Grey reef sharks are often curious about divers when they first enter the water and may approach quite closely, though they lose interest on repeat dives. They can become dangerous in the presence of food, and tend to be more aggressive if encountered in open water rather than on the reef. There have been several known attacks on spearfishers, possibly by mistake, when the shark struck at the speared fish close to the diver. This species will also attack if pursued or cornered, and divers should immediately retreat (slowly and always facing the shark) if it begins to perform a threat display. Photographing the display should not be attempted, as the flash from a camera is known to have incited at least one attack. Although of modest size, they are capable of inflicting significant damage: during one study of the threat display, a grey reef shark attacked the researchers' submersible multiple times, leaving tooth marks in the plastic windows and biting off one of the propellers. The shark consistently launched its attacks from a distance of 6 m (20 ft), which it was able to cover in a third of a second. As of 2008, the International Shark Attack File listed seven unprovoked and six provoked attacks (none of them fatal) attributable to this species.
Living in warm shallow waters often near coral reefs in the Western Atlantic, from Florida to Brazil, the Caribbean reef shark (Carcharhinus perezi) is the most abundant shark in the Caribbean. It feeds mostly on bony fishes and rarely attacks humans. Despite the shark's abundance in some regions, it has a high mortality rate from bycatch and is sought by commercial fisheries for its fins and meat. It is illegal to catch Caribbean reef sharks in U.S. waters. The International Union for the Conservation of Nature (IUCN) lists the species' status as "Near Threatened."
The grey reef shark (Carcharhinus amblyrhynchos, sometimes misspelled amblyrhynchus or amblyrhinchos) is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often seen in shallow water near the drop-offs of coral reefs. The grey reef shark has the typical "reef shark" shape, with a broad, round snout and large eyes. This species can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad, black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.9 m (6.2 ft) long.
On the infrequent occasions when they swim in oceanic waters, grey reef sharks often associate with marine mammals or large pelagic fishes, such as sailfish (Istiophorus platypterus). There is an account of around 25 grey reef sharks following a large pod of bottlenose dolphins (Tursiops sp.), along with 25 silky sharks (C. falciformis) and a single silvertip shark. Rainbow runners (Elagatis bipinnulata) have been observed rubbing against grey reef sharks, using the sharks' rough skin to scrape off parasites.
Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth's history. In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits.