Category Archives: Feeding and foraging

A hungry red tide is a dangerous red tide

By John Upton

When fertilizer or sewage runs into a waterway, or when phosphorous and nitrogen rise up from the ocean depths, algae can converge and feast and mushroom on the buffet of growth-inducing nutrients.

But scientists have discovered that starving a poisonous red tide of its nutrient supply can trigger a very dangerous and counterintuitive response.

Red tides are freaky types of algae blooms. They often occur in the ocean or in salty bays, and they frequently produce poisons. Scientists prefer the term “harmful algal bloom,” since a red tide isn’t always red and it is most certainly not a tide.

Illustrated by Perry Shirley
Illustrated by Perry Shirley

The most common type of algae in Gulf of Mexico red tides is a dinoflagellate called Karenia brevis. The neurotoxin produced by these single-celled creatures help protect them from predation: Would-be hunters can die if they take a mouthful. But as the red tides break down, the poison escapes from the plankton cells and it can drift through the marine environment, poisoning it. The toxin can even spray into the air, aerosolized by crashing waves, where it can get into lungs and trigger serious ailments in people and other animals. The Floridian West Coast is often the worst affected.

Concentrations of the poison in each of the algae cells varies widely — from a mild 1 picogram per cell to a treacherous 68 picograms per cell. Needless to say, figuring out what causes a bloom to be especially poisonous would be valuable for public health officials.

Since Karenia brevis uses nutrients to grow, one may assume that starving them of phosphorous and nitrogen, such as by preventing fertilizer or sewage runoff into the Gulf, would protect the environment from their poisons.

But that’s only true up to a point. If you can keep nutrients out of the water, a bloom will not materialize, so there will be no danger of the waterway being poisoned by it. But if the nutrient supplies suddenly dry up, an existing bloom will switch into a defensive mode, stop growing and become very toxic.

The ecological theory to describe this response comes to us from botany. It is called the carbon:nutrient balance hypothesis.

North Carolina scientists grew samples of the dinoflagellate in water taken from the Gulf in a laboratory. Some samples were fed plenty of phosphorous, but others received very little. The scientists found that K. brevis strains living with limited phosphorous supplies produced 2.3 to 7.3 times more poison than did those that had plenty of phosphorous available.

“Because PbTxs [K. brevis brevetoxins] are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth,” the scientists wrote in their paper, published last month in PLoS ONE.

The algae samples living without much phosphorous put their carbon to a defensive use, since it couldn’t be used as effectively for growth. The proportion of carbon that each cell used to produce poison as much as doubled when phosphorous was limited.

This is consistent with the carbon:nutrient balance hypothesis. When vegetation has lots of carbon and lots of nutrients available, it invests those building blocks of life into fast growth. But when nutrients, be they phosphorous or nitrogen, are in short supply, the carbon is put to a different use: Defense against predators.

It also helps explain some of the late season bursts in toxicity noticed in the red tides: They become poisonous after they have greedily slurped down the last of the available nutrients.

This research was limited to phosphorous. But previous research uncovered a similar red tide response when nitrogen was limited.

The discovery could help public health managers predict the potency of red tides in the Gulf of Mexico. By measuring the amount of phosphorous in the ecosystem, it could become possible to determine how dangerous the red tides will become.

Study: ‘safe’ nitrogen levels unsafe for wildflowers

By John Upton

When we think about air pollution, it’s easy to imagine airborne chemicals that kill or stunt wildlife by infiltrating tissues and disrupting cellular processes. But that is not the case with nitrogen pollution.

Nitrogen pollution is released from vehicle exhausts and power plant smoke stacks, which liberate the long-dormant compounds from tainted fossil fuels. Nitrogen is a fertilizer — plants lap it up — and farmers and gardeners have a habit of using too much of the stuff, causing it to spill into waterways and over nearby habitats.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

When airborne nitrogen pollution fertilizes nutrient poor ecosystems, such as the rocky, serpentine soils of inland California, the native plant species that long ago adapted to the difficult growing conditions can be quickly edged out by weeds. It’s a typical case of environmental havoc helping generalist species displace specialists.

Governments are aware of the hazards of nitrogen pollution and they set limits that are considered safe. But scientists who studied wildflower populations growing within so-called safe limits of nitrogen pollution discovered major impacts on the native flowers.

“We studied many grasslands along the natural gradient of pollution across Europe,” Manchester Metropolitan University Professor Nancy Dise, one of the authors of the study, which was published in December in the Proceedings of the National Academy of Sciences, told The Ecologist. “We found that at even relatively clean sites, low levels of pollution had an effect on the abundance of some plant species.”

The scientists say their findings highlight the need for governments to review pollution rules and to vigorously protect areas that have not yet been tainted.

“Our results highlight the importance of protecting currently unpolluted areas from new pollution sources,” they wrote in their paper. “We cannot rule out ecological impacts from even relatively small increases in reactive N deposition.”

When T7 attacks — watch a virus infect a cell

Illustration by Perry Shirley

By John Upton

The E. coli was doomed. This gut-dwelling microbe was trapped in the company of a predator. A T7 bacteriophage, a virus that propagates by inserting its DNA into bacteria, had been deposited nearby.

