In this episode we dive into the concept of reefs. Reefs today are one of the most crucial environments in the oceans. They promote extremely high biodiversity and protect coast lines. Today we are accustomed to coral reefs, but throughout history many organisms have built reefs that proved just as important to ancient ocean life.
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What is a reef?
A reef is technically just a shallow ridge that reaches near or above the ocean’s surface. This means that there are actually a number of things that can count as reefs, typically falling into three categories: inorganic, artificial, and organic.
Inorganic reefs include rock structures and sand bars. Artificial reefs are built by humans for various purposes including agriculture, wave protection, conservation, and even to make more ideal surfing waves. Organic reefs are those built gradually by organisms, including coral, algae, molluscs, and more.
Reefs Through Time
During the vast span of time that life has existed in the oceans, reefs have been built by a diversity of organisms going all the way back to the Cambrian (530 million years ago). Reefs have been built by ancient sponges, clams, and algae, as well as extinct and modern corals.
Modern reef-building corals are the stony Scleractinia. Coral is a member of the group Cnidaria, which also includes jellyfish, anemones, and sea pens. Corals are typically colonial, formed by thousands of coral polyps. The polyps build calcium carbonate skeletons to support and protect their soft bodies.
Coral can form a variety of reef types. Fringing reefs form along shores and extend like shelves. Barrier reefs stand apart from the shore, closing off a shallow lagoon. Finally atolls are barrier reefs formed around an island that has eroded away, leaving the reef as a circle enclosing a lagoon in the ocean. One reef type can actually progress into the next over time.
Coral reefs are extremely important to modern environments and economies, but are highly threatened. Major threats include climate change, chemical and physical pollution, sediment run off, and physical damage to reef from anchors and tourism.
Check out The Encyclopedia Earth: Coral Reef for more of an overview of coral reefs.