An Exploration Aboard the R/V Agassiz “How Do You Make A Lake Trout?” An Exploration Aboard the R/V Agassiz CE3501 – Environmental Engineering Department of Civil & Environmental Engineering Michigan Technological University

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. C H Ca N P O 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.

Today in the Lab We will have three exercises analyzing samples collected with the plankton net and the PONAR dredge. 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. You will be asked to develop a food web based on your analysis of the samples collected in the field. No, fool. A food web!

Phytoplankton Phyto = plant Green algae 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. Image by Spike Walker 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. cyanobacteria diatoms Plankton = free-floating http://user.unif-rankfurt.de/~schauder /cyanos/cyanos.html http://wfrc.usgs.gov/research/fish%20populations/STMaule5.htm

Paradox of the Plankton 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? http://courses.bio.psu.edu/fall2005/biol110/tutorials/tutorial30.htm As you look through the microscope Today, consider what ‘tricks’ different algae might use to gain an edge over its competition. Know any algae tricks?

Zooplankton Zoo = animal 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. There are three major types of zooplankton, listed here in increasing order of size: rotifers, copepods and cladocerans. cladoceran rotifer Image by Spike Walker Image by Ron Neumeyer copepod http://www.hudsonregional.org /mosquito/program.htm Most zooplankton are filter-feeders, using beating hairs or ‘arms’ to create currents that funnel the phytoplankton and other particles into their ‘mouths’. Plankton = free-floating

Negative Phototaxis Photo = light 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. Computer image of a layer of zooplankton located 25-45 meters below the surface in Lake Superior. Can you imagine how zooplankton might benefit from this behavior? Taxis = touch

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 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. zebra mussels http://users.mo-net.com/ flotilla6/zbra_msl.htm http://epa.gov/greatlakes/ active/2004/jul04.html McKenna 2007 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.

My latin name is Chironomus Benthos – familiar faces: bloodworms 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), burrowing into the mud and feeding on settled phytoplankton and dead organic matter. 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. 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. My latin name is Chironomus Source: http://ohioline.osu.edu/hyg-fact/2000/2129.html

My latin name is Chaoborus 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. Many organisms have developed special ‘tricks’ to help them better survive in http://www.life.uiuc.edu/ib/109/ 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? The dark spots in the otherwise transparent body of the phantom midge are swim bladders that help them float. My latin name is Chaoborus http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmay05/swgallery1.html

Fish - Planktivores 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. http://www.nature.com/nature/journal/v412/n6845/fig_tab/412387a0_F1.html http://pond.dnr.cornell.edu/nyfish/Salmonidae/cisco.html The lake herring is a common planktivore in Lake Superior and is a major food source for lake trout. Lake herring are often smoked and sold in fish shops around the lake. ‘vore’ = eat

Fish - Benthivores 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 www.anglinguk.net 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 http://www.nanfa.org/NANFAregions/oh/Ohio0802/ www.rudybenner.com ‘vore’ = eat

Fish - Piscivores 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. http://dnr.wi.gov/org/caer/ce/news/DNRNews ‘vore’ = eat