Oysters can build reefs too!

Written by Megan Munkacsy

Why is it that when we pack for beach vacations we bring our most beautiful pieces: a new bathing suit, that bright dress we never get to wear, the pair of shoes we splurged on last month. Maybe we even push a little harder at the gym the week before. We want to peacock our prettiest selves on land, yet once we step foot in the water, so many of us immediately slip into our goofy snorkel masks, shamelessly posing for a picture with our nostrils pressed open for all of our friends to see, our eyes pulled back and our foreheads imprinted with the most unflattering marks.

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Figure 1. Remnant Oyster Reef in Georges Bay, St Helens, Tasmania. (Photo: Chris Gillies)

It is because no matter how unflattering we may look on land, once we place those crazy masked faces in the water, a whole new world emerges – the world of a reef. Tentacled creatures in colors no home improvement store paint section could recreate grasp at particles floating by and sway in the current moving around the reef. Shrimp float past, seeming to peddle a tiny invisible bike in a gear much too low for their terrain. Nearby a small fish darts past as one only slightly larger lunges from a previously unnoticed crevice, nipping at its neighbor. Algae and soft corals, sponges and the tinsel of bacterial slime oscillate back and forth, creating the slow strobe flashes of sunlight refracting through the water. Peripherally, seagrass beds border the community which thrives on this living structure, a reef which demands a new set of communication tools in order to completely encapsulate.

This reef is not made of corals, however. Unknown to the majority of people, there is a bivalve (think: clam and its relatives) that builds biotic, or living, reefs. Oysters are two-shelled animals which thrive in brackish waters along the coastlines of the world. The scene above is what you would expect to see on a healthy oyster reef. Unfortunately, oyster reefs worldwide are nearly or completely functionally extinct, due in large part to development, over-harvesting, and disease. These reefs, which were once so abundant they determined marine navigation and shipping lanes, are now reduced to relatively small clumps surrounded by mud.

History

Looking back, oysters have played an impressive role in history and culture. Native coastal communities around the world built piles of shells, called “middens”, from the discards of their shellfish heavy diets. In the southwest of France, middens have been found with over a trillion shells per pile. According to Carolyn Tillie’s Oyster: A Global History, oysters are our oldest food, appearing in cookbooks from the 300 ADs and the archeological findings of Troy. In fact, the Greek goddess Aphrodite is said to have been born from an oyster shell.

Before New York City was the “Big Apple”, it was the “Big Oyster” and leftover shells from the restaurants were crushed and used to line the first roads of today’s geographically largest city. Oysters as food played a major role in feeding pioneers who flooded to the gold rush of the early 1900s in the Western United States, and were so abundant that it is said they were fed to prison inmates by the dozen. Those of us familiar with Lewis Carrol’s Through the Looking Glass and What Alice Found There know the poem “The Walrus and The Carpenter” from 1871, in which he describes oysters, “thick and fast they came at last, And more, and more, and more”.

The history of the oyster and its impacts on politics, art, and daily life is fascinating. Today, however, oysters and their benefits are so little known that if you Google “biotic reefs” oysters are not mentioned in the first five pages of search results, nor do they come up in related search suggestions. This is a travesty because oysters are critical contributors to the health of our coastal waters, fisheries, and even the protection of our coastal developments.

Ecosystem Services

Oysters are a keystone species. Like mangroves and seagrasses, they provide a disproportionate amount of ecological benefits to the organisms that live near, around, and within them relative to their population numbers. They are a nursery for baby fishes and other invertebrates, they foster bacterial communities which transform nitrogenous runoff into atmospheric gasses, they help control algae blooms, and they filter out particles in the water which prevent sunlight from feeding seagrass beds.

Oysters don’t always grow in reefs, however they are most effective and healthiest as a reef. Oddly enough it is more common today to find a few disparate oysters on the bottom of an estuary than it is to find a naturally occurring reef. In the first stages of life, oysters are actually mobile. They float like plankton through several life stages, usually taking about two weeks, before they develop an eyespot which can detect shadows and begin looking for a place to settle. Oysters typically seek out calcium carbonate surfaces, such as other oyster shells and even coral reefs, to settle on; but since the name of the game is survival, they will often attach to other surfaces as well, such as rocks, wooden pylons, and even the bottoms of boats. This lifestyle is how oysters build reefs, with every new generation created during months of warm weather and then settling on top of a reef to build a new age class. However, with reef structures basically nonexistent, oysters often settle on random surfaces with just enough space for a single oyster.

When they have the chance to grow in a reef structure, oysters are powerful protectors. Oyster reefs are nature’s version of jetties or riprap, slowing down the incoming tides and waves onto our shorelines. Without this restriction, shorelines erode and real estate which was once safely off of the high tide mark teeters dangerously close to the edge of the water. When oyster reefs take hold along coastlines that experience a large amount of erosion, the erosion not only slows down or even ceases, but often sediment will begin to build up along the shore, rebuilding areas that were lost.

Economics

Oyster reefs do all of this for our ecosystem alone, but what about the ways they are important to economies? Directly, oyster reefs provide jobs to people around the world via harvest, shucking houses, the pearl industry, aquaculture, and food service. Indirectly, oysters improve water quality. They support fin fisheries, both recreational and commercial. They clean our waterways to provide swimmable waters, encouraging recreation and tourism. Oyster reefs reduce nitrogen from fertilizer pollution and runoff, and consume algae. Both of these services provide for the human health of even those who are not actively swimming in the water by reducing algae blooms. Off of the coast of Florida this summer, events such as algae blooms have become so extreme they are affecting people’s respiratory systems. A 2012 paper by Grabowski and others estimates the economic benefits, both direct and indirect, of oyster reefs to equal up to nearly $100,000 USD annually per hectare of oyster reef.

Reefs are powerful communities and ecological tools. Currently, the world is watching with bated breath as we work to improve our lifestyles in order to preserve our coral reefs. However, oyster reefs are often overlooked in our quest to improve the waters we hold so beloved. They have provided for us for centuries, and continue to improve our coastal lands and aquatic systems, our quality of life along the coast, and our economies. The story of oyster reefs provides us with a cautionary tale of what could be lost if we don’t act as responsible stewards for our currently healthy reefs, as well as the promise of science-based work successfully contributing to the rebuilding of the reefs of the world.

Resources:

What are oyster reefs?

For more information email the author: megmunkacsy@gmail.com

2 thoughts on “Oysters can build reefs too!

  1. This is a great article on oyster “reefs” which help​ed​ me understand their biological significance as well as their historical and economic place in our lives. ​ The course of my life of ​​l​iving nea​r​ bays, rivers and oceans​ ​has been enriched ​immerserably ​by oysters in ways I was not aware of before reading this article.

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    1. Hi Helen, thanks for commenting, it is always very rewarding to hear that our articles are educating our readers and the general public. It is our goal to make science for accessible to all. We hope you continue following reefbites!!

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