While many aquarium capable invertebrates are quite hardy, even in captivity, there are many that have specific issues that make them extremely delicate in our care. For example, sponges are very hardy once established in a reef tank. The problem occurs during their introduction. Because sponges are susceptible to drying out and often rely on the water to keep their tissues from collapsing in on themselves, it’s crucial to keep them submerged in water at all times. This is also the case for several other species, but usually not so for corals, as they have hard skeletons and internal structures that keep the tissue in tact.