Sharks Are Important To Our Survival
The reality is, like them or not, sharks are crucial to the health of our planet. For millions of years, sharks have played a vital role in the oceans’ food web, keeping our largest and most important ecosystem healthy. The oceans produce more oxygen than all the rainforests combined, remove almost 1/3 of the atmosphere’s manmade carbon dioxide, and control our planet’s temperature and weather.
Ecosystem Health And Biodiversity
As predators, sharks keep prey populations (seals, fish, etc) in balance by hunting the sick and weak animals and ensuring the fittest of them survive. When apex shark populations decline, it can cause rapid increases in their prey populations, creating a ripple effect throughout the food chain known as a trophic cascade. A study in Belize showed that a spike in grouper population (due to the overfishing of sharks) resulted in a decimation of the parrotfish population and other herbivores, which are important grazers of macroalgae. The resulting overgrowth of macroalgea smothered the coral reefs, which, when healthy, provide shelter for nearly one quarter of all known marine species, generate half the earth’s oxygen and absorb nearly one-third of the carbon dioxide generated from burning fossil fuels.[1] Healthy coral reefs also bolster fisheries and tourism and provide storm protection.
In many cases, just the presence of sharks can help preserve the ecosystem by intimidation. In seagrass meadows where tiger sharks patrol, the turtles are scared away which prevents them from overgrazing the grasses. While seagrass meadows account for less than 0.2% of the of the world’s oceans, they sequester approximately 10% of the carbon buried in ocean sediment.[2] Reduction of these meadows results in stored carbon being released back into the atmosphere, increasing the acidity of the ocean and resulting in less carbon being absorbed from the atmosphere.
Sharks As Carbon Sinks
“Blue carbon” is the concept of carbon being absorbed by the world’s oceans. Carbon is found in all living things and when land animals and plants die or become part of the food web, a significant amount of their carbon is released to the atmosphere. Large sharks are comprised of about 10-15% carbon. When these sharks die, they sink to the bottom of the ocean, where they are consumed by deep sea dwellers and the remains decay to become part of the sediments, thus sequestering the carbon in the deep ocean. When sharks are removed from the ocean for human consumption or other uses, the carbon is no longer sequestered and is released into our atmosphere.
The Danger Of CO2
Carbon Dioxide (CO2) in the atmosphere from burning fossil fuels has increased by 35% in the last 150 years.[3] Fossil fuels like coal and oil contain carbon that plants pulled out of the atmosphere through photosynthesis over the span of many millions of years; we are returning that carbon to the atmosphere in just a few hundred years. While the oceans effectively absorb about a third of this atmospheric CO2, it is not without a cost. CO2 reacts with seawater to form carbonic acid, resulting in the oceans becoming 30% more acidic over the last 150 years.[4] Rising acidity reduces carbonate, a significant component of shell building. As the seas become more acidic, shells could literally dissolve and studies have determined that this acid could erode sharks’ teeth and dermal denticles (skin).[5] The reduced oxygen in the water also makes it increasingly difficult for fish to breathe.[6] The results could be devastating for marine food webs- threatening commercial fish stocks, collapsing fishing industries and creating food insecurities for millions of people.
Sharks have a vital role in marine food webs but the interconnectedness of these webs mean they not only exert influence but are affected by changes as well. Shark conservation is not just protecting sharks directly; it is also reducing our carbon footprint, reducing plastic and other pollution, and making sustainable seafood choices.
[1] Jamail, D. (2021, March 11). Coral reefs could all die off by 2050. Retrieved March 22, 2021, from https://www.ecowatch.com/coral-reef-bleaching-2408656490-2408656490.html#:~:text=While%20coral%20reefs%20only%20cover,generated%20from%20burning%20fossil%20fuels.
[2] What is blue carbon? (2019). Retrieved March 07, 2021, from https://www.thebluecarboninitiative.org/about-blue-carbon#:~:text=Although%20seagrasses%20account%20for%20less,much%20carbon%20than%20terrestrial%20forests*.
[3] Steig, E. (2004, December 22). How do we know that recent co2 increases are due to human activities? Retrieved March 22, 2021, from https://www.realclimate.org/index.php/archives/2004/12/how-do-we-know-that-recent-cosub2sub-increases-are-due-to-human-activities-updated/
[4] Speer, L. (2016, December 15). The global problem of ocean acidification. Retrieved March 22, 2021, from https://www.nrdc.org/experts/lisa-speer/global-problem-ocean-acidification
[5] Nuwer, R. (2019, December 19). Ocean acidification could eat away At SHARKS’ teeth and scales. Retrieved March 22, 2021, from https://www.scientificamerican.com/article/ocean-acidification-could-eat-away-at-sharks-teeth-and-scales/
[6] Miller, S. (2016, May 10). Acidification and low Oxygen put fish in double jeopardy. Retrieved March 22, 2021, from https://www.si.edu/newsdesk/releases/acidification-and-low-oxygen-put-fish-double-jeopardy