Sun, warming your skin. Sand, tickling your toes. Warm, calm tropical water to swim in. And maybe a coconut or two? If you love your beach, do thank a reef. Especially in Moorea, French Polynesia, where coral reefs protect the beaches.*
Moorea and the islands of French Polynesia: where they are and where they came from
You probably already know that French Polynesia is in the South Pacific Ocean. Actually, it’s quite literally in the middle of the South Pacific, with not much besides open ocean around it. It has 118 islands, and many of them are known for their spectacular beaches.
French Polynesia’s beaches exist because of ancient coral reefs.
So where did these beaches come from, and how did they get to the middle of the ocean? Well, even if you haven’t heard of Moorea, you’ve probably heard of its sister islands, Bora Bora and Tahiti. Like many of French Polynesia’s islands, they’re extinct volcanoes that have sunk beneath the surface of the water. The ‘island’ is all that’s left of the peak.
In other words, all those famous beaches are actually on the sides of ancient volcanoes. And they exist because coral reefs grow on the upper slopes of the volcanoes as they sink. These separate the ocean outside from the water inside, and so the volcanoes leave spectacular blue lagoons behind. Depending on how far the volcanoes sink and how quickly the corals grow, the entire process can take anywhere from 100,000 to 30 million years.
Coral reefs are all that stand between Moorea’s tropical beaches and the open ocean.
Some volcanoes have sunk completely beneath the water, leaving only the lagoon and the reef. These are atolls. Meanwhile, others have a small peak left in the middle, with water all around it surrounded by the reef. These are barrier reefs, and Bora Bora is a great example, though Wikipedia calls it an atoll for some reason. And when the reef is still hanging out on the side of the volcano, it’s called a fringing reef.
Moorea has both fringing and barrier reefs, and a much bigger and higher volcano ‘island’ to go with them. (Don’t worry, it’s still extinct.)
Coral reefs and coastal protection
As you may have noted, coral reefs are the only thing standing between the island and lagoon and the ocean. Thanks to their dense physical structure, they absorb and break ocean waves – they’re a natural breakwater. They protect the shore from cyclones, tsunamis, or storms, keep the lagoon calm, and stop waves and currents from eroding coasts and beaches. Which makes sure we can keep enjoying those stunning views, beach days, and scuba or boating trips. (By the way, we’re not really counting them here, but aesthetics, recreation, and tourism are great examples of cultural ecosystem services.)
It costs $38 million to replace the protection provided by Moorea’s coral reef – for free.
Without the reef, we’d need to replace the protection it provides by building something to replace it. And that costs money. Some areas of Tahiti use a wall device where there is no barrier reef, which would cost $38 million if it were to replace all of Moorea’s reef. Other options cost even more, which makes the reef even more valuable.
So here is Moorea, with its beaches. There is sparkling turquoise water. And keeping it all safe is the coral reef. Next time you go off for a tropical beach vacation, we hope you’ll thank the reef.
*We’re a little unclear on the spelling. We’re using Moorea here, but the traditional spelling seems to be Mo’orea, or Mo’ore’a according to Wikipedia.