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Grey reef sharks are fast-swimming, agile predators that feed primarily on free-swimming bony fishes and cephalopods. Their aggressive demeanor enables them to dominate many other shark species on the reef, despite their moderate size. Many grey reef sharks have a home range on a specific area of the reef, to which they continually return. However, they are social rather than territorial. During the day, these sharks often form groups of five to 20 individuals near coral reef drop-offs, splitting up in the evening as the sharks begin to hunt. Adult females also form groups in very shallow water, where the higher water temperature may accelerate their growth or that of their unborn young. Like other members of its family, the grey reef shark is viviparous, meaning the mother nourishes her embryos through a placental connection. Litters of one to six pups are born every other year.
The snout is rather short, broad, and rounded, without prominent flaps of skin beside the nostrils. The eyes are large and circular, with nictitating membranes (protective third eyelids). There are 11–13 tooth rows in either half of both jaws. The teeth have broad bases, serrated edges, and narrow cusps; the front 2–4 teeth on each side are erect and the others increasingly oblique. The five pairs of gill slits are moderately long, with the third gill slit over the origin of the pectoral fins. The first dorsal fin is high and falcate (sickle-shaped). There is a low interdorsal ridge running behind it to the second dorsal fin, which is relatively large with a short free rear tip. The origin of the first dorsal fin lies over or slightly forward of the free rear tips of the pectoral fins, and that of the second dorsal fin lies over or slightly forward of the anal fin. The pectoral fins are long and narrow, tapering to a point. The dermal denticles are closely spaced and overlapping, each with five (sometimes seven in large individuals) horizontal low ridges leading to marginal teeth.
In California, Reef Check helps ensure the long-term sustainability and health of the nearshore rocky reefs and kelp forests. Reef Check California volunteers are divers, fishermen, kayakers, surfers, boaters, and a wide range of Californians who take a proactive role in making sure that our nearshore ecosystems are healthy and well managed. We monitor rocky reefs inside and outside of California's marine protected areas (MPAs). We work with marine managers, researchers and the public to provide the scientific data needed to make informed, science-based decisions for the sustainable management and conservation of California's ocean environment. We would love your support, volunteer today!
WWF works to preserve the coral habitats where reef sharks live through the creation and improved management of marine protected areas, elaboration of fisheries management plans, and the introduction of fishing bans to protect vulnerable species including reef sharks. WWF also promoted the understanding that communities can derive more economic value from reef sharks through tourism than through their capture. We support local communities to set up appropriate ecotourism systems and infrastructure to ensure well-managed and sustainable shark tourism operations.
Sandbar shark (C. plumbeus): The sandbar shark has a snout that is shorter than the width of its mouth and a large first dorsal fin originating over the axis of the pectoral fin (the Caribbean reef shark’s first dorsal fin is further from the head than the sandbar shark). Unlike the Caribbean reef shark, the sandbar shark has widely spaced non-overlapping dermal denticles that lack defined teeth on their free edges.
Grey reef sharks feed mainly on bony fishes, with cephalopods such as squid and octopus being the second-most important food group, and crustaceans such as crabs and lobsters making up the remainder. The larger sharks take a greater proportion of cephalopods. These sharks hunt individually or in groups, and have been known to pin schools of fish against the outer walls of coral reefs for feeding. Hunting groups of up to 700 grey reef sharks have been observed at Fakarava atoll in French Polynesia. They excel at capturing fish swimming in the open, and they complement hunting whitetip reef sharks, which are more adept at capturing fish inside caves and crevices. Their sense of smell is extremely acute, being capable of detecting one part tuna extract in 10 billion parts of sea water. In the presence of a large quantity of food, grey reef sharks may be roused into a feeding frenzy; in one documented frenzy caused by an underwater explosion that killed several snappers, one of the sharks involved was attacked and consumed by the others.
