Smooth Skinned Sharks: Ocean Acidification Proofs Harmful to Top Predator

Jacqueline Dziergwa, Sarika Singh, Christopher R. Bridges, Sven E. Kerwath, Joachim Enax, Lutz Auerswald. Acid-base adjustments and first evidence of denticle corrosion caused by ocean acidification conditions in a demersal shark speciesScientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-019-54795-7

As we careen toward the end of our second month of quarantine, there is only one thing on everyone’s mind…

SHARKS.

Okay, so maybe it’s just me who’s worrying about sharks, but it’s with good reason. While media corporations focus on coverage of the COVID-19 pandemic, the public is missing out on other pressing issues our world is facing. The most important of these matters: sharks are becoming smooth.

But in all seriousness, scientists recently discovered that marine life faces yet another threat from rising CO2 emissions.  A new study conducted by German research teams suggests projected rates of ocean acidity will degrade shark skin on a global scale in the future.

The Burning Issue

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Graphic depicting the chemical reaction that occurs when carbon dioxide is absorbed by seawater, the resulting increase in acidity and its effect on shelled marine life. Source: Wikipedia Commons

Ocean acidification is the result of increased carbon emissions caused by burning fossil fuels. The ocean is a major CO2 sink, meaning it absorbs a large percentage of COreleased into the atmosphere. This is beneficial in that less of the planet-warming greenhouse gas remains present in the atmosphere; however, it has significant negative side effects on marine life.

 

Acidity Basics 

When the ocean absorbs carbon dioxide from the Earth’s atmosphere a series of chemical reactions occur. The result of these reactions: hydrogen ions. The presence or lack of hydrogen ions determines whether a solution is acidic or basic.

The pH scale measures the acidity or alkalinity of a solution. The ocean currently has a pH level of 8.1. This number is projected to drop to 7.3 by the year 2300. On the surface, this might seem like an insignificant change, but that is not the case. The pH scale is logarithmic, not linear. A drop of 0.1 is equivalent to a 30% increase in acidity. A drop of 0.2 is equivalent to a 150% increase in acidity.

A drop of 0.8 seems a little more significant now, doesn’t it?

Studying Sharks

Scientists have studied the impact of ocean acidification on bottom-dwelling marine life like corals, shellfish and mollusks  for years. Recently researchers at Heinrich-Heine University Duesseldorf and the University of Duisburg entered uncharted waters in efforts to discover how ocean acidification affects an apex marine predator.

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Puffadder Shyshark camouflaged by coral at Partridge Point.              Source: Wikipedia Commons 

Their experiment was straightforward. The team exposed an experimental group of puffadder shysharks Haploblepharus edwardsii to acidic seawater with pH of 7.3 and a control group to regular seawater. After a period of several weeks the sharks were examined by the team. Researchers found the experimental group on average suffered significantly more damage to the tooth-like scales known as dermal denticles that cover their skin than the control group.

 

The Deal with Denticles 

Sharks possess rough sandpaper-like skin. The coarse texture is caused by specialized scales called denticles. Denticles closely resemble shark teeth in their shape and composition. The tightly packed, triangular scales allow sharks to move effortlessly through the water by reducing drag.

Scientists found significant damage to a shark’s denticles can have lasting effects on the animal by limiting their ability to catch and consume prey. Corrosion of the scales makes a shark’s skin more smooth limiting its ability to swim. In addition to the damage it deals to denticles, increased levels of acidity harms shark teeth by wearing down the outer enamel.

Why You Should Care     

Shark movies are a million-dollar industry. From Jaws to Sharknado, these films educate us and put money into the hands of those who need it most, the Hollywood elite. Movies about smooth-skinned sharks would never become blockbuster hits. I mean a smooth shark isn’t even scary. It’s basically just a seal with sharp teeth.

Okay, but actually … Ocean acidification is bad news. Plain and simple. Rising CO2 levels prove especially harmful to shellfish and mollusks because the acidic water eats away at their calcium carbonate shells. Damaging these sensitive species can have a cataclysmic effect on marine ecosystems. If shellfish and mollusks disappear from the ocean floor, their loss could create a chain reaction as many marine organisms rely on these species  for food.

At the top of the food web is humans, who would also feel the loss of these bottom dwellers. Roughly 20% of the world’s population rely on seafood as their main source of protein and threatening this source of food could be particularly detrimental to impoverished nations.

Silver Linings 

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CLAMS… A Fictional Movie. Source: Laine Farber

Mollusks like oysters and mussels tend to get overlooked by the public because they lack personality. This is not the case with sharks. Love them or hate them, people have strong feelings about these fearsome predators. There has never been a beloved novel about a massive blood-thirsty mussel or a series of dreadful science fiction movies about an odd oyster-based weather event, and there probably never will be. Despite their crucial role in the ecosystem and economic value, bivalves don’t pop on the silver screen. Luckily sharks do.

Hopefully this study will inspire readers to make behavioral changes in efforts to reduce their carbon footprint, because while most readers likely are not smitten with bivalves, they might just have a special place in their hearts for these cantankerous cartilaginous fish.

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Laine Farber

Laine Farber

I am a recent graduate of Louisiana State University. With a background in journalism and a love of science, I have a passion for making stories easy to understand and enjoyable to read. I currently work as the Move With the River Gallery Manager at the Louisiana Children's Museum where I teach our youngest generation all about the Mississippi River. After work I head home to work some more! In my spare time, I produce and host educational science podcast for young audiences and curious adults called Nature Nerds! It's a zany, fact-filled show sure to entertain. If you grew up watching "The Magic School Bus" or "Zoboomafo", then Nature Nerds is a show for you! When I am not teaching kids, editing or recording silly robot voices for the podcast, you can find me painting or feeding dry corn to ducks. For more information follow me on Instagram @lainefarber and @nature.nerds.with.laine

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