Effects of Heated Effluent on Hermatypic Coralsat Kahe Point, Oahu!

PAUL L. JOKIEL2 ANDSTEPHEN L. COLES3

ABSTRACT: The effect of thermal enrichment on hermatypic corals wasinvestigated at Kahe Point, Oahu, Hawaii. The reef off the Kahe Power Plantwas surveyed before and after an increase in thermal discharge that accom­panied plant expansion. Abundances of dead and damaged corals correlatedstrongly with proximity to plant discharge and with levels of thermal enrich­ment. Nearly all corals in water 4° to 5° C above ambient were dead. ]n areascharacterized by temperature increases from 2° to 4° C, the corals lost zoo­xanthellar pigment and suffered high mortality rates. Damage to the corals wasmost severe in late summer, and coincided with annual ambient temperaturemaxima. During the winter months the surviving corals slowly regainedzooxanthellar pigment, but there was high mortality of corals during therecovery period. When generating capacity of the plant was increased from270 to 360 megawatts, the area of dead and damaged corals increased from0.38 hectare (0.94 acre) to 0.71 hectare (1.76 acre).

STUDIES of thermal tolerance among thehermatypic corals have been limited tolaboratory investigations involving short­term exposure to lethal temperatures(Mayer 1917, 1918; Mayor 1924; Edmond­son 1928; Yonge and Nicholls 1931). Theprimary purpose of the present study was toevaluate the effects of heated discharges onhermatypic corals through field observa­tions, with particular emphasis on the sub­lethal long-term effects occurring in areas ofmarginal thermal stress. The approach em­ployed was a survey of the coral fauna atKahe Point, Oahu, before and after an in­crease in thermal discharge from a powerplant operating at this location.

1 Hawaii Institute of Marine Biology contribution no.418. CORMAR contribution 7. This work partially sup­ported by EPAgrants 18050 DDN and R800906. Manu­script received 15 May 1973.

2University of Hawaii: Hawaii Institute of MarineBiology, P.O. Box 1346, Kaneohe, Hawaii 96744; andDepartment of Oceanography, Honolulu, Hawaii96822.

3Department of Zoology, University of Hawaii,Honolulu, Hawaii 96822.

STUDY SITE DESCRIPTION

The Kahe Point Power Plant of theHawaiian Electric Company (HECO) is anoil-fired steam electric generating station lo­cated on the west coast of the island of Oahunear Kahe Point (Iat. 22°22' N, long. 158°08'W). Cooling water for the plant is withdrawnfrom the ocean at the intake basin locatedapproximately 300 m to the north of KahePoint and is returned to the sea at an outfalllocated on a small beach some 200 m to thesouth (Fig. 1). During November 1971,three 90-megawatt generating units were inoperation (KI, K2, K3), drawing a total ofapproximately 14 m3/sec (230,000 gallonsper minute) of seawater for cooling purposesand discharging this water at approximately5° to 6° C over intake temperature. Averageambient (natural) water temperatures forthis area range from a low of approximately24° C in March to a high of 27° C in earlySeptember. During periods of southerlywinds, heated effluent is blown north alongthe coast and into the intake, producing ab­normally high discharge temperatures.Long-term weather records available from

2 PACIFIC SCIENCE, Volume 28, January 1974

Kahe Point, Oahu• , three meter

isobath stations

Scale Imererslo:;=

FIG. I. Map of Kahe Point area showing bathymet­ric stations.

the National Climatic Center indicate thatsoutherly winds in this region are rare (fre­quency of occurrence less than 9 percent)and generally occur during the wintermonths. Kahe Unit 4 (K4) began full opera­tion on 25 July 1972. This unit is of the samecapacity as K l-K3 and increased the wasteheat discharge rate by over 30 percent.

Waters receiving thermal effluent fromthis plant are unrestricted from circulationwith the open ocean. The ocean floor in thearea immediately off the plant is an ancientreef platform that slopes moderately awayfrom the shoreline, reaching the 10 misobath at a distance of from 200 to 300 mfrom shore. The bottom in this area consistsofareas where modern reef corals have builtstructures on the old reef platform, inter­spersed with sand flats and sand channels. Ingeneral, the reefs of this area, and in particu­lar those coral reefs south of Kahe Point, areconsidered to be among the richest inHawaii. Of the corals, the most prevalentspecies are Pocillopora meandrina var.nobilis Dana and Porites lobata Dana.

Kahe Point and the sea cliffs to the southare formed by an uplifted limestone benchwhich rises approximately 5 meters abovethe ocean surface. The area to the northconsists of calcareous sand beaches. Close

inshore to the beach, sand movement andbreaking waves prevent coral development.Outside of this shallow surf zone is an areaof greater topographical relief where coralsgrow on the higher elevations, and sand fillsthe pockets and channels between. Appar­ently, in areas relatively close to shore andnear the bases of reef outcrops conditionsperiodically become unfavorable to coraldevelopment, as evidenced by numerousdead Pocillopora meandrina skeletons.These corals probably were killed by burialunder shifting sand or by turbidity createdduring unusual conditions of high surf(Chamberlain, unpublished report, 1971,"Marine environmental impact analysis,Kahe Power Plant," submitted by B-KDynamics, Inc., Rockville, Maryland, toHawaiian Electric Co.).

During preliminary surveys we noticedthat corals in the area under the immediateinfluence of the power plant outfall showeda pattern atypical of this coastline. All coralswithin 120 m of the outfall had been com­pletely eliminated, and only their deadskeletons remained. This dead zone wasquite unlike other areas along the coastlinewhere the recognizable dead heads of P.meandrina were found interspersed amongliving specimens of the same and otherspecies. Coral destruction off the outfallwas complete and not localized in channelsand nearshore regions. The dead zonegraded into a zone where surviving coralshad lost their pigmentation. Farther fromthe outfall the zone of colorless and deadheads graded into an area where living cor­als appeared normal. The striking differ­ences that we observed led us to undertake amore detailed study of this region.

