HAB LESSON PLAN - PART 3: Trophic Transfer in Food Webs, grades 6-8

Food chains and trophic transfer lesson plan

(Developed by Sarah Heinzelman and C. Mengelt, 2005; revised and illustrated by B. Prezelin, 2006):

Title: "Why did the seals (or dolphins or whale) get sick and become stranded?"

Focus: Trophic transfer of energy and food (and sometimes toxins) through the marine food web

Grade Level: Grade 6

Focus Question: "How does an algal toxin get into seals (or dolphin) to make them sick?"

(NB: seals and other marine mammals can get sick for other reasons, e.g. injury, viruses, etc)

Learning Objective:

- Students learn about the marine food web

- Students will learn to recognize the major difference(s) between the marine and terrestrial food chain

- Students will hear about the concept of trophic transfer of energy and toxins

Materials:

- Newspaper article on the sea lions (or dolphins) strandings (a copy per student)

- Animal pictures laminated on string with a carabiner/hook

- Several balls of string/yarn (around 8)

- 15-20 little pieces of paper (around 2x2 inches), some of which around 4-8 are black (symbolizing toxins)

Audio/Visuals:

Google search of "news" and 'red tide' ' toxic algae' ' animal stranding' , ' domoic acid', ' PSP', " shellfish", "sea lions", "dolphins" and combinations thereof should provide recent news articles. Animal pictures can be found online via Google images search engine. Some examples are provided below.

From: http://www.nrc-cnrc.gc.ca/multimedia/picture/life/nrc-imb_limp_e.html

Clams (and mussels and crabs) filter microscopic algae (phytoplankton) and can become toxic when eating toxic algae; in turn, animals (including humans) get sick when eating contaminated shellfish. The shellfish don't get sick because the toxin is a neurotoxin that specifically affects parts of the brains of mammals. When the toxic algae go away in the environment, the shellfish slowly 'detoxifies', washing the contaminated algae and toxins from their gut over a period of a few weeks.

From: http://www.dnr.state.md.us/fisheries/oxford/research/fwh/strandingprogram.html

Bottle nose dolphin

Harp Seal feeling sick because it ate contaminated shellfish or fish.

Teaching Time: variable, each component 20-30 minutes.

Background Information:

Marine mammals (whales, dolphins and seals) eat fish that eat shrimp that eat microscopic algae (phytoplankton). Some types of phytoplankton make chemicals that are not harmful to them or shrimp or fish, but are toxic when they accumulate in the diet of marine mammals or when humans eat contaminated shellfish (e.g. crab, clams, abalone, etc)that also eat these algae.. The two types of toxins best studied are those associated with "red tides" of some dinoflagellates, a class of algae, and those associated with diatoms, another class of algae, of the genus Pseudo-nitzschia. The toxin in dinoflagellates is called saxotoxin. The toxin in Pseudo-nitzschia is a chemical called domoic acid.

Alexandrium, a toxic dinoflagellate.

Saxitoxin was the first algal toxin discovered and is produced by the dinoflagellate Alexandrium. They produce a highly potent neurotoxins (which affects brains) that, if consumed, cause paralytic shellfish poisoning (PSP). This usually happens when humans eat contaminated shellfish that have been feeding on Alexandrium. It can cause numbness, breathing problems and even death.

Pseudo-nitzschia multiseries (Photo credit - Yasuwo Fukuyo), a toxic diatom. Long view of cell is shown at Left, magnified view of shell is shown at Right, top and bottom.

