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.
Despite sharks being portrayed as notorious aggressive animals, very few incidents have involved blacktip reef sharks, none being fatal. Still the importance of an apex predator is vital to a balanced and healthy ecosystem. Unfortunately, this species is very susceptible to reef gill netting. And sharks all around continue to be threatened by fishing pressure resulting in a decrease in many shark populations.
This species is commonly found in shallow waters on and near coral reefs and occasionally in brackish waters. Juveniles are typically found in extremely shallow water (±15 to 100 cm) inside lagoons, often swimming along the shoreline; adults typically occur on shallow parts of the forereef, often moving over the reef crest and onto the reef flat at flood tide. Individual adults inhabit a relatively small home range of ±2.5 km2 and appear to reside close to their home reef but occasionally cross deepwater channels between adjacent reefs.
Reef sharks play a major role in shaping Caribbean reef communities. As the top predators of the reef and indicator species for marine ecosystems, they help maintain the delicate balance of marine life in reef environments. Reef sharks are highly valued for their meat, leather, liver oil, and fishmeal, which make them prone to overfishing and targeting. Yet, their importance for the tourism industry makes them more valuable alive than dead. In 2011, Honduras declared its waters to be a permanent sanctuary for sharks, making fishing for these species completely forbidden.
Blacktip reef sharks are regularly caught by inshore fisheries and are vulnerable to depletion because of their small litter sizes and long gestation periods. Traumatogenic. May become aggressive to spear fishers and are reported to bite people wading in shallow water. Generally marketed fresh (as fillet), may be dried, salted, smoked or frozen. Fins are valued for shark-fin soup; a market that is decimating shark populations worldwide. They are also sought for their liver as source of oil.
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.
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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.