tional Corporation, San Diego, CA, 1985), pp. 25-39.

26. T. Poggio et al., in Proceeditngs: Image UtnderstandingWorkshop, Cambridge, April 1988 (Morgan Kauf-mann, San Mateo, CA, 1988), pp. 1-12.

27. T. A. Cass, in ibid., pp. 640-650.28. We have exploited the labeling of discontinuities (E.

B. Gamble, D. Geiger, T. Poggio, D. Weinshall, inpreparation) in recognition experiments. In addi-tion, our integration scheme allows us to segmentthe scene into different depth planes, for instance,thereby considerably reducing the combinatorics ofmodel-based recognition.

29. Our formulation of the integration problem in termsof MRF does not imply that the algorithms arenecessarily stochastic. Deterministic approximationsto the more general stochastic schemes may workquite well, especially in situations where redundantand contradictory data from several sources effec-tively set the initial state of the system close to thesolution. We have, in fact, found that gradientdescent in the space of the depth and the line processoften works quite well. We routinely use a mixeddeterministic and stochastic strategy (17) in whichthe continuous (depth) process is deterministically

updated while the line process is updated stochasti-cally. Other strategies may also be effective (8), suchas space-variant filtering, for instance, coupled withedge detection. In addition, time-dependent sched-ules of the coupling parameters can be useful. Theyare somewhat similar to simulated annealing, whichcan also be effectively used, though it is quite slow.

30. H. H. Builthoff, personal communication.31. J. F. Canny, IEEE Trans. Pattern Anal. Mach. Intell.

PAMI-8 (no. 6), 679 (1986).32. This report describes research done within the Arti-

ficial Intelligence Laboratory. Support for the A. I.Laboratory's artificial intelligence research is provid-ed by the Advanced Research Projects Agency of theDepartment of Defense under Army contractDACA76-85-C-0010 and in part under Office ofNaval Research (ONR) contract N00014-85-K-0124. Support for this research is also provided by agrant from ONR, Engineering Psychology Divi-sion, and by a gift from the Artificial IntelligenceCenter of Hughes Aircraft Corporation to T. Pog-gio.

4 May 1988; accepted 12 August 1988

Earthquake-Caused Coastal Uplift and Its Effects onRocky Intertidal Kelp Communities

JUAN CARLOS CASTILLA

The coastal uplift (approximately 40 to 60 centimeters) associated with the Chileanearthquake of 3 March 1985 caused extensive mortality of intertidal organisms at theEstacion Costera de Investigaciones Marinas, Las Cruces. The kelp belt of thelaminarian Lessonia nigrescens was particularly affected. Most of the primary spaceliberated at the upper border of this belt was invaded by species of barnacles, whichshowed an opportunistic colonization strategy. Drastic modifications in the environ-ment such as coastal uplift, subsidence, or the effects of the El Ninio phenomenon arecharacteristic of the southern Pacific. Modifications in the marine ecosystem thatgenerate catastrophic and widespread mortalities of intertidal organisms can affectspecies composition, diversity, or local biogeography.

ON 3 MARCH 1985 AT 19:47 Amajor earthquake, with a surfacewave magnitude of 7.8, occurred

in central Chile (1). The seismic wave origi-nated in the sea bed 40 km west of thecoastal town of Algarrobo (33°20'S,71°40'W) at a depth of approximately 15km (2). The average horizontal displace-ments in coastal zones were in a northwestdirection and of magnitude approximately25 cm (3). Studies on the vertical compo-nent of deformation suggest a mean conti-nental uplift of about 33 cm. Maximumuplifts of approximately 45 to 50 cm wereobserved in coastal areas, such as El Quisco.The coastal marine station (ECIM) of thePontificia Universidad Cat6lica de Chile (4),located on a 500-m stretch of exposed rockyshore at Las Cruces, is 15 to 20 km fromboth El Quisco and Algarrobo. The seismicwave caused both horizontal and verticalcoastal displacements (3) at ECIM. I inde-pendently checked rocky shore uplifts atECIM, using previously known fixed bench-marks that were leveled and referred to the

extreme low water spring (ELWS) (5). Theuplifts (Table 1) found at ECIM, about 44to 59 cm, were roughly within the rangedetermined by Instituto Geognrfico Militar(3).

