Written by – La Tisha Parkinson
Sharks are often considered to be the terrifying beasts of the sea, ready to attack without a moment’s notice. As such, the idea that sharks can be beneficial is often difficult to grasp. However, in the past four hundred and thirty-six years, there have only been seventy-six confirmed, unprovoked shark attacks in the Caribbean, that averages to be much less than one attack per year. Therefore, it is fair to say that sharks inhabiting Caribbean waters do not pose a threat to humans. Now, we must ask ourselves, how are sharks beneficial to the Caribbean? In this piece we will examine the important role sharks play in coral reefs in the Caribbean.
Caribbean reef with healthy corals, Bermuda, 2013 © Catlin Seaview Survey
Coral reefs in the Caribbean provide a host of ecosystem services such coastal protection, reef fisheries, and tourism appeal. While coral reefs are the most diverse undersea ecosystems, they are very fragile. Coral reefs can be damaged from the bottom-up, meaning the corals themselves are affected through disturbances such as changes in temperature which is a consequence of climate change, changes in light availability which is a consequence of a change in population dynamics brought about by overfishing, damage caused by storms and hurricanes, and finally, coral death brought about by disease. Many of the bottom-up damages caused to coral reefs are exacerbated by climate change. These bottom-up changes have been named responsible for the decline in coral reefs in the Caribbean, from 50% in the 1970s to less than 20% today. However, top-down disturbances also damage corals reefs. Top-down disturbances occur through the removal of higher level organisms in the coral reef ecosystem’s food web.
Sharks are considered apex predators, as they at the top trophic level of food webs. Sharks therefore have the ability to alter the species composition, and trophic structure of reefs, so much so, that research has shown that coral reefs with a large number of apex predators tend to be more diverse and have higher densities of individual species.
Sharks: The Dark Knights
Sharks keep coral reefs healthy by preying on the old, weak, and sick individuals. In this way they reduce the spread of communicable, and genetic diseases throughout various prey populations. In addition to keeping reefs healthy in this regard, sharks regulate prey population size. In regulating the prey population size, sharks ensure that prey populations do not overgraze in the case of herbivores, and overkill in the case of carnivores, which ensure that reef resources are not depleted to the point where they are not cannot be replenished.
The Ecological Role of Sharks on Coral Reefs (Roff, George et al. 2016)
Additionally, sharks protect the corals themselves by preying on coral-eating fish. Some fish such as the Foureye Butterfly Fish, Filefish, and Triggerfish feed on coral polyps, while others feed directly on corals themselves, such as the Parrotfish, and Surgeonfish. While Parrotfish work to help reefs by eating algae off of the corals, these omnivores also destroy reefs by eating the corals themselves, which is usually done while they are eating the algae on the corals; this is a key reason why their populations need to be regulated. Sharks play a crucial role in maintaining these particular prey populations through direct and indirect control, thereby protecting corals and allowing more time for coral regeneration than time for coral degradation. Imagine then, the role sharks play in maintaining a balance in the entire coral reef ecosystem.
The Fate of Reef-Dwelling and Reef-Associated Sharks in Caribbean Coral Reefs
The reef-dwelling, and reef-associated sharks of the Caribbean include: Bonnethead, Blacknose, Atlantic Sharpnose, Sand Tiger, Blacktip, Tiger, Spinner, Silky, Lemon, Bull, Sandbar, Nurse, Whale, Caribbean Reef, Scalloped Hammerhead, Great Hammerhead, and Smooth Hammerhead.
Shark populations are susceptible to devastation by mild levels of fishing mortality because they have conservative life history traits such as slow growth rates, late sexual maturity, and low fecundity. For decades sharks have been targeted for their liver, skins, meat, and fins; this has been exacerbated by recent trends in juvenile harvesting. Caribbean reef sharks are being overfished to such an extent that of the 17 shark species previously identified, according to the International Union for the Conservation of Nature (IUCN) Red List, on the global scale, two are listed as endangered, four as vulnerable, and eight as near threatened, with the main threat to all being overfishing. Compounding the effects of overfishing on shark populations, humans are increasing the degradation of shark habitats and nurseries. Additionally, overfishing of shark prey is reducing the available food source for sharks.
Research has shown that anthropogenic pressures have led to a decline in sharks in the Greater Caribbean, such that only the Nurse shark has been frequently seen in recent times. The areas where the other sharks are seen in the Greater Caribbean are areas where there is a low human population density, or areas where there are strong fishing regulations or conservation methods in place. This strengthens the suggestion that humans are the reason for a decline in reef sharks in the Greater Caribbean.
Additional evidence for the effects of fishing on shark populations in the great Caribbean can be seen with the presence of the nurse shark. According to research, the Nurse shark has a low rebound potential, which means that even mild levels of fishing would be enough to ravage its population, however, it is the most commonly seen shark in the Greater Caribbean. This suggests that its species is not targeted by fisheries, which is likely because it has the least value for its meat and fins .
At the end of Batman: The Dark Knight, Jim Gordon tells his son, that Batman is
“the hero Gotham deserves, but not the one it needs right now. So we’ll hunt him. Because he can take it. Because he’s not our hero. He’s a silent guardian, a watchful protector. A dark knight.”
Sharks are a lot like Batman, but they’re not Batman, so don’t hunt them, because they cannot take it.
Sharks: The Dark Knights Rise
Batman went into hiding at the end of Batman: The Dark Knight, and at the beginning of Batman: The Dark Knight Rises, we see that criminals had run amok in Gotham and people were calling for Batman to return. It was a long and onerous road that led Batman to return to full strength and protect Gotham once more. This is exactly what we need for our sharks. We have seen the effects on our reefs when our apex predators are removed. The other species, like the criminals in Gotham, will also run amok. We must be willing to take that onerous road to help our dark knights rise again.
Some Caribbean governments have recognised the importance of sharks to our most diverse marine ecosystem, and as such are trying various measures of conservation. One such measure is encouraging locals to eat Lionfish instead of shark in order to allow shark populations to have time to recover, while trying desperately to deplete Lionfish populations as they are wreaking havoc in our reefs. While this is a great approach, it would help if governments put as much effort into educating the public about the importance of sharks as they put into educating the public about the destruction caused by Lionfish. Once the perception of sharks has changed from villains to heroes, then governments can consider investing in shark tourism.
Our Reefs Need Their True Heroes
It is too late to stop the bottom-up devastation incurred to coral reefs through anthropogenic climate change, however, we can reduce the occurrence of top-down devastation of our reefs by protecting our sharks. If we get rid of our heroes, who will protect our coral reef cities? When we invest in protecting our sharks, we are inadvertently investing in maintaining the biodiversity of our coral reefs. Sharks are our keystone species, therefore, they are the reason coral reefs provide the plethora of ecosystem services to humans that they do. Sharks are as vulnerable as the reefs they protect, therefore, we’ve got to do better. Sharks want to protect our reefs, we must let them. Caribbean coral reefs without sharks, are a lot like Gotham without Batman; hopeless.
A coral deadzone in Bonaire, 2013. © Catlin Seaview Survey
La Tisha Parkinson is the Marketing and Communications Officer for the Trinidad and Tobago Chapter of the Caribbean Youth Environment Network. She is currently reading for a B.Sc. in Biology and Environmental Natural Resource Management at the St. Augustine campus of the University of the West Indies.