METHODS

Four distinct classes of coral conditionwere recognized: dead, bleached, pale, andnormal. The dead class applied only to thebranching coral P. meandrina, because thedead skeletons of other species found herewere difficult to distinguish from the sub­strate. The "bleached" category includedonly specimens with tissue that had lost

Effects of Heated Effluent on Hermatypic Corals-JoKIEL AND COLES 3

most of its zooxanthellar pigment, becomingcolorless as a result. Bleached corals take onthe pure white coloration of their skeletalmaterial. The term "pale" was applied tocorals that had lost a great deal of symbiontpigment, but still retained enough zooxan­thellae to give them a definite translucentbrownish to deep amber coloration. The"norma]" category was reserved for coralsthat displayed the opaque yellow-greens andbrowns characteristic of healthy coral. Thebleached, pale, and normal classes gradedinto one another, but for the most part couldbe readily differentiated.

Temperature, salinity, and oxygen pro­files were determined on 19 November 1971(1300 hours) at eight stations running paral­lel to the shoreline at approximately the3-meter isobath and at the outfall. Oxygenmeasurements were made with a YellowSprings Instrument Co. model 54 oxygenmeter and temperature-salinity measure­ments with an Industrial Products RS5-3induction salinometer. Plume current ve­locities were measured with a Tsurumi­Seiki-Kosakusho model 313 current metersecured at various distances from the outfallstructure. Plume surface velocities werealso measured by timing floats acrossknown distances. Water temperaturesthroughout the Kahe area were measured atvarious times throughout the November1971 to November 1972 time interval byswimmers diving with a hand held mercurythermometer calibrated in 0.1 0 C units. On17 November 1972, Peabody-Ryan modelF-8 thermographs were set at two pointsalong the outfall transect and at one point onthe control transect during normal tradewind weather (winds NE, 8 to 10 knots).Complete intake and discharge temperaturerecords were supplied by HECO. These in­cluded intake temperatures for each unittaken at 2-hour intervals, as well as a dailyoutfall temperature measured at time ofpeak electrical generation. The intaketemperature varied diurnally by 10 to 20 C,generally with a maximum at 1500 hours.Daily peak discharge temperature and1500-hour intake temperature were plottedfor the period of the survey (November 1971through November 1972 inclusive).

We mapped the area using informationfrom various sources (U .S. Geological Sur­vey Map N2115, Towill Aerial PhotographsNos. 4484-2 and 4125-3, HECO engineeringdrawings, and from information that we col­lected in the field by direct measurementalong the shoreline and by sextant sightingsbetween fixed landmarks). At the northernedge of the damaged zone, the seaward andshoreward limits of the pale-bleached coralswere established by direct measure alongtransect lines. At the southern edge, we de­termined these limits by direct measurealong the shoreline of Kahe Point. In addi­tion, we secured buoys along the boundariesof the damaged areas and made sightings ofthe buoys with a sextant from fixed shorepoints. Sighting coordinates were thentransferred to the map, establishing theinner and outer boundaries of these zonesand enabling an areal estimate of the dam­aged zone to be made.

In November of 1971 we selected a sitealong the discharge plume where complicat­ing effects of wave action, irregularbathymetry, and sedimentation appeared tobe minimal. A permanent transect line wasestablished by driving marked iron stakesinto the reef. The transect began 100 m fromthe outfall, at the nearshore termination ofhard substrate, and extended 57 m acrossthe zones of dead, pale, and bleached coralsand into the area of normal corals (Fig. 2). A1 m2 frame, subdivided with wire into 100square subsections, was used to estimatecoral coverage for each species and condi­tion. The 57 quadrats along the transectwere measured in this manner.

In November of 1972 the permanenttransect was again measured and a parallelcontrol transect was run approximately 80 mnorth of the outfall transect. The controltransect was laid out over a section of reefthat lies outside of the direct influence of thethermal discharge. Although a heated sur­face layer was present, bottom tempera­tures approximated ambient (Figs. 3 and 4).The control transect was selected so as toduplicate conditions along the outfall tran­sect with respect to substrate type, depth,distance from shore, and distance from thesand channel. The control transect was dis-

4

. '/• , '1, , /

.~-;,/ ControlTransect

PACIFIC SCIENCE, Volume 28, January 1974

N

. '., t-

, 1./)../

(. .,'_:" ..I

Kahe Point, Oahu

Discharge Plume axis3 or less units Inoperation

Discharge Plume axis4 units in operation

1972 Extension ofpole - bleoched zone

1971 Pole - bleoched zone

0 50I

Sco Ie ( meters)

FIG. 2. Detailed map of area off outfall showing locations of permanent outfall transect, control transect, areasof damaged corals for 1971 and 1972, and directions of plume axis with three units and four units in operation.

Effects of Heated Effluent on Hermatypic Corals-JoKIEL AND COLES 5

continued at a distance of 147 m from shore,at the termination of hard substrate.

During the November 1972 survey, 15specimens of bleached Pocillopora mean­drina were tagged with numbered plastictags. In addition, replicate normal P. mean­drina heads were removed from the zoneim'mediately outside of the region of palecoral and transplanted to one location in thezone of normal corals (control) and to twolocations in the damaged zon~ (at 116 m and137 m from outfall).

Photosynthetic pigment concentrationscorresponding to bleached, p':lle, and nor­mal conditions of Pocillopora meandrina,Porites lobata, and Montipora verrucosa(Lamarck) were measured. Discs of 7 mmdiameter and 5 to 10 mm thickness wereremoved from the upper surfaces of Poriteslobata and Montipora verrucosa with a corkborer. These contained all of the coral tissueand its associated symbionts from 0.33 cm2

of coral'surface, along with a plug of under­lying skeletal material. The extreme hard­ness of Pocillopora meandrina skeletonprecl uded use of thi s method, so branches ofthis species of approximately 40 g were sub­stituted.

