Fish populations may be suffocating and other stories

Environmental News Network 03 April 2003

Adapted by Cameron Walker and Victoria Schlesinger, edited by Kathleen M. Wong, California Academy of Sciences

Fish Populations May Be Suffocating

Low oxygen conditions could be cramping the reproductive capabilities of fish. A report in the Journal of Environmental Science and Technology suggests that oxygen deficiency, or hypoxia, may be as harmful to watery creatures as pesticides or toxic metals.

Rudolf Wu of the City University of Hong Kong and colleagues raised carp under hypoxic conditions; the oxygen-starved fish developed smaller sexual organs and lower hormone levels than carp raised with normal oxygen levels. In addition, only 5 percent of the larvae from the low-oxygen carp survived, compared to 90 percent of normal fish larvae.

Low oxygen conditions can be a problem when nutrient levels rise, boosting algae growth and further sapping available dissolved oxygen. Wu says that hypoxic "dead zones" in the world's waterways, such as the one off Louisiana and Texas in the Gulf of Mexico, could severely threaten populations of fish and possibly other aquatic species.

Drought Dried Out the Mayans

Studies of soils may have unearthed another clue to the Mayans' mysterious demise. The prosperous Central American society collapsed suddenly between the years 800 and 910. Theories about the cause of their downfall have ranged from overpopulation to climate change.

Now the most detailed sediment analysis ever conducted near the Mayans' main population centers indicate a long dry spell and three severe droughts may have brought the civilization to its knees.

Gerald H. Haug, now at Potsdam's Geoscience Center, and colleagues sampled sediments from the Cariaco Basin off the coast of northern Venezuela. The researchers tallied levels of titanium, an element which fluctuates with rainfall levels, to uncover three periods of low rainfall on the Yucatan peninsula. They report in the journal Science that these droughts match up with archeological records, suggesting that the population suffered three waves of collapse during the same time frame.

First Footprints Fled Disaster

The oldest known human footprints have been found preserved in ash on the side of a volcano in southern Italy. Paolo Mietto of Italy's University of Padua and colleagues say the 56 footprints were left by people fleeing a volcanic eruption 325,000 years ago.

The prints head away from the volcano's center and indicate those who made them were in a tearing hurry. Three humans around five feet tall slid, side-stepped, and rushed down the steep, 80-degree pitch of the mountain.

The scientists, who published their findings in the journal Nature, say it's impossible to determine whether the tracks were left by people of the Homo erectus or Homo heidelbergensis persuasion. One thing they are certain of, however, is that the trails were left by hominids who walked on two legs. While these may be the earliest known human footprints, fossilized hominid prints discovered in the 1970s date back more than 3 million years.

The Battle of the Birds

The bird world's most adept freeloader, the cuckoo, has been outmaneuvered by one of its hosts. Cuckoos lay their eggs in the nests of other birds, leaving host birds with the draining task of raising the parasitic chick. To make matters worse, cuckoo chicks often eject any nestlings from their rightful home.

Many birds have evolved to recognize cuckoo eggs. But once hatched, the impostors are usually home free. Now Rebecca Kilner of Cambridge University in England and others report in the journal Nature that they have for the first time found a host who can recognize parasitic cuckoo chicks.

The superb fairy-wrens of New South Wales, Australia, can discern the begging calls of Horsfield's bronze-cuckoo chicks 40 percent of the time — and let them starve. Yet the wren cannot recognize the cuckoo's eggs, which are almost identical to its own. Kilner says the lengthy breeding season in Australia may account for the wren's unique recognition ability. Once an alien chick is spotted, the wrens, unlike many other birds, have a chance to lay again.

In a case of evolution caught in action, cuckoo chicks are now learning to better mimic the calls of fairy wren chicks.

Ancient Speakers Clicking Along

The language of the San hunter gatherers of Southern Africa is replete with unusual clicking sounds. A new study has pointed out the ancient roots of these so-called click languages, suggesting that the sounds may have been part of the earliest forms of human language.

There are about 30 modern click languages, each with a set of four or five click sounds; most are spoken by people in southern Africa. One of these click-speaking peoples, the Ju|'hoansis', are known to have extremely ancient origins.

Geneticists Alec Knight and Joanna Mountain from Stanford University traced the genetic lineages of one of the few click language groups in East Africa and have concluded that the split between the east African group and the Ju|'hoansis' might be the oldest known division in the human population. Because both groups speak a click language, these unique sounds were likely present in the language of their common ancestor. While geneticists still debate the exact timing of this split as well as why the click languages have remained in use, it's clear that clicks might clue modern listeners in to the sounds of the ancients.

Risky Radiation Levels Discovered on Mars

Any future settlers on Mars will need to stay under cover. New information collected by the unmanned spacecraft Odyssey suggest that radiation levels on Mars are high enough to harm anyone living on the planet's surface.

High levels of radiation are present throughout the galaxy, but Earth's thick atmosphere and strong magnetosphere block most of the cancer-causing energy from reaching our planet's surface. By contrast, astronauts on a mission to Mars would surpass their radiation exposure limits in only three years. Some scientists conclude that radiation levels on Mars are so high that even extraterrestrial organisms would need to hunker down underground.

Other immediate dangers on the planet's surface would include periodic bursts of intense sun radiation not deflected by Mars' thin atmosphere. Each of these storms would require astronauts and their vehicles to take shelter for more than a week.