What actually is Undaria pinnatifida (Undaria)?

As most of you will have read in previous newsletters there is an ongoing local eradication attempt underway in Sunday Cove, Breaksea Sound to remove Undaria after a single mature specimen was found in April 2010.


The programme is still running and proving to be very successful.  We are still finding the occasional small individual from time to time (the most recent being the August 2014 survey) but the team believe that they are still on track to remove it from Sunday Cove and keep Fiordland pest free.


However, Undaria is a very interesting seaweed and has quite a unique life history, so to try and help everyone understand why it can be so invasive, below is a brief explanation of its (very strange) life cycle.


Undaria life cycle stages

Starting at number 13 on the picture.........


The twisted base of a mature Undaria stem (called a stipe) contains all of the spores that will foster the next generation of Undaria individuals.  The spores released from a mature Undaria specimen are microscopic (1) and contain both male and female individuals.  A single mature Undaria specimen can release millions of spores during its reproductive cycle which is why Undaria can be so invasive.  Those spores settle on the seabed after a brief period of actively looking for somewhere suitable to live, where they change into either a male or female gametophyte (sperm or egg producing individual) (2, 3, 4).  If a male and female settle close to one another (~1mm) the sperm fertilises the egg attached to the female gametophyte and creates what is the beginnings of an Undaria plant (5-9).  These stages of sexual reproduction are almost more like how an animal reproduces rather than a plant which is what makes Undaria such a strange critter!!


Once that stage has been completed there is now a fertilised baby Undaria (10, 11) that just needs to wait until conditions are right for it to grow in to a plant that we can see with the naked eye.  This can take a long time (potentially years) before being kicked in to action by increasing sunlight or a change in seawater temperature.  Once the biological conditions are right the Undaria individual starts to grow in to a juvenile that you can recognise (12), then after only 4-5 weeks in the height of its ‘growing season’ it is ready to start the cycle over again (13)


So, in the space of only a couple of months Undaria has the ability to drop of a boats hull or mooring rope, grow to maturity and spawn the next generation of Undaria!!  That’s pretty invasive!! 


Hopefully, by knowing a little more about how Undaria lives it will make you realise what a tricky customer we are dealing with.  As always if you would like more information about the programme in Sunday Cove or have any Biosecurity questions please contact Derek Richards at Environment Southland (derek.richards@es.govt.nz)

Derek Richards, Environment Southland