Although still abundant at Cocos Island and other relatively pristine sites, grey reef sharks are susceptible to localized depletion due to their slow reproductive rate, specific habitat requirements, and tendency to stay within a certain area. The IUCN has assessed the grey reef shark as Near Threatened; this shark is taken by multispecies fisheries in many parts of its range and used for various products such as shark fin soup and fishmeal. Another threat is the continuing degradation of coral reefs from human development. There is evidence of substantial declines in some populations. Anderson et al. (1998) reported, in the Chagos Archipelago, grey reef shark numbers in 1996 had fallen to 14% of 1970s levels. Robbins et al. (2006) found grey reef shark populations in Great Barrier Reef fishing zones had declined by 97% compared to no-entry zones (boats are not allowed). In addition, no-take zones (boats are allowed but fishing is prohibited) had the same levels of depletion as fishing zones, illustrating the severe effect of poaching. Projections suggested the shark population would fall to 0.1% of pre-exploitation levels within 20 years without additional conservation measures. One possible avenue for conservation is ecotourism, as grey reef sharks are suitable for shark-watching ventures, and profitable diving sites now enjoy protection in many countries, such as the Maldives.
A heavy-bodied shark with a "typical" streamlined shape, the Caribbean reef shark is difficult to distinguish from other large requiem shark species. It usually measures 2–2.5 m (6.6–8.2 ft) long; the maximum recorded length is 3 m (9.8 ft) and the maximum reported weight is 70 kg (150 lb). The coloration is dark gray or gray-brown above and white or white-yellow below, with an inconspicuous white band on the flanks. The fins are not prominently marked, and the undersides of the paired fins, the anal fin, and the lower lobe of the caudal fin are dusky.
The grey reef shark is native to the Indian and Pacific Oceans. In the Indian Ocean, it occurs from South Africa to India, including Madagascar and nearby islands, the Red Sea, and the Maldives. In the Pacific Ocean, it is found from southern China to northern Australia and New Zealand, including the Gulf of Thailand, the Philippines, and Indonesia. This species has also been reported from numerous Pacific islands, including American Samoa, the Chagos Archipelago, Easter Island, Christmas Island, the Cook Islands, the Marquesas Islands, the Tuamotu Archipelago, Guam, Kiribati, the Marshall Islands, Micronesia, Nauru, New Caledonia, the Marianas Islands, Palau, the Pitcairn Islands, Samoa, the Solomon Islands, Tuvalu, the Hawaiian Islands and Vanuatu.
Blacktip reef sharks are fast, pursuit predators that prefer reef fishes, but also feeds on stingrays, crabs, mantis shrimps and other crustaceans, cephalopods, and other mollusks. In the Maldives, this species has been documented feeding cooperatively on small schooling fishes, herding them against the shore and feeding en masse. Feeds heavily on sea snakes in northern Australia. A large individual (1.6 m) was observed attacking a green sea turtle, Chelonia mydas, in North Male’ Atoll, Maldives.
^ Garla, R.C.; Chapman, D.D.; Shivji, M.S.; Wetherbee, B.M.; Amorim, A.F. (2006). "Habitat of juvenile Caribbean reef sharks, Carcharhinus perezi, at two oceanic insular marine protected areas in the southwestern Atlantic Ocean: Fernando de Noronha Archipelago and Atol das Rocas, Brazil". Fisheries Research. 81 (2–3): 236–241. doi:10.1016/j.fishres.2006.07.003.
Cyanobacteria do not have skeletons and individuals are microscopic. Cyanobacteria can encourage the precipitation or accumulation of calcium carbonate to produce distinct sediment bodies in composition that have relief on the seafloor. Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms, but they still exist today (stromatolites are microbial mounds with a laminated internal structure). Bryozoans and crinoids, common contributors to marine sediments during the Mississippian (for example), produced a very different kind of mound. Bryozoans are small and the skeletons of crinoids disintegrate. However, bryozoan and crinoid meadows can persist over time and produce compositionally distinct bodies of sediment with depositional relief.