As the T7 landed on the surface of its prey, it was being watched by University of Texas Medical School researchers. They were watching the attack using cryo-electron tomography – a technique that creates 3-dimensional pictures from multiple microscopic images taken at freezing cold temperatures. They watched in graphic close-up detail as a virus infected a cell.

The virus was smaller than its prey. It looked like a bloated tick, with six folded legs made of protein at one end of its body. The legs formed a circle around a retracted tail. As the T7 landed on the bacterium, it extended some of its fibrous legs. It used the legs to walk along the surface of its prey, feeling for a suitable place to attack. Once it found the right location, it stopped walking and stood still. It planted its legs, extended its retracted tail and jammed it through the cell wall and into the victim. It pumped in its DNA. Then it retracted the tail, and the hole in the cell wall healed back over.

The attack was complete. The hapless bacterium now harbored the virus.

“The complete process we describe is unique to T7 and its relatives,” Ian Molineux, one of the researchers, told me. The study was published Thursday in the journal Science. “But some aspects, in particular fibers binding to the head and walking over the cell surface, are probably quite general.”

Carnivorous plant catches prey with catapult

Drosera glanduligera, a short-lived sundew, uses outstretched tentacles to catapult prey into its traps, which appear as dark orifices akin to mouths / Courtesy: PLoS ONE

By John Upton

When animals evolved from plants, well over a billion years ago, they flourished by feasting on their vegetative cousins. Then some plants growing in nutrient-poor soil turned that trick back around on animals: Carnivorous plants evolved and began to feast on some of the animals that feasted on plants.

Perhaps the most famous carnivorous plant is the Venus fly trap. The snapping ‘mouth’ of this plant puts it in ecologists’ ‘active’ trap category. Pitcher plants, by comparison, use ‘passive’ traps – an insect tumbles into a sticky vase-like leaf and is digested.

Sundews are one of the largest groups of carnivorous plants, relying on passive traps to capture their prey. But German scientists studied unusual specimens native to southern Australia and reported that they use active tentacles to catapult passing insects into their otherwise passive traps.

“Prey animals walking near the edge of the sundew trigger a touch-sensitive snap-tentacle, which swiftly catapults them onto adjacent sticky glue-tentacles,” the researchers, from University of Freiburg, reported in the online journal PLoS ONE. “The insects are then slowly drawn within the concave trap leaf by sticky tentacles.”

Here, watch:

Oil dispersant upshot — bacteria feasted after BP spill

By John Upton

During its Deepwater Horizon oil spill, BP wickedly used 1.8 million gallons of oil dispersants to hide the slick. The chemical cocktail known as COREXIT 9500 caused the crude oil to dissolve in water instead of float on its surface. Among other things, the move destroyed plankton communities and threw the Gulf of Mexico’s food chain into chaos.

But one of life’s most primitive forms benefited greatly from this poisonous approach.

Hydrocarbon-eating bacteria feasted on the oil and methane as it swirled around in the gulf’s water column. New research published in Environmental Science and Technology reveals that the bacteria consumed at least 200,000 tons of the stuff, converting some of it into biomass that passed up the food-chain while also releasing the greenhouse gas carbon dioxide. The feeding frenzy reached its peak nearly three months after the oil rig explosion killed 11 workers, the scientists found.

“Certainly, some of the hydrocarbons were respired to CO2,” John Kessler, a Rochester University professor who co-authored the paper, told me in an email. “But some of that oily food had to go into supporting an increase in the microbial population.”

TV news report on the impacts of oil dispersants on gulf plankton communities:

How to save imperiled native bees — video

By John Upton

Much of the world is in a crisis that most of the world knows nothing about: Native pollinators, the bees, bats, butterflies, hummingbirds and other creatures needed by crops and wild plants, are disappearing.

While reporting for Grist over the weekend on an effort to tally bees, named The Great Sunflower Project, I interviewed Oakland bee-lover Celeste Ets-Hokin at her pollinator garden. I threw together this two-minute video, in which Ets-Hokin describes the pollinator problem and explains how easy it is to help.

Flies pay ultimate price for sex

By John Upton

If you were spending an amorous weekend camping in the woods and you suspected that a bloodthirsty cougar was prowling outside in the dark, would you stay perfectly still in your tent, perhaps clutching a knife? Or would you blithely get busy with your lover, potentially alerting the cat to your presence, knowing full well that copulation could lead to decapitation?

Versions of this unlikely scenario are played out constantly in the wild. But while it has long been hypothesized that mating by insects and other animals increases their risks of predation, firm evidence of such risks has been a little bit hard to come by.

When houseflies mate, they risk being eaten by bats / Flickr: DeeJayTee23

To test one such scenario, German researchers used video cameras to monitor common houseflies in a barn filled with cows and fly-eating Natterer’s bats. When the flies lay on the cowshed’s ceiling or ambled across it, they were virtually immune to predation. The researchers didn’t spot a single bat attack on a walking fly during four years of research. The bats couldn’t find their prey: Their echolocation equipment simply wasn’t sensitive enough.

