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Coral Reefs Need Our Help!

One of the most biodiverse ecosystems in the world, coral reefs are in serious peril. Coral reefs take up about 1% of the ocean floor but are home to 25% of all ocean species including more than 4,000 species of fish.

What is a coral reef?

Coral reefs are colonies of individual animals called polyps. The polyps have tentacles to feed on plankton at night and they play host zooxanthellae—symbiotic algae that live within the coral’s tissues and gives them color. The algae need carbon dioxide and waste products from the coral for photosynthesis. In turn, through photosynthesis the algae nourish the coral with oxygen and organic compounds. The coral uses these compounds to synthesize calcium carbonate (limestone) with which it constructs its skeleton.  This skeleton contains bands, like tree rings, that record environmental changes in temperature, water chemistry and water clarity.

Why should we care about coral reefs?

Coral reefs are also known as the speed bumps of the ocean. These structures act as a natural barrier, helping to slow down and shrink waves hurtling toward the shoreline and thereby protecting coastlines and the 200 million people living along the coasts from hurricanes.

We receive many other benefits from coral reefs. Stationary animals, coral are constantly evolving chemical defenses as protection from predators.  Scientists are developing new medicines from the coral-produced compounds to help treat cancer, arthritis, bacterial infections, Alzheimer’s disease, heart disease, viruses and many others.

Coral reefs also provide us with food and construction materials. They also contribute heavily to the economy via tourism.

Why are coral reefs endangered?

Believe it or not coral reefs can get stressed out! There are a variety of different factors that contribute to the stress of coral reefs. For example, rising temperatures globally causes coral bleaching. Also, additional carbon dioxide oceans absorb every day contributes to increased acidification which reduces the water’s ability to carry the calcium carbonate that corals need to build skeletons.

Additionally, overfishing is changing the coral reefs ecosystem with anchors and nets destroying the natural habitat.  And when sediment and other pollutants settle on coral reefs it can speed the growth of damaging algae and lower overall water quality. With lower water quality the sunlight may not be strong enough to reach the zooxanthellae to go into photosynthesis.

How can we help?

Scientist are working to find some solutions, but all of us can join the effort to help coral reefs by reducing our carbon footprints. Try recycling or using more reusable products. Join the skip-the-straw movement reducing single-use plastic waste. Only eat fish sourced sustainably. Or, donate to organizations and support companies committed to cleaning up our oceans.


Baby Shark! Shark Reproduction Continued

Shark reproduction is pretty strange to begin with. But for sand tiger sharks, it is even weirder.

Sand tigers are the largest sharks you’ll see at the Greater Cleveland Aquarium. Their mating behavior is pretty ferocious.

We don’t know what prompts female sand tigers to be ready to mate. They must be mature enough in age—somewhere in their teens—and the females must also be ready to mate, which happens about every two years. We are not sure how (or if) females select mates. Scientists are still studying this!

When sand tigers mate, the much smaller males must bite and forcibly flip over the much larger and thicker-skinned females.

But before the sharks get to that point, there is a period of courtship behavior—sort of like shark dating.

Males might follow a female, swimming behind and slightly below her in the water. Then he might escalate to tailing, during which he very closely follows her. The next step is nosing. The male will follow the female very closely, with his nose, or rostrum, very close to her cloaca. (The cloaca is a shark’s reproductive canal and its way to poop. Both males and females have a cloaca.) Then the male will nudge the female, then bite her fins or body—all the while hoping to bite her and flip her over to mate.

If the male is successful, he will bite the female on the pectoral (arm-position) fin and try to flip her over. She then will become catatonic and will allow mating.

But, if the female is not interested at any point, she may bite the male right back! And remember, the females are much larger and thicker-skinned than the males. Female sand tigers can also circle close to the bottom to prevent males from approaching her to bite.

If the female is interested in mating, she may point her nose downward and allow the male a better chance to bite her.

Then the male sand tiger can hold the female’s cloaca with his clasper. Claspers are two finger-like appendages that all male sharks, skates, and rays have behind their pelvic fins. The male can then deliver his sperm, cloaca to cloaca before swimming away.

The female can store the male’s sperm for an unknown amount of time—perhaps a year, perhaps more—until it seems a good time to carry pups.

Now things get even stranger.

The female sand tiger has two uteruses. So sand tigers can carry two totally separate pregnancies.

