Estuaries

I absolutely love the written word. Why? Because we can have so many names for the same subject/object and it can confuse those who don’t know all the different words.

For instance, estuaries can also called be bays, sounds, sloughs, or lagoons. Though, a coastal lagoon is different from an estuary, but we’ll get to that in a later post—let’s just agree for now that common names are a blessing and a curse.

Estuary is a very broad term because it includes both fresh and brackish water ecosystems, and there are three types of estuaries: salt-wedge, partially mixed, and fully mixed. Each type of estuary is determined by how the fresh and salt water mix.

Today, we’ll just start with a broad overview of coastal estuaries.

An estuary is an area where fresh water from a large stream or river mixes with the salt water from the ocean. This mixing results in brackish water, a chaotic medium between fresh and salt water. Brackish water is too salty to be considered fresh water, but not salty enough to be sea water.

What do I mean by chaotic? The salinity of an estuary changes with every season, passing day, and cycle of the tides. For instance, at high tide the salinity will be higher than at low tide because there is more ocean water mixing with the river water. During the rainy season, the salinity will be lower because the river/stream will have a lot more fresh water from the land runoff than normal, mixing more fresh water than usual with the ocean water. This chaotic nature makes estuaries interesting ecosystems for organisms to adapt to.

Due to their long, funnel-like shape, most estuaries don’t experience a gradual rise and fall of the tides. Instead, the tides rush into the estuary with such force that they create strong currents and even wall-like waves called tidal bores. With the tide comes offshore sediments that get deposited in the estuary as mud, and with the high rate of sedimentation, this mud builds up and creates special habitats within the estuary. In the tropics, these mud areas are called mangrove swamps; everywhere else, they’re called tidal mudflats and salt marshes—but I’ll discuss these habitats in detail later.

Estuaries are crucial to both the land and the ocean.

Estuaries provide a rich source of food for waders and shorebirds. Various types of migratory birds will stop at an estuary to consume worms and crustaceans that live in the mud before continuing on their way. Estuaries also provide breeding grounds for both land and aquatic animals.

One of the greatest functions of an estuary is that it is a natural water filter, helping to ensure that the water coming from the land is as clean as possible before entering the ocean. The process of filtration is complicated and requires a lot more explanation than I have time for today.

The take-away message for this post: estuaries are highly important to the ocean and the land, and they have recorded high levels of productivity for centuries. A lot of the early settlements of man were found in estuaries, such as the Nile Delta, the Ganges, and the Yellow River valley. Even many of today’s popular coastal centers, like New York City and London, were developed on estuaries. And because they attract us, estuaries are also highly susceptible to pollution and need to be protected.
Sources:
Ocean the Definitive Visual Guide made by the American Museum of Natural History
https://www.britannica.com/science/estuary/Geology-and-geomorphology#ref335485
https://oceanservice.noaa.gov/facts/estuary.html
https://www.nationalgeographic.org/encyclopedia/estuary/

Continental Shelf

How many people believe that wherever the beach ends, that’s where the open ocean begins? When I was younger, I believed that too. While the continental shelf is part of the ocean, it is different from the open ocean.

The open ocean is a massive body of water that goes down thousands upon thousands of feet. Obviously, there’s a bit more to it, and the open ocean is divided into zones that I’ll go over at some point, but at the moment, let’s just call the open ocean a massive body of water.

The continental shelf, by contrast, is a continuation of the continent that exists just under the surface of the ocean.

During the last ice age, many of these shelves were above the water and acted as extra land for species to use. In fact, it is believed that the Bering Strait, which allowed humans to cross from Eurasia to North America, was one of these continental shelves. These areas were exposed to the open air because of the decrease in sea level due to colder temperatures. However, after the ice age, a lot of the glacial ice melted and the sea level rose again, covering up the continental shelves.

Since the last ice age, these areas have been very important to the ocean and to those who live on the coasts of the continents, man and beast alike.

Continental shelves have shallow seas, with average depths between 300‒600ft (100‒200m) that are fed by rivers from the mainland. These rivers carry all sorts of things to the ocean—fresh water, sediment from erosion, and vital nutrients from land run-off—all of which mix together to make for a very productive environment. Continental shelves support all sorts of environments for marine life, like coral reefs, kelp forests, sea grass beds, etc.

The shallow, nutrient-rich water allows algae and other plant life to get enough sunlight and other components for photosynthesis, and from there the environments create themselves. Plants bring in plant-eaters, and the herbivores bring in predators. These areas are also important because their environments provide space for many of the oceans’ inhabitants, such as sharks, dolphins, and various fish, to breed and have their young—so these places act as nursery grounds!

The continental shelves are also important to you because that’s where a lot of the fish you eat comes from. There are all sorts of fish farms and commercial fishing operations that occur off the coast, providing food for the continent’s population, and even to other continents as well, depending on the species being caught or raised.

Even before modern times these areas have provided major support to coastal human populations because of the amount of fish and other resources found there. Now, these places also provide income from tourism because inland-dwelling people want to experience the beauty of the ocean for themselves.

Thank you for letting me share with you what continental shelves are and why they’re so important to us. They harbor so much life, and they provide benefits for not only the ocean but for many of us on land. They contain coral reefs, kelp forests, and various sea bed environments that are so important to the ocean and its inhabitants and, by extension, to all of us!

Sources and other cool links to help you learn more:
Ocean: The Definitive Visual Guide made by the American Museum of Natural History
Ocean: A Visual Encyclopedia made by the Smithsonian
https://marinebio.org/oceans/continental-shelves/
https://www.nationalgeographic.org/encyclopedia/continental-shelf/
https://www.britannica.com/science/continental-shelf
*note on the links: they have more of a geological look into the continental shelves like how they’re formed, their layout, etc.*