Why were living sponges placed in Ca2 plus Mg2 plus free seawater overnight?

Living sponges are often placed in a solution of Ca²⁺ and Mg²⁺ in free seawater to study their physiological responses and to maintain their osmotic balance. Calcium and magnesium ions are essential for various cellular processes, including maintaining cell structure and function, as well as facilitating certain biochemical reactions. The overnight immersion helps ensure that the sponges remain healthy, hydrated, and able to perform their natural filtering and feeding functions in a controlled environment. This setup is commonly used in research to investigate sponge Biology and ecology.