Immediately after removal, the discswere placed in test tubes containing 0.5 ml ofdistilled water and frozen in Dry Ice. The P.meandrina branches were placed in plasticbags and frozen, all samples being kept indarkness so as to prevent photooxidation ofpigments.

In the laboratory, extraction of the pig­ments was accomplished by adding 4.5 ml of100-percent acetone to the test tubes con­taining the frozen cores, shaking the con­tents vigorously, then storing them in a re­frigerator for 24 hours. The frozen P. mean­drina branches were placed in glass contain­ers containing 100 ml of90-percent acetone,and the same procedure was followed. Atthe end of the 24-hour extraction period, thesamples were reshaken, centrifuged, andthe light extinction of the supernatant mea­sured in a 1 em cell at wavelengths from750 to 320 nm, with a Beckman DB-Ggrating spectrophotometer with continuousrecorder.

Concentrations of chlorophylls a, b, and c

-- Control Reef .-- 1)9 Meiers from Outfall---- 150Melers from Outfall

, I i

17 November 1972

TRANSECT BOTTOMTEMPERATURES

~ 29

°~ 28E.~27

30 ,

lO lO'"~O ;0~

Ql

<l>E

I

~[J ~[2]t-CLW0

31 -,-,----,-----,--,---------,-----,---.-,.-

2St---t----j---i---I'---+---t--L1-1100 1200 1300 IdOO 1500 1600 1700

TIME OF DAY

~[] ~o25 27 29 31 25 27 29 31

TE M PER AT URE (O()

FIG. 3. Temperature profiles for the 3-m isobathstations taken at approximately 1300 hours on 19November 1971 under trade wind conditions.

05E' '~'HJ ~REDICTED TIDE

0.0 I I ---,m--",---1'-- I

1100 1200 1300 IdOO 1500 1600 1-,'('TIME OF DAY

FIG. 4. Thermal environment at two locationsalong permanent transect and on control reef, as relatedto state of tide and time of day for 17 November 1972.

6 PACIFIC SCIENCE, Volume 28, January 1974

in mg and of total plant carotenoids inMSPU (one MSPU approximates one mg)were determined by using the formulae ofParsons and Strickland (in Strickland andParsons 1968). Because the symbiotic zoo­xanthellae of corals contain no chlorophyllb, its presence in a sample was assumed tooriginate from the filamentous algae thatpenetrate the coral skeleton below the levelof living coral tissue. The very lowchlorophyll b concentrations suggest thatcores were shallow enough to avoid most ofthe filamentous algae layer. Corrections fornonzooxanthellar chlorophylls a and c werecalculated from measured values ofchlorophyll b (Strickland and Parsons1968) and subtracted from total chlorophyllsa and c.

RESULTS

Thermal Environment

Temperature profiles for 19 November1971 (Fig. 3) show the influence of thermaldischarge on the thermal structure of theregion. A more detailed analysis of thisstructure is in Chamberlain (unpublished,1971, B-K Dynamics report) and Sea-Test(unpublished report, 1972, "Physicalstudies of Kahe," submitted to HawaiianElectric Co.).

At the discharge point, the velocity of thejet was measured at 3 m/sec with a tempera­ture exceeding ambient by 5° to 6° C. Afterleaving the outfall, the heated effluent en­trained small amounts of slightly coolerwater and sand from the beach shallows as itmoved seaward, scouring a channel from 1to 1.5 m in depth. At a distance offrom 30to50 m from the outfall, the velocity di­minished to about I m/sec, and the tempera­ture ranged from ambient +4° to + 5° C. At50 m from the outfall at the end of the outfalljetty, the plume entrained large volumes ofcooler water from the north, producing ed­dies of warm and cool water which ranged intemperature from ambient + 1° C to ambient+5° C. The formation of these eddies, com­bined with variations in current velocitiesdue to surf beat, produced an environment

characterized by rapid fluctuations in tem­perature. These fluctuations were of reducedintensity along the bottom, but even theretemperatures routinely changed by as muchas 2° C within several seconds. At a distanceof about 80 to 100 m from the outfall, thevelocity diminished and the effluent spreadover the surface, producing thermal stratifi­cation. The heated layer was generally be­tween I to 2 m in thickness; organisms livingbelow this depth were not visibly influencedby its effects.

After K4 became operational, the direc­tion of the plume axis shifted to the south,and the area enclosed by each elevatedisotherm increased (Fig. 2). What originallyhad been a scoured channel west of the out­fall became filled with sand, as was an areathat was formerly a region of dead coralheads.

Results of the analysis of power planttemperature records are shown in Fig. 5.Long-term mean open ocean temperaturesfor the area off Oahu are presented as anapproximation of normal ambient tempera­ture.

Results of the in situ thermograph studyare presented in Fig. 4. Ambient benthictemperature conditions (25.5° C) weremeasured on the control reef. Thermographtracings for the outfall transect show a slightenrichment before 1500 hours that increasesgreatly with ebbing tide. As the level of thetide decreased, the heated surface layerbegan to make contact with the bottom. Thearea of dead and damaged coral at 139 mfrom the outfall showed a maximum en­richment of + 3° to +4° C, while the outertermination of the zone of pale and bleachedcoral (150 m from outfall) showed tempera­tures of 2° to 3° C over ambient.

Coral Pigment

Replicate absorption curves for pigmentextracts from normal, pale, and bleachedconditions of Montipora I'ermcosa areshown in Fig. 6. Substantial reductions oftotal curve areas and of peak heights withbleaching occur at all wave lengths except inthe 330-nm region. The pattern shown in thefigure also typifies absorption curves for

Effects of Heated Effluent on Hermatypic Corals-JoKIEL AND COLES 7

34

32uo

30wa:::::>~ 28a::wa..::E 26w~

24

22N D

1971J F

DASHED L1NE- MEAN OPEN OCEAN

M AM J J AS 01972

N

FIG. 5. Daily Kahe outfall temperature measured at time of electrical generation peak and intake temperatureat 1500 hours plotted for November 1971 to November 1972.

