Re:Controlling Caulerpa

Pete Giwojna

Dear Carrie:

The vigorous growth of the Caulerpa macroalgae is a good thing in a way because it utilizes nitrates for growth and when you subsequently harvest it and pull out the excess Caulerpa, you are exporting nutrients from the aquarium. So it’s really helping to safeguard your water quality.

The lettuce nudibranch does indeed feed on certain types of Caulerpa and Bryopsis algae in the aquarium, not hair algae, as is sometimes reported. But they don’t graze on the macroalgae like a snail as you might expect. Rather, they essentially suck the chloroplasts from certain Caulerpa and incorporate those chloroplasts into their own living tissue in a process known as kleptoplasty. The chloroplasts they have hijacked in this manner will then continue to produce food for the nudibranch via photosynthesis if the aquarium receives enough light. This method of feeding, plus the fact that they don’t always feed on the type of Caulerpa that is getting out of hand, makes them a somewhat unreliable means of controlling your rampant Caulerpa growth. There’s no guarantee they will practice their kleptoplasty on the grape Caulerpa that you need to control, Carrie.

So I think I would just continue to pull out the surplus Caulerpa, removing whole, intact strands as often as necessary to limit its growth. And if that gets to be a pain in the neck, then you could consider pulling it all out and replacing it with slower growing macroalgae such as red or gold Gracilaria, maiden’s hair, or Chaetomorpha turf algae, a.k.a. spaghetti algae.

Best of luck reigning in your Caulerpa, Carrie!

Happy Trails!
Pete Giwojna

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