AMER. ZOOL., 32:707-718 (1992)
Sporadic Disturbances in Fluctuating Coral Reef Environments:
El Niflo and Coral Reef Development in the Eastern Pacific1
PETER W. GLYNN
Division of Marine Biology & Fisheries, Rosenstiel School of Marine & Atmospheric Science,
4600 Rickenbacker Causeway, University of Miami, Miami, Florida 33149-1098
AND
MITCHELL W. COLGAN
Department of Geology, College of Charleston, Charleston, South Carolina 24924
SYNOPSIS. The disastrous effects of the intense 1982-83 El Nino-Southern
Oscillation (ENSO) bring new insight into the long-term development of
eastern Pacific coral reefs. The 1982-83 ENSO sea surface warming event
caused extensive reef coral bleaching (loss of symbiotic zooxanthellae),
resulting in up to 70-95% coral mortality on reefs in Costa Rica, Panama,
Colombia and Ecuador. In the Galapagos Islands (Ecuador), most coral
reefs experienced >95% coral mortality. Also, several coral species experienced extreme reductions in population size, and local and regional
extinctions. The El Nino event spawned secondary disturbances, such as
increased predation and bioerosion, that continue to impact reef-building
corals. The death of Pocillopora colonies with their crustacean guards
eliminated coral barriers now allowing the corallivore Acanthaster planci
access to formerly protected coral prey. Sea urchins and other organisms
eroded disturbed corals at rates that exceed carbonate production, potentially resulting in the elimination of existing reef buildups. In other reefbuilding regions following extensive, catastrophic coral mortality, rapid
recovery often occurs through the growth of surviving corals, recruitment
of new corals from nearby source populations, and survival of consolidated reef surfaces. In the eastern Pacific, however, the return of upwelling
conditions and the survival of coral predators and bioeroders hamper
coral reef recovery by reducing recruitment success and eroding coral reef
substrates. Thus, coral reef growth that occurs between disturbance events
is not conserved. Repeated El Nino disturbances, which have occurred
throughout the recent geologic history of the eastern Pacific, prevent coral
communities from increasing in diversity and limit the development and
persistence of significant reef features. The poor development of eastern
Pacific coral reefs throughout Holocene and perhaps much of Pleistocene
time may result from recurrent thermal disturbances of the intensity of
the 1982-83 El Nino event.
INTRODUCTION
The community structure of long-lived
ecosystems, like coral reefs, results from past
as well as present biological and physical
agents. Observable, testable daily processes
1
I
o
From the Symposium on Long-Term Dynamics of
Coral Reefs presented at the Annual Meeting of the
American Society ofZoologists, 27-30 December 1991,
at Atlanta, Georgia.
(e.g., competition and predation) that impact
reef development are often the focus of field
research. However, rare but intense physic a la n d
biological disturbances that are not
quantifiable over short experimental periods have profound effects on the community composition and structure of long-lived
ecosystems (e.g., Connell, 1978; Paine and
j - v : n 1Q81- r n n n p l1l 1 a n d K e o u e h 10R5^ V m ' V**l>
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Wethey, 1V85; M o r a n , WHO).
T h e 1 9 8 2 - 8 3 El N i n o e v e n t , of u n c o m -
707
708
P. W. GLYNN AND M. W. COLGAN
- 30N
20N
10N
2°C Anomaly
> 1 month envelope
> 6 month envelope
11 month envelope
130W
120W
110W 100W 90W
80W
70
30N
20N
10N
20S
3"C Anomaly
> 1 month envelope
> 6 month envelope
11 month envelope ' "
.
130W
120W
.
110W 100W 90W
.
80W
30S
70W
FIG. 1. Eastern Pacific sea surface temperature anomalies of 2°C (A) and 3°C (B) that occurred during the
1982-83 ENSO event. Shading patterns indicate the
duration of thermal elevation within specific locations.
The equatorial eastern Pacific reef region is delineated
(Oceanographic Monthly Summary, 1982, 83).
mon intensity in recent history, stressed the
long-lived coral reef ecosystems of the eastern Pacific (Fig. 1). This disturbance significantly altered the reef-building environment, perhaps stressing these coral reefs
beyond their ecologic threshold (see Knowlton, 1992). Recovery from this disturbance
has been slow, and secondary disturbances
following the event are currently causing
longer-term changes to local coral reef communities (Glynn, 1990).
