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The brown macroalgae, Ascophyllum nodosum, or knotted wrackweed, occurs within the intertidal zone along rocky shores in Maine and other northern latitude regions in Canada, Iceland, Ireland, Scotland, Norway, Sweden, and Germany.  In most countries, it is harvested commercially, and this is the case in eastern Maine where harvests have occurred from Cobscook Bay south and west to Gouldsboro Bay.  You can purchase Ascophyllum as a fertilizer from Maine Seaweed in Steuben, Maine.  In Cobscook Bay, annual turnover rates of Ascophyllum range from 29 to 71% (average = 54%) which means that the biomass of this alga turns over approximately every two years (Vadas et al. 2004).  That is, the proportion of naturally-occurring Ascophyllum standing biomass lost annually (expressed as turnover rates) is over 50%, and this turnover was not related to commercial harvesting since none occurred when the Vadas et al. (2004) study was conducted (1995-1996).  Natural losses of seaweed biomass is due to a variety of factors including grazers (the smooth periwinkle, Littorina littorea), storms, winter ice, and reproduction when tissues are lost after spawning occurs.

Severe winter storms can cause extensive windrows along the upper intertidal shore where Ascophyllum can wash up and be collected easily.


Dr. Raul Ugarte, Acadia Seaplants, Ltd., stands on a windrow of Ascophyllum nodosum in the upper intertidal along a shoreline of New Brunswick, Canada in November 2008.  Dr. Ugarte calculated that 40,000 metric tons of the macroalgae were released in one night alone.  (Photo courtesy of Dr. Ugarte)


Classroom experiment

An experiment occurs when one or more factors is/are manipulated to determine whether or not the factor has some effect (positive or negative) on one or more variables.  An experiment is the result of a straightforward process that begins with an observation.


Ascophyllum has been used for centuries by farmers in many countries as fertlizers and soil amendments.  In an extreme example, residents of the soil-poor Aran Islands (Galway Bay - West coast of Ireland) created soil for vegetable gardens by mixing Ascophyllum with sand.  For many residents who live near the coast of Maine, seaweed washed up along the shore is carried to gardens where it is used as an organic fertilizer and soil amendment.

The next step is to describe several different reasons why you think Ascophyllum may be helpful for farmers or gardeners.

Model (Theory)

A model is a statement that describes what you think is the explanation for the observed phenomenon. 

For the case of using Ascophyllum as a fertilizer, one explanation may be that Ascophyllum serves as a natural fertilizer and can be used as a replacement for inorganic (chemical) fertilizers.  Another explanation may be that as Ascophyllum decomposes, its breakdown products help to create new soil.

The next step is to use one or more of the models, or theories, about why you think the observations have occurred,  and then to make a prediction based on the model.

Hypothesis (Prediction)

A hypothesis is a statement that makes a prediction assuming the model is correct.  For example, if you think the reason that gardeners use Ascophyllum as a fertilizer is that it helps plants grow faster than soil by itself, then you might make the following prediction:  "If I add Ascophyllum to soil, then I predict that whatever I grow (let's say it is a bush bean seed), will grow faster or produce more fruit than beans grown in soil without Ascophyllum."  Why?  Because I think the model is correct.  If beans do not grow any better in soil with Ascophyllum vs. soil without Ascophyllum, then my prediction is incorrect and quite possibly my model is incorrect.

The next step is to devise a null hypothesis that can be tested experimentally.

Null hypothesis

A null hypothesis is a statement of "no difference."  In this case, my null hypothesis would be:

Ho:  There is no effect of adding Ascophyllum to soil on the variable I measure (plant growth rate; size of flower; number of fruits; weight of fruits, etc.).

The alternative hypothesis, Ha, would be:  There is an effect of adding Ascophyllum to soil on the variable I measure.

The next step is to devise a critical test (experiment) to test the veracity (truthfulness) of the null hypothesis.  There are many different ways to test the same null hypothesis.  The object of the test is to do everything in your power to disprove what you think will occur (typically, this is the alternative hypothesis).  That is, the strength of the scientific method is devising the most powerful critical test that attempts to disprove your prediction (hypothesis)

Critical test (experiment)

Here is an experiment that will test whether or not Ascophyllum as a soil amendment or fertilizer will result in increased growth or enhanced fruit (of beans) compared to using soil by itself.  In this experiment, there is one factor (A Soil Treatment) with four levels:

I.     4 parts soil : 0 parts ground, dried Ascophyllum

II.    3 parts soil : 1 part ground, dried Ascophyllum

III.   2 parts soil : 2 parts ground, dried Ascophyllum

IV.   1 part soil   : 3 parts ground, dried Ascophyllum

The experiment will include five examples, or replicates, of each of the treatments. 

