A bucket full of seaweed, or ‘bryozoa, I promise it really is an animal’

A bucket full of seaweed, or ‘bryozoa, I promise it really is an animal’

I want kids to break away from the stereotype that science is all about old bearded white men discovering things a long time ago, or the image that is everywhere of someone in a lab coat and goggles peering quizzically at a test tube.  Science is about being entranced in the world around us and thirsting to know more about it.  What better place to explore this than the beach?


A handful of seaweed in a bucket of seawater
A handful of seaweed in a bucket of seawater

For this activity you will need and extensive list of equipment.


Only teasing!

For this activity you will need a bucket.

Also a suitable sea shore (ours is highly turbid due to a lot of clay in the water, so we drove along the coast to Eastbourne).

Fill your bucket almost full of pebbles (or sand) then top up with sea water.  The purpose of the pebbles is to limit the area you are looking in to so it is a shallower depth, which makes it easier to see things, so you don’t need anything in the bottom if you are using a  tray instead.  Scoop up a handful of seaweed from the water’s edge. You can have fun looking at the seaweed washed up along the strandline too, but for this activity the fresher from the sea the better. Pop your weed into your bucket and sit and stare at it for ages and ages and ages.

I say stare at it for ages because at first you probably won’t notice much beyond the different textures and colours of the weed.  Then (like one of those ‘magic eye’ pictures from the 1980s) once you get your eye in you will suddenly start to notice a lot more. Shrimp for example.  If you look closely at the image above you will see a thin line in the top left corner of the water in the bucket – that was a shrimp, one of four we spotted darting crazily around.  Well, I say shrimp, but it was actually an amphipod as it was curved like a ‘c’ shape, my knowledge of which is confined to the freshwater ‘shrimp’ gammarus so I’ll move swiftly on…

You will start to notice more things about the seaweed itself, like some of it doesn’t look very seaweedy, and other bits that are definitely seaweed which are crusted in lacy stuff.  These not quite seaweeds and lacy crusty things are bryozoa.  Bryozoa are animals.  I promise.  They really are.

bryozoa community encrusting seaweed
bryozoa community encrusting seaweed

It’s hard to see if you’re reading this on a small screen, so it’s well worth opening the image and taking a closer look, but you will notice a lacy crusting on this piece of weed.  About a quarter of the way from the left is a piece that has detached from it’s substrate that looks like the continent of Africa.

Bryozoa are tiny animals that live in colonies.  Some are frondy and look a lot like little mats of sea weed ( Bryozoa means ‘moss animal’, they got renamed ectoprocta recently, but that sounds like a disease of older men, so I’m sticking with bryozoa), some are encrusting, some make hard calcium deposits, others don’t.  The palaeontologists and geologists amongst you may recognise them from their well preserved remains, which I believe include graptolytes, one of the key fossils used to date rocks.

Bryozoa are a good hook into a fascination with science because they are easy to find and they are not what they look like.  Either they look like a plant, or they don’t look alive at all.  Some assign different bodily functions to different members of the colony, with some being defensive, others feeding, and yet others focusing on reproduction, while in other species every colonist is more or less identical.  Some  are ‘simultaneous hermaphrodites’ – each individual both eggs and sperm at the same time.  Others, as in the one I think I have here Membranipora membrancea is a ‘protandrous sequential hermaphrodite’ changing from male to female (much like the clown fish made famous by ‘Finding Nemo’ – now there’s a film that would be very different if it was biologically accurate!).


colony of bryozoan encrusting a piece of seaweed
colony of bryozoan encrusting a piece of seaweed

The colony of bryozoa we found today starts off life as a fertilized egg floating in the ocean, which hatches into a free-swimming larvae and swooshes around as part of the zooplankton (animals that can’t swim against ocean currents, those that can, including adult fish, are the ‘nekton’).  Eventually the baby bryozoan (bryozoan singular, bryozoa plural) settles down to life attached to something like a frond of seaweed and then gets on with the business of maturing and reproducing either sexually as described above, or asexually by budding (like yeast, or amoebas) to form a colony.


There are websites written by bryozoologists (my new favourite word) but I don’t think they are particularly useful unless you are already a serious enthusiast.  For this topic I don’t think you can beat Wikipedia, especially as it has nice little segways off into other interesting things).

The contents of your bucket of seaweed will vary each time you do this activity, and it’s a super activity for the whole family as with younger children you can just have fun counting things whizzing around, or describing the colours, patterns and textures of the weed, then branch out into identification and life cycles with older kids.  Take pictures or make sketches of unfamiliar things to look up later, or grab a field guide to take with you (the field Studies Council make excellent plasticised ID sheets for a whole host of topics including seaweeds and rockpools).

A magnifying glass is often useful (I used to take my geologists loupe but having leant it to a friend on what turned out to be a rather extended basis I now use a £10 mini microscope of the kind you find in the pocket money sections of national trust shops and garden centres).  You can always add useful kit to a trip out, but ultimately the only important thing is the bucket as it allows you to develop skills with kids of sitting and observing closely (which depending on the mood of the kids could be a few seconds or half an hour).  The more you look, the more you’ll see.



Notes: usual safety precautions apply around young kids and water, plus clothing and supplies appropriate to the conditions – you know what to do.





  • Plutonium Sox

    10th July 2017 at 8:47 pm Reply

    What a great activity, and I love the idea of taking a magnifying glass too! We might have to do that next time we go rock pooling. I’ll take a bucket to do this activity too!

    • admin

      13th July 2017 at 3:42 pm Reply

      I really like low tech, low equipment activities. We went out today with the full kit – butterfly net, bug pots, books, ID charts, binoculars etc.. and it was all useful, but guess who gets to carry it all on the walk home 🙂

  • Fiona Cambouropoulos

    17th July 2017 at 9:38 pm Reply

    Well it certainly doesn’t need much to get this experiment underway so long as you live by the coast, but wow that is a lot of information to take on board. I feel quite ignorant of how much I didn’t know, I won’t looks at a piece of seaweed with such disregard in future!

    Thank you for sharing with me on #Countrykids

    • admin

      18th July 2017 at 1:22 pm Reply

      It’s what I love about natural history, science – everything really – there’s always so much to find out, we only ever really scratch the surface

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