oscillation
event (ENSO). This resulted in mass coral bleaching and a 50 % reduction of live
coral cover on Uva Reef (Glynn 1985a), which was followed by a dramatic
increase in the population size of D. mexicanum from 2–5 ind m
-2 pre 1983 to
60–100 ind m
-2 post 1982-83 ENSO (Glynn 1988, 1990; Eakin 1991, 1992). Such
large numbers of D. mexicanum resulted in high rates of reef framework erosion,
shifting the reef environment into a state of near accretionary stasis (Eakin 1992;
Glynn 1997). Low predation pressure (with the removal of potentially important
fish predators as a result of over-fishing), increased habitat availability, and the
increased abundance of benthic algae as a result of the newly dead coral substratum allowed D. mexicanum to attain high population densities (Glynn 1988).
However, such a large population of D. mexicanum could not be sustained and
in the year 2000 the population of D. mexicanum dropped to near 1974 levels
([10 ind m
-2 ) (Eakin 2001).
The ability of damselfish in the eastern Pacific to exclude Diadema from their
territories appears to be a very different situation to that reported in the Caribbean.
The territorial action of Stegastes acapulcoensis (Fowler, 1944) on Uva Reef
results in few sea urchins being present in their territories (Glynn 1990), with
consequently lower levels of erosion (6.3 mm y
-1 ) than elsewhere on the reef
(21.8 mm y
-1 ) (Eakin 1992).
Ecological studies on irregular echinoids in Panama have focused on sand
dollars. Seilacher (1979) studied the distribution of Mellita quinquiesperforata
(Leske, 1778) (as Mellita lata Clark, 1940), a subjective junior synonym of M.
quinquiesperforata) at Maria Chiquita on the Caribbean coast of Panama. This
species lives partially buried in the sand (with some of the apical surface exposed)
and is restricted to a 4 m wide region of the surf-zone that runs parallel to the
beach (Seilacher 1979). This species was observed feeding along this zone, but
migrated to deeper water when the intensity of the wave action increased.
The behavioural ecology of a population of Mellitella stokesii (L. Agassiz,
1841) (as Encope stokesi L. Agassiz, 1841 [sic]) was studied over a year at Venado
Beach, on the eastern Pacific coast of Panama by Dexter (1977). Densities of this
species were reported to vary from a low of 19 ind m
-2 in the rainy season to a
114
S. E. Coppard and J. J. Alvarado
was found to rarely defend its feeding areas against D. antillarum and therefore
had little effect on its distribution.
On the Pacific coast of Panama grazing by D. mexicanum results in the
bioerosion of the predominantly Pocillopora spp. coral reefs (Glynn 1988).
This species contributes 78 % of the overall bioerosion 13 kg m
-2 y
-1 produced
by benthic eroders (Glynn 1988; Eakin 1991). Analysis of faecal pellets has
revealed that the diet of D. mexicanum consists of 75.2 ± 11.03 % coral and
only 23.0 ± 11.4 % of crustose coralline algae (CCA). In contrast the diet of
Toxopneustes roseus (A. Agassiz, 1863) is composed of approximately 20 %
coral and 80 % of CCA (Glynn 1988). This highlights the potential damage
D. mexicanum poses to reef structures, particularly when present in large numbers.
Such a threat was realised following the 1982–83 El Niño Southern Oscillation
event (ENSO). This resulted in mass coral bleaching and a 50 % reduction of live
coral cover on Uva Reef (Glynn 1985a), which was followed by a dramatic
increase in the population size of D. mexicanum from 2–5 ind m
-2 pre 1983 to
60–100 ind m
-2 post 1982-83 ENSO (Glynn 1988, 1990; Eakin 1991, 1992). Such
large numbers of D. mexicanum resulted in high rates of reef framework erosion,
shifting the reef environment into a state of near accretionary stasis (Eakin 1992;
Glynn 1997). Low predation pressure (with the removal of potentially important
fish predators as a result of over-fishing), increased habitat availability, and the
increased abundance of benthic algae as a result of the newly dead coral substratum allowed D. mexicanum to attain high population densities (Glynn 1988).
However, such a large population of D. mexicanum could not be sustained and
in the year 2000 the population of D. mexicanum dropped to near 1974 levels
([10 ind m
-2 ) (Eakin 2001).
The ability of damselfish in the eastern Pacific to exclude Diadema from their
territories appears to be a very different situation to that reported in the Caribbean.
The territorial action of Stegastes acapulcoensis (Fowler, 1944) on Uva Reef
results in few sea urchins being present in their territories (Glynn 1990), with
consequently lower levels of erosion (6.3 mm y
-1 ) than elsewhere on the reef
(21.8 mm y
-1 ) (Eakin 1992).
Ecological studies on irregular echinoids in Panama have focused on sand
dollars. Seilacher (1979) studied the distribution of Mellita quinquiesperforata
(Leske, 1778) (as Mellita lata Clark, 1940), a subjective junior synonym of M.
quinquiesperforata) at Maria Chiquita on the Caribbean coast of Panama. This
species lives partially buried in the sand (with some of the apical surface exposed)
and is restricted to a 4 m wide region of the surf-zone that runs parallel to the
beach (Seilacher 1979). This species was observed feeding along this zone, but
migrated to deeper water when the intensity of the wave action increased.
The behavioural ecology of a population of Mellitella stokesii (L. Agassiz,
1841) (as Encope stokesi L. Agassiz, 1841 [sic]) was studied over a year at Venado
Beach, on the eastern Pacific coast of Panama by Dexter (1977). Densities of this
species were reported to vary from a low of 19 ind m
-2 in the rainy season to a
114
S. E. Coppard and J. J. Alvarado