ENVE Environmental Engineering An Exploration Aboard the R/V Agassiz Ms. Anika Kuczynskt & Dr. Marty Auer The Department of Civil & Environmental Engineering Michigan Technological University “How Do You Make A Lake Trout?”

How Do You Make A Lake Trout? All living things need chemicals to provide structure and energy to provide power. Chemicals are available in the air, water and soil and energy is available from the sun. However, these sources of chemicals and energy are not directly available to a lake trout. The chemicals and energy must be collected and converted to an available form. This is the job of the food chain. In this exploration, we will examine the base of the food chain where chemicals and energy are first captured and higher levels where they are transferred to make a lake trout!

Today on the Boat We will collect plankton samples from the water using a fine mesh net and sediment samples from the lake bottom using a PONAR dredge. The sediment samples will be processed with a sediment elutriator (critter catcher) to separate out the animals.

Food Web The exploration is based on the concept of the food chain. In nature, material and energy transfer are a bit more complicated, involving a collection of food chains or a food web No, fool. A food web!

Phytoplankton Plankton = free- floating The capture of chemicals and energy in lakes is the job of plants, including larger species such as water lilies and smaller forms called algae. Plants take chemicals such as carbon, nitrogen and phosphorus directly from the water and use built in ‘antennae’ (chlorophyll) to capture the sun’s energy. The chemicals and energy are then combined through the process of photosynthesis to make more plant material. The phytoplankton (free-floating algae) capture chemicals and energy, but a problem remains in making a lake trout. The phytoplankton are microscopic and thus are too small to make a suitable meal for a large fish. It is the job of the higher levels of the food chain to concentrate the chemicals and energy, ultimately making them available to the lake trout. Phyto = plant 0populations/STMaule5.htm /cyanos/cyanos.html cyanobacteria diatoms Green algae Image by Spike Walker

Paradox of the Plankton Know any algae tricks? Paradox = mystery The Competitive Exclusion Principle states that whenever two species compete for the same resource, one species will win, eliminating or excluding the other species. Yet, when we look in lakes and oceans we see a tremendous diversity of species. Does this violate the principle? As you look through the microscope Today, consider what ‘tricks’ different algae might use to gain an edge over its competition.

Plankton = free-floating Zooplankton are microscopic, free-floating animals that graze on the phytoplankton, concentrating the chemicals and energy captured lower on the food chain and transferring it to higher levels. Zoo = animal Zooplankton There are three major types of zooplankton, listed here in increasing order of size: rotifers, copepods and cladocerans. Most zooplankton are filter-feeders, using beating hairs or ‘arms’ to create currents that funnel the phytoplankton and other particles into their ‘mouths’. Image by Spike Walker Image by Ron Neumeyer /mosquito/program.htm rotifer copepod cladoceran

Zooplankton exhibit a behavior called negative phototaxis, meaning that they ‘fear’ light. Because of this behavior, most zooplankton are found well below the surface in the daytime, migrating toward the surface to feed on phytoplankton at night. Taxis = touch Photo = light Negative Phototaxis Can you imagine how zooplankton might benefit from this behavior? Computer image of a layer of zooplankton located meters below the surface in Lake Superior.

Benthos Benthos = bottom The benthos are animals that make their homes on and in the bottom sediments of lakes. Forms familiar to many of us include The benthos might be considered a lake’s clean-up crew. Phytoplankton that settle to the lake bottom, especially species that are to large to be consumed by grazing zooplankton, are collected by the benthos. Bottom-feeding fish then prey upon the benthos, transferring the chemicals and energy up the food chain. snails, clams, and zebra mussels. A shrimp-like organism, Diporeia, is the primary food source for lake whitefish. The early life stages of insects are among the most common members of the benthos and are of great importance in the food chain. flotilla6/zbra_msl.htm zebra mussels active/2004/jul04.html McKenna 2007

Benthos – familiar faces: bloodworms Source: The bloodworm is one of the most common members of the benthos in Portage Lake. They are not ‘worms’, but rather the larvae stage of the midge, a non-biting insect related to the no- see-um. Adult midges lay their eggs (up to 3,000 in a single mass) on the surface of the water where they sink to the bottom and hatch in about a week. After hatching, they become larvae (bloodworms), They are called bloodworms because of their red color, a result of high levels of haemoglobin in their blood. As in our bodies, haemoglobin carries oxygen and helps the midge larvae inhabit low oxygen environments in the mud. After several weeks in the mud, the larvae become pupae and swim to the surface where they are emerge as adults. The adults do not feed and only live about 3-5 days. Adult midges are often seen in summer as swarms around outdoor lights. burrowing into the mud and feeding on settled phytoplankton and dead organic matter. My latin name is Chironomus

Benthos – familiar faces: phantom midges A second common member of the benthos in Portage Lake is the phantom midge, a relative of the bloodworm. But unlike the bloodworm that eats settled phytoplankton and dead organic matter, phantom midge larvae a carnivores (meat eaters) preying on zooplankton. uk.org.uk/mag/indexmag.html? uk.org.uk/mag/artmay05/swgallery1.html My latin name is Chaoborus The dark spots in the otherwise transparent body of the phantom midge are swim bladders that help them float. Many organisms have developed special ‘tricks’ to help them better survive in nature. The high haemoglobin levels in bloodworms is one example. Can you figure out what the phantom midge’s trick is? What are two reasons why this might help it survive?

Fish - Planktivores ‘vore’ = eat Plankton = free-floating plants and animals Fish that depend on zooplankton as their major food source are called planktivores. These fish filter or strain zooplankton from the water using comb-like structures called gill rakers. Particles trapped by the gill rakers become more concentrated as they move further into the mouth and the fish finally swallows a soup of plankton. Rainbow smelt and lake herring are common planktivores in Lake Superior and are major food sources for lake trout g_tab/412387a0_F1.html rainbow smelt lake herring The annual smelt run attracts fishing enthusiasts from around the region. Lake herring are caught commercially, smoked and sold in fish shops around the lake. commons.wikimedia.org

Fish - Benthivores ‘vore’ = eat Benthi = Bottom animals Fish that depend on benthos or bottom animals as their major source of food are called benthivores. Fish that feed in this manner have specially-developed mouths that make it easier to capture their prey. Sturgeon with mouth extended The lake sturgeon is a benthivore common to Lake Superior that grows to lengths exceeding 6 feet and can weigh more than 100 pounds. Other bottom-feeding fish in Lake Superior include the whitefish and the sculpin which prey on the crustacean Diporeia. Lake Whitefish Sculpin

Fish - Piscivores ‘vore’ = eat Pisci = fish Fish that prey on other fish as their major source of food are called piscivores. The dominant native piscivore in Lake Superior is the lake trout. Fish biologists recognize to different strains of lake trout in Lake Superior: leans and siscowets (or fats). The diets of the two strains differ because leans live in shallow water and fats in deep water. Leans favor smelt as prey, while the diet of fats is more varied and includes a significant number of sculpin.