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P.W.Glynn
causing little damage to the skeleton (Chaetodontidae, Pomacentridae) to
abrading or breaking apart colonies in the feeding process (Balistidae,
Scaridae, Tetraodontidae). Individual tetraodontids, Arothron meleagris
(Bloch and Schneider), can typically ingest 10 g (dry weight) of pocilloporid branch tips daily. During the feeding forays the pufferfish also remove
an approximately equal mass of branch tips, which are not ingested but fall
to the bottom. The balistid, Pseudobalistes naufragium (Jordan and
Starks), has the interesting habit of biting off 3- to S-cm knobs from colonies of Porites lobata. This behavior exposes endolithic bivalves (Lithophaga spp.), which are then eaten by the balistid. If the discarded pori tid fragments remain on a coarse sand bottom they often survive and continue to
grow as disks or potato-shaped colonies, encircling the parent colony
(Guzman 1988). The often high level of disturbance of bottom sediments
by fishes and invertebrates on rubble substrates also serves to promote the
survival of coral fragments (coralliths), which frequently assume a spherical shape due to frequent colony rotation and nearly equal growth on all
surfaces.
Clearly, large amounts of coral tissue and skeletal material are consumed and bioeroded on eastern Pacific reefs, in accordance with Highsmith's (1980) model relating elevated rates of bioerosion with increasing
rates of productivity. Under usual conditions, coral reefs have continued to
grow and accumulate calcium carbonate at relatively high rates. For example, before the 1982-1983 ENSO disturbance, reef-wide maximum calcification rates amounted to 10 kg m- 2 yr- 1 on a reef at Uva Island in the Gulf
of Chiriqui, Panama (Fig. 19.1, site7; Fig. 19.2D), and to 8-16kg m- 2 year- 1
in the Galapagos Islands (Glynn et al. 1988). After the ENSO event, CaC0 3
loss due to bioerosion exceeded gains, resulting in net reef framework
losses. In a model comparison of CaC0 3 budgets before and after the
1982-1983 ENSO, Eakin (1996) estimated that the 2.5-ha Uva Island reef
was eroding at a rate of 4,800kg year- 1 • However, the rates of bioerosion
were highly variable with some reef zones continuing to show positive net
accretion. By ejecting sea urchins from their algal lawn territories, damselfish significantly retard bioerosion in shallow reef zones. Most of the erosion is due to sea urchins (Diadema), with boring sponges, bivalves and
fishes also contributing significantly. On Galapagos reefs, damselfish also
eject Eucidaris, but the high abundance of the sea urchins and low rates of
coral recruitment are leading to a rapid disappearance of reef frameworks
(Reaka-Kudla et al. 1996).
P.W.Glynn
causing little damage to the skeleton (Chaetodontidae, Pomacentridae) to
abrading or breaking apart colonies in the feeding process (Balistidae,
Scaridae, Tetraodontidae). Individual tetraodontids, Arothron meleagris
(Bloch and Schneider), can typically ingest 10 g (dry weight) of pocilloporid branch tips daily. During the feeding forays the pufferfish also remove
an approximately equal mass of branch tips, which are not ingested but fall
to the bottom. The balistid, Pseudobalistes naufragium (Jordan and
Starks), has the interesting habit of biting off 3- to S-cm knobs from colonies of Porites lobata. This behavior exposes endolithic bivalves (Lithophaga spp.), which are then eaten by the balistid. If the discarded pori tid fragments remain on a coarse sand bottom they often survive and continue to
grow as disks or potato-shaped colonies, encircling the parent colony
(Guzman 1988). The often high level of disturbance of bottom sediments
by fishes and invertebrates on rubble substrates also serves to promote the
survival of coral fragments (coralliths), which frequently assume a spherical shape due to frequent colony rotation and nearly equal growth on all
surfaces.
Clearly, large amounts of coral tissue and skeletal material are consumed and bioeroded on eastern Pacific reefs, in accordance with Highsmith's (1980) model relating elevated rates of bioerosion with increasing
rates of productivity. Under usual conditions, coral reefs have continued to
grow and accumulate calcium carbonate at relatively high rates. For example, before the 1982-1983 ENSO disturbance, reef-wide maximum calcification rates amounted to 10 kg m- 2 yr- 1 on a reef at Uva Island in the Gulf
of Chiriqui, Panama (Fig. 19.1, site7; Fig. 19.2D), and to 8-16kg m- 2 year- 1
in the Galapagos Islands (Glynn et al. 1988). After the ENSO event, CaC0 3
loss due to bioerosion exceeded gains, resulting in net reef framework
losses. In a model comparison of CaC0 3 budgets before and after the
1982-1983 ENSO, Eakin (1996) estimated that the 2.5-ha Uva Island reef
was eroding at a rate of 4,800kg year- 1 • However, the rates of bioerosion
were highly variable with some reef zones continuing to show positive net
accretion. By ejecting sea urchins from their algal lawn territories, damselfish significantly retard bioerosion in shallow reef zones. Most of the erosion is due to sea urchins (Diadema), with boring sponges, bivalves and
fishes also contributing significantly. On Galapagos reefs, damselfish also
eject Eucidaris, but the high abundance of the sea urchins and low rates of
coral recruitment are leading to a rapid disappearance of reef frameworks
(Reaka-Kudla et al. 1996).