This entry is written by Stuart Sandin, Assistant Researcher of Marine Ecology at the Scripps Institution of Oceanography.
When taking toll of the ocean, there is no organism quite as intimidating as the shark. With their sleek body plan, inquisitive behavior and, yes, sharp teeth, their presence changes the mood of all swimming nearby. It is precisely this imposing presence that underlies the importance of sharks to marine environments.
A blacktip reef shark seen during the current Phoenix Islands expedition (Photo: Jim Stringer)
Imagine being a fish in sharky waters--if you are smaller, sicker or slower than a friend nearby, then you will be the likely target of the swift strike by these apex predators. In this way, sharks serve as a critical filter by filtering out less able fish and structuring fish communities. On coral reefs with healthy shark populations, the typical prey fish is large and fit. These bigger sharks serve different roles than their smaller-bodied counterparts, eating different foods, moving larger distances, and generally "holding the fort" of reef communities.