FIG. 6. Absorption spectra for replicate acetoneextracts of bleached, pale, and normal specimens ofM0l1lil'0/'{/ ,·art/cos{/.

Porites [ohata and Pocillopora meandrina.Principal absorption peaks occur at 665,430, and 330± 10 nm, with smaller peaks at630 and 480 nm. The peaks can be compared

to absorption maxima of known photo­synthetic pigments (Jeffrey and Haxo 1968,Bogarad 1962). The 665 nm peak correspondsto chlorophyll a concentration; 630 nm tochlorophyll c; 480 nm to plant carotenoids;and the 330 nm peak to an unidentified, col­orless compound suggested to be an ultraviolet (UV), light-absorbing substance(Shibata 1%9, Kawaguti 1969).

Concentrations of the photosyntheticpigments corresponding to various degreesof pigment loss for the three coral speciesare listed in Table I. Order of magnitudedifferences between pigment concentra­tions of normally colored versus bleachedcorals were found for all three species.Small amounts of chlorophyll a and plantcarotenoid were extracted from bleachedspecimens, suggesting that a few zooxan­thellae are still retained by visibly colorlesscorals. However, bleached Porites [ohataspecimens sampled nearest the outfallcontained no chlorophyll a or c and littlecarotenoid, indicating that these specimenscontained virtually no zooxanthellae. Thesecorals were taken from an area where noother species but Leptastrae purpurea Dana

=NORMAl===PAlE::::.:-.:-BlEACHED

o3o!c;o,--L-..,.4o!c;o,----L-~5!,-;OO,--...L.-----,-6!,-;OO,----L-----,;~-----'

Wavelength, om

1.0

c<l>o

8 PACIFIC SCIENCE, Volume 28, January 1974

TABLE I

PIGMENT CONCENTRATlONS* AND 330 NM PEAK HEIGHTS

CORRESPONDING TO VARIOUS DEGREES OF CORAL BLEACHING.

OPTICAL

CHLOROPHYLL CHLOROPHYLL TOTAL PLANT DENSITY AlSPECIES COLORATION A C CHLOROPHYLL CiA CAROTENOIDS 320-335 NM

Pocil/opul'll bleached 0 0 0 0 0.45 1.99mealldrilla 3.42 0 3.42 0 3.30 1.60

normal 118 85.4 204 .72 219 3.08135 81.8 217 .61 234 2.86

MO/ltipol'll bleached 2.22 0 2.22 0 6.0 1.33\'t!rl'l(('().\'(/ 2.55 0 2.55 0 3.9 1.22

1.54 0 1.54 0 3.0 1.19pale 4.95 5.61 10.6 1.14 13.5 .71

7.09 2.88 10.0 .41 15.0 .86normal 17.7 11.0 28.7 .62 52.5 .86

17.9 9.1 27.0 .51 51.0 .74Porites bleached:{ohata closest 0 0 0 0 1.95 .80

specimen 0 0 0 0 2.55 .77to outfall 0 0 0 0 2.70 .82

bleached:specimen from 1.35 0 1.35 0 5.25 1.47center of 0.17 0 0.17 0 2.55 1.13bleachedzone 0.76 0 0.76 0 3.90 1.30

pale 1.07 3.94 5.01 3.7 18.0 1.562.81 2.47 5.28 .88 28.5 1.69

normal 37.0 27.8 64.8 .75 81.0 1.5428.2 25.2 53.4 .89 67.5 1.75

·Concentralions in j.J./cm'l for MOll1ipom and Por;fe.\·, in p./40 g skeletal weight for Podllo[Jora.

were still living, and the Porites [obataspecimens were probably living near theirupper thermal tolerance limits.

The 330 nm absorption peak showed noconsistent decrease with bleaching. In fact,bleached Montipora verrucosa showed anincrease in 330 nm absorption over pale ornormally colored specimens, but this pat­tern did not hold for the other two species.The absorption peak at 330 nm, therefore,may be associated with coral tissue ratherthan algal symbionts.

During the winter months, total recoveryof coral pigment appeared to accompanydecreasing water temperature, althoughcasual observations suggested that coralmortality was high during the recoveryperiod. By 29 February 1972 no pale orbleached corals could be found in the Kahe

Point area, but a few specimens of normallypigmented coral were observed in areaswhere only pale and bleached specimensoccurred the previous fall. During a period ofobservation in late February, kona (south­erly) wind conditions produced intense re­circulation of heated effluent. Ambientwater temperature at this time was 23° C,intake water temperature was 27° C, anddischarge temperature 32° C (ambient +9°C). However, temperatures among the in­nermost living corals along the dischargeplume ranged from 26° to 2r C, the samethermal enrichment value (ambient +4° C)normally encountered during trade windconditions. These data suggest that benthicthermal enrichment along our coral transectmight not have been increased significantlyduring periods of recirculation.

30 Normal

20

10

o-1-__~.I-_

~ 10~ Bleached _I t!oj-----------....I*J1':~ Po" .. I U

20

10

O-+-'\r-r-----,-~--,_-

o 100 110 120 130 140 150Distance From Outfall (meters)

o 100 110 120 130 140 150Distance From Outfall (meters)

FIG. 7. Percent coverage by various conditions of the coral Pocillopora meandrina along outfall transect on 26November 1971 and 17 November 1972.

