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nique needs to be modified so that it worksat much warmer temperatures that pre-serve the samples’ biologically relevantstructures. —A. GOHO

Origins ofSmeltingLake yields core of pre-Inca silver making

According to 16th-century Spanishaccounts, an Incan ruler who reigned nearly600 years ago discovered Cerro Rico, amajor silver deposit in southern Bolivia’sAndes Mountains. More recently, archae-ological discoveries have documented theIncas’ extensive efforts to mine silver oreand extract the precious metal in smeltingoperations.

It now appears, however, that the Incaswere latecomers to silver production. Athriving silver industry existed in southernBolivia about 1,000 years ago, accordingto a new study. Four centuries before com-parable Incan operations, Bolivia’sTiwanaku culture probably launched sil-ver mining at Cerro Rico and the large-scale smelting of silver ore, say Mark B.Abbott of the University of Pittsburgh andAlexander P. Wolfe of the University ofAlberta in Edmonton.

The two geologists extracted a sedimentcore from a lake near Cerro Rico and meas-ured concentrations of five metals associ-ated with smelting. “Our data imply thatseveral thousand tons of silver were pro-duced in pre-Incan times,” Abbott says.

He attributes the scarcity of silver arti-facts in Bolivia dating back a millennium toa combination of looting at archaeologicalsites, transport of silver elsewhere in theAmericas as a trade item before the Span-ish conquest, and export of silver overseasby the Spanish after conquest.

The ratio of metals such as silver, lead,and antimony in the lake core indicateswhether smelting occurred, and radiocar-bon analyses provided age estimates for soillayers in the core. Cerro Rico ores weresmelted from A.D. 1000 to A.D. 1200, aperiod ending close to the time thatTiwanaku society collapsed, the research-ers conclude in the Sept. 26 Science.

Silver smelting declined markedly for thenext 2 centuries, they say. From A.D. 1400to A.D. 1650, the practice again flourished,

first among the Incas and then their Span-ish conquerors.

The new findings on early silver produc-tion support the view that Tiwanaku soci-ety grew considerably around 1,000 yearsago, shortly before severe drought con-tributed to its breakup, remarks archaeol-ogist Alan L. Kolata of the University ofChicago. Kolata directs an ongoing exca-vation of the Tiwanaku capital on Bolivia’swestern border.

That project has unearthed many silverartifacts, including ceremonial masks, rings,and tubes packed with pigment. Kolatafinds it “somewhat surprising but plausi-ble” that Tiwanaku society producedthousands of tons of silver, asAbbott and Wolfe contend.

“The [new] estimate ofthe tonnage of silver pro-duced prior to Incainvolvement . . . isremarkable,” com-ments archaeologistHeather Lechtman ofthe MassachusettsInstitute of Technol-ogy. However, the lat-est archaeological evi-dence indicates thatTiwanaku society collapsedbetween A.D. 900 and A.D.950, before the proposed start ofsilver production, she says.

Archaeological investigations under wayin central and southern Bolivia need toidentify other early cultures that may haveinitiated silver mining and smelting,Lechtman holds.

Analyses of metal concentrations inother Bolivian lakes will also prove crucialin disentangling the origins of silver pro-duction, Abbott says. —B. BOWER

BreathlessReef fish cope with low oxygen

Despite their seemingly idyllic surround-ings, coral reef fish show unexpected tough-ness, according to a new analysis of fish res-piration.

In the first tests of low-oxygen toleranceamong reef fish, all 31 species captured offthe coast of Australia did surprisingly well,says Göran E. Nilsson of the University ofOslo. The reef fish matched the perform-ance of the epaulette shark, famed for sur-viving oxygen drops in tide pools cut offfrom the surf, Nilsson and Sara Östlund-Nilsson report in an upcoming Proceedingsof the Royal Society of London B.

When respiration physiologists look foradaptation to low oxygen, they pokearound in still waters, such as swamps and

tide pools, says Nilsson. But coral reefs?“It’s not something that most people havebothered about,” he says. Plenty of churn-ing there should mix the seawater wellenough to avoid oxygen drops.

Nilsson didn’t think to look for low-oxygen tolerance at reefs until he began toobserve mouth brooding in cardinalfisharound Lizard Island on Australia’s GreatBarrier Reef. A male of these small reef fishtakes a female’s egg mass, sometimes aquarter of his body weight, into his mouthfor a week or two, until the eggs hatch. Sincethe egg mass might inhibit water flowthrough the mouth to the gills, Nilsson

wondered whether these fishhave a special capacity to

tolerate low oxygen. To test the cardinal-

fish, the researcherssealed them tem-porarily in con-tainers with sea-water and asensor for oxygenconcentration.Many organisms

keep consumingthe available oxygen

at a steady rate untilthere’s so little left that

they no longer metabolizenormally. Thecardinalfish surprised Nils-son by breath-ing steadilyuntil the oxy-gen concentra-

tion had dropped to 20 percent of its nor-mal concentration.

At first, Nilsson says, he thought he’dfound especially low oxygen tolerance incardinalfish. For comparison, he decidedto test reef fish that don’t carry broods intheir mouths. Surprisingly, he says, all thespecies he caught showed low-oxygen tol-erance.

Data by other researchers show that somefreshwater fish such as trout proved onlyhalf as tolerant of low oxygen as the reeffish did. The most tolerant of swamp fishrequire only a little less oxygen than themost tolerant of the reef fish do. Nilssonnotes that no one has made comparablemeasurements on ocean fish away fromreefs.

Perhaps reef fish hide in low-oxygen cul-de-sacs of coral, Nilsson speculates. In labmeasurements, he found that those pock-ets can have oxygen concentrations below20 percent of saturation.

Physiologist Jeff Graham of the ScrippsInstitution of Oceanography in La Jolla,Calif., says that plenty of questions remain.He’d like to see comparisons between fishthat hide in reef nooks and those thatdon’t. —S. MILIUS

SCIENCENEWSThis Week

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REEF REFUGE It maylook like paradise, but havethe fish hiding amongthese coral spikes adaptedto an oxygen shortage?

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