The impact of long spined urchins (Centrostephanus rodgersii) on Poor Knights biodiversity is marked. Even over the past 3 years.
This image was taken at Trevor’s Rocks. It is near ‘The Gardens’, Maioro Bay at the Poor Knights. Named for the swathes of kelp that adorned every available surface.
The landscape looks very different now. With coraline turf punctuated by large black urchins in the shallows.
These barrens are spreading within a marine protected area - which at first glance seems to go against what we’ve learnt about MPAs turning the tide on kina barrens.
Unsurprisingly, ecosystems aren’t as simple as a food web scribbled on a whiteboard. A number of factors have led to the continued spread. Including the increase of the subtropical urchins range due to warming oceans, lack of crayfish predation and the fact that the snapper there just aren’t big enough to get their jaws around them.
Nick Shears from the University of Auckland is conducting a trial of manually removing the urchins. With results due in the next year.
There is still evidence to support that no take areas provide a big role in turning the spikey mesopredator tide. As long as the barrens are caused by their smaller cousin and the areas are large enough.
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