The discovery of domoic acid (DA) poisoning by Pseudo-nitzschia occurred in Canada when people got sick and died after eating shellfish that had been filter feeding on this diatom genus. The toxin DA affects the neurological network in the brain, in particular the part of the brain associated with short term memory. Early symptoms include nausea, vomiting and may lead to disorientation, memory loss, seizures and even death. Doctors refer to this type of poisoning as amnesic shellfish poisoning (ASP) as it affects the memory of the victims. Such symptoms were associated with DA poisoning of sea lions and brown pelicans in Monterey Bay, California, in 1991. Since this first discovery of such a Pseudo-nitzschia harmful algal bloom (HAB) on the west coast of the United States, many more HAB blooms of toxic Pseudo-nizschia have occurred from Canada to Mexico and caused the death of thousands of marine mammals. (for more information, do an internet search of "HAB", " Pseudo-nitzschia australis", "domoic acid" and "ASP")

To find out what was killing seals and sea birds in Monterey Bay in 1991, scientists looked at their stomachs and found they had been eating large amounts of anchovies (small fish that occur together in very high numbers). They looked at the stomachs of the anchovies and found large concentrations of Pseudo-nitzschia cells. The scientists suggested that the anchovy were the vectors (the means by which) DA came to be in the diet of seals such that DA was released into of the stomach of seals when they ate the contaminated anchovy. The DA moved from the stomach to the blood stream of the seal and affected the brain of this marine mammal and caused it to become sick and sometimes die. The more the seal eats, the more severe the symptoms and the higher the chance that the seal will strand itself on a beach and die. This is one example of how a toxin can make it up the food chain.

There are other reasons why marine mammals get sick and strand themselves on beaches. Animals may be injured, either by prey or interaction with human activities (e.g. boat or ship strikes, entanglement in fishing gear, bullet wounds). Animals may be sick due to ingestion of plastics, a disease or, in case of pups, separation from parents and subsequent starvation. When ill, some animals become disoriented and strand because their sense of where they are is confused. There are also other dangerous pollutants that may have been dumped, like the fertilizer DDT or lead or mercury, which slowly accumulates in the fatty tissue of animals as they eat contaminated fish and/or phytoplankton. This slow bioaccumulation of a poison can lead to poor health or lower reproduction success, as was the cause of the DDT-induced decline in pelican populations (DDT made their eggs very fragile). When DDT was banded from use and no longer entered the ocean from land runoff from farms, the pelican population was restored.

Learning Activity I - Reading and Discussion:

a) Hand out a newspaper clipping on a marine mammal (seal, dolphin, whale) stranding...

b) Start class by reading newspaper article about the dolphin stranding.

c) Discuss article in class - questions for discussion:

a) How could you find out what killed them? (Suggested answers: do a necropsy: i.e. look at the food content in it's stomach, look at physical wounds on the outside, look at internal injuries, look at whether there was head trauma)

b) Has anybody seen a sick dolphin, sea lion or harbor seal at the beach before? If so what did you do? What's the proper thing to do? Tell them that by law, the Marine Mammal protection act, it is illegal for people other than trained and certified mammal rescue staff to handle, or harass these animals, therefore they need to call the nearest Marine Mammal rescue center (give them the local phone number) immediately and tell them were you found the animal and describe the symptoms.

c) Do you think this is a problem for the ecosystem? Or is it just a natural part of the cycle of life? (No right answer for this one... currently being investigated by marine scientists; it depends how big the resident population is, what the birthrate is and how many sea lions die each year because of this.)

d) See Marine Mammal site at http://nmml.afsc.noaa.gov/education/marinemammals.htm

Learning Activity III - Lecture on Food Web:

Show diagram of the Marine Food Web or/and discuss the resulting food chain after students hung their animals in the above categories: For added insight on fitting phytoplankton into food webs, see the following educational website: http://www.bigelow.org/edhab/fitting_algae.html

simple food chain from phytoplankton to shrimp to small fish to larger fish to marine mammals.

complex food web with many interactions between predator and prey, but the phytoplankton are still the base of any one of the several food chains.

