Coral Reefs Need Our Help!

March 20, 2019

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.

-Crystal

Baby Shark! Shark Reproduction

March 7, 2019

Diving

Written by Greater Cleveland Aquarium

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