Since sand tigers are ovoviviparous, they lay eggs internally and then give live birth. But for sand tigers, life starts under difficult circumstances. Around 20 eggs may be fertilized in each uterus. Then the eggs develop into shark embryos. The embryos grow bigger and consume all the nutrition in their individual eggs.

Then the biggest, strongest sand tiger pup in each uterus eats all of its siblings. Intrauterine cannibalism! That is what scientists call it.

The surviving sand tiger pup eats whatever new eggs keep arriving in the uterus until it is ready to be born.

After eight or nine months’ gestation, the pup is born. It will be more than three feet long and totally independent immediately.

Scientists are still learning about sand tiger shark reproduction. At the Greater Cleveland Aquarium we have seen mating behavior, but no pups yet.

– Nora Morrison

Baby Shark! Shark Reproduction

In the Shark Gallery seatube, we often hear guests singing “Baby Shark” and sometimes we are asked how baby sharks are born. The answer to that is really fascinating.

There are around 500 species of sharks that we know of, and sharks are extremely varied in their size, body shape and how they reproduce.

All baby sharks begin when a male shark and a female shark mate. How sharks find each other, how they select mates and why they decide to mate is still something scientists are investigating.  The male normally bites the female to hold onto her and flip her over, and then uses his fingerlike appendage, called clasper, to deliver sperm.  Since female sharks are generally bigger than male sharks, this can be difficult for males.

The female shark can store the male’s sperm until the time is right to fertilize the eggs–sometimes even waiting for years! Then things get even stranger.

Baby sharks, which are known as pups, can be born in three quite different ways.

First, some sharks lay eggs. We call this oviparous. The “mommy shark” lays an egg case in a good spot and swims away. The egg case, which is sometimes called a mermaid’s purse,” can be perfectly camouflaged to blend in with the sea floor or algae. The egg includes all of the nutrition the pup will need to grow from a fertilized embryo to a fully functioning shark pup. When the pup is ready, it emerges from the egg case and is totally independent.

Second, some sharks grow from eggs–but inside the mother shark’s body. This is called ovoviviparous. In this type of reproduction, there is no placenta to link the “mommy shark” and the “baby shark.” The shark pup gets all of its nutrition from its own egg yolk, other egg yolks, or (yikes!) from eating its fellow fertilized eggs or other pups. Ovoviviparous sharks give live birth to a fully independent pup. This is how sand tiger sharks, like the ones you can see at the Greater Cleveland Aquarium, reproduce.

And third, some sharks do have a placenta and directly support the shark embryo until it is ready to be born as a pup. This is called viviparous, and is also how humans are born. When the shark pup has matured enough, it is born and swims away. This is how sandbar sharks, which you can also see at the Aquarium, have pups.

All sharks are born ready to fend for themselves! As soon as they’re born, shark pups are ready to swim, hunt and grow.

-Nora Morrison

Gender Reveal: Fish

“Is that fish a girl or a boy?” is a common question we get asked at the Aquarium.  With some species it is a very easy question to address but with others it can be a bit more complicated.  (Sometimes the answer can even be both!)

If a species is sexually dimorphic, males and females will look different from each other.  Sometimes this is just a subtle variation in color or shape but it can also mean the two sexes look radically different from one another. A good example of this is a species of angler fish. The females of this species can grow to over a foot long, while males only grow to about half an inch!

Some species of fish show no sexual dimorphism and it can be impossible to tell the difference between males and females without looking inside the animal’s body.  For some species at the Aquarium we can make an educated guess based on mating behaviors, but for others we just don’t know. The green moray eels in the Shark Gallery are one example of a fish that has no sexual dimorphic traits. Both sexes look identical.

Adding another layer of complication is the fact that some fish have the ability to switch sexes throughout their lifetime while others are both male and female at the same time. This is known as hermaphroditism, and there are many different forms. There’s simultaneous hermaphroditism, seen in species of hamlets, where the animal has both male and female reproductive organs and can play either role in mating. A more common type is sequential hermaphroditism, where an animal changes from one sex to the other at some point in its life.  This can be further broken down into more categories: changing from male to female (protandry), female to male (protogyny), male to hermaphrodite (protandrous hermaphroditism) or female to hermaphrodite (protandrous hermaphroditism).  This phenomena is not uncommon and you may be surprised at how many fish you know that fall under one of these categories.