There are many different ways to set up the experiment.  The approach below is only one example.  This may not be how you might test these same treatments.

At the conclusion of the experiment you will have measured one or more variables.  You should take the average measurement of each treatment and compare the averages among the treatments.  This should allow you to see which treatment (if any) performed better than another.


Setting up the Experiment

A.  Creating the plant pots

You can use plastic plant pots, peat pots, or anything that you can imagine that will hold soil and allow some drainage after watering.  Here, we have used pots made from recycled office paper or newsprint.  We have created the pots using a simple folding technique that is shown in the accompanying PowerPoint.



You may want to double up on the scrap paper and use two pieces together to make a pot.  This will help if the soil you use is heavy.




B.  Collecting, drying, and grinding the Ascophyllum



Go to the shore and collect as much wrack as you need.

Drying the Ascophyllum can occur outside, or in a greenhouse (it takes about 4-5 days in a greenhouse)

A tote full of dried Ascophyllum will fit into a 30-gallon plastic bag

The dried Ascophyllum is hard and brittle.

You can break it up with your hands, and this will get it ready for grinding.


A crank-type meat grinder will work just fine.


You can grind the Ascophyllum as finely as you wish.  This is the size of the ground seaweed used in the classroom experiment.

The experiment required about 3 liters of ground Ascophyllum.  This was approximately one-half of the garbage bag.


C. Preparing the experimental units

The plant pots become your experimental units.  What is an experimental unit?  An experimental unit is an object that is randomly assigned to a particular treatment in your experiment.  In this experiment, twenty experimental units (plant pots) are required because there are five replicate units being used for each of the four treatments.  Step one is to assign a treatment to a unit.  This requires making labels for your units so that you can affix them to each unit so that you can follow the fate of the bean in that particular unit. 


The labels are affixed to the plant pots (experimental units) using tape.



Next, we create the soil treatments.  Obtain a bag of potting soil, and then use a one-gallon plastic bag with a zip-lock to mix the ground Ascophyllum.  Each treatment, including the control (100% soil) needs to be "mixed" and handled the same way.

Four containers are filled to the 500 ml mark with potting soil.

The soil from each container is poured into the bag, and then the soil is mixed for about one minute.

Here are four containers to be used for the treatment that requires 3 parts potting soil and 1 part Ascophyllum.

Again, pour each of the containers into a plastic bag, and mix for about a minute to ensure a thorough distribution of soil and ground Ascophyllum in the bag.  Repeat this same procedure for the two remaining treatments.



Next, add about 250 ml of soil from each bag and place the soil in the appropriately labeled experimental unit (plant pots)


The units have all been filled with soil, and are now ready to accept one bean seed each.

These are bush bean seeds that should produce fruit within 50-55 days.  Place one seed on the top of the soil in each experimental unit.

Push the seed about 2-inches below the soil surface, then water each experimental unit using 100 ml of tap water.

Place the units (plant pots) in some container so that you can move them as a single unit, and arrange the units randomly in the container so that the replicates of each treatment are distributed throughout the container in an irregular fashion.  This randomization ensures that any uncontrolled factor such as sunlight, temperature, shade, etc. is spread out among the units as much as possible. 

Water twice weekly at 100 ml per pot each time.  If your conditions are more extreme (heat/dryness), you will need to water more.  Do not add any fertlizer to the water.  The object is to determine if Ascophyllum will act as a natural fertilizer.

Once the beans germinate and begin to grow, you will have to spread out the plant pots using a larger container to hold them as the plants will begin to grow together and entwine each other.  Spread the experimental units apart enough so that the plant in a unit has no physical contact with the plant in an adjacent unit.


D. Data collection

You must decide what variable or variables you wish to measure.  You can measure days to germination; height of plants once or twice weekly for the duration of the test; number of bean pods (fruits) produced per plant.  You may wish to measure the mass of the pods produced per plant.  It is your decision about what variable you will measure.

You will need something to record your observations (both qualitative and quantitative) such as a data sheet.  The data sheet can be used to make comments about the color of the leaves, or some other physical appearance of the plants that you would like to remember.  You may wish to take photos of the units from time-to-time to help with your data collection.  At some point, you will want to take a physical measurement (height, mass, number), and will need a data sheet to help you with these quantitative measurements. 

Please contact Colleen Haskell or Brian Beal if you have any questions.


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