284
P.W.Glynn
Within the eastern Pacific region, local upwelling systems also can influence the structure and distribution of coral communities. While coral reefs
occur within the three major eastern Pacific upwelling centers in the Gulfs
of Tehuantepec (site 3), Papagayo (site 5), and Panama (site 8), they are
usually more numerous, larger and older (with thicker framework accumulations) in non-upwelling areas, such as Cafio Island/Golfito area (site
6), Gulf of Chiriqui (site 7), and Gorgona Island (site 10; Fig. 19.1) and their
associated biota are somewhat different. For example, zooxanthellate
hydrocorals (Millepora, two species) and the crown-of-thorns sea star
[Acanthaster planci (Linnaeus)] are associated with coral reefs in the Gulf
of Chiriqui, but not in the Gulf of Panama (Glynn 1974).Another area subject to strong upwelling, devoid of coral communities and reef development, is the western shore of the Galapagos Islands where the Equatorial
Undercurrent surfaces (Pak and Zanfeld 1973). Here, astride the equator,
sea surface temperatures (SSTs) dip below 15 oc, nutrients are usually in
high concentration, and the littoral marine communities consist predominantly of macroalgae (Glynn and Wellington 1983). Anomalously
high SSTs also can affect coral reef development. The magnitude and duration of positive sea temperature anomalies that accompanied the
1982-1983 and 1997-1998 El Nino-Southern Oscillation (ENSO) events
correlated with local patterns of coral bleaching (loss of symbiotic zooxanthellae) and mortality (Glynn et al. 1988). Coral mortality and subsequent bioerosion have resulted in significant degradation of reefs throughout the equatorial eastern Pacific and the virtual elimination of the coral
reef biotope from the Galapagos Islands.
Several other factors, like the availability of stable substrates, degree of
exposure to wave assault, and water quality, can influence eastern Pacific
reef development. Since much of the mainland coast supports mangrove
ecosystems, freshwater lagoons, estuaries and sandy/muddy beaches, coral
reefs occur along rocky coastal stretches that offer suitable conditions for
their development (i.e. sites 1, 2, 3, 4, 6, 7; Fig. 19.1 ). Unlike coral reefs in
most other biogeographic regions, eastern Pacific reefs are constructed
mainly of branching corals which are not typically well consolidated
by crustose coralline algae or underwater cementation. Therefore, reef
frameworks are relatively fragile and tend to develop best on rocky shores
sheltered from the full force of open seas, such as in bays and on the leeward sides of offshore islands. This dependency on sheltered locations is
well illustrated by the distribution of coral reefs along the Huatulco coast
(site 3; Figs. 19.1, 19.2C). Paradoxically, patch reefs even occur inside the
Punta Entrada estuary (Gulf of Chiriqui), their presence due presumably
to a saltwater wedge that sustains relatively high salinity conditions in
this marginal setting. Coral reefs also occur in the Panama Bight (sites 8, 9)
P.W.Glynn
Within the eastern Pacific region, local upwelling systems also can influence the structure and distribution of coral communities. While coral reefs
occur within the three major eastern Pacific upwelling centers in the Gulfs
of Tehuantepec (site 3), Papagayo (site 5), and Panama (site 8), they are
usually more numerous, larger and older (with thicker framework accumulations) in non-upwelling areas, such as Cafio Island/Golfito area (site
6), Gulf of Chiriqui (site 7), and Gorgona Island (site 10; Fig. 19.1) and their
associated biota are somewhat different. For example, zooxanthellate
hydrocorals (Millepora, two species) and the crown-of-thorns sea star
[Acanthaster planci (Linnaeus)] are associated with coral reefs in the Gulf
of Chiriqui, but not in the Gulf of Panama (Glynn 1974).Another area subject to strong upwelling, devoid of coral communities and reef development, is the western shore of the Galapagos Islands where the Equatorial
Undercurrent surfaces (Pak and Zanfeld 1973). Here, astride the equator,
sea surface temperatures (SSTs) dip below 15 oc, nutrients are usually in
high concentration, and the littoral marine communities consist predominantly of macroalgae (Glynn and Wellington 1983). Anomalously
high SSTs also can affect coral reef development. The magnitude and duration of positive sea temperature anomalies that accompanied the
1982-1983 and 1997-1998 El Nino-Southern Oscillation (ENSO) events
correlated with local patterns of coral bleaching (loss of symbiotic zooxanthellae) and mortality (Glynn et al. 1988). Coral mortality and subsequent bioerosion have resulted in significant degradation of reefs throughout the equatorial eastern Pacific and the virtual elimination of the coral
reef biotope from the Galapagos Islands.
Several other factors, like the availability of stable substrates, degree of
exposure to wave assault, and water quality, can influence eastern Pacific
reef development. Since much of the mainland coast supports mangrove
ecosystems, freshwater lagoons, estuaries and sandy/muddy beaches, coral
reefs occur along rocky coastal stretches that offer suitable conditions for
their development (i.e. sites 1, 2, 3, 4, 6, 7; Fig. 19.1 ). Unlike coral reefs in
most other biogeographic regions, eastern Pacific reefs are constructed
mainly of branching corals which are not typically well consolidated
by crustose coralline algae or underwater cementation. Therefore, reef
frameworks are relatively fragile and tend to develop best on rocky shores
sheltered from the full force of open seas, such as in bays and on the leeward sides of offshore islands. This dependency on sheltered locations is
well illustrated by the distribution of coral reefs along the Huatulco coast
(site 3; Figs. 19.1, 19.2C). Paradoxically, patch reefs even occur inside the
Punta Entrada estuary (Gulf of Chiriqui), their presence due presumably
to a saltwater wedge that sustains relatively high salinity conditions in
this marginal setting. Coral reefs also occur in the Panama Bight (sites 8, 9)