El Nino events occur when shallow waters
off northwestern South America enter a pronounced warming trend (Wyrtki, 1975; Philander, 1983;Rasmusson, 1984; Cane, 1986;
Hansen, 1990). El Nino is part of a global
atmospheric phenomenon known as the El
Nino-Southern Oscillation (ENSO). At the
height of an intense ENSO event, the eastern Pacific's normally cool, highly productive waters warm and productivity declines.
El Nino events of greatly varying intensities
have appeared sporadically in the eastern
Pacific (Quinn et al., 1987), but the intensity
of the 1982-83 El Nino event was perhaps
unprecedented in recorded history (Glynn,
1990).
The 1982-83 El Nino event significantly
raised sea surface temperatures (SST) for
several months causing widespread coral
bleaching (loss of zooxanthellae) and death
to corals and other reef organisms (Glynn,
1983, 1984,1988a, 1990; Glynn et al, 1989;
Lessios et al, 1983; Robinson, 1985). Secondary disturbances following the initial
mortality of corals continue to impact coral
communities 9 yr after the initial event. The
severity of the 1982-83 event and the following secondary disturbances suggest that
strong El Nino warming events are partially
responsible for the impoverished coral fauna
and meager coral reef development in the
eastern Pacific. Thus, with frequent upwelling, sporadic El Nino warming disturbances
add another physical constraint to eastern
Pacific reef development (Dana, 1975;
Glynn, 1977; Colgan, 1990). Before the
1982-83 event, El Nino's detrimental effects
to coral reefs were unknown, and El Nino
was considered somewhat unimportant in
the history of eastern Pacific reef building
(e.g., Durham, 1947; Stoddart, 1969; Stehli
and Wells, 1971; Porter, 1974; Dana, 1975;
Glynn et al., 1983; Glynn and Wellington,
1983). In this paper, we examine how ecologically rare but recurring intense El Nino
disturbances can significantly influence the
long-term dynamics of eastern Pacific reef
development and history. Also, these infrequent catastrophic events could give addi-
EL NINO AND CORAL REEF DEVELOPMENT
tional insight into the reasons why eastern
and western Pacific coral reefs differ so much
from each other.
709
1977; Glynn and Wellington, 1983; Hallock
and Schlager, 1986). In upwelling areas, like
the Gulf of Panama, reefs are poorly developed with a median reef thickness ranging
EASTERN PACIFIC CORAL REEFS
between 3.4 and 4.9 m (Wellington, 1982;
Eastern Pacific reef building corals have Glynn and Wellington, 1983). In contrast,
a strong species affinity with the western the largest eastern Pacific reefs occur in the
Pacific. However, only 18 species of scler- nonupwelling Gulf of Chiriqui, but they are
actinian and 3 species of hydrozoan corals only 1 to 2 hectares in lateral extent, weakly
form reefs in the eastern Pacific compared zoned, and grow in shallow (< 10 m) waters.
to over 510 coral species in the western Poorly cemented, interlocking branches of
Pacific (Glynn and Wellington, 1983; Veron Pocillopora build the reef framework, and
and Kelly, 1988). Eastern Pacific SST (24° massive colonies of Pavona spp., and Porito 29°C, Dana, 1975) overlaps the thermal tes spp., and branching Millepora spp. comrange for vigorous reef growth (i.e., 25°C to monly inhabit the reef (Glynn et ai, 1972;
28°C, Wells, 1956; Stoddart, 1969). A rising Glynn and Macintyre, 1977). Warmer water
sea level enabled reef building on the con- conditions in the nonupwelling Gulf of Chitinental shelf to begin on both sides of the riqui permit a slightly higher mean growth
Pacific Ocean (Goreau, 1969; Adey, 1978; rate of Pocillopora, to 3.9 cm/yr, compared
Fairbanks, 1989). In the eastern Pacific, sea to 3.1 cm/yr in the Gulf of Panama (Glynn,
level neared its present height around 4,000 1977).
years ago (Curray et al, 1969; Hopley, 1982).
