The Pacific oyster is picky about temperature in most of its life stages. For maturation and spawning to be completed, temperatures higher than 16-20 degrees are required for several days in a row. After hatching, the larvae, too, are very sensitive to low temperatures. Therefore, it has been assumed that Skagerrak has functioned as a temperature barrier against the northward spreading of larvae produced off the Swedish and Danish coast. Researchers from The Norwegian Institute for Water Research (NIVA) wanted to investigate this assumption further.