Archives: Biology

What is a Wetland?

A Wetland is described by the plant species that live in it. If an area is wet enough for long enough to support a majority of plants that are adapted to wet conditions then you have a wetland. An example might be a patch of land that is dominated by cattails. Since cattails are adapted to a life where they are partially submerged by water, then the area would be considered a wetland, even if it is dry for a part of the year. Not all wetlands are restricted to freshwater habitats either.  Many saltwater marshes thrive in the salty coastal zones.

Types of Wetlands

There are many types of wetlands. Scientists often divide them up into the following groups.

• Marshes
• Swamps
• Bogs
• Fens

Marshes are characterized by the presence of soft-stemmed vegetation adapted to saturated soils. These are typically grasses, sedges or rushes. Some common ones include prairie potholes, the expanses of the Everglades, and salt marshes.

Swamps are characterized by the domination of woody plants. There are many different kinds of swamps including the cypress swamps of Louisiana, Red Maple swamps in the Northeast and the Mangrove forests of tropical and subtropical regions.

Bogs are distinctive wetlands that are low in nutrients and often contain very acidic water and extensive peat deposits. Bogs are also one of the stages of succession as a lake fills in.

Fens are different from bogs in that they receive their water supply from either runoff or groundwater (not rainfall). This usually results in a different water chemistry. Fens have either neutral or alkaline waters and are typically not stages in lake succession.

Where are Wetlands Found?

Wetlands are found all over the world, within almost every terrestrial biome from deserts to alpine tundra. The map below shows the distribution of wetland areas in the United States. Notice the abundance of wetland areas in the Southeast, the Mississippi river system and in the northern states of Minnesota and Wisconsin.

Plants in a Wetland

Plants that are adapted to moist and humid conditions (such as those found in wetlands) are called hydrophytes. These include cattails, water lilies, bulltongue, sedges, tamarisk, and many kinds of rush.

Wetland plants are adapted to the saturated conditions that persist for a majority of the year. The different vegetation types in a wetland can be divided up into emergents, floating, and submerged plants.

An Invasive Wetland Plant: Hydrilla

For the species profile of a wetland plant we decided to pick hydrilla. It is an extremely competitive invader that we have only recently found ways to control. Of particular interest, there is a small fly larvae that eats through hydrilla. We filmed the following episode at the Army Corp of Engineer’s Lewisville, TX, research facility and at their Vicksburg, MS, research facility.

How you can help Save Wetlands

This may or may not come as a surprise, but Wetlands have been reported to be the most threatened ecosystem in the world today. People often see wetlands as wastelands and non-productive land, and these valuable regions are filled in and destroyed. This is endangering human, plant, and animal life at an alarming rate. So what can you do? To help, we’ve found some great links to help you plan your course of action:

• Volunteer your Vacation to Save a Wetland: Earthwatch.org is an organization that actually pairs researchers with volunteers in all kinds of habitats. Go to the webpage and search wetlands. You’ll see all sorts of trips planned. They change all the time so search often.
• Donate $$$ to a Charity: We’ve linked here to the contact page for the Common Sense Environmental Fund that funds research and conservation projects. You give your money to them, and they pick the most qualified conservation initiatives to help fund.
• Join a Wetland Monitoring Group: The Izaak Walton League can help set you up with a local group. Give them a call at 1-800-BUG-IWLA.
• Reduce, Reuse, and Recycle: This is a no-brainer, but we might as well remind you. Everything you can do to reduce your trash will trickle down to less waste in our waterways, including wetlands.
• Be creative, and explore your own wetlands. Find something that you can do like setting up bird shelters, picking up trash, or just monitoring a wetland month to month. You’ll find that you’ll enjoy the time you spend at your wetland, and you’ll want to do everything you can to keep it just like it is.

Lakes and Ponds represent a freshwater biome type that is generally referred to in the scientific community as a lentic ecosystem (still or standing waters). Scientists that study lakes and ponds are known as limnologists. In this overview we hope to describe a few of the biotic (plant, animal and micro-organism) interactions as well as the abiotic interactions (physical and chemical).