Reefs of the Galapagos Islands are typiThe average accumulation rates of some cally small (less than 100 m2), thin struceastern Pacific reefs (e.g., 3.1-3.9 m/1,000 tures usually composed of a single predomyr, Gulf of Chiriqui, Panama, [Glynn and inant species. In 17 reef building localities,
Macintyre, 1977]) are similar to many reefs Pocillopora damicornis predominated in 10
elsewhere in the Pacific (e.g., 3.2 m/1,000 communities, Pavona clavus in six, and
yr, Great Barrier Reef, One Tree Reef Porites lobata at one location (Glynn and
[Davies and Marshall, 1980]). Despite the Wellington, 1983).
similar starting times and accumulation
rates, western and central Pacific areas have
1982-83 EL NINO-SOUTHERN
experienced more vigorous reef developOSCILLATION (ENSO)
ment than eastern Pacific areas (Glynn et
El Nino-Southern Oscillation (ENSO), a
al., 1972; Glynn, 1976). Eastern Pacific reefs complex atmospheric and oceanographic
are commonly small, isolated, monospecific phenomenon, sporadically alters large scale
thickets of Pocillopora or massive colonies
of Porites and Pavona growing usually 5-6 atmospheric pressure systems, wind sysm high and 150 m wide (Glynn, 1976; Glynn tems, rainfall patterns, ocean currents and
and Macintyre, 1977; Glynn and Welling- sea level within the tropical and subtropical
ton, 1983; Wellington, 1984;Colgan, 1991). Pacific Ocean (Bjerknes, 1969,1972;Wyrtki,
These small reefs occur from southern Baja 1975, 1979, 1985; Cane, 1983, 1986; RasCalifornia to the central coast of Ecuador musson, 1985;Enfield, 1987). In the eastern
including offshore islands such as the Gala- Pacific, SSTs increase and equatorial and
coastal upwelling of cool, nutrient-rich
pagos Islands (UNEP/IUCN, 1988).
waters decreases (Cane, 1986; Hansen,
Turbidity and a shallow (20 m), fluctu- 1990). Other related disturbances include
ating thermocline act to restrict reef growth increased rainfall and flooding, increased
(Allison, 1959; Stehli and Wells, 1971; Dana, sediment loads and turbidity in coastal
1975). Reefs of the eastern Pacific must cope waters, and abnormally high sea level stands,
with seasonal upwelling of cool, nutrient- rougher seas and coastal erosion (Caviedes,
rich waters that directly and indirectly slow 1984; Hansen, 1990).
reef growth (Glynn and Stewart, 1973; Dana,
Most devastating to eastern Pacific coral
1975; Glynn, 1977; Glynn and Macintyre, communities was the coral bleaching and
710
P. W. GLYNN AND M. W. COLGAN
mortality that resulted from the elevation
of SST that accompanied the 1982-83 El
Nino event (Fig. 1). All equatorial eastern
Pacific zooxanthellate reef coral species suffered some degree of bleaching and mortality during the prolonged warming (2-3°C
above normal) period (Cortes et al., 1984;
Robinson, 1985; Glynn, 1990). A controlled El Nino simulation experiment
(Glynn and D'Croz, 1990) and observations
of other thermal stresses {e.g., Edmondson,
1928; Jokiel and Coles, 1977) substantiate
the link between temperature elevation and
coral mortality.
at Cano Island, Costa Rica, to 97% in the
Galapagos Islands (Glynn et ai, 1989). This
strong response was correlated with the geographic gradient of highest SST anomalies
observed at these locations (Fig. 1).
While most branching colonies died,
many large, massive colonies suffered only
partial mortality (Hughes and Jackson,
1980). After 1983, some colonies regenerated, but most continued to lose tissue
because of bioerosion, predation, and damselfish activities (Glynn, 1990).
Some coral species disappeared from particular sites. For example, Porites panamensis colonies were not observed on most
BIOLOGICAL CONSEQUENCES OF EL NINO
coral reefs in Panama after 1983, and PocilReef-associated species responded in var- lopora elegans, Pocillopora damicornis, and
ious ways and on different time scales to the Tubastraea tagusensis in the Galapagos
1982-83 El Nino event. Some were Islands disappeared from all known sites
impacted during the disturbance and others where they were formerly abundant. These
showed changes several months to years fol- species have reappeared over the last few
lowing the warming event (Glynn, 1990). years, but often not in their former habitats
(Glynn, 1990).
Many disturbances continue today.