Porites lobata (1971)

100 110 120 130 140 150Distance From Oulfoll (meters)

O+--'lr---.------r--.-----,---,_-"o

Pori tes lobata (1972)

~"t : I

~I

fL-o Bleached

I

:j Pale J f- -~60

tQ)

0>

~Normal~ 50

0U

E2400

CD

30

20

10

Normal

o-+-v--,--,_----,--~---o 100 110 120 130 140 150

Distance From Outfall (meters)

10

100r I Pale I I J '.. -'-L--' --"_ L.... _

';400>oQ)

>(:30

Eo

020CD

FIG. 8. Percent coverage by various conditions of the coral Porites lobata along outfall transect on 26November 1971 and 17 November 1972.

9

IO PACIFIC SCIENCE, Volume 28, January 1974

Transect

Results of the 1971 outfall transect arepresented in Figs. 7-9. Virtually all deadcoral occurred within 135 m from the outfall.Normally pigmented corals ranged from 130m to beyond the transect's seaward termina­tion. Bleached and pale corals formed aband of transition between the dead andnormal zones. The clear demarcation be­tween living and dead zones, the bleachedtransition zone, and the general reduction incoral coverage approaching the outfall indi­cated a detrimental influence of the outfallplume on these organisms.

Figs. 7 and 8 present data in detail for thetwo major species. The data for Pocilloporameandrina indicate a gradation seawardfrom dead through bleached and pale headsto normal coloration. Pale Porites {obataheads were found well into the Pocillopora

meandrina dead zone, which indicates great­er resistance to thermal stress by the formerspecies. In the 1971 transect, some paleMontipora I'ermcosa was found well intothe zone where other species appeared nor­mal. Loss of pigment in this species is oftenrelated to factors such as high light intensityas well as to increased temperature (Coles1973). This species occurs naturally in palecondition in shallow areas of Kaneohe Bay,Oahu.

The same pattern of damage observed inNovember 1971 was again observed inNovember 1972 but by then had become farmore extensive. Most of the pale andbleached heads encountered in 1971 haddied, and the area of normal corals outsideof the 1971 zone of damage had become paleor bleached. Pocillopora meandrina, withits readily recognizable dead skeleton, en­abled a comparison of all conditions of this

100 110 120 130 140 150D;slonce From Outfall (meters)

Pole 0' Bleached

Normal

o

20

10

~0'"Ol

~

~ 60a

U

E50a

aa:l

40

30

20

Normal

100 110 120 130 140 150Distance From Outfall (meters)

oO-+-Jv--,---,----"r--"........,~

10

30

40

20

"co

::r:::All,,5':(.~~'l ::~A~:~1~ol~--l 11 .• U oU~

701Pole 0' Bleoched

10

.: 0 --"v------- - .I&_-_....-~---+"oo

U

~ 60

EG 50--

FIG.9. Percent coverage for all coral species encountered along outfall transect on 26 November 1971 and 17November 1972.

Effects of Heated Effluent on Hermatypic Corals-JoKIEL AND COLES II

species along the transect between 1971 and1972. These data are summarized in Table 2.The increase in dead, bleached, and palecoverage was matched by a correspondingdecrease in normal coral coverage.

TABLE 2

CHANGES IN COVERAGE (DECIMETER2) OF

Pocillopora mealldrillaENCOUNTERED ALONG TRANSECT

COVERAGE

(DECIMETER') % CHANGE

CONDITION 1971 1972 BETWEEN SURVEYS

Normal 251 1\7 -53.4Pale 30 35 + 16.7Bleached 40 51 +28.8Dead 157 264 +68.1

478 467

An analysis of the transect data was con­ducted, but, because an estimation of coralcoverage on the transects involved use of aproportion (% of I m2

) and because cover­age frequently was less than 30 percent, itwas necessary to employ the arcsin trans­formation before applying parametric statis­tical methods (Sokal and Rohlf 1969). At-test of differences between abundances ofliving coral per m2 quadrat in 1971 andabundances in the same quadrats in 1972shows that a highly significant decrease inliving coral coverage occurred along thetransect between 116 and 157 m from theoutfall (p <.0005, paired comparisons). Bythe same analysis, dead P. meandriJ1(/ headsshowed a highly significant increase(p<.0005). Total living coral encounteredalong the transect deceased by 44 percentduring the year. The weighted mean dis­tance, defined as (abundance X distance) /abundance, of all bleached and pale coralsencountered in the transect was 134 m in1971 and increased to 142 m from the outfallin 1972. These data indicate that the centerof damage along the transect shifted out­ward by approximately 8 m during theI-year time interval. Damage was minimalin the area of the outfall transect since theaddition of K4 caused the direction of the

plume axis to shift farther to the south. Thecenter of damage along the new plume axisshifted outward an estimated 30 to 40 mbetween the two sampling dates.

The results of the control transect (Fig.10) indicate that good coral coverage canexist under conditions that appeared to besimilar to the outfall transect in every re­spect except in the degree of thermal stress.Living coral coverage along the controltransect was not significantly correlatedwith distance from shore (r = 0.19). Alongthe outfall transect, total live coral coverage(normal, pale, and bleached conditions)showed a high correlation with increasingdistance from the outfall (r = 0.78, p <.001).Most of the corals encountered in the outfalltransect were dead or damaged (pale orbleached condition), whereas those encoun­tered on the control transect were normal.A t-test of difference between the z-trans­formed correlation coefficients indicatedsignificance atthe p < .00 I level.

Areal Estimate of Damage

The total area of pale and bleached coralsbefore and after the beginning of operationofK4(26 November 1971 vs.15November1972) is shown in Fig. 2. The area of dam­aged corals (pale and bleached condition)covered an area of approximately 0.23 hect­are (0.57 acre) in 1971. An area of deadcoral heads covering approximately 0.15hectare (0.37 acre) existed inside this zone.By November 1972 an additional 0.33 hect­are (0.82 acre) was pale or bleached, whilemost of the pale and bleached area observedin 1971 became a zone of dead coral. Thedead coral zone of 1971 was largely buriedby sand.

