Dear Janet,

There can be many reasons for the morphological change like environmental factors like intensity and duration of light  or even the chemical constitutional change  of the medium.

You may have to investigate by altering few aspects.

Good luck!

Dear Janet,

The Provasoli medium is extremely rich and in no way close to what seaweeds can experience in natural conditions. I do not know if you transferred them from natural conditions to culture with Provasoli medium, but a strong/rapid change in nutrient conditions (and also light conditions) is a stress and that can trigger sporulation.

I once received Porphyra (Pyropia) grown on Provasoli medium and transferred them to ambient seawater. That triggered sporulation and I got thin and discolored blades, which eventually disintegrated.

The period of adaptation and a gradual change can also be important.

All the best,

Thierry Chopin

Many article reported that on sterile culture of Ulva (without bacteria), could effect on the morphological of Ulva。Some substance produce by bacteria  to promote growth of Ulva, like thalusin.  So the presence of bacteria very importan

This could be strong water movement