It is well established that the zonationpatterns of intertidal organisms are deter-mined by biotic and abiotic factors (6-8).Among the latter, desiccation and tempera-ture stress can play key roles determining theupper limit of sessile organisms. Hence, inChile, even under normal weather condi-tions during ELWS tides at around noon-time on sunny days, intertidal macroalgaehave been observed to die (bleaching) (9).Moreover, substantial modification of inter-tidal landscapes has been documented (10,11) as a result of increases in seawatertemperature. Similarly, coastal uplifts orsubsidences resulting from earthquakes ornuclear testing have modified the intertidalzonation patterns or induced mortalitiesamong sessile or mobile species (12-15).

Since 1974 the zonation and dynamics ofthe central Chile rocky intertidal shore have

been studied (16, 17). Immediately beforethe March 1985 earthquake I was engagedin an intertidal research program at LasCruces (18). Transects had been made ran-domly at selected sites, and species composi-tion, primary space, percent coverage, andthe change through time in biomass of themacroalga Lessonia nigrescens were assessed(19). The first two field surveys were con-ducted on 9 to 10 February and 5 to 8March 1985. I report here on the effects ofthe coastal uplift on ECIM rocky shorecommunities and particularly on the struc-ture and dynamics of the lower rocky shorefringe, the so-called L. nigrescens belt (9, 16,20).

Six 1-m-wide transects in the L. nigrescenskelp zone, extending 2.5 m from their inter-tidal upper to lower limit and 3 to 7m apart,were randomly chosen (21). Vertical differ-ences between the lower and upper limits ofthe belts were 1 to 1.55 m. Each belt,identified by means of poxy putty marks,was divided vertically into five 0.5-m plots(1-m horizontal axis, 0.5-m vertical axis).Plots A (upper limit) to E (lower limit) weresampled 8 to 11 times during the 36-monthstudy. The maximum holdfast diameter (d)of each L. nigrescens plant within each plotwas recorded and the biomass was calculated(22).

Figure 1 shows the change in the L.nigrescens biomass with time. In the upperplots, A and B, the biomass before theearthquake was about 15 kg m 2, wetweight; this was considered the normal pat-tern (23). A significant decrease in biomass,accompanied by a change in the color of theplants from brown to yellow and the subse-quent mortality of the stipes and holdfasts,was evident toward the end of 1985. ByFebruary-March 1986 all plants had disap-peared from the upper plots. No recoloniza-tion has been observed up to February1988. The biomass record for the middleplot, C, was similar, but the biomass de-crease was obvious only in early 1986. ByFebruary 1987 almost all plants had disap-peared from this plot as well, and no recolo-nization has since been observed. Plots Dand E, the lower plots, behaved differently.At plot D a drastic decrease in L. nigrescensbiomass was observed in early 1986 (23)(about 6 kg m-2 by February 1987), but byFebruary 1988 the biomass had increased toabout 15 kg m2. Plot E showed compara-tively less change in L. nigrescens biomass,with values between 20 and 33 kg m-2. Inplot F (not part ofthe original study becausethe kelp was absent) L. nigrescens was abun-

Estacion Costera de Investigaciones Marinas, Facultad deCiencias Biol6gicas, Pontfficia Universidad Cat6lica deChile, Casilla 114-D, Santiago, Chile.