Transplants

Of the 15 bleached P. meandrina headstagged during November 1972, only onesurvived in early February 1973 and it was ina bleached condition. One of the two headsthat had been transplanted into the deadzone (116 m from the outfall) was dead inFebruary 1973 and the other was pale. Thetwo heads transplanted to the bleached zone

12

10

o40

30

PACIFIC SCIENCE, Volume 28, January 1974

Control Transect (1972)

Dead C~ meandrina)

Pocillopora

meandrina

(Normal)

~ 20

Q)

Ol

~ 10Q)

>ovE 0o

o 50a:l Pori tes lobata

(Normal)

Q)

~ 60Q)>o

vE 50o

oa:l 40

Total Living Coral(Normal)

Distance From Shore (meters)

40

30

20

10

oDistance From Shore (meters)

30

20

10

o100 110 120 130 140

FIG. 10. Percent coverage of corals encountered along control transect on 24 November 1972.

(137 m from the outfall) were paled, whilethe pair in the control transect remainedalive and normally pigmented.

DISCUSSION

The pattern of coral destruction is clearlyrelated to discharges of heated effluent fromthe Kahe Point Power Plant. Percent abun­dance of dead, bleached, and pale corals

encountered in the transect is correlatedwith outfall discharge and increased dis­charge resulted in increased damage.

Condition of corals off the outfall re­flected the complex thermal conditionscreated by wave action and irregular bottomrelief. Often a coral head growing on top of arock pinnacle was visibly damaged by ther­mal stress, while its neighbor, located on theside of the outcrop at a slightly greater

$I ."!fMJ 4.,.W

Effects of Heated Effluent on Hermatypic Corals-JoKIEL AND COLES 13

depth, was not damaged because it was liv­ing below the heated surface layer. As pre­viously shown, fluctuation in the benthicthermal environment resulted from the ris­ing and the falling of tides. Downward mix­ing of effluent by surf further complicatedthe thermal environment in some regions. Inaddition, slight shifts in the direction of theheated plume were induced by changes inwind direction, wind velocity, state of tide,surf conditions, direction of offshore cur­rents, and presumably many other factors(Chamberlain, unpublished, 1971, B-KDynamics report; and Sea-Test, unpub­lished report, 1972).

Of the coral species encountered in theKahe Point region, Leptastrea purpureaDana appeared to be the most tolerant ofelevated temperatures. Normal specimensof this species were occasionally found inareas where all other corals had been com­pletely eliminated by thermal stress. Theinnermost zone off the outfall was charac­terized by dead coral heads, a few smallcolonies of normal L. purpurea, and a ther­mal environment of 4° to 5° C over ambient.This zone graded through an area where afew highly bleached specimens of Poriteslobata survived. Apparently Porites ever­manni Vaughan, a closely related but un­common species, is better able to withstandthermal stress because a few normal speci­mens measuring 10 to 20 cm in diameterwere found associated with the bleached P.lobata heads. In addition, a few specimensof pale to normal Montipora patula Verrilland Porites compressa Dana were found,although they appeared to be in poor con­dition.

Seaward, another zone characterized by ahigher coverage of surviving corals and byambient temperatures of + 3° to +4° C wasidentified. Corals consisted of dead andhighly bleached Pocillopora meandrina,bleached Montipora verrucosa, pale tobleached Porites lobata, normal P. ever­manni, pale to normal P. compressa, andnormal Leptastrea purpurea.

An outermost zone of marginal thermalinfluence approximating the benthic am­bient +2° to +3° C isotherm was identified,characterized by bleached to pale

Pocillopora meandrina and Montipora ver­rucosa, with other species appearing normalin pigmentation. This zone grades into anarea of visibly unaffected corals at the am­bient + 1° to +2° C benthic isotherm includ­ing some Montipora flabellata Studer andPa vona varians Verrill, corals which werenot encountered within the stressed zone.The general distribution of these twospecies at Kahe suggests that they normallydid not occur close to shore. Therefore,their exclusion from the area of thermal in­fluence may not be the result of thermalstress, but may be more strongly influencedby other factors such as turbidity.

Effects of heated effluent on coral havebeen noted in Biscayne Bay, Florida, in anarea receiving discharge from the TurkeyPoint Power Plant (L. Lee Purkerson, per­sonal communication). Observations madein the summer of 1970 showed allSolenastrea hyades coral colonies to havebeen eliminated within the area directly ef­fected by thermal discharge. In areas ofmarginal influence, about half of the col­onies were found dead, with the remainderbeing noticeably damaged. S iderastreasiderea, a hardy estuarine coral, was able toreestablish itself within the zone of max­imum thermal effects during the winter andspring months but was killed during the fol­lowing summer. In zones of marginal influ­ence, S. siderea heads were pale and ap­peared to be susceptible to overgrowth byalgae and encrustation by other life forms.

The increase of nearly 100 percent in anarea of total dead and bleached corals (0.38hectare to 0.71 hectare) between 1971 and1972 at first seems unusually large whencompared to the 30-percent increase inheated discharge. In the simplest case, onewould expect a linear increase in affectedarea with an increase in thermal discharge.However, Norman Buske, who has investi­gated the dynamics of the Kahe discharge,predicted the more extensive effect (per­sonal communication, December 1971). Heattributes the increased damage to the de­sign ofthe outfall structure. The outfall tun­nel was constructed with a sharp bend justbefore the discharge point. At discharges ofless than 14 m3/sec (three units operating)

14 PACIFIC SCIENCE, Volume 28, January 1974

the effluent is directed seaward along theoutfall jetty, while above this value (fourunits operating) it is deflected to the south.With the addition of K4, the plume directionis unstable and can swing north and south,affecting a much wider area than wouldnormally be the case. Furthermore, whenthe plume shifts to the south, it moves into aturbulent area created by waves strikingagainst Kahe Point and is mixed verticallydownward to depths as great as 3 meters.Normally it would be expected to stratify atthe I to 1.5 meter depth and would notstrongly influence the corals growing belowthis level. HECO has stabilized plume di­rection by maintaining full volume dischargeat all times, but occasionally units will haveto be taken off the line for maintenance.

