Designing and conducting an experiment around something as complex as ecology might sound overwhelming. So I decided to share with you a serie of article to explain the different steps to conduct an experiment in marine ecology with a concrete example (i.e. one of my own experiment). Last time, I told you about what to do before conducting an experiment. If you haven’t already read it, check this article first!

Steps to conduct an experiment:

#1: Defining your questions and hypothesis to plan your experiment

#2: Conducting your experiment to prove or disprove the hypothesis

#3: Collecting samples after an experiment

#2 Conducting your experiment to prove or disprove the hypothesis

2.1. Identify your independent and dependent variables

A controlled scientific experiment is set up to test whether a variable has a direct effect on another. A variable is something that may vary such as number of individuals, body size or life expectancy.

The independent variable is commonly known as the cause, while the dependent variable is the effect.

For instance, in the statement A causes B, A is the independent variable and B is the dependent.

INDEPENDENT variable = CAUSE

DEPENDENT variable = EFFECT

A controlled experiment can only manipulate one variable at a time. If more than one variable is manipulated, it is impossible to say for certain which caused the end result and the experiment is invalidated. That is why you need to plan to have controls and to measure all variables possible while the experiment is running!

2.2. Setting up your experiment

To set up an experiment in marine ecology, you need to build the system (in our case study, we have aquariums with a flow-through system) and to collect organisms you want to include.

Watch our case study:

SPECIES PRESENT IN OUR AQUARIA

Fish

Sand goby

(Pomatoschistus minutus)
This small fish is one of the most common small predator in the Baltic Sea!

Non-native worms in the Baltic Sea

Marenzelleria spp.

The worm Marenzelleria spp. is one of the most successful non-native species in the Baltic Sea. First observed there in 1985, they quickly colonized the entire sea, occupying a dominant position in the ecosystem.

Boccardiella ligerica

The non-native worm Boccardiella ligerica was first found in southwestern Finland in 1963. They are small and live in a tube constructed of mucus and sediment.

Most common invertebrates in the Baltic Sea

Clams
(Limecola balthica)

Mosquito larvaes (Chironomidae)

Snails (Hydrobia sp.)

Worms (Oligochaeta)

2.3. Checking your experiment

It is important to check up your experiment while it is running to make sure that all variables are the same in all aquariums., except for the one we are interested in.

I challenge you to answer some questions!

[qwiz style=”border-width: none !important; border-color: #cccccc !important;” align=”center”]

[q multiple_choice=”true”] What is an independent variable?

[c*] a cause

[f] Right! The independent variable is commonly known as the cause!

[c] an effect

[f] False, try again 🙂

[q multiple_choice=”true”] What is a dependent variable?

[c] a cause

[f] False, try again 🙂

[c*] an effect

[f] Right! If the independent variable is commonly known as the cause, the dependent variable is the effect. For instance, in the statement A causes B, A is the independent variable and B is the dependent.

[q multiple_choice=”true”] An essential thing to think about while planning an experiment?

[c*] Randomizing your treatments

[f] Randomizing is ESSENTIAL while planning an experiment. If you don’t randomize your treatment you are not gonna be able to conclude anything at the end of your experiment. Think about it before, when you are planning!

[c] Where you are gonna leave for vacations after ending your experiment

[f] This can be a good idea to plan a holiday because it can be quite an intensive work to set up an experiment but maybe try another answer 🙂

[q multiple_choice=”true”]

Which species is the most successful non-native worm in the Baltic Sea?

[c] Boccardiella ligerica

[f] The worm Boccardiella ligerica is also a non-native species in the Baltic Sea but is less successful in the Baltic Sea than Marenzelleria spp.

[c*] Marenzelleria spp.

[f] GOOD JOB!! The worm Marenzelleria spp. is one of the most successful non-native species in the Baltic Sea. First observed in the Baltic Sea in 1985, they quickly colonized the entire sea, occupying a dominant position in the communities.

[q] Which predator species was added in our aquariums?

[c*] Show me the answer    

[f] The sand goby (Pomatoschistus minutus) which is one of the most common small predator in the Baltic Sea!

[x]

Exit text
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[/qwiz]

References

Share your own tips, comments or experiences below!

Next time, I am going to tell you about: how to collect samples and take down an experiment!

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