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While the coral covering the ocean looks

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like an unchanging formation of rocks it

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is actually home to one of the most

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diverse ecosystems on the planet. Climate

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change has led to an alteration of reefs

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that has had a profound effect on the

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ecosystem and led to the rise of another

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organism in its place: sponges. Sponges

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look like the coral that makes up such

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reefs but their growth or replacement of

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coral is changing the biodiversity of

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the ecosystem. In this video we're going

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to talk about the biological

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implications of coral reefs to sponge

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reefs but before we discuss their

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importance we need to define what

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exactly coral reef is and how it differs

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from a sponge reef. Coral is comprised of

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two different types: hard coral, the

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structured coral reefs, and soft coral

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which grows off the hard coral and

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provides support for the organism. These

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two coral types compose the majority of

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the reefs you see when scuba diving or

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watching Blue Planet. Sponges on the

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other hand are simple multicellular

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organisms that mimic coral and act as

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homes for the reef's inhabitants. Sponges

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unlike coral recycle nutrients in the

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water and are much more resilient to

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temperature changes. As our environment

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continues to change coral reefs are

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slowly being replaced by sponge reefs

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This has important biological

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implications for the coral reefs and the

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ocean ecosystem at large, including coral

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bleaching and deteriorating biodiversity

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Healthy coral have a symbiotic

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relationship with a microscopic algae

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that live in their tissues. These algae

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are their primary food source and give

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them their color. But changes in ocean

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temperature are causing algae to leave

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the coral's tissue and the loss of its

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major food source is resulting in

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bleached coral that is more susceptible

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to disease. In their place sponges are

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becoming the new foundation for these

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changing ecosystems. So what are the

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implications of sponge proliferation in

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the place of coral? A study done on the

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Indo-Pacific reef system claims that

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reductions in environmental quality

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may favor sponge dominated reefs but

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that these reefs will likely be low

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diversity systems as they do not promote

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biodiversity in the same way

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coral does. Other evidence suggest sponges

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cause harm to coral themselves. In hopes

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of avoiding predators sponges secrete an

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acidic fluid that often reacts with the

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coral reefs and causes structural issues

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that compromise its overall health. The

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rise of one and fall of another is

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producing negative effects including a

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loss in the parity between the two

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organisms. Ecologist Jasper de Goeij

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says that while corals build the reef

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sponges do in part break down reefs and

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having a balance between those two is

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important. He continues that sponges

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could continue to take over the reef and

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assuming they fail to promote

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biodiversity like coral do could lead to

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a die-off in species. Other evidence

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however suggests that sponge

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proliferation has beneficial effects on

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the ecosystem. Firstly sponges create

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nutrients for organisms by filtering

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bacteria into food that coral could not

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otherwise produce. Marine biologists at

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the University of Amsterdam found that

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sponges absorb carbon and nitrogen from

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the water and converted it into

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filtering cells that line a sponge's

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interior walls. The sponges quickly shed

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those linings which were then eaten by

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larger organisms. So is the rise of

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sponges amid falling coral numbers

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definitively good for the ecosystem? Well

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it's not that simple

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The question of good or bad is dependent

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on what is being measured. From some

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perspective sponge proliferation is good

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for organisms and vulnerable coral alike

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Their ability to act as resilient

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habitats for organisms while creating

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food sources is inherently valuable as

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coral reefs deteriorate further but the

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very resilience of sponges also means a

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rising disparity in coral and sponge

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numbers and that difference can lead to

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coral reefs becoming overwhelmed

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Ultimately in a web as complex as an

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entire ecosystem every small alteration

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has effects that can redefine the

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entirety of the ecosystem. So why should

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we care? While it may seem unimportant

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the health of coral reefs worldwide is

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vital to our daily life. Much of the

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world's food comes from fishing that

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with the collapse of coral reefs could

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lead to drastic reductions in fish

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stocks. Coral reefs also have important

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medicinal implications. The chemical

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compounds that make up coral are used to

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treat diseases such as HIV, leukemia and

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skin cancer and some research shows that

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they could even be the key to drugs that

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cure Alzheimer's and heart disease. They

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even support local economies. 

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Researchers at the Australian National

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University recently valued the

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ecosystems total services and goods at

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upwards of three hundred and fifty

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billion dollars a year and in Florida

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alone they used more than 35 thousand

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jobs and provided over four billion in

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state revenue. The biological

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implications of coral reefs to sponge

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reefs are vast. Their effects will not be

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felt only in the ocean but across a wide

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range of industries in the coming years

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