Going buggy

Creepy-crawlies are lifeblood of Kenai River

Posted: Sunday, June 11, 2006

 

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  Diving beetles, larger than a quarter as adults, have an interesting life span, according to David Wartinbee. As larvae, they live in water. They pupate out of the water briefly then return, where they are aggressive predators. Photo by M. Scott Moon

A tiny mayfly nymph, less than a quarter of an inch long, is seen through the lens of a microscope in a laboratory at Kenai Peninsula College. Mayflies spend about a year of their lives as aquatic insects before taking wing for just two days.

Photo by M. Scott Moon

Every year salmon swim up the Kenai River to spawn and their ocean-fattened bodies die, delivering a bounty of nutrients to life in the Kenai River. But the salmon would not feed the river if the river did not first feed the salmon.

Aquatic insects are salmon’s favored fare, in particular chironomids, a family of aquatic insects that nurse salmon smolt and other juvenile fish into adulthood.

In their adult stage of life, chironomids are most commonly known as midges, the tiny flying insects that find every mouth, eye and nose opening when you walk through a cloud of them.

 

A caddisfly nymph is shown outside the case it builds as a home during its time at the bottom of Kenai Peninsula streams.

Photo by M. Scott Moon

But like most aquatic insects, chironomids spend the majority of their lives as aquatic insects and provide juvenile fish with an important food source, said David Wartinbee, a biology professor at Kenai Peninsula College.

“We looked at the silver salmon smolt on the Moose River and when we looked in the guts it was almost entirely these small chironomids, because they’re very abundant and they’re just the right size,” he said.

As aquatic insects, the more glitzy caddisflies, mayflies and stoneflies are more widely recognized than the chironomids, but their numbers pale in comparison.

 

David Wartinbee pokes through a pan of water and sediment from the bottom of Slikok Creek during a search for tiny water bugs that make the stream home. The Kenai Peninsula College professor has studied aquatic insects for a quarter of a century.

Photo by M. Scott Moon

“We might have 50 total species of, say, caddisflies mayflies and stoneflies, but yet in the Kenai River, I’ve found 86 species of just the chironomids,” Wartinbee said.

While chironomids can spend anywhere from approximately two weeks to several years as an aquatic insect, they typically spend only a couple of days as an adult, aerial insect. This characteristic is generally true of all aquatic insects.

Mayflies, for example, spend a year as an aquatic insect, but only one to two days as an adult, leaving little time for breeding.

“The old joke is if she has a headache on that day, forget it, she isn’t going to breed,” Wartinbee said.

Aquatic insects must rush to breed because once they become adults, very few have a functional gastrointestinal track and have to mate before they exhaust the energy reserves they built up as an aquatic insect.

 

"All I have to do is pick up the scum off the top of the stream and I find these by the thousands."

David Wartinbee, biology professor,

Kenai Peninsula College

Photo by M. Scott Moon

Even the aquatic insect with which we are most familiar, the mosquito, does not feed. Rather, the blood the female mosquito sucks from our veins provides nutrients to its eggs. And while the female can lay eggs even if she does not find blood, her breeding potential is boosted significantly if she does.

“If it never finds or gets a blood meal the female will lay maybe 300 eggs, but if she finds a blood meal she’ll lay 1,000 eggs,” Wartinbee said. “So it’s to her benefit to take a chance on flying over to you to get a blood meal.”

Pretty much everything an aquatic insect does once it becomes an adult is aimed at breeding.

 

With a sample-gathering net in hand, Kenai Peninsula College professor David Wartinbee scans the bank of Slikok Creek for a good place to search for water bugs. He is particularly interested in a family of insect known as chironomids, which are the most abundant insects in the Kenai River and an important source of food for young fish.

Photo by M. Scott Moon

Even the swarms of adult chironomids gather not to create clouds around our heads, but to attract mates.

The cloud is made up of male chironomids singing a mass serenade that humans can’t tune into.

But female chironomids do. Drawn by the swarm’s romantic song, the female chironomids fly into it and by the time they have fallen out, they have mated and are ready to look for a place to lay eggs.

From the egg to adulthood, the chironomids develop through four different life stages: egg, larva, pupa and adult.

After a chironomid hatches from the egg it enters the second and longest stage of its life as a larva.

On a recent drizzly spring morning, Wart-inbee hiked to the bank of the Kenai River from behind KPC to retrieve these and a variety of other aquatic insects.

 

Caddisflies are a common sight along Kenai Peninsula streams, where they nourish fish, both as flying adults (pictured here) and as tiny waterborne larvae.

Photo by M. Scott Moon

Wartinbee dipped a fine white net into the flowing water and held the top of the net firmly against the riverbed. In the current, the net ballooned outward, and Wartinbee kicked at some rocks upstream to dislodge aquatic insects and send them into the mouth of the net.

