Seaweed, seaweed everywhere and not a plant to eat

Seaweed, seaweed everywhere and not a plant to eat

Like many Kiwis, to me there are only three types of seaweed: Seaweed Beachus – seaweed washed up at the beach; Seaweed Sushius – seaweed used in sushi; and Seaweed Fish Linius – seaweed that your fishing line gets tangled in.

But that terrible seaweed joke, aside from demonstrating my woeful ignorance of seaweed, doesn’t do justice to the extraordinary variety of seaweed that’s out there.

So, to make sure I’m not going into the upcoming Science Live: Coastal Creatures event completely blind, I decided to see what I could find out about seaweed. Here are some facts I’ve uncovered that you mightn’t have known about seaweed:

  • Seaweeds aren’t plants, they’re actually algae
  • Given that they’re algae, it makes sense that seaweeds don’t have roots, flowers or fruit. They reproduce through spores
  • Seaweeds can range in size from the microscopic to massive kelps more than 30m in length
  • The deepest seaweed in New Zealand waters has been found at depths of more than 200m off the KermadecIslands
  • Some seaweeds have developed special floatation devices, including air-filled chambers, to keep them near the surface in reach of sunlight
  • There are believed to be about 900 different species of seaweed living in New Zealand waters. Many are still waiting to be described by science, while there are undoubtedly even more that we’re yet to even discover!
  • Believe it or not, there’s even a type of crab that camouflages itself using living seaweed!


Speaking of seaweed-camouflaged crabs, to celebrate Science Live: Coastal Creatures, we have a signed copy of pre-eminent seaweed expert Dr Wendy Nelson’s new book to give away: New Zealand Seaweeds: An illustrated Guide, published by Te Papa Press.

All you have to do is tell us what type of crab is pictured below. Email your answer to by 4pm, Monday 9 December 2013 and we’ll randomly pick a winner from those who get the answer right. This competition is only open to people residing in New Zealand. Employees of Te Papa and their immediate families cannot enter.

What type of crab is this?


  1. Hi Gwynn,
    As one of Te Papa’s botany curators, I’m pretty comfortable with algae being “plants”. I take a kind-of functional view that plants are organisms that photosynthesise (use sunlight to convert carbon dioxide to sugars). Seaweeds (and other algae) photosynthesise, so in this context can be considered plants.
    That does put me at odds with the first section of Wikipedia (, where only land plants are emphasised, but they do give a more nuanced view in their Definitions section.
    Of course, my functional view of “plant” gets me into trouble with things like Euglena, which photosynthesises but moves and ‘eats’ like an animal ( Nature doesn’t do straight-forward.

    1. Author

      Straight-forward is definitely the last thing nature does.

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