If bladder wrack is uncovered by the tide ,it flops onto the ground why does this happen?

Fucus vesiculosus has a number of morphological adaptations that are extremely beneficial. First, the organism has evolved what is called a holdfast. This is root-like structure that connects the entire organism to the substrate or ground. The holdfast ensures that the organism doesn't float away from an area that it has evolved to thrive in, for example, moving from an area of lower temperatures to higher temperatures, and also changes in the salinity of the water. The picture to the right shows a holdfast of another brown algae. Notice the root-like structures that are all over the substrate.