After repeating this procedure several times in the Kenai River and a nearby creek, Wartinbee had collected a miniature universe of aquatic insects in a plastic tray.

At first glance, the tray appeared to contain little more than dirty water. But a closer inspection revealed a plethora of aquatic insects.

Among the largest aquatic insects wiggling about in the mix was a caddisfly larva. Caddisflies are best known for their distinctive cases. Like moths, caddisflies produce silk. But instead of using it to spin a cocoon, caddisflies use the silk to glue tiny pieces of rock, vegetation and other debris together to create a protective case for its soft body, like a seashell housing a hermit crab.

The materials a caddisfly larva selects to build its case are largely determined by the body of water they live in.

 

A stonefly nymph, magnified many times, is pictured eating a wormlike chironomid. While the tiny creature is a mouthful for the nymph, it is a perfect meal for a young fish. "It's hamburger-size for a small salmon fry," Wartinbee said.

Photo by M. Scott Moon

In a lake, where the water moves very little, a caddisfly may build its case using largely vegetative debris. But in a river, where water is moving quickly, caddisflies are likely to use heavy materials such as sand, small rocks and bits of metal, making them popular with gold panners.

Poking through the water in the tray with a tiny eye dropper, Wartinbee isolated several chironomid larvae, also known as lunch meat to a large number of aquatic predators. The pale worm-like larvae are about the shape and size of fingernail clippings and floated around in Wartinbee’s tray of water as if waiting to become a meal.

And as a third species of aquatic insect would soon demonstrate, young fish are not the only animals that think chironomids are delicious.

Among the many insects in his tray, Wartinbee also identified a stonefly nymph and poured it and a couple of other insects into a small dish for closer inspection.

But the stonefly quickly reduced the number of insects in the dish by one, as it latched onto a chironomid larva and gobbled the creature like a helpless, fat noodle.

Not all the chironomids in the tray were larvae. Chironomids also live in water through the pupa stage of their lives, a sort of transitional state between its life as a larva and adulthood. As a pupa, a chironomid develops a protective casing around a large portion of its body.

 

Diving beetles, larger than a quarter as adults, have an interesting life span, according to David Wartinbee. As larvae, they live in water. They pupate out of the water briefly then return, where they are aggressive predators.

Photo by M. Scott Moon

In the casing, the chironomid’s larval features transform into those of an adult aerial chironomid. The casing is similar to the chrysalis a monarch caterpillar uses when it transforms into a butterfly. When the chironomid finishes its transformation this casing, also known as the exuviae, is discarded.

Although no longer valuable to the chironomid, the discarded exuviae provide aquatic insect researchers with a convenient tool for finding out which chironomids are living in a body of water.

In the tray of debris, water and aquatic insects Wartinbee collected, tiny exuviae floated like leaves on the surface of a pond. And just as one might be able to examine a leaf to find out what tree it came from, Wartinbee has spent many hours collecting and examining exuviae found in the Kenai River to find out what species of chironomids they came from.

“All I have to do is pick up the scum off the top of the stream and I find these by the thousands,” Wartinbee said.

Collecting exuviae is the easy part. Identifying what species each of the collected exuviae belongs to requires hours of examining them through a microscope.

Unlike tree leaves, exuviae are measured in millimeters. And the chironomid family is diverse, with more than 2,000 species in the Nearctic Region, an ecozone that includes most of North America, Greenland and the highlands of Mexico, and 20,000 species worldwide.

When compared to warmer regions, Alaska and other northern regions have rigorous and hard-to-survive climates, including short, intense growing seasons and harsh winters. So fewer aquatic insects can be found living in Alaska than in the Lower 48.

Although the number of chironomids living in the Kenai River, for example, may sound like a lot, 86 species is a sharp drop from the chironomid diversity found in, say, Washington or Oregon, where a stream may contain as many as 150 species, Wartinbee said.

And as you move to the northernmost regions of Alaska, species diversity becomes even thinner.

Whereas the Kenai River has approximately 50 species of caddisflies, mayflies and stoneflies, for example, Alaska’s tundra streams, such as the Kuparuk River, may have only six to eight species of these insects, Wartinbee said.

This low species diversity, however, is not limited to just insects.

“As we go north we find fewer and fewer species of everything,” Wartinbee said.

And when a species goes extinct, it has a much greater impact in a place with low species diversity. Consequently, ecosystems in these regions are also more sensitive to disturbances.

“So when you look at things we do on the North Slope, (for example,) we have to be very, very careful,” Wartinbee said. “Because the impact can be one, very long term, and two, we can very easily do damage that you might not even notice in a different area.”



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