The three eastern Pacific Millepora spePrimary Biological Consequences
cies bleached in early 1983 (JanuaryElevated SST during the 1982-83 El Nino March), and by April 1983 none could be
event severely disturbed eastern Pacific found alive. Since then (to December 1990)
coastal reefs from northwestern Costa Rica only Millepora intricata recruits have been
to southern Ecuador, and the offshore reefs found alive, and the other species, Millepora
at Cocos and Galapagos Islands. Branching platyphylla and Millepora boschmai, are now
corals bleached first and massive, platy and presumed extinct (Glynn and de Weerdt,
nodular genera (e.g., Gardineroseris, Pavona, 1991). Possibly a few recruits of Acropora
Porites, and Psammocora)
generally valida that arrived in Colombia shortly
bleached a few weeks later in Panama before 1983 (Prahl and Mejia, 1985), like(Glynn, 1983). Bleaching occurred in coral wise did not survive (Prahl, 1985).
colonies living as deep as 20 m, and within
2-4 wk of bleaching, the coral tissue atro- Secondary biological consequences
phied and numerous colonies died (Glynn,
Coral mortality was not limited to the
1983; Glynn et ai, 1985).
initial warming event. Subsequent imporDeath occurred in all coral species, but tant changes included (a) feeding by the sea
was greatest among fast-growing, branching star corallivore Acanthaster planci on corals
colonies of Pocillopora spp. and Millepora that were previously unavailable to it, (b)
spp., and some massive colonies of Gardi- expansion of algal lawns of territorial damneroseris planulata (Glynn, 1983, 1984; selfishes (Stegastes spp.) to cover coral parGuzman et al, 1987). Although all Pana- tially damaged by El Nino or by Acanthasmanian reefs were devastated, coral mor- ter, and (c) persistent grazing of sea urchins
tality was slightly greater in upwelling areas (Diadema mexicanum and Eucidaris
(e.g., 84%, Gulf of Panama) than in non- thouarsii) on dead coral surfaces, thereby
upwelling localities (e.g., 76%, Gulf of Chi- seriously eroding reef framework structures
disturbed in 1983 (Figs. 2, 3).
riqui [Glynn et al., 1989]).
Secondary disturbances in Panama hamCoral mortality rates were related to magnitude and deviation of high temperature pered the regeneration of massive corals that
anomalies. Coral mortality ranged from 51% suffered partial mortality. The 1982-83 El
EL NINO AND CORAL REEF DEVELOPMENT
711
FIG. 2. Grazing Diadema mexicanum erode a colony of Gardineroseris planulata partially damaged during the
1982-83 ENSO event. Uva Reef, Gulf of Chiriqui, Panama, depth 4 m. (Photo by J. Feingold, Dec. 1990.)
Nino event did not change population densities of Acanthaster planci, nevertheless, its
impact increased (Glynn, 1985). Before
1983, continuous thickets of Pocillopora spp.
coral surrounded many bottom areas at the
Uva reef. Acanthaster, thwarted by the coral's nematocysts and crustacean guards, seldom crossed these thickets (Glynn, 1983).
The widespread death of Pocillopora colonies removed this biotic barrier, and Acanthaster could now enter and feed on formerly protected, massive corals. For
example, Pocillopora colonies that encircled
21 of 22 massive colonies of Gardineroseris
planulata suffered mortality, and, within a
year, Acanthaster preyed upon those massive corals (Glynn, 1985).
Damselfishes that have colonized dead
coral surfaces sometimes caused additional
coral death through the enlargement of their
territories and algal lawns (unpublished
observations). The coral-damselfish interaction is complex because damselfish also
protect nearby corals from Acanthaster
attack (Glynn and Colgan, 1989), and from
external bioeroders such as sea urchins and
fishes (Wellington, 1982; Sammarco et al,
1986; Eakin, 1988; Glynn, 19886).
Microscopic and filamentous algae quickly
colonized dead corals which were soon covered by algal turf or coralline algae (Glynn,
1984; Robinson, 1985). Sea urchin grazing
on these algae accelerated bioerosion, greatly
reducing the prospect of long-term coral reef
development (Fig. 3, [Glynn, 1990]). After
coral death, an intact corallum can support
future recruitment so that reef accretion may
continue (Moran, 1986; Colgan, 1987).
However, echinoid grazers erode reef buildups and may determine whether reefs accrete
or not (Stearn and Scoffin, 1974; Hutchings,
1986; Birkeland, 1988).