Lakes and Ponds Video

In this Untamed Science video we explore the lakes and ponds biome. While the rest of the crew enjoys the lake, Haley takes off canoeing in an effort to describe this amazing biome.

Lake Zonation

A lake can be divided into different zones: the littoral zone, the limnetic zone, the euphotic zone and the benthic zone. These zones are illustrated bellow.

Lake Stratification

Intense heating of the surface waters of a lake help create a strong stratification of lake waters. The upper layer is known as the epilimnion.  This layer is affected by winds and stays fairly well mixed. Just below the epilimnion is the thermocline where the water stops mixing. It serves as a boundary layer for the cold, deep water below.  The hypolimnion is the cold, deep-water, stagnant layer. This layer often has very low oxygen in the water. This is often accompanied by dissolved hydrogen sulphide and other sulfurous gases.

Lake Cycling and Turnover: Temperate Lake Model

In temperate lakes, the changing of the seasons help move water in the lake. Tropical lakes often stay stratified because warm water always stays on the top. In temperate lakes the winter months chill the surface water so that it gets colder than the water underneath, causing it to sink. This happens in the spring and fall as shown in the diagram bellow.

How do lakes form?

There are many different ways that a lake can form. One common way that lakes have formed in northern North America is through the recession of glaciers. Many of the lakes in Minnesota were formed in this way. The rift lakes in Africa are formed through tectonic activity as two plates separate from one another. Lake Tanganyika was formed in this way. Another great example of lake formation is the creation of oxbow lakes.  These lakes are formed when a meandering river bend is pinched off from the main channel.

How do lakes die?

Lakes by nature are ephemeral.  They all receive sediment input from rivers and streams that lead into the system.  Given that the lake is not expanding through tectonic activity, a lake has a limited existence.  The exact time that the lake may survive depends on the rate of sedimentation and the depth of the lake.

Common Invasive Species in Lakes and Ponds

In the US, as in many countries, rivers and streams have been damned up creating lakes that did not exist before the dam construction. This creates a lot of new habitat for both animals and aquatic plants that can begin to colonize the area. It also provides a great place for invasive species to take hold, especially when there are little to no native plants in the area that are already filling available niches.

Some of the common invasive species in lakes and ponds include zebra mussels, sea lampreys, hydrilla, water hyacinth and Eurasian water milfoil.

An Example Species: Alligator Snapping Turtle

The Alligator Snapping Turtle is found throughout the southeastern United States and can be a formidable sit and wait predator in this habitat.  It can grow to be over 100 years old and can be over 3 feet in length.  For this species profile video we traveled to Mississippi and the Vicksburg Army Corp of Engineer Research Facility.

Resources

• More about Lake Turnover
• More about Alligator Snapping Turtles

“Underwater Rainforests”

Coral Reefs have been called the rainforests of the ocean because of their rich biodiversity. Unfortunately they are also in becoming increasingly threatened.  Not only is global warming going to affect the survival of coral reefs, but other human activities threaten the entire ecosystem.

What are Coral Reefs?

Let us start our definition of this biome by defining what corals are. Corals are small animals that belong to the phylum Cnidaria together with anemones, jellyfish and hydroids. All Cnidarians have stinging organs called cnidocysts. If you’ve ever been stung by a jellyfish you know the effects of these stinging organs.

Corals are generally divided up into hard (scleratinian) corals and soft corals. It’s the hard corals that build the framework of the coral reefs. In the Indo-Pacific waters, approximately 500 species of hard corals are known. Soft corals, also called octocorralina, lack the hard calcium carbonate structure that hard corals build. Most have a fleshy structure with small silica spicules, like internal spines, that give them extra support. The majority of the corals are colonial with several thousand small individuals.

Where are Coral Reefs found?

Coral Reefs are almost exclusively found in tropical and sub-tropical waters across the globe. Scientists have recently found coral reefs in temperate waters such as off the Atlantic coast of Norway, but in general when we talk about coral reefs we refer to the diverse tropical reefs that may hold several hundreds of species of hard reef-building corals alone. These reefs form the framework for an incredible diversity of other organisms.