One of the most recognizable fish at the Aquarium is the clownfish.  What some people don’t know is that clownfish are actually sequential hermaphrodites—protandry to be exact. When it comes to clownfish hierarchy, the female is dominant.  She is the largest fish in the group and the next largest is her male mate. The remaining fish in the group are smaller, undeveloped and unable to breed. If the female dies, the largest male then grows and becomes female and the next fish in line matures to assume the role of breeding male.

Groupers, angelfish, gobies, damselfish and wrasses (my favorite being the rooster hogfish) all fall under the protogynous category.  This means that these species start out as females and can quickly switch and become males if the dominate male leaves.  This type of hermaphroditism is more common and benefits the fish by allowing them to produce the maximum number of offspring.  It is a size-based reproductive strategy with large, strong males protecting the nesting sites of many smaller females.  For these species it is beneficial for females to produce many offspring while small and then become males when they themselves are bigger.  It is also beneficial because it’s a big ocean out there and sometimes difficult to find another member of your species let alone one of the correct sex. The ability to switch sexes means these fish have more opportunities to find a mate.

Hermaphroditism has evolved independently in fish many times and has proven to be a successful reproductive strategy throughout the animal kingdom.


Rooster hogfish are both sequential hermaphrodites and sexually dimorphic.  Can you spot the differences between the female (top) and the male (bottom)?

– Kelsey Scheutzow, Greater Cleveland Aquarium Diver

Scuba Cylinders

Scuba equipment is absolutely critical to keeping divers protected and alive. Today, I want to talk about the one piece of gear that we divers need and is often overlooked—the scuba cylinder. Scuba cylinders supply air, enabling us to explore the underwater world that we have come to love. They come in many different shapes and sizes to serve different needs.

Back when the sport of scuba diving started, many innovative divers would actually take, used fire extinguishers and convert them for diving purposes. Today, we know this is not the best option, but just 40 or 50 years ago there was not much in the way of “dive shops” to go to. In fact back in those days a person could just walk into a local department store and buy most of what he or she needed to dive. It wasn’t until the creation of the first dive training and certification agencies that the sport started to become a little more like what you may recognize today.

Modern scuba cylinders come in two main materials: steel and aluminum. Each of those has their place within the industry. Steel is really the preferred choice of technical divers that go into the darkest reaches of the underwater world. It is more durable, has a better weight balance and can be more easily filled to higher pressures–all the way up to 5000 PSI (pounds per square inch).

Aluminum on the other hand is lighter and cheaper, so for the recreational diver or for the dive operation that needs a large supply of them, this becomes the better choice. Aluminum is not as forgiving when it comes to its durability and cannot be filled to as high a pressure. Aluminum cylinders can be bought in almost any color your heart desires. While, steel are usually galvanized dipped and look just like your neighbor’s chain link fence…lol.

Cylinder capacity is dictated by several factors. First, divers have to consider just how long you intend to stay underwater and the depth, since the deeper you are the more air you will use. Your breathing rate is the last piece of information to consider. Cylinder capacity is measured in cubic feet, and they can range from 3 cubic feet to more than 120 cubic feet. An average recreational aluminum scuba cylinder has a capacity of 80 cubic feet and generally weighs about 35 pounds and more than 42 pounds when full.

What do we put in scuba cylinders? That’s actually a bit of a trick question. Many people think that cylinders are full of oxygen but that is relatively unusual, most cylinders have air. What is air? Air is 78% nitrogen, 21% oxygen and 1% trace elements. It is very important for a diver to know what is in his or her scuba cylinder because diving with a gas mixture different from air can have consequences. Diving pure oxygen at depth can be a fatal mistake! One alternative gas some divers use is nitrox, which is similar to air but with less nitrogen and more oxygen. Using nitrox in our cylinders allows diver to stay at depth for longer and we divers love that.

So next time you are thinking “awwww . . . it’s just a cylinder,” you may want to ponder just a bit longer. Cylinder purchases and fills are important and if you are buying the lime green cylinder because it’s cool, there may be more to think about.

– Matthew Ballish

Lake Erie: Under the Waves

Written by: Halle Minshall & Ray Danner


There’s more to Lake Erie than meets the eye. We talked to one of the Greater Cleveland Aquarium’s divers about his experiences exploring this Great Lake’s hidden depths while surveying historical shipwrecks.

Lake Erie has a long history of shipping traffic and ideal water conditions for preservation. Still, you might be surprised to know that there are an estimated 1,400 shipwrecks in Lake Erie alone. With an average depth of just 62 feet and a maximum depth of 210 feet, the wrecks of schooners, barges, tugs and sidewheel steamers are mostly accessible to SCUBA divers.

