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Great Lakes Ecosystems Threatened by Food Scarcity

Great Lakes Ecosystems Threatened by Food Scarcity

Declines of the food resources that feed lake organisms are likely causing dramatic changes in the Great Lakes, according to a new U.S. Geological Survey (USGS) study.

USGS scientists and partners found that since 1998, water clarity has been increasing in a majority of the Great Lakes, while phytoplankton (the microscopic water organisms that feed all other animals), native invertebrates and prey fish have been declining.

These food web changes fundamentally affect the ecosystem’s valuable resources and are likely caused by decreasing levels of lake nutrients, and by growing numbers of invasive species such as zebra and quagga mussels.

"These findings provide critical information to help decision-makers understand changes that are affecting the Great Lakes fishery that generates about $7 billion for the economy each year," said Suzette Kimball, acting director of the USGS. "The work is the result of a strong public-private collaboration and greatly contributes to managers' ability to deal effectively with the changes occurring in these unique and vast freshwater ecosystems so important to our nation."

The study found that inputs of phosphorus—the nutrient that limits phytoplankton growth—have declined in the Great Lakes since 1972, when the Great Lakes Water Quality Agreement was signed. The growing numbers of invasive species such as zebra and quagga mussels have caused phosphorus levels to decline further over the last decade in some lakes by filtering out phytoplankton and the nutrients therein. These decreases in nutrients have the potential to affect the smallest organisms up to the top predators: in Lake Huron, for example, plankton and fish appear to be controlled by declining nutrients or food.

"Our study provides a comprehensive ecological report card that highlights existing gaps in scientific understanding and monitoring of the complex Great Lakes ecosystems," said David "Bo" Bunnell, USGS scientist and lead author of the study. "Ideally, it will spur future research to more rigorously test some of the predictions born from our relatively simple analyses."

The Great Lakes provide valuable ecosystem services to the 30 million people that live within the watershed, but portions have been degraded since the industrial era. In 2010, the U.S. government initiated the Great Lakes Restoration Initiative, the largest investment in the Great Lakes in two decades, investing approximately $1 billion over the past four years.

USGS partners in this new study include the CSC information technology firm, U.S. Environmental Protection Agency, Ohio State UniversityUniversity of Wisconsin-Green BayMichigan State University, National Oceanic and Atmospheric Administration, Michigan Department of Natural Resources, University of Michigan, U.S. Fish and Wildlife Service and University of Illinois at Chicago.

The report is published in the journal BioScience.

Visit EcoWatch’s BIODIVERSITY and WATER pages for more related news on this topic.

A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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