What is the author's purpose in discussing "temperatures in intertidal areas?" A. To emphasize the idea that warm temperatures can be just as dangerous to algae as cold temperatures B. To identify a limiting factor for algae common to both tropical seas and waters at higher latitudes C. To compare the causes of seaweed mortality in tropical seas and in seas at higher latitudes D. To note an exception to the idea that temperature does not limit the growth of algae in tropical and subtropical waters