The food chain described above is one component of a more complex marine food web. A food web attempts to illustrate the complexity of trophic interactions in the marine environment and to visualize s some of the representatives of the different levels in a marine food web. Just like in the terrestrial food web, all new food energy comes into the food web as plants. This is because plants can make 'food' by using only light as energy and simple chemicals ( water and carbon dioxide) to make 'sugar' which can then go on to be made into all kinds of foods (protein, carbohydrates, fats). This plant process is termed photosynthesis and is carried out by the primary producers. On land we think of green plants as primary producers; In the ocean the primary producers are mostly algae, the microscopic members of which float in the sea and are called phytoplankton (phytoplankton = "phyto" Greek for plant, and "plankton"=Greek for drifter). Most phytoplankton are not green but orange!! Phytoplankton are eaten (consumed) by micro-zooplankton which, in turn, eaten by larger animals (zooplankton, fish, sea birds, marine mammals). Can you guess where the term “zooplankton” comes from? Yes, Greek for "animal - drifter". Due to the small size of the primary producers in the ocean, the marine food web in general has many possible links before they reaches the top predators such as sharks, sea birds and marine mammals.

The energy that a unit of food, like a phytoplankton cell, provides to the animal that eats it (a consumer)is used by the animal to stay alive, grow and eventually reproduce. A portion of the food unit that is consumed will pass through the stomach and be excreted as urine and feces. These waste materials are consumed by bacteria and support the growth of a microbial community in the sea and releases the kinds of simple nutrients that the phytoplankton will need to grow. Therefore it is a type of natural recycling.

As a food unit is consumed and a portion released as waste, only a portion of the original energy and biomass of the food unit is available to be passed up the food chain when another predator eats the predator that ate the phytoplankton! Therefore the higher up the animal is in the food chain, the more energy has been lost along the way... One estimate is that each step in the food chain, about 80-90% of the food unit energy is waste and only 10-20% of the food unit energy is passed to the next step up the food chain. Thus much of the food energy in the ocean is being released as waste and is recylced to its simplest chemical structures by the activity of bacteria.

An example of food energy transfer and the benefit of vegetable: per 1 unit energy stored in plants, only 0.1 unit energy will be stored in the herbivores that eat plants. When a carnivore (like us) eats an animal herbivore, only 0.01 unit of the original plant food energy will be gained. A top predator like a shark gains only 0.0001 unit of the original plant energy that fueled the food chain. Some would argue that eating low in the food-chain (ie vegetables) is the most efficient way from an energy stand point and that plant food rich in protein is the best source of efficient nutrition for underfed human populations

In the sea, it is the complexity of the food web that provides a stability to the ecosystem and would be lost if the major animals were no longer present. If lots of seals died because of toxic algae, what would be the affect on the fish they ate??.. What might happen to the smaller animals if these fish became too abundant because there were fewer seals to eat them ? Scientists who study the food web in nature and how it might change and what the consequences of that change might be are called ecologists..

Learning Activity III - Food Web Game and Transfer of a Toxin:

1) Have students form a circle

2) Hand out pictures of animal and plants in the food web you have already discussed. Each student will wear a picture of one member of the food web around their neck so it's clearly showing to the other students. Make sure that the top predators are not all standing next to each other in the circle.

Some examples:

Pelican

Red Crab

Scallops

Oysters

Clams

Mussels, http://wdfw.wa.gov/gallery/view_photo.php?set_albumName=album07&id=mussels

Rockfish, http://wdfw.wa.gov/gallery/view_photo.php?set_albumName=album29&id=edcop

Lincod, http://wdfw.wa.gov/gallery/view_photo.php?set_albumName=album29&id=sturgeon_001

Sardines, http://wdfw.wa.gov/gallery/view_photo.php?set_albumName=album29&id=sturgeon_001

Anchovy

Shrimp (Krill)

Sea Urchin Larva, http://www.imagequest3d.com/photos/zooplankton/

Copepod, http://www.imagequest3d.com/photos/zooplankton/

Microzooplankton (herbivores eat phytoplankton) http://www.imagequest3d.com/photos/zooplankton/

Dinoflagellates (nontoxic kind) http://www.imagequest3d.com/photos/zooplankton/

Diatoms (nontoxic kind) http://www.imagequest3d.com/photos/zooplankton/

3) Hand out a ball of yarn/string to the first top predator, who needs to first hook the end of the string to the hook/carabener on his/her own animal

4) Ask the student to then throw the yarn to the food item he/she would choose to eat