How did you get involved in Lake Erie shipwreck diving?

Ray: I am always looking for interesting dive opportunities. I began volunteering with the Maritime Archaeological Survey Team (MAST), a nonprofit group founded in 2000 and dedicated to documentation, study and education pertaining to the underwater resources in the Great Lakes. MAST trains divers of any skill and experience level in the finer points of underwater surveys so that they can join the field teams in Lake Erie. We use a lot of the same skills to survey a shipwreck as we do diving at the Aquarium.

How many shipwrecks have been surveyed?

Ray: So far ONLY five have been surveyed and registered as official archaeological sites with the State of Ohio, meaning there are lots of unrealized survey opportunities. The freshwater of Lake Erie aids in the preservation of these shipwrecks so there are a good number yet to be located and identified.


What do you do when you survey the wrecks?

Ray: We lay a tape measure as a baseline running the length of the wreck. From there, we use a method called trilateration to nail down the distances from one object to another and determine the relative position and size of all items on the wreck. It can be challenging to do underwater measurements in three dimensional space, especially in cold water with low visibility. Learning underwater communication techniques and task-loading strategies is very important for all of the divers. Each dive team is assigned a small section of the wreck to survey and it can take several dives to cover even a 5-foot section of a shipwreck. After each dive all of the diver teams come together to input there new data onto a working map and sort out what data points are of priority for the subsequent dives. Through this tedious process an image is slowly formed of the bits and pieces of shipwreck lying on the lake bottom.

Two divers measuring the hatch cover of the Schooner the Dundee in Laker Erie. The diver on the left is recording the distance from the baseline to the interior edge of the hatch cover. The diver on the right is holding position on the baseline as a reference point. (Photo Credit: Jack Papes)

That sounds really interesting can I get involved?

Ray: Yes, MAST hosts a workshop every spring at the Great Lakes Museum, which trains local divers and non-divers alike. During the classroom training workshops, you’ll practice using mock surveys and the trilateration method for measuring and mapping a wreck. A final lesson is held in the waters of the White Star Quarry where divers put their new skills to the test.

Why is this important?

Ray: Lake Erie is closely tied to the lives and livelihoods of many Ohioans and it is a great resource. I think it is extremely interesting to take a look at how we used this resource in our past with the shipping and transporting of goods along the lakes shores. In learning about these shipwrecks we also learn how much we need to protect the lake they rest within.

PADI International Women’s Dive Day

As a dive instructor and the Greater Cleveland Aquarium’s Dive Safety Coordinator, PADI International Women’s Dive Day is a special time to share what I love. From my perspective, SCUBA diving has great value. It is a lifelong skill and a key to a hidden world. Diving also helps to build confidence, foster new relationships and cultivate a sense of independence.

What else is out there in the two-thirds of our planet covered by water? The sea provides a limitless number of new experiences. As a dive professional who does hundreds of dives a year, you may think I have become immune to the wonder and amazement diving provides, but I am constantly marveling over new sights and new interactions. For example, I was diving with sharks when a large, fully grown female tiger shark swam over to me, looking into my eyes with her massive ones before nudging me out of her way. Interactions like these, while being REALLY COOL, also cause a change in perspective. This mighty creature wasn’t interested in confrontation. We were able to coexist peacefully in her world. Intuitively, I knew she was not seeking to harm me but now I have lived it. I have had experiences many only dream of and from them I have learned to think for myself to form my own opinions. I now relish the times where my comfort level is exceeded by a large shark’s close encounter.

Diving is all about personal growth and development. In challenging you to do things you find uncomfortable and allowing you to struggle until you learn to put all of the pieces together, diving helps you build confidence. When teaching someone how to dive, there inevitably are skills that give each student difficulty. Coaching them through and past these difficulties is rewarding for both me and them. For example, the fundamental SCUBA skill of clearing your mask is not as simple as it might seem for new students. While it’s not a technically tricky skill, it requires mental strength to overcome the discomfort of having water on your face. This breakdown—when our brain tricks our body into panicking—must be controlled from within. This self-governing, self-control aspect of SCUBA diving sets a foundation for learning how to overcome mental obstacles in everyday life.

