Photo of Bluebell Woods in Sussex Photo of Bluebell Woods in Sussex

How to Make a Map Using Seaweeds

Channelled Wrack – Pelvetia canaliculata

Seaweeds are algae and like every other organism they have their preferred habitat. But each species of seaweed has its own niche, which means that we can learn to make a map by discovering the habitat niches of the seaweeds we find along the coast.

There are about 12,000 known seaweeds and doubtless many more still to be discovered. We can’t possibly hope to get to know them all personally.

The best place to start is with a stretch of coastline you can visit regularly, or at least get to know over a a few days, perhaps on holiday.

Bladder Wrack – Fucus vesiculosus

If you walk from the water’s edge away from the sea several times, from different start points and at different times, you will start to notice a pattern. Some seaweeds favour the strip nearest the water, others thrive much higher up the beach.

It’s a good idea to vary the time and ideally different times of the month, as the aim is to do this at different stages of tide. You see a lot more of the lower stretches of a beach at low tide and lots more at ‘low water springs’, the lowest tides.

If you do this enough times you will start to notice a simple pattern. There are three main bands:

Seaweeds that are mainly found very near the water.

Those that do well halfway up the beach.

And those at the top end.

The habitat range is straightforward:

Some seaweeds need almost constant immersion in seawater.

Some don’t like to dry out but are happy out of the water for hours.

And then there are some that can survive for longer periods of time in moist air but not directly in the water.

There are as many subtleties to this map as there are seaweed species, but the simplest method is to look for Channelled species, then Bladder seaweeds and finally Saw (or serrated) seaweeds. The good news is these names all give you a clue to the look of these seaweeds.

As you go from high to low, you:

Check the Beach for Seaweeds.

Channel, Bladder and Saw.

So if you scroll upwards and look at the photos on this page, you’ll see them in that order: Channel at the top of the beach and page, then Bladder half way down and finally Saw at the bottom of the page and the beach.

Saw or Serrated Wrack – Fucus serratus

This technique is taken from the bestselling book, The Lost Art of Reading Nature’s Signs (North America) / The Walker’s Guide to Outdoor Clues & Signs (UK).


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