Aquaria/Reefkeeping

Reefkeeping, or reef-keeping and sometimes reef keeping, is a marine aquarist hobby of creating, maintaining, and actively sustaining a living captive reef, within an aquarium, complete with various life forms common to coral or other types of reefs.

Introduction
"An aquarium (plural aquariums or aquaria) is a clear-sided container in which water-dwelling plants and animals (usually fish, and sometimes invertebrates, as well as amphibians, marine mammals, and reptiles) are kept in captivity, often for public display; or it is an establishment featuring such displays."

Light
Two light levels: photosynthetically active radiation (PAR, ~400-700 nm), PAR of 80 versus 180 µmol m-2 s-1 have been used to grow "crustose coralline algae (CCA), a desired group of benthic calcifying algae", on two "types of rock (initially bare coral rock and rock preconditioned for 12 weeks under low light)".

"In general, pink CCA's developed more quickly than red CCA's, with 4.31-10.44% versus 2.45-4.56% cover after 9 weeks, respectively. Pink CCA grew more quickly on non-preconditioned rock; after 9 weeks of culture, pink CCA showed higher percentage cover and larger colony size on initially bare rock compared to preconditioned rock. In contrast, red CCA showed higher percentage cover and colony density on preconditioned rock. Although higher pink and red CCA colony densities were found at higher light intensity, no effect of irradiance was found on relative CCA cover. In addition, red CCA colony size was larger at the lowest irradiance, for both rock types."

Crustaceans
Crustaceans are arthropods. Their skeletons are on the outside of their bodies. Shrimp, crabs, lobsters, barnacles and hermit crabs are all crustaceans. Crustaceans have jointed body parts and often have many legs. Crustaceans have two pairs of antennae. Most crustaceans live in the sea and include animals, such as lobsters and crabs. Two types live on land – rolie polies, also known as isopods, pillbugs or sowbugs, and crayfish. Reference: About Crustaceans

Fish
Dragonets such as the Mandarinfish on the left are bottom-dwelling fish that constantly hunt tiny invertebrates for food, but in an aquarium most starve to death unless a refugium or place for the invertebrates to reproduce safely without any fish being able to reach them is provided.