But once the flies started to get busy they emitted clicks and other subtle buzzing noises that helped the bats zero in on their distracted prey. Approximately one out of four copulating couples were attacked by a bat, often providing the predator with a hearty meal of two flies, the researchers reported in today’s issue of Current Biology.

“I can only speculate what the original function of this buzzing sound is,” Max Planck Institute for Ornithology researcher Stefan Greif told me. “My guess is that it’s a byproduct of the movements transmitting the sperm. Maybe it’s also easing the female that it really is a male jumping on her, and not a predator.”

So why would the flies choose to mate if it increased their chances of being gobbled up? Well, reproduction is the name of the game in the wild, and flies have only a short timeframe in which they can do it. After hatching from eggs and developing as asexual maggots, the average housefly will live winged and fancy free for just two to three weeks.

Natterer’s bats use the sound of mating flies to help them find their prey / Courtesy: Current Biology

Houseflies are an r-selected species, meaning the populations breed as fast as they can and are willing to take risks doing so. Houseflies endure high levels of predation and other pressures that would take heavy tolls on populations of K-selected species, such as elephants and tortoises, which breed slowly and carefully.

Studies of amphipods, water striders and locusts – all of which are r-selected species – have produced similar results.

“Maybe the cost ‘out in the wild’ is lower than in the cowshed, where we get more predators,” Greif said. “But on the other side, as there are so many flies in the cowshed, overall reproductive success might be so high that it outweighs and counterbalances the evolutionary pressure put on by the bats.”

French fry to falcon — a modern food chain

By John Upton

A hunk of potato planted in a field sprouts into a leafy plant. A potato swells in the soil beneath the low canopy, fostered by water, fertilizer and pesticide, before it is torn out by a tractor and scrubbed and sliced by machine. A sliver of it tumbles into a plastic bag that is filled, sealed, frozen and trucked to a downtown fast food store.

When I was reporting for the Bay Citizen last year, editor Jonathan Weber snapped this falcon feasting on a pigeon outside our newsroom windows

The French fry is boiled in oil and lands in the bottom of a cardboard holster. The customer’s gluttony is satiated before his super value meal is done and the chip lands near a trash can, spinning in a waterfall of leftovers and packaging. It is grabbed by a rock pigeon which, hours later, is snatched up by a Peregrine falcon and fed to fledglings in a nest on an office building’s roof.

Peregrine falcons were nearly wiped out in the United States by the 1970s, their shells made fatally fragile by DDT sprayed to keep mosquitoes at bay. The poison bioaccumulated in the food chain and became concentrated in the falcons. The remarkably large raptors recovered spectacularly after the chemical was banned and American Peregrine falcons were removed from lists of endangered species in the 1990s.

As the populations recover, they have mastered the city environment, nesting on buildings and bridges. By preying heavily on the ubiquitous pigeons that eat our voluminous waste, they have established a food chain that runs from farm to trash to scavenger to urban predator.

But new and old threats nag at these birds all around the world.
Old: Falconers steal chicks from nests to be reared as hunters (and, increasingly, for lucrative commercial purposes – landfills hire falconers to scare away seagulls).
New: Toxic flame retardants used in furniture seep as dust into the environment and have been discovered bioaccumulating at high levels in Peregrine eggs.

The flame retardant threat is pronounced in California, where a strict law based on outdated science mandates the use of such chemicals at certain levels. Last week, Gov. Jerry Brown ordered a review of the 37-year old law in a bid to protect human health and wildlife. The review, by the California Bureau of Electronic and Appliance Repair, Home Furnishings and Thermal Insulation, is expected to establish a new industry standard that will be adopted as law by other governments.

The threat of poaching, meanwhile, is as established as the milleniums-old sport of falconry. To help curb that threat, scientists often try to keep vulnerable locations of nesting falcons a secret.

Here is a video from YouTube of commercial falconer Steve Vasconcellos keeping gulls away from a dump at Half Moon Bay, California. Vasconcellos was in talks with the San Francisco Giants to scare seagulls away from the waterfront ballpark, but the franchise’s operations manager recently told me the team had balked at the price tag, which I understand would have been well over $100,000 a year.

What’s that bumblebee buzz?

Flickr: bagsgroove

By John Upton

The seemingly menacing deep buzzing noise produced by a bumblebee rings out only when the insect reaches a flower. It’s not a warning or a threat, nor is it a noise produced by flight. It’s called sonication — rapid movements of a bee’s muscles that create vibrations to shake pollen loose from a flower’s anther.

This feeding strategy is also known as buzz pollination, and it’s a faculty lacked by the smaller European honeybees. But the sound is disappearing from landscapes everywhere along with the bumblebees that produce it. In a story that coincided with national pollinator week, I reported yesterday for Grist on the decline of native American bumblebees, a terrifying phenomenon that has long been overshadowed by the plague of colony collapse disorder.

Bumblebees need flower-rich habitats and they need to be able to feed without sucking up insecticides. Every flowering plant relies on pollination, and bumblebees do much of that work.

Here’s a video from YouTube showing a sonicating bumblebee. Perhaps you remember a time when this sound was more common.