The longest coral reef system on Earth is the Great Barrier Reef off the east coast of Australia. This massive reef system stretches more than 2,000 km and can be seen from space!

What do coral reefs need to live?

For most reef building corals to survive they need to have a few special requirements met. For example, at any time the average water temperature can not be less than about 18-20 degrees Celsius. For this reason, tropical coral reefs are generally found between 30 degrees north and 30 degrees south of the Equator.

Since there is no shortage of sunlight, nutrients soon become the limiting factor for primary producers. So the waters around tropical coral reefs are in fact relatively nutrient poor. Yet still, they support this incredible diversity of life. The answer to the energy equation is working together. Most corals have developed a symbiotic relationship with a small microalgae called a zooxanthellae. This small dinoflagellate is incorporated in the coral tissue and actually is what gives corals their beautiful colors. As other algae, the zooxanthellae use sunlight to photosynthesize and produce so much energy that it can also provide the coral with almost all of its energy needs (scientists have found that about 98 percent of the energy may be from the zooxanthellae). In return the algae can take up nutrient-rich waste products from the coral. Because of this symbiotic relationship corals can only grow relatively close to the surface where the water is clear enough for the zooxanthellae to perform photosynthesis.

The hard coral reef structure is made of calcium carbonate that the coral secretes as it grows and expands the colony.

Animals on a Coral Reef:

It would be impossible to list here all the animals that live on a coral reef. There are simply too many. Some of the groups of animals frequently seen on the reefs include Sea Fans (type of soft coral), Sharks, Butterfly fish, Nudibranchs, Sea stars, Cuttlefish, and Clownfish. But also even some reptiles such as turtles and sea snakes. All in all there are thousands of animals that make the coral reefs their home.

Threats to Coral Reefs

Coral reefs are being threatened around the world because of many different factors. Their special requirements to survive also make them relatively sensitive to change. We know that most ecosystems are able to adjust to changes fairly well, given enough time. The problem today is that changes are happening so fast that most animals don’t have time to keep up. And coral reefs especially.

Many coral reefs are relatively close to land. This makes them easy to access and also easily affected by everything that goes on on land. Road construction, coastal clearing, agriculture, and more result in a lot of sediment and pollutants that get washed out to sea with the monsoon rains that fall in tropical areas. Simple sedimentation in the water may be enough to kill the reefs both by directly covering the corals but also by decreasing light penetration of the water so much that the symbiotic zooxanthellae algae are unable to photosynthesize.

Another factor is over-fishing. When too many fish are taken out of a system the balance is disturbed. Many of these fish eat algae and control the abundance of algae on the reef. When the fish is removed, the fast-growing algae can take over. Destructive fishing methods such as cyanide and dynamite used in some parts of the world also directly affect the structure of the coral reefs. A coral reef that has been blown away by dynamite needs many, many years to recover.

Global warming is also causing the sea temperatures to rise. Even though corals need relatively warm water to survive, there is a limit. When the water gets too warm, it affects the corals and the zooxanthellae algae negatively. The algae disappears from the coral and the corals become “bleached”. This basically means that the coral structure is left naked but still alive without the symbiotic algae. Most corals can only survive a short period without the symbiotic algae. If water conditions don’t change back to normal during this time also, the coral will die.

One more thing… directly breaking of a branch of a coral could mean removing more than 10 years of construction. Don’t encourage breaking the corals for souvenirs. Leave them in the water to look at. Don’t encourage people who sell the corals to continue. In other words, don’t break or buy corals, please.

What can you do to help?

The only way to protect these amazing environments is to provide an incentive for people to protect them. Ecotourism is one reason to save these reefs. Visit a coral reef, and learn as much as you can about it. Talk to the locals, and tell them how important a healthy reef is to your visit. If you want to do more, visit noaa.org.

Links to more information on Coral Reefs

Check out and play around with a Global Information System (GIS) database for coral reefs. ReefBase GIS maps provide all the layers to visualize how different types of coