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.
Typically a solitary animal, juvenile blacktip reef sharks will commonly conjugate in shallow regions during high tide. Vulnerable to larger predators, they will reside in shallower areas until larger in size. Blacktip reef sharks tend to be more active during dawn and dusk, but like most sharks they are opportunistic feeders. Their diet consists of crustaceans, squid, octopus, and bony fish.
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Another danger posed to humans by the Caribbean reef shark involves the accumulation of toxins in the flesh of the shark. Since sharks are apex marine predators, they may contain toxic levels of mercury and other heavy metals due to bioaccumulation (increasing concentrations at higher levels in the food web). It was found that methylmercury levels (MeHg) in sharks off the coast of Florida were higher than the FDA guidelines.

Based on morphological similarities, Jack Garrick in 1982 grouped this species with the bignose shark (C. altimus) and the sandbar shark (C. plumbeus), while Leonard Compagno in 1988 placed it as the sister species of the grey reef shark (C. amblyrhynchos). A phylogenetic analysis based on allozyme data, published by Gavin Naylor in 1992, indicated that the Caribbean reef shark is the sister taxon to a clade formed by the Galapagos shark (C. galapagensis), dusky shark (C. obscurus), oceanic whitetip shark (C. longimanus), and the blue shark (Prionace glauca). However, more work is required to fully resolve the interrelationships within Carcharhinus.[3]
A profitable ecotourism industry has arisen around this species involving organized "shark feeds", in which groups of reef sharks are attracted to divers using bait. Some US$6,000,000 is spent annually on shark viewing in the Bahamas, where at some sites a single living Caribbean reef shark has a value between US$13,000 and US$40,000 (compared to a one-time value of US$50–60 for a dead shark).[14] This practice has drawn controversy, as opponents argue that the sharks may learn to associate humans with food, increasing the chances of a shark attack, and that the removal of reef fishes for bait may damage the local ecosystem. Conversely, proponents maintain that shark feeds contribute to conservation by incentivizing the protection of sharks and educating people about them. Thus far, there has been little evidence that shark feeds have increased the risk of attack in the surrounding area.[8][15] Shark feeding has been outlawed off the coast of Florida, but continues at other locations in the Caribbean.[4]
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.[4] 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.[13] 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.[4] Photographing the display should not be attempted, as the flash from a camera is known to have incited at least one attack.[3] 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.[14] As of 2008, the International Shark Attack File listed seven unprovoked and six provoked attacks (none of them fatal) attributable to this species.[29]
Corals, including some major extinct groups Rugosa and Tabulata, have been important reef builders through much of the Phanerozoic since the Ordovician Period. However, other organism groups, such as calcifying algae, especially members of the red algae Rhodophyta, and molluscs (especially the rudist bivalves during the Cretaceous Period) have created massive structures at various times. During the Cambrian Period, the conical or tubular skeletons of Archaeocyatha, an extinct group of uncertain affinities (possibly sponges), built reefs. Other groups, such as the Bryozoa have been important interstitial organisms, living between the framework builders. The corals which build reefs today, the Scleractinia, arose after the Permian–Triassic extinction event that wiped out the earlier rugose corals (as well as many other groups), and became increasingly important reef builders throughout the Mesozoic Era. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of the scleractinian corals, whose skeletons are aragonite. However, there are some unusual examples of well-preserved aragonitic rugose corals in the late Permian. In addition, calcite has been reported in the initial post-larval calcification in a few scleractinian corals. Nevertheless, scleractinian corals (which arose in the middle Triassic) may have arisen from a non-calcifying ancestor independent of the rugosan corals (which disappeared in the late Permian).