Sea urchin populations increased greatly
following the 1982-83 ENSO event on many
severely disturbed coral reefs in Panama and
the Galapagos Islands. In Panama, Diadema mexicanum densities on the dead
Pocillopora framework increased from 3 to
712
P. W. GLYNN AND M. W. COLGAN
FIG. 3. An eroded colony of Porites lobata at Pajara Island, Cocos Island, depth 8 m. Sea urchins (Diadema
mexicanum) graze on top of the coral colony. (Photo by I. G. Macintyre, Nov. 1990.)
80 inds./m 2 . In the Galapagos Islands, Eucidaris thouarsii moved from non-reefal substrates to dead, algal covered, coral frameworks increasing their numbers from 5 to
50 inds./m 2 (Glynn, 1990). Diadema and
Eucidaris are important because of their
abilities to excavate and erode coral framework. Field studies, in Panama and the
Galapagos Islands, of erosion caused by sea
urchins grazing on reef surfaces demonstrated that substrata with high sea urchin
densities were undergoing erosion in excess
of the net carbonate production measured
before 1982 (Glynn, 1988/)). These values
underestimate the amount of reef framework destroyed because sea urchins often
undercut coral colonies which are then more
susceptible to toppling and further breakage
(Colgan, 1991; Malmquist, 1992; Eakin,
personal communication). In Panama and
the Galapagos Islands, non-echinoid, largely
internal bioerosion {e.g., clionid sponges,
polychaetous annelids, and lithophagine
bivalves), accounts for xk to xli of the total
bioerosion (Glynn, 1990). Many eastern
Pacific reef structures that have accumulated over 100s of years are now being rapidly reduced to sediments (Glynn, 19886).
Since 1983, nearly all large Galapagos
corals have suffered progressive tissue mortality and erosion. Populations of two species in Academy Bay showed significant
mean decreases in their dead colony diameters of 19.8 cm (Porites lobata, n = 12 colonies) and 35.3 cm (Pavona clavus, n = 9)
from May 1985 to April 1989 (Mests, P <
0.01 in both cases [Glynn, 1990]). The mean
decreases in colony size observed at Academy Bay over the 4 year period were 21.3%
in Porites and 36.8% in Pavona (Glynn,
1990). The large numbers of Eucidaris feeding on and in the massive corals erode large
colonies (Glynn, 19886). As seen at Urvina
Bay, the hollowing of massive corals leads
to their fragmentation and collapse (Colgan,
1991). In the Galapagos Islands, these large
massive corals are undergoing rapid erosion
and most colonies probably will not regenerate.
Coral reef recovery has been assessed
EL NINO AND CORAL REEF DEVELOPMENT
continuously in Costa Rica, Panama and
the Galapagos Islands, and little coral
recruitment has occurred. Heavy sea urchin
grazing can have a destructive effect on coral
recruitment (Sammarco, 1980, 1982). In the
Galapagos Islands, numerous small pocilloporid corals were observed in 1988 and
1989, and all have recruited to the tops or
sides of basalt boulders where Eucidaris was
rarely found. A similar recruitment pattern
was seen among Pocillopora uplifted at
Urvina Bay (Colgan, 1990). Coral recruits
have not returned to former reef surfaces,
and if present trends continue new coral reef
growth will be initiated on barren basalt
rather than antecedent reef carbonate.
EL NINO AND EASTERN PACIFIC HISTORY
Coral reefs in the eastern Pacific date back
to the Cretaceous Period (Durham and Allison, 1960; Durham, 1966). Since then, reef
building has occurred sporadically with most
vigorous reef production occurring in the
Oligocene (Frost and Langenheim, 1974).
The most recent period of reef building
started when rising seas flooded the continental shelf. In an attempt to understand
the differences between eastern and western
Pacific coral reefs, and to place El Nino
events into an historical context, we will
briefly examine this latest episode of eastern
Pacific reef building.
Sea level rise
Sea level reached a minimum about
18,000 years ago, exposing the continental
shelf and island platforms where eastern
Pacific coral reefs once grew (CLIMAP,
1976,1981). During this latest sea level lowering, the exposed Pleistocene thin carbonate accumulations apparently eroded away.
