Coral Reefs: This Ecosystem – It’s Alive!
Did you know corals are actually tiny animals, and these giant reef structures are made up of millions of exoskeletons, with mouths and stomachs? Now you do.
Corals use calcium and carbonate ions from seawater to build these exoskeletons, building reefs that can go on for miles (such as the Great Barrier Reef, which stretches over 2,300 kilometers or 1,400 miles!). There are thousands of unique species of corals all over the world, building diverse underwater cityscapes that provide habitat and food sources for about a quarter of the world’s fishes.
These living landscapes are some of the most complex ecosystems on Earth, growing from nearshore shallows to the ocean floor. Coral polyps are clear, but often gain vibrant colors from the various species of microalgae growing along the reefs. This diverse landscape of plants and animals earns coral reefs the nickname “the rainforests of the ocean.”
(Check out the Smithsonian’s 3D digitizations of coral here!)
Fun fact: Coral reefs provide food and income for millions of people; their benefits to humans alone have an estimated value of $10 trillion per year.
Parrotfish: Protecting Reefs… By Snacking
Speaking of coral reefs – these ecosystems don’t act alone. It’s common for algae to grow on bleaching reefs, which can compete with the coral for nutrients and sunlight. Luckily, to parrotfish, algae looks a lot like lunch.
A major threat to coral ecosystems is bleaching, a stress response to higher sea temperatures. This usually causes problems for fish species, but it also allows algae to grow, meaning parrotfish continue to thrive. Their marine munchies can actually help bleached reefs recover by keeping algae at bay (no pun intended).
Using their beak-like teeth, parrotfish scrape algae and other microorganisms off coral, creating large areas of open coral surface available to be colonized by beneficial microalgae and cyanobacteria. This mutualism between the coral and parrotfish helps keep both populations stable in the face of rising sea temperatures. (Read more here!)
Fun fact: There are around 80 identified species of parrotfish around the world, with a wide variety of sizes and colors. They exist basically everywhere tropical reefs do.
Oysters: What Can’t They Do?
Not all oysters create pearls, but they’re still worth their weight in gold.
Oysters’ most important jobs are twofold: not only do they like to build big colonies, creating reef structures with similar benefits to coral, but adult oysters can filter up to 50 gallons of water per day. As a keystone species, oyster reefs provide habitat for a number of small animals and a food source for larger ones. In addition, oyster reefs grow quickly and can provide protection from storm surge and waves along shorelines.
These busy bivalves improve biodiversity, water quality, storm resilience, and more, so much so that N-EWN partners are working on a number of projects to promote oyster reefs as a nature-based solution (also called “oyster-tecture” – get it? We make ourselves shuck-le). Learn more about how USACE’s Engineering With Nature® program is using “living shorelines” to protect coasts here.
Fun fact: There are a number of shoreline restoration projects all over the world that recycle oyster shells from restaurants to protect shorelines! Learn more from New York City’s Billion Oyster Project or Athens, Georgia’s Shell to Shore program.
Horseshoe Crabs: Shifting Seafloor Sediments
Have you ever been to the beach and noticed a very intelligent rock with a long spiny tail walking by? Meet the horseshoe crab.
Horseshoe crabs act more like excavators than engineers: they dig pits in the sand to lay eggs or forage, changing the geomorphology and hydrology of their habitats, and subsequently the turbidity of the water. They’re also a keystone species for many coastal systems, with their tiny eggs providing a critical food source for shorebirds.
The super-adaptive coastal crawlers are one of the oldest animals on Earth, and they’re not going away anytime soon. However, hundreds of thousands of horseshoe crabs are hunted each year for, of all things, their blood. Horseshoe crab blood contains a chemical compound called limulus amebocyte lysate, or LAL, which is used to test the safety of vaccines and medications. There are movements promoting more humane alternatives, though – learn more about it here!
Fun fact: This famous horseshoe crab blood everyone’s after? It’s blue. No really, look it up.
Spartina Grass: Protecting Shoreline Landscapes
It’s important to note that not all ecosystem engineers are animals – plants do their part to structure and protect their habitats too!
Spartina grass, commonly found in coastal salt marshes and wetlands, functions similarly to coral and oyster reefs in that these meadows provide habitat, nurseries, and food sources for species, but they’re also hard at work underground.
These grasses, commonly known as cordgrass, have roots that stabilize marsh sediments and prevent erosion. The sturdy sprouts have a strong influence on the physical environment, as well as their neighbor species, in a biome that faces significant threats from climate change and sea level rise. The tightly packed roots hold sediment together so tightly that cordgrasses can directly improve water filtration and build shorelines, all while absorbing wave energy from tides.
Fun fact: Species diversity for Spartina grasses is highest in the east coasts of North and South America, particularly in Florida. Learn more about how our partners at the University of Florida are using plant and animal interactions to build coastal resilience here.
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