The intertidal rocky shore 

identifying seaweeds 

By Dr J Floor Anthoni (2007)
Note! this used to be a very large page, now split into smaller parts.
Seaweeds, particularly those that grow old, form the basis of plant life and animal life that depends on these,  on the rocky shore. Few seaweeds are able to live out of the water in bright sunshine for even short periods, so most are found below the low tide line or in deep rock pools. 
  • introduction: Introduction to seaweeds
  • coralline algae: Coralline algae are like growing stones as a hard crust over the rock or as segmented leaves
  • green seaweeds: Green seaweeds are usually lush and edible
  • brown seaweeds: Brown seaweeds are tough and able to survive wave action
  • red seaweeds: Red seaweeds are finely structured, weak and suitable for deeper waters.
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Having a temperate climate, New Zealand has a vast number of sea weed species. On and around the rocky intertidal, already many can be found, even though by far most prefer to live in deeper waters. Seaweeds form the basis of life for a relatively small community that lives on the shore and in the intertidal. But there always remains a vast input of food from the sea around, in the form of plankton and detritus.
Being unable to move around, seaweeds have to cope on the place where they 'germinated'. In fact, seaweeds germinate twice, much like mosses and ferns do. First a non-sexually reproduced spore settles on the rock, growing to a gametophyte, usually too small to notice. Male and female gametophytes then reproduce sexually and their offspring settle to grow out to new seaweeds.

Seaweeds do not need roots for finding water and nutrients, because they live in the water. So their leaves are at the same time their roots. Most do have root-like structures (holdfasts) but these are only for attaching to the rock. Some holdfasts are round discs, whereas others look like short roots. Some seaweeds grow from wandering roots (rhizomes). Some seaweeds grow like crusts where the leaf is also the holdfast.

On the rocky shore we can meet a vast array of seaweeds: coralline algae, green, brown and red seaweeds.