SCIENCE, VOL. 242440

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dant by the beginning of 1986 owing to thesettlement of juvenile plants; this observa-tion suggests a change in the lower intertidallimits of the kelp belt, as compared with theoriginal study. By February 1987 L. nigres-cens biomass in plot F was about 15 kg m2,and by February 1988 it had reached 30 kg

-2m

Changes in primary space cover over timewere determined at three levels in the L.nigrescens belt (Fig. 2): (i) upper level (plotsA and B), (ii) middle level (plots C and D),and (iii) lower level (plot E). At the upperlevel there was evidence of the mortality ofL. nigrescens and of the presence of articulateand crustose coralline algae a few monthsafter the earthquake. By February 1986 thecover of the algae was almost zero. Asprimary space became available, it was im-mediately occupied by barnacles, mostlyChthamalus scabrosus and to a lesser extentJehlius cirratus, which readily settled on theseplots and thereafter established a belt (24).The cover of barnacles increased from 18 to

66% in the 3 years after the earthquake (25).At the middle level a similar process oc-

curred. Bleaching of macroalgae was ob-served later. For example, the cover of crus-

tose coralline algae diminished from about30% in March 1985 to about 10% in Febru-ary 1988. Chthamalus scabrosus increased itscover in these plots from less than 5% inMarch 1985 to 56% in February 1988. Atthe lower level (only plot E was studiedbecause of the inaccessibility of plot F) fewchanges were observed. The primary space

cover of L. nigrescens increased from about20 to 45%. No barnacles settled at this plotin amounts exceeding 5%, and thereforethey are included under the "other species"category in Fig. 2. A decrease in the cover ofcrustose and articulate coralline algae was

also observed at this plot. No settlement ofthe competitively dominant intertidal mus-

sel Perumytilus purpuratus has been observedto date.

In Alaska, Plafker (26) used intertidalbarnacles to determine changes in the eleva-tion of coastal areas due to the great earth-quake of 27 March 1964. Studies on lami-narian and coralline algae after the earth-quake (27) demonstrated dramatic changesin zonation patterns and in the relativeability of those organisms to survive underconditions of coastal uplift. Most corallinealgae require nearly continuous submer-gence, and coastal uplift is bound to affecttheir populations and eventually the com-

munity.Similar sudden and dramatic ecologically

catastrophic events attributed to El Nifiophenomena (11) have substantially modifiedintertidal landscapes. Hence, extensive mor-

talities of adult L. nigrescens, resulting in the

21 OCTOBER I988

Fig. 1. Lessonia nigrescensbiomass change along timein different intertidal plots(A = upper Lessonia border;F = lower border). Biomassand standard errors (bars)are based on six readings perplot. Asterisks indicate ob-servations with zero bio-mass.

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Table 1. Coastal vertical movement of rocks at ECIM (Las Cruces) associated with the 3 March 1985earthquake. Each set of readings was taken at the same location between 5 and 20 min before thecalculated tide table low tide of the corresponding day (5).

Relativeheight (cm) Approximate

Date referred to ELWS uplift(cm)

Mean (SD)

Wall 1Before earthquake20 August 1982 65.3 (4.1)*1 December 19826 October 1982

After earthquake3 June 1985 109.9 (5.3)t +44.64 June 1985

Wall 2Before earthquake

6 October 1983 172 (3.9)*After earthquake

3 June 19854 June 1985 231 (7.2)t +59.0

*Data from twelve readings taken by two operators. tData from eight readings taken by four operators.

REPORTS 441

I9

Fig. 2. Changes in primary space cover along timeat three levels of the Lessonia nigrescetns intertidalbelt: plots A and B, upper; C and D, middle; andE, lower; 0, Barnacles; 0, Lessonia nigrescens; *,bare space; *, other species; C], Corallina spp.alive; *, Corallina spp. dead; A, lithothamnioidalive; A, lithothamnioid dead; 0, Hildenbrandiasp.; ~, Codium ditnorphum alive; C, Codium dimnor-phum dead; 0), Gelidum chiletnse. Averages andstandard errors (bars) are based on six readingsper plot.

