Elements of the Aquarium - Molybdenum

Forms
Mo

Information
Molybdenum is a transition metal and is an important trace element in natural saltwater that is used by the symbiotic algae (zooxanthellae) in corals because it affects the protein synthesis, metabolism, and growth. These enzymes in plants catalyse the reaction of oxygen in small molecules, as part of the regulation of nitrogen-, sulfur- and carbon cycles.

Molybdenum is most often found in conjunction with Strontium for use in the aquarium environment and has also been noted to help the growth of coralline algae.

Sources
http://en.wikipedia.org
http://www.fishlore.com