In the western Pacific, subaerial exposure
only partially eroded thick carbonate buildups, thus a limestone foundation for future
reef growth was preserved (Stoddart, 1969;
Davies, 1983). During the last Ice Age, the
equatorial eastern Pacific region was less
conducive to reef growth than today because
of higher ocean productivity and lower SST
(CLIMAP, 1976, 1981; De Vries and
Schrader, 1981; Reimers and Suess, 1983;
Schramn, 1985; Lyle et ai, 1988). Unlike
the western Pacific, there is no evidence of
reef building in the eastern Pacific during
713
the last sea level low stand. Rising seas
flooded the shelf and conditions for coral
reef growth improved in the eastern Pacific.
In the eastern Pacific, sea level neared present elevation around 2,000-4,000 years ago
(Hopley, 1982). Western Pacific reefs developed and grew on Pleistocene reef platforms, giving the false appearance of continuous growth. In the eastern Pacific
however, corals settled on barren, rocky
substrates, and necessarily initiated reef
building de novo. The oldest dated coral
retrieved from the base of a reef in Panama
is only 5,600 years old (Glynn, 1976).
Coral recruitment and reef growth
With the stabilization of sea level, corals
likely recruited to the newly flooded platform from refuge areas within the eastern
Pacific, from the central Pacific and possibly
from both source areas. In the recent history, coral recruits probably continue to
arrive in the eastern Pacific from the west.
Recently two central Pacific coral species,
Acropora valida and Porites (Synaraea) rus,
were discovered in the eastern Pacific (Cortes and Murillo, 1985; Prahl and Mejia,
1985). Earlier accounts of other central
Pacific corals encountered in the eastern
Pacific include single colonies of Montipora
and Acropora (Durham, 1947; Wells, 1983;
respectively). Other reef-associated taxa
similarly have recruited to the eastern Pacific
from the west. For example, the gastropods
Charonia tritonis, Conus tessulatus, Cymatium mundum, Cymatium
muricinum,
Cypraea moneta, Cypraea talpa, and Mitra
mitra have been reported recently in the
eastern Pacific (Emerson, 1989, 1991). The
strengthening of the equatorial counter current during El Nino events may be responsible for some of these species introductions
(Richmond, 1990). Corals colonized the
eastern Pacific forming the small, poorly
zoned reefs in the region.
El Nino frequency
Since the closure of the Isthmus of Panama and establishment of the present Pacific
circulation, some 3.5-2.8 million years ago
(Duque-Caro, 1990), El Nino events may
have affected the eastern Pacific during sea
level high stands (Colgan, 1990). Sedimentologic and archaeological data show that El
714
P. W. GLYNN AND M. W. COLGAN
Nino events have been a recurring phenomenon in the eastern Pacific throughout the
Holocene(Nialse/a/., 1979; De Vries, 1987;
Wells, 1987,1990). How often have El Nino
events, of the intensity of the 1982-83 event,
altered the reef building environment of the
eastern Pacific?
Since the 1982-83 El Nino event affected
many old corals, this provides one clue concerning the recurrence interval of major
ENSO warming events of the intensity of
the 1982-83 disturbance. For example, in
the Galapagos Islands, five El Nino damaged Porites colonies (each with ages
exceeding 300 years) and one Pavona colony (over 400 years old) have undergone
irreparable erosion (Glynn, 1990). On an
uplifted portion of Urvina Bay, Galapagos
Islands, large Pavona clavus and Porites lobata colonies attest to similar long, although
punctuated intervals of growth (Colgan,
1990, 1991). For example, a single large colony of Pavona clavus (max. diameter, 12
m), estimated to have been 350 years old at
the time of the uplift (Dunbar et ai, 1987),
survived at least 31 strong or very strong El
Nino events (Quinn et ai, 1987) suggesting
that these earlier events were not so severe
as the El Nino of 1982-83 (Glynn, 1990).
In the Galapagos Islands, pocilloporid
framework dimensions indicate that several
reef blocks attained 1.0-1.2 m in vertical
thickness over a period of 180-200 yr. The
thickest accumulation of 2.7 m was found
in Cormorant Bay, Floreana Island, and
suggests that the fringing reef there experienced nearly uninterrupted growth during
the last 500 yr. In the Gulf of Chiriqui, Panama reef block thicknesses of 1.0-1.5 m
were most frequently encountered, suggesting that uninterrupted reef growth occurred
there over a period of 135-175 years. Several notably thick sections of pocilloporid
frameworks in the Secas Islands (2.0-2.5 m)
suggest that some Panamanian reefs grew
almost continuously for about 300 yr before
the 1983 mortality event.