Another factor which may have contrib­uted to the increased coral damage was theperiod of unusually high discharge tempera­tures which occurred in September andOctober of 1972 (see Fig. 5). However, be­cause the pi ume was directed to the northduring recirculation and because coolingand mixing with ambient water are greatlyenhanced by the high winds, it is possiblethat benthic temperatures in the damagedarea were not increased over those encoun­tered in the survey.

On 5 October 1972, John McCain andJames Peck of HECO (personal communi­cation) marked off a 10 m square section ofthe reef along our transect at a distance of139 to 149 m from the outfall, with our tran­sect line as the south edge. A total of 66bleached Pocillopora meandrina heads lo­cated within the square were tagged. Agradual decline in the number of heads wasobserved in the following months. By 14December 1972 only six living heads re­mained, and these had lost nearly half of theoriginal tissue area. These results and theresults of our tagging and transplants indi­cate that equilibrium had not yet been estab­lished at the time of our second survey andthat coral destruction continued to occur,even though ambient water temperature wasdecreasing during this period. It also dem­onstrates the importance of long-term sub­lethal effects and brings into question thepractice of using short-term tolerance limits

to predict environmental damage. Exposureto increased levels of thermal loading did notappear to kill the corals outright but gradu­ally weakened and eliminated them over aperiod of time.

We expect that damage to the coral reefatKahe Point will continue even without fur­ther increases in thermal discharge. Mostof the bleached and pale corals probably willcontinue to be eliminated with time. A simi­lar situation has been reported from Bis­cayne Bay, Florida (Roessler and Zieman1969). Although thermal discharge from theTurkey Point Power Plant remained con­stant during the period from September 1968to September 1969, damage to the shallowwater Thalassia (turtle grass) communityincreased. In September 1968, an area of 12to 14 hectares (30 to 35 acres) off the outfallwas devoid of all vegetation except blue­green algae. Surrounding this was an area ofapproximately 20 to 24 hectares (50 to 60acres) where all macroalgae had been elimi­nated and the Thalassia heavily damaged.By September 1969 the barren area had in­creased to about 20 hectares (50 acres) andthe surrounding damaged areas to 38 to 39hectares (70 to 75 acres).

Although the obvious environmentalparameter being altered in the Kahe dis­charge is temperature, changes in other fac­tors must also be considered. Measure­ments made by ourselves and others(Chamberlain, unpublished, 1971, B-KDynamics report; Sea-Test, unpublishedreport, 1972; and John McCain, personalcommunication) indicate that salinity andoxygen saturation are not appreciably al­tered in the area of the discharge. Toxicsubstances are not added to the coolingwater of this plant. Contamination of thedischarge water caused by corrosion ofmetallic surfaces within the power plantis probably insignificant. On 28 July 1972samples of water were taken at eight loca­tions along the coastline at Kahe, includingthe intake and outfall. Analyses for 31 of themost important elements and ions (includingCu, Zn, AI, Ni, Pb, Cr, Fe, Co, and Cd)revealed no detectable differences(Stearns-Roger Inc., unpublished report,1973, "Environmental assessment Kahe

Effects of Heated Effluent on Hermatypic Corals-JoKIEL AND COLES 15

Generating Stations units 5 and 6," submit­ted to Hawaiian Electric Co.). The substratealong the transect did not change during thesurvey, although the inner portions of the1971 dead coral zone became covered withsand when K4 became operational.

Increased turbidity resulted from the dis­charge of heated effluent and coincided withdegree of thermal stress, necessitating ananalysis of the relative importance of thesetwo components in producing the damage.Johannes (unpublished) observed the shallowwater reef community off Kahe Point for aperiod of I year when it was continuouslybeing subjected to extremely turbid watercreated by beach excavations during theconstruction of the plant. During thisperiod, corals continued to flourish, proba­bly because water movement (wave actionand currents) prevented corals from beingcoated with fine material. This observationis in agreement with the conclusions ofMarshall and Orr (1931), who studied theeffects of sedimentation on corals of theGreat Barrier Reef. Our observations led usto conclude that turbidity was the less im­portant of the two factors in the destructionof corals at Kahe. During the winter of1971-1972 we observed a complete recoveryof pigment in corals that had survived thehigh temperatures of the previous summer;they again became bleached in the summerof 1972 and recovered in the winter. Weattribute these phenomena to temperature,because turbidity appeared to remain un­changed. Such annual loss of zooxanthellarpigment in response to naturally producedhigh summer temperatures has also been re­ported by Shinn (1966). Furthermore, wewere able to locate an area in the field wherethe two effects could be separated.

Near Kahe Point, the bottom relief ishigh, with rock outcrops extending from thebottom into the heated surface layer. Tur­bidity created by wave action on the sandybottom is greatest near the bases of the out­crops, whereas thermal stress is greatestnear the surface. Corals growing at or nearthe tops of the outcrops experience highthermal stress and low turbidity, whereascorals growing near the base experience lowthermal stress and high turbidity. Corals

found near the tops of these outcrops weredead or obviously damaged by the heatedeffluent (pale or bleached condition),whereas corals growing at slightly greaterdepths (excluding corals at the very basethat may die when buried by sand) appearednormal. Therefore, we conclude that atKahe Point temperature was the principalfactor in determining the observed patternof damage.

The association between corals and theirintracellular algal symbionts appears to beeasily disrupted, and as such provides a val­uable indicator of thermal stress. The re­lease of symbiotic zooxanthellae by coralsand the consequent loss of photosyntheticpigment as a response to physical stresshas been observed by other investigators(Yonge and Nicholls 1931, Goreau 1964,Shinn 1966, and Wells et al. 1973), but hasnot been quantitatively measured.