5) The prey (person with that prey item) catching the ball of yarn then needs to hook the string on his/her animal and proceeds with throwing the yarn to his/her prey item of choice

6) This step is repeated until it reaches the algae

7) At this point the teacher can hand a new ball of yarn to another top predator and repeat step 3-6... a top predator can start this more than once as each top predator may choose more than one prey item. It is also possible to use a different color of yarn to represent toxic algae and when one animal gets too many, then they have to step out of the food web and the consequences of their absence can be appreciated. Even more elaborate would be to have the lost animal to return as the food they eat, in order to demonstrate how they prey abundance increases in the absence of the predator... but only so long as their if enough food to eat. The absence of one animal may mean that higher predators starve and that lower prey are eventually overgrazed.

8) At the end (once the teachers feels enough links have been made) the students should appreciate the web they created and how many connections they've made between the different items in the food web - this can be reinforced by encouraging one or two students to tug slightly on the string... and see what happens

9) After the game is completed the students should take their animals and hang them on a board (either with pins on a cork board or with tape on a black board) in the appropriate categories that the teacher has already labeled:

Top Predator

↓

Carnivore

↓

Herbivore

↓

Primary Producer

Learning Activity IV - Trophic Transfer of Energy and Toxins:

1) Teacher calls for 5 volunteers

2) Students line up in front of the class, spread evenly as far apart as the classroom allows.

3) Each gets one of the pictures used in the previous game:

i. Algae, i.e. primary producer

ii. Copepod, i.e. herbivore

iii. Anchovy, i.e. herbivore/filer feeder

iv. Tuna, i.e. carnivore

v. Shark, i.e. top predator (carnivore)

4) Primary producer gets 15 pieces of paper, 4 of which are colored (blue) symbolizing toxin

5) The first student (the algae) walks towards the next trophic level (the copepod) along the walk the teacher instructs the "Algae" to breath, which results in a loss of 1 piece of white paper, which the student is instructed to drop to the ground

6) The "algae" then hands over the reminding 14 pieces of paper to the copepod, symbolizing the energy transfer to the next trophic level when the algae is eaten by the copepod

7) The "copepod" then starts walking towards the "anchovy" - this time the teacher instructs the student to drop 1 piece of white paper because the copepod has to pee.

8) As the "anchovy" walks towards the "tuna" the teacher tells the student to drop 1 piece of white paper for breathing and 1 piece of white paper for pooping.

9) During the last step, when the “tuna” walks over to the shark the student is instructed to loose again 2 pieces of white paper, one for peeing and one for pooping.

10) When the shark receives all the pieces of paper, the student needs to count aloud to the class how many pieces of papers of each color he/she has received.

The shark should now hold 9 pieces of paper, of which 5 are white and 4 are blue. The teacher needs to point out that this has now increased the relative amount of toxin in the animals body due to the process of bioaccumulation. The teacher should also now brief the class on what they have seen/learned during the game. The fact that which each trophic transfer energy is lost due to the biological processes needed to maintain body function, that does not translate into growth, i.e. biomass. Only about 10% of the prey's mass will be transferred up to the next trophic level. Hence the shorter the food chain the more efficient. Therefore, the lower humans eat in the food chain the more people can be fed on the same amount of primary producer.

Evaluation:

Have students write an essay (or have the write a short presentation arguing in front of the class as if it was the United Nation, NOAA or a funding agency, telling them why their research project to study phytoplankton and zooplankton should be funded). Why it is important for the conservation of marine mammals that scientists study phytoplankton and zooplankton, the tiniest creatures in the food web?

Science standards:

Six Grade

Ecology 5 - Organisms in the ecosystems:

a) Energy enters the ecosystems as sunlight and is transferred by producers into chemical energy through photosynthesis and then from organism to organism through food webs.

b) Students know matter is transferred over time from one organism to others in the food web and between organisms and the physical environment.

c) Students know populations of organisms can be categorized by the functions they serve in an ecosystem.

d) Students know different kinds of organisms may play similar ecological roles in similar biomes.