Every sea weed has an optimal temperature in which it can grow to its maximum.They generally prefer low temperatures. As it goes higher from this optimal,first the fully grown plant will shed out the 2X spores followed by its growth reduction.Finally with still higher temperatures,the plant will die. This is seen in almost all weeds except a few. For e.g.in Cystociera & Turbinaria, being much more hardy,this doesn't happen.