Day 1 of Life Beneath the Keel

On Sunday 13 September, at 1800 BST, The Island Trust is live streamingLife Beneath the Keel’ from Plymouth Yacht Haven as part of the Ocean Institute’s virtual Maritime Festival. This is the first in a series of blogs about the marine life we hope to discover then.

Day 1:  31 August 2020 | Seaweeds

Seaweeds are macroscopic algae – they are big enough to be seen with the naked eye, and they come in three colour groups; green, brown and red.  Although the three colours are indicative of the depth they evolved to live at, we do find examples from each group on marina pontoons.

  1. On the shore green seaweeds live at the top of the shore, where they get lots of light.  Ulva lactuca, sea lettuce as its name implies you can eat this as lettuce.
  2. Brown weeds live further down the shore. The change in colour is the result of different chemicals which they produce to help them photosynthesise using light at different wavelengths resulting from refraction through more water. If you go rockpooling you will be familiar with bladder wrack. It is often found wrapped around ropes, ladders and chains rather than growing on the pontoon. The bladders help it to float and get more light when the tide comes in and the weed increases the pressure in them so that they don’t collapse as the water gets deeper causing the seaweed to sink, and then releases the pressure as the tide goes out so it doesn’t become too buoyant.
  3. Wakame, a brown weed often eaten in Japanese cuisine, in UK is an invasive non-native species (INNS). It was brought over with Pacific oysters as packing in the incorrect belief that the water was the wrong temperature for it to reproduce. It also arrived on shipping.
  4. Devil’s tongue is red seaweed, lives in deeper water. Another INNS, slippery to the touch, but not making the fingers slippery.  Slipperiness helps protect algae from damage when wave action rubs the fronds against rocks or other sea weeds. This, too, was probably also introduced into European waters via mariculture and shipping.
  5. Carragheen or Irish Moss is another red seaweed. For those who think they don’t eat seaweed, if you eat ice-cream, the chances are you do. Caragheenan is made from this seaweed and used as a stabiliser in ice-cream. It improves the mouth feel, making it ice cream, and not just crunchy bits of ice. If you want to know more about caragheenan’s use in ice cream go to

John Hepburn, Ocean Discoverability Project Manager
31 August 2020