depopulation of large areas of rocky shoresin northern Chile, are well documented(10).Both kinds of catastrophic events, earth-

quakes and El Nifio phenomena, are cyclicaland affect large areas of the Chilean coast-line. For instance, seven earthquakes of sur-face wave magnitude greater than 7 oc-curred in central Chile in the last century(1). Further, it has been calculated that therecurrence time for earthquakes of magni-tude greater than 8.2 to 8.4 is about86 ± 10 years (1). An El Nifho (28) occurson average every 4 years, with intervalsbetween successive events as short as 2 yearsand as long as 10 years (29).These kinds of sudden and drastic modifi-

cations in the environment, which are char-acteristic of the southeastern Pacific, cancause substantial changes in marine ecosys-tems and can generate catastrophic mortali-ties that can affect local biogeography, spe-cies composition and diversity, and biomass;they can enhance local and more widespreadlatitudinal patchiness [much the same asmortalities produced by disease outbreaks(30-32) or predation (33)]. Examples of thehistorical and ecological importance of dras-tic and catastrophic events and their effectson marine communities have been reported(34, 35) for the Northern Hemisphere. Thequestion of whether some of the rockyintertidal species have evolved in response tothese cyclical catastrophic events is particu-larly challenging. Recently (36) it was dem-onstrated that marine organisms respondrapidly to intense perturbations (predation)within ecological time frames.

REFERENCES AND NOTES

1. L. Ponce, S. K. Singh, G. Suarez, J. Vargas, Itf Tic.SC/RP 20312i.5 (Centro Regional de Sismologiapara America del Sur, Lima, Peru, 1985), p. 1.

2. The tectonic plates in motion are Nazca and SouthAmerica. The speed of the seismic wave caused bythe March 1985 earthquake was about 5 krn sec-'.

3. Departamento de Procesamiento v Calculo, Insti-tuto Geogrifico Militar, Terra Aust. 29, 5 (1986).

4. Estaci6n Costera de Investigaciones Marinas(ECIM), Las Cruces, in operation since December1982.

5. Two benchmarks identified on rocks of ECIM, onenext to the seawater intake at the south cnd of thestation and another in the northern border, wereused to independently check on rock upliftings.Tides in this coastal line are of the mixed diurnal-

80-Plots A and B

60

40 Earthquake3 March 1985

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Mar. July Sep. Nov. e Apr June July Feb F

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21

1985 1986 1987 1988

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:1~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1Mar. July Apr. Sep. Oct. Nov. 1 Feb. Mar. Apr.

1985 1986July Feb. "" Feb.

1987 1988

SCIENCE, VOL. 242

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442

semidiurnal type with greatest amplitude of about1.80 m.

6. J. R. Lewis, The Ecology of Rocky Shores (EnglishUniv. Press, London, 1964).

7. J. Connell, Annu. Rev. Ecol. Syst. 3, 169 (1972).8. R. T. Paine, in Changing Scenes in Natural Science, C.

E. Goulden, Ed. (Special Publication 12, Academyof Natural Sciences, Philadelphia, 1977), pp. 245-270.

9. B. Santelices, S. Montalva, P. Oliger, Mar. Ecol.Prog. Ser. 6, 267 (1981).

10. R. Soto, Invest. Pesq. (Chile) 32, 199 (1985).11. R. T. Paine, Estud. Oceanol. 5, 9 (1986).12. C. Darwin, Geological Observations (Appleton, New

York, 1897).13. The Great Alaska Earthquake of1964 (National Acade-

my of Sciences, Washington, DC, 1971).14. P. Bodin and T. Klinger, Science 233, 1071 (1986).15. P. A. Lehendik, Mar. Biol. 20, 197 (1973).16. J. C. Castilla, Medio Ambiente 5, 190 (1981).17. R. T. Paine et al., Am. Nat. 125, 679 (1985).18. The research program was designed to evaluate the

ecological role played by man as a predator on therocky shore ofcentral Chile. Castilla and Duran (33)and D. Oliva and J. C. Castilla [Publ. Stazione Zool.Napoli I Mar. Ecol. 7, 201 (1986)] discuss the aimsof the program.