Our determinations of photosyntheticpigment concentrations per cm2 for normalPorites and M ontipora are in agreementwith val ues reported by Margalef (1959) forvarious Caribbean corals and Maragos(1972) for Pacific species. Our chlorophyll aestimates for normal Porites lobata averageabout four times those of Roos (1967) forPorites asteroides sampled at Curacao.Pigment extractions appeared to be com­plete, as the coral plugs were colorless at theend of the 24-hour extraction period. How­ever, Maragos (1972) has since found thatcrushing the coral before extraction in­creases the accuracy of the method. Theprecision of replicates and large differencesbetween pigment concentrations corres­ponding to bleaching states clearly demon­strate a strong photosynthetic pigment ingradient corals along the transect. The pig­ment gradient ranged from values that areequivalent to those obtained by other inves­tigators to virtually no measurablechlorophyll in the highly stressed corals.

Absorption in the 330 nm UV region hasbeen suggested to be of adaptive signifi­cance to corals (Margalef 1959, Kawaguti1969, and Shibata 1969). The increase in theabsorption in this region by bleachedMontipora vermcosa (Table 1) might be in­terpreted as reflecting an increase in UV

16 PACIFIC SCIENCE, Volume 28, January 1974

TABLE 3

CORALS RANKED ACCORDING TO DATA FROM EDMONDSON (1928: TABLE 5)

CORAL SPECIES TIME ELAPSED (HOURS)

3 5 8 10 18 24

Leptastrea pl/rpl/rea A A A A A A

Porites compressa A A D

Porites fobata A A D

Montipora patii/a A A D

Montipora I'errl/cosa A D

Pocil/opora meandrina D

NOTE: Survival time of Hawaiian corals arreT they were raised to :nc Cal a rate of 2" C per hour and were maintained at that level for 24 hours. D.specimen dead: A. alive at the end of the specitied period.

absorption material in response to loss ofphotosynthetic pigment. However, M. ver­rucosa is the only one of the three speciesdemonstrating this. The UV peak maymerely be a manifestation of the amount ofcoral tissue remaining on the skeleton, assuggested by the decrease in 330 nm absorp­tion by Porites lobata taken nearest the out­fall.

With the elimination of the zooxanthellaeand their associated pigments, other pig­ments in the coral tissue were unmasked,resulting in some heads (mostly Pocilloporameandrina) taking on pastel hues of yellow,pink, violet, and occasionally green. Thisobservation supports the results of otherworkers (Kawaguti 1937, 1944, 1969;Shibata 1969) who found evidence that cer­tain coral pigments are found outside of thezooxanthellae.

Mayer (1917) observed that the ability ofacoral species to resist high temperatures isconversely related to the metabolic rate(oxygen consumption). Pocillopora, thecoral most sensitive to thermal stress atKahe Point, also has the highest metabolicrate (Franzisket 1964). Porites lobata hasan intermediate metabolic rate, whereaslarge polyp corals such as Leptastrea pur­purea are known to have lower metabolicrates (Mayer 1917, Mayor 1924, Franzisket1964). This generalization was originallybased on short-term laboratory results, butit also appears to hold under field condi­tions.

Tables 3 and 4 compare resistance ofcoralsto acute temperature rise as reported by Ed-

TABLE 4

CORALS RANKED IN ORDER OF RESISTANCE TO

THERMAL STRESS AS DETERMINED FROM

OBSERVATIONS AT KAHE POINT, OAHU. HAWAII

Strongly Resistant: Leptastrea pl/rpl/reaDana (synonym:

Fa\'ia hawaiiensis)Porites compressa DanaPorites fobala DanaMontipora patllfa VerrillMontipom \'errucosa (Lamarck)

Least Resistant: Pocillopom meandrinavar. nobifis Dana

mondson (I928), with our evaluation of therelative resistance to temperature stress ofcorals at Kahe based on observed bleachingand mortality. Both approaches show thesame resistance patterns among the com­mon species. This agreement further sub­stantiates the argument that thermal stress isthe principal factor involved in producingthe observed coral mortality.

The absolute temperature level, ratherthan degree of enrichment over seasonalambient levels, appears to be the criticalfactor, as indicated by recovery of the coralsduring the winter months in areas wherethermal enrichment levels were as high asthose of the previous summer. Our observa­tions at Kahe indicate a lethal temperatureof 31 0 to 320 C for most Hawaiian species ofcoral, which is also in agreement withEdmondson's (I928) results. Prolonged ex­posure to temperatures of 300 to 31 0 C ap­pears eventually to pale, bleach, and kill

Effects of Heated Effluent on Hermatypic Corals-JoKIEL AND COLES 17

most of the common coral species encoun­tered at Kahe. Temperatures approaching30° C probably are sublethal and may, ifprolonged, lead to the destruction of themore sensitive coral species. These obser­vations are in agreement with results oflaboratory studies conducted by us in whichthe same paling and bleaching effects ob­served at Kahe were also produced underlaboratory conditions (Coles 1973, andJokiel et aI., unpublished).

A question remains as to the relative im­portance of absolute high levels of tem­perature vs. stress imposed by rapid tem­perature fluctuations (thermal shock). Rapidtemperature fluctuations occurred through­out the year but acute coral damage wasobserved only during periods of maximumambient temperatures. Temperature fluctu­ations may be more important when thetemperature approaches the tolerance lim­its.

ACKNOWLEDGMENTS

We wish to thank Dr. John McCain andthe staff of HECO for their cooperation inthis study. The work was conducted underthe direction of Dr. SidneyJ. Townsley andDr. John E. Bardach. We are indebted toDrs. James Maragos and Robert Johannesfor their advice during the course of thestudy and for their comments on the originalmanuscript.

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EDMONDSON,C. H.1928. The ecology ofanHawaiian coral reef. Bull. Bishop Mus.,Honolulu 45. 64 pp.

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