5th June 2020

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Kia ora,

Working out the area that something covers (measured as a percentage) is a very important skill for ecological surveys - including Mm²! It is a quick and easy way to record the ground surface (substrate) and the density of seaweed/s in your quadrat. Find out more on how to calculate percentage cover here

Tools for Calculating Percentage Cover

Figuring out the cover of different substrates and seaweed species can be a bit of a brain exercise in itself. Luckily there are some easy ways to help you calculate percentage cover while doing an Mm² survey! All you need is:

The lid from a 2-litre ice-cream container
A ruler
A permanent marker
A pair of scissors

Then you can make your own 10cm x 10cm quadrat (or 1% of your 1m²) using these three easy steps:
1. Use the centre of the lid for the centre of your 10 cm² quadrat
2. Measure out a 10cm x 10cm square using the ruler and permanent marker
3. Carefully cut out the square so your lid has a hole in the centre
These instructions will be available on our website shortly under 'Resources'

In biology, there are always some exceptions to the rules. You may come across some animals that live in colonies (e.g. sponges or ascidians) and again, it can be tricky to separate the number of individuals. In this case, it is better to record these kinds of species as a percentage cover - this is where your 10cm x 10cm square can be very handy!

Estimating Numbers

You can also use your 10cm x 10cm square when you have LOTS of individuals of a species in a concentrated area. A great example of this is the columnar barnacles (Chamaesipho columna) and little black mussels (Xenostrobus neozelanicus) in the picture below. Instead of counting all the individuals in your 1m² quadrat, using your 10cm x 10cm square, you can do an estimate.

Simply place your 10cm x 10cm on an area where there is a high density of a species and count all the individuals (of one species) in this area.
Count how many other areas with a similar density of your chosen species are present in your m².
Multiply the number of areas by the number of individuals that counted in the 1% area (e.g. 7 % cover x 100 individuals = 700 individuals present in your quadrat)
Record this information on your datasheet
Repeat for other species in necessary

Mm2 and Maths

Mm² can be used a great way to develop mathematics skills in a practical and hands-on manner. If you want to assess the accuracy of estimations of substrate cover, you can print out a photo of your quadrat on A3 paper. Divide your photograph into 100 evenly sized squares and assign each square with a substrate type. Tally up your results and compare them to what you found on the shore. See below for an example

New Resources Online!

We have recently updated our datasheets and instructions on how to do an Mm² survey for both rocky and sandy/muddy shores. You can find them on our r esource page. Instructions on how to make and use a 10cm x 10cm square and how to assess your substrate cover in the classroom will also available here shortly. So keep an eye out!

Keep Up to Date with Us!

Don't forget to follow us on Facebook, Twitter and Instagram at @marinemetre2. On social media we post relevant articles and activities as well as share what our Mm2 community has been up to. So we want to hear from you! Whether it is finding something weird and wonderful or simply just a great day out exploring - get in touch with us so we can post it on social media or under 'Community Stories' on our website.

Up Next....

We will be going over some helpful resources to assist you with identifying life on the shore!

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