Thus, Glynn (1990) concluded from the
ages of corals and reef frame structures
damaged in 1983 that a disturbance comparable to the 1982-83 El Nino event has
probably not occurred in Panama and the
Galapagos Islands for as long as 400-500
years.
If we assume that El Nino events occurred
every 200-500 yr then during this latest
phase of reef growth (approximately the last
6,000 years) between 12 and 30 El Nino
events of the magnitude of the 1982-83
event could have interrupted eastern Pacific
reef building. What then would be the consequences of catastrophic El Nino events on
the course of reef building?
The consequences of catastrophic
El Nino events
As a consequence of the 1982-83 El Nino
event, eastern Pacific corals died, species
disappeared and reef growth slowed or
halted. Varied and persistent biotic disturbances have slowed reef recovery following
the 1982-83 event. In the aftermath of this
disturbance, previous coral buildups erode.
The coral recruitment that has been
observed, for the most part, has occurred
away from sites of previous buildups.
Therefore, communities of large massive
colonies and continuous stands of branching corals probably will disappear to be
replaced by non-reef-building benthic
assemblages. If large populations of grazing
sea urchins and fishes persist, it is possible
that an alternate stable community dominated by filamentous algae and crustose coralline algae would develop (see Knowlton,
1992).
In the western Pacific, following extensive
and catastrophic coral mortality, rapid
recovery occurs through the growth of surviving corals and recruitment of new corals
to surviving reef frameworks (Pearson, 1981;
Colgan, 1987; Done, 1992). In the eastern
Pacific, recruitment and the potential for
new reef growth in many areas is occurring
away from the sites of previous buildups.
This shifts reef building and carbonate production to new locations, causing reef growth
to be temporally and spatially discontinuous. During at least the last 6,000 years,
intense El Nino events have probably
repeatedly disrupted eastern Pacific reef
growth. The reef growth that does occur
takes place over a relatively narrow timeframe of 300-500 years between major El
Nino events. Because of widespread coral
mortality and rapid bioerosion, reef formation and initiation of growth between El
Nino events is seldom preserved. The cycle
EL NINO AND CORAL REEF DEVELOPMENT
715
of El Nino perturbations and bioerosion
prevents corals from growing and maintaining large, persistent reef frameworks.
versity of Costa Rica; Centro de Ciencias
del Mar y Limnologia (L. D'Croz), University of Panama; Smithsonian Tropical
Research Institute (J. B. C. Jackson), PanSUMMARY
ama; Estacion Cientifica Charles Darwin (G.
Eastern Pacific coral communities appar- Reck, D. Evans), Galapagos Islands, Ecuaently survived near their physiologic tol- dor. Permission to work in Panama was
erance limits: stressed by cool, nutrient-rich, granted by the Direction de Recursos Marupwelling waters (Glynn and D'Croz, 1990). inos, Ministerio de Comercio e Industrias,
Recurrent intense El Nino events further and in the Galapagos Islands by the Galaaggravate these conditions, causing harmful pagos National Park Service (M. Cifuentes,
thermal effects in an already harsh environ- H. Ochoa, F. Cepeda). TAME, an Ecuadoment for hermatypic corals (Glynn, 1988a). rean national airline, subsidized air travel
In contrast to the benefits once associated to the Galapagos Islands.
with El Nino warming events, the very strong
This research was supported by the Schol1982-83 occurrence (Gill and Rasmusson, arly Studies Program, Smithsonian Insti1983; Hansen, 1990) demonstrated harmful tution, and the Biological Oceanography
consequences in three ways (Glynn, 1988a). Program, U.S. National Science FoundaFirst, elevated sea-water temperatures tion to PWG, EAR 8508966 to MWC, and
caused widespread coral mortality without a Chancellor's Special Research Fund grant,
a concomitant decrease in coral predators University of California, Santa Cruz.
and bioeroders (Glynn, 1983, 1984, 1989;
Contribution from the University of
Robinson, 1985). Secondly, with some coral Miami, Rosenstiel School of Marine and
refugia disrupted, Acanthaster planci entered Atmospheric Science.
and killed formerly protected coral prey
Charles Darwin Foundation Contribu(Glynn, 1985). Thirdly, with coral reef tion Number 485.
growth halted or at a near stand-still, internal borers (e.g., lithophagine bivalves and
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