Sea Stars
Arm regeneration in starfish is related to sub-lethal predation. Sonnenholzner and
Lawrence (2002) collected few starfish with signs of sub-lethal predation at Los
Frailes, Manabí. They found that one of the 54 specimens collected in their study
had four arms and two others had regenerating arms. They observed that the
parrotfish Scarus perrico is the predator of the tan starfish P. unifascialis. Nonetheless, the strength of the body wall, and the availability of food may affect the
susceptibility to predation (Lawrence 1987). The low incidence of wounded or
regenerating arms in the population of P. unifascialis suggests parrotfish are less
inclined to feed on it, probably due to its strong body wall.
6.3.5 Interacting Effects of Echinoderms on Benthic Communities
Sea Urchins
Of all benthic consumers, sea urchins are known to be one of the most influential
taxa affecting community structure (Lawrence 1975). Sea urchins have the
potential to influence the distribution, relative abundance and species composition
of algae and other sessile invertebrates (Kitching and Ebling 1961, Paine and
Vadas 1969), thereby determining the biomass, diversity and productivity of
marine communities. In Ecuador, studies on this topic have been done only in the
Galápagos Islands, with the pioneer work of Peter W. Glynn in the late 1970s. In
an assessment of coral growth versus coral attrition from grazing, Glynn et al.
(1979) showed that E. galapagensis reduced coral growth in the Galápagos. He
reported individuals of E. galapagensis grazing heavily on live hermatypic pocilloporid corals, including Pocillopora damicornis, P. elegans, P. capitata and
also Pavona clavus. Given that urchins were more abundant along the reef edge,
grazing was more intense there. The study suggested E. galapagensis might limit
reef growth, especially by interfering with the development of reef frame and its
lateral expansion. By comparing Panamá to the Galápagos, Glynn et al. (1979)
attributed the lower buildup of coral in the Galápagos to a much heavier sea urchin
grazing and suggested this difference was due to a lower predation of sea urchins
in the Galápagos.
Almost a decade later, Glynn (1988) showed that the distribution and population densities of E. galapagensis changed dramatically following the 1982–83 El
Niño disturbance. Once abundant in off-reef and reef edges areas, sea urchins
moved to the center of the dead reef frameworks of Porites and Pavona, causing
bioerosion rates that ranged from 49 to 99 g CaCO 3 m
-2 day
-1 . Before 1983,
E. galapagensis at high densities grazed extensively on live pocilloporid corals
(Glynn et al. 1983). However after the El Niño event these corals were locally
6 Echinoderms of Ecuador
215
Arm regeneration in starfish is related to sub-lethal predation. Sonnenholzner and
Lawrence (2002) collected few starfish with signs of sub-lethal predation at Los
Frailes, Manabí. They found that one of the 54 specimens collected in their study
had four arms and two others had regenerating arms. They observed that the
parrotfish Scarus perrico is the predator of the tan starfish P. unifascialis. Nonetheless, the strength of the body wall, and the availability of food may affect the
susceptibility to predation (Lawrence 1987). The low incidence of wounded or
regenerating arms in the population of P. unifascialis suggests parrotfish are less
inclined to feed on it, probably due to its strong body wall.
6.3.5 Interacting Effects of Echinoderms on Benthic Communities
Sea Urchins
Of all benthic consumers, sea urchins are known to be one of the most influential
taxa affecting community structure (Lawrence 1975). Sea urchins have the
potential to influence the distribution, relative abundance and species composition
of algae and other sessile invertebrates (Kitching and Ebling 1961, Paine and
Vadas 1969), thereby determining the biomass, diversity and productivity of
marine communities. In Ecuador, studies on this topic have been done only in the
Galápagos Islands, with the pioneer work of Peter W. Glynn in the late 1970s. In
an assessment of coral growth versus coral attrition from grazing, Glynn et al.
(1979) showed that E. galapagensis reduced coral growth in the Galápagos. He
reported individuals of E. galapagensis grazing heavily on live hermatypic pocilloporid corals, including Pocillopora damicornis, P. elegans, P. capitata and
also Pavona clavus. Given that urchins were more abundant along the reef edge,
grazing was more intense there. The study suggested E. galapagensis might limit
reef growth, especially by interfering with the development of reef frame and its
lateral expansion. By comparing Panamá to the Galápagos, Glynn et al. (1979)
attributed the lower buildup of coral in the Galápagos to a much heavier sea urchin
grazing and suggested this difference was due to a lower predation of sea urchins
in the Galápagos.
Almost a decade later, Glynn (1988) showed that the distribution and population densities of E. galapagensis changed dramatically following the 1982–83 El
Niño disturbance. Once abundant in off-reef and reef edges areas, sea urchins
moved to the center of the dead reef frameworks of Porites and Pavona, causing
bioerosion rates that ranged from 49 to 99 g CaCO 3 m
-2 day
-1 . Before 1983,
E. galapagensis at high densities grazed extensively on live pocilloporid corals
(Glynn et al. 1983). However after the El Niño event these corals were locally
6 Echinoderms of Ecuador
215