19. The point-intercept method was used: a 1 m by 1 mstring-grid quadrat with 171 intersection points wasapplied to the surface. Percent coverage was calculat-ed by angular transformation.

20. E. P. Guiler, Pap. Proc. R. Soc. Tasmania 93, 165(1959).

21. All L. nigrescens belts selected were in rocks withinclinations of 45° or less and presented a similargeological composition consisting primarily ofmetamorphic gneiss with lamprophyre intrusives.They were oriented south and received water splashthrough littoral channels.

22. I calculated the L. nigrescetis biomass (b), wet weight,for three types of plants according to the followingformulas: (i) for undamaged plants, b = 0.7208 d(where d is the maximum diameter of holdfast); (ii)for half-damaged plants (less than 50% of the stipesdead), b = 0.5593 d; and (iii) for fully damagedplants (more than 50% of the stipes dead),b = 0.2035 d.

23. Lessonia nigrescens biomass determinations carriedout on six different opportunities (1982 to 1984) atLas Cruces showed values ranging between 13 to 20kg m-2, wet weight, at the upper intertidal borderand 27 to 38 kg m-2 at the middle and lowerborders. The mean overall biomass of this kelp atLos Molles, central Chile, was about 33 kg m- [B.Santelices, "Manejo de praderas de Lessonia nigrescensen Chile Central" (final report, Subsecretaria dePesca, Chile, 1981)].

24. Newly settledJ. cirratus and C. scabrosus are difficultto identify in the field. After 3 to 5 months, about90% of the barnacles at this level were C. scabrosus,and they reached 100% by the end of the study.

25. R. T. Paine [Paleobiology 7, 553 (1981)] argued thatin Chilean rocky shores both species of barnaclesshowed a "weed" colonization strategy.

26. G. Plaflker, Science 148, 1675 (1965).27. H. W. Johansen, in (13), pp. 35-68.28. M. A. Cane, Science 222, 1189 (1983).29. W. H. Quinn etal., Fish. Res. Bull. 76,663 (1978).30. M. L. Dungan et al., Science 216, 989 (1982).31. H. A. Lessios et al., ibid. 226, 335 (1984).32. T. P. Hughes et al., Bull. Mar. Sci. 36, 377 (1985).33. J. C. Castilla and R. Duran, Oikos 45, 391 (1985).34. P. K. Dayton and M. J. Tegner, Science 224, 283

(1984).35. D. S. Wethey, Ecology 66, 445 (1985).36. R. H. Seeley, Proc. Natl. Acad. Sci. U.S.A. 83,6897

(1986).37. Supported by projects Direcci6n de Investigaci6n

Universidad Cat6lica 63/84 and Fondo Nacional deInvestigaci6n Cientifica y Tecnol6gica 86/1100. Ithank D. Oliva, E. Ortiz, R. Bustamrante, and R.Durnn for field assistance and helpful discussions.Two anonymous referees made valuable commentson the manuscript.

18 April 1988; accepted 21 July 1988

Activation of Muscarinic Potassium Currents byATPyS in Atrial Cells

ANGELA S. OTERO,* GERDA E. BREITWIESER, GABOR SZABO

Intracellular perfusion of atrial myocytes with adenosine 5'-(-y-thio) triphosphate(ATP-yS), an ATP analog, elicits a progressive increase of the muscarinic potassiumchannel current, IK(M), in the absence of agonists. In this respect, ATP-yS mimics theactions of guanosine triphosphate (GTP) analogs, which produce direct, persistentactivation of the guanyl nucleotide-binding (G) protein controlling the K(M) channel.The effect ofATPyS on IK(M), however, differs from that produced by GTP analogs intwo aspects: it requires relatively large ATP-yS concentrations, and it appears after aconsiderable delay, suggesting a rate-limiting step not present in similar experimentsperformed with guanosine 5'-(-y-thio) triphosphate (GTP-yS). Incubation of atrialhomogenates with [35S]ATPyS leads to formation of significant amounts of[35S]GTPyS, suggesting that activation of IK(M) by ATP'yS arises indirectly through itsconversion into GTPyS by cellular enzymes. ATPyS is often used to demonstrate theinvolvement of protein phosphorylation in the control of various cellular processes.The finding that cytosolic application ofATPyS can also lead to G-protein activationimplies that experiments with ATP-yS must be interpreted with caution.

