When does a nudi become an adult?

January 19, 2002
From: Andrea Bradley

Dear Bill,
I don't know how answerable this question is, but how big does a nudibranch (specifically chromodorids & phyllidiids)have to be to be considered an adult? I have a lot of size data from a survey I did with Operation Wallacea but am unsure what to do with it.
Andie Bradley


Bradley, A., 2002 (Jan 19) When does a nudi become an adult?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6037

Dear Andrea,
The first thing an ecologist will say to you is that it is vital to plan how you are going to collect your data before you start your investigation. It is also important to have at least a general idea on whether there is any point in collecting the data in the first place. In general collecting work it is valuable to record size, colour, depth, and information on food (or probable food), egg masses etc. All this helps in the longterm to build some basic background knowledge about the species.

If you are interested in lifecycles, growth rates or other specific ecological information then it is very necesary to plan out how you are going to study this and what are the most appropriate methods to employ. I am afraid the size at which an animal will reach sexual maturity differs with different species. We also know that in some species that have been studied, nutrition plays an important role in growth, and so an animal can reach sexual maturity at quite different sizes depending on whether it is well fed or not. In other examples, temperature can affect growth rates, so again size of sexual maturity can also differ.

Another complicating factor is that in some species the male reproductive system matures weeks or months before the female system, so you have the phenomenon of very small animals (functional males) mating with much larger animals.

Data on size, such as yours, may give us some maximum size information, and may possibly give us some clues to life histories, if it is collected for long enough, but basically it needs to be treated with considerable caution.
Best wishes,
Bill Rudman

Rudman, W.B, 2002 (Jan 19). Comment on When does a nudi become an adult? by Andrea Bradley. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6037

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