There is no strict phenotype on who can and cannot become a great diver. Historically, SCUBA diving has been a male-dominated industry. This needs to change. Women can become fantastic divers. Children (ages 10 and older) can become fantastic divers. You don’t have to be an amazing swimmer to become a fantastic diver. You don’t have to be wealthy to become a fantastic diver. You don’t even have to live near an ocean to become a fantastic diver. For SCUBA diving to continue to grow it must become more open and inclusive. For this reason, the Aquarium’s dive team wants to share our experiences, answer your questions, and encourage your participation in learning about SCUBA diving on July 21. Come join us!

– Halle Minshall

International Women’s Dive Day

Let’s take a look at our women divers in action!

Our diver suiting up for a swim with the sharks.

Getting the diving gear ready to go!

Heading into the tank for one of our four daily dives for the day!

Twice a day, our divers will do a maintenance dive as well as two full face mask dives.

Our divers do an outstanding job cleaning our exhibits and keeping them looking squeaky clean for our guests.

Dive shows are a great way to learn more about our divers and what their job entails. Guests are able to interact with the divers and get to experience some of their daily tasks.

Our divers sanitize after every dive to make sure they don’t contaminate the water when going from fresh to salt water or vice versa. The divers also clean the corridor exhibits, in addition to the sea tube pictured above.

5 Things More Dangerous Than Sharks When You’re 47 Meters Down: A Diver’s Perspective

We recently saw 47 Meters Down. The new shark thriller starring Mandy Moore is designed to get your heart pumping, for sure. The fact that the silver screen has a habit of making us unnecessarily scared of sharks aside, the things that made us fear for the survival of the novice diving duo at the center of this horror flick had nothing to do with the animals that surrounded their dive cage.

1. Inexperienced divers going to significantly deeper depths than those for which they are trained can be a recipe for disaster even without a shark in the mix. Due to the effects of pressure, the volume of air a diver consumes in a given time typically increases with their depth—go deeper breath more. Other factors can also cause a diver’s air consumption rate to increase including exertion while swimming, speaking and cold water, just to name a few. Stress is also a major contributor to air consumption so two inexperienced divers being harassed by sharks like those portrayed in the film would result in a drastic increase in air consumption. At 47 meters even an experienced diver with a fantastic air consumption rate would quickly drain their scuba cylinder, probably in less than 20 minutes. An inexperienced diver swimming, talking and being harassed by sharks MIGHT make it five minutes at that depth.

2. The full face mask system used in the movie would be extremely dangerous for these inexperienced divers. Humans convert 5% of the oxygen we breathe into carbon dioxide which is then exhaled. The masks in the film do not have separate chambers for new and exhaled gas which would result in the diver breathing in carbon dioxide. The effects of breathing carbon dioxide on the surface are rapid breathing, rapid heart rate, fatigue, nausea and headache. Other, more severe effects can develop if the carbon dioxide exposure is not reversed. Underwater all of these effects would be more even sudden and life threatening.

3. According to the US Navy dive decompression tables a diver may spend up to five minutes at 160’ (47 meters) without needing to decompress during their ascent. The longer a diver stays underwater the greater their exposure to “the bends” becomes. The bends is a layman’s term for decompression sickness, which is caused by the accumulation of nitrogen breathed under pressure. This does not pose a problem until a diver begins to surface and nitrogen bubbles form in the bloodstream. The bubbles can cause the bends. The amount of time it would take a diver to safely surface increases as the amount of time s/he spends at that depth increases. It would actually take more than four hours to safely surface from a 60-minute dive at a depth of 160 feet.

4. Another risk often faced by divers at depths exceeding 80 feet is nitrogen narcosis. Commonly referred to as “rapture of the deep,” nitrogen narcosis makes a diver feel and act like they are inebriated, lacking inhibitions and generally numb to any concerns. Luckily nitrogen narcosis has not been known to leave any lasting effect so long as divers recognize it and ascend enough to limit its effects. It is easy to imagine the havoc nitrogen narcosis could play on a diver who needs to be very mindful of their surroundings and sharks!

5. Even in warm water hypothermia is a risk. Not wearing a proper fitting full coverage wetsuit can set up a diver for problems. Water can pull heat away from a diver’s body 25 times faster than air. Hypothermia’s effects on the body start with shivering which can become violent and lead to loss of coordination and function. In bikini-style suits the likelihood divers at 47 meters down would experience more than just a mild hypothermia is high.
Given the depth, equipment, clothing and stress factors, it would be a challenge for the most experienced divers to survive under these circumstances.

— Halle Minshall, Dive Safety Coordinator, & Erik Helgesen, Exhibit Diver