I NTERNAL DIALYSIS OF ATRIAL MYO-cytes with hydrolysis-resistant GTP an-alogs evokes muscarinic receptor-inde-

pendent activation of IK(M) (1, 2) with anorder of effectiveness (GTPyS > GMP-PNP - GTP > GMP-PCP; where GMP-PNP is guanylyl imidodiphosphate andGMP-PCP is guanylyl (3,-y-methylene)-di-phosphonate) that parallels their bindingaffinities to purified G proteins (3, 4). Wefound (5) that intracellular application ofATP-yS, an ATP analog, has effects thatclosely resemble those ofGTP analogs (1, 6)on IK(M)- This result could be interpreted asa lack of specificity of the nucleotide siteinvolved in muscarinic activation of cardiacK+ channels, thus weakening the G-proteintransduction hypothesis, since ATP interactspoorly, or not at all, with the GTP bindingsite of purified G proteins (7). Alternatively,the actions of ATP-yS could stem from (i)contamination by GTP-yS, (ii) formation ofa stable thiophosphorylated protein in-volved in channel gating, or (iii) conversionof ATPyS into its guanosine counterpart.The experiments reported here were de-signed to distinguish among these possibili-ties.The effects of intracellular application of

ATP-yS on K+ currents were examined insingle myocytes dissociated enzymaticallyfrom bullfrog atrium, with the tight-sealwhole-cell voltage clamp technique (1, 8).Calcium and Na' currents were blocked byextracellular cadmium and tetrodotoxin, re-spectively. Outward and inward currentswere measured at the end of 250-ms pulsesfrom a holding potential of -85 to -45 mVand -135 mV, respectively. Figure IAshows these values, plotted as a function oftime, beginning 1 min after the disruption

of the patch membrane; the patch pipettesolution contained 2.5 mM ATP-yS. A grad-ual increase in both inward and outwardcurrent is observed after 7 min of dialysis.Superfusion ofthe cell with 1 ,uM acetylcho-line (ACh) 10 min after patch rupture causesa rapid, albeit small, increase in current;washout of agonist 1 min later has littleeffect on the current levels, indicating per-sistent activation of IK(M)- The membranecurrents elicited by the test pulses are shownin Fig. 1B, which illustrates the appearanceof the characteristic relaxation of IK(M) (1,9) well before agonist was applied. Thecurrent-voltage (I-V!) relations measured atvarious times during this experiment areplotted in Fig. IC. It is clear that the voltagedependence of the current activated byATP-yS differs from that of the backgroundK+ channel, IKI, and parallels that observedduring ACh application. External applica-tion of 0.1 mM BaCl2, but not 1 FLMatropine, completely blocks the membranecurrents elicited by ATP-yS. By these crite-ria, the current that develops during intra-cellular perfusion with ATP-yS is indistin-guishable from IK(M), whether elicited byagonist application or by intracellular dialy-sis with GTP analogs (1).We examined the effect of loading cells

with different ATP-yS concentrations in ex-periments similar to that in Fig. 1. Afterreceptor-independent activation hadreached a steady level, 1 puMACh was added

A. S. Otero and G. Szabo, Department of Phvsiologyand Biophysics, University of Texas Medical Branch,Galveston, TX 77550.G. E. Breitwieser, Department of Phvsiology, JohnsHopkins University School of Medicine, Baltimore, MD21205.

*To whom correspondence should be sent.

21 OCTOBER I988 REPORTS 443