Re: How many eggs do jellyfish produce?

Hi Rhian,

Your question is surprisingly difficult to answer, considering that I'm 
working on jellies (we don't call them "jellyfish," because they aren't fish 
at all) for my Ph.D.  It appears that nobody has ever bothered to count how 
many eggs a mature medusa can produce, or how many larvae she may be 
brooding on her oral arms -- at least, I was not able to find any records of 
such counts.

What I do know, from my own experience, is that a female medusa of Aurelia, 
the moon jelly, can brood thousands of planula larvae.  A few years ago I 
harvested brooded planulae from a female Aurelia medusa and settled the 
larvae to start a family of clones.  This medusa wasn't very large (less 
than 20 cm in diameter), but she carried thousands and thousands of larvae.  
I snipped off a tiny bit of the brood, and liberated hundreds of planulae, 
dozens of which settled and metamorphosed into the polyp stage of the life 
cycle.  FYI, the brooded larvae look like small clumps of cottage cheese on 
the mother's oral arms.

So my guess, based on my own observations and common sense thinking, but no 
empirical data, is that jellies have very high fecundity rates, producing 
eggs by the tens of thousands.  When a female medusa is brooding, she may be 
carrying thousands of developing larvae on her body. Even when the female 
isn't brooding larvae, she may have hundreds to thousands of eggs in various 
stages of development in her gonads. 

I hope this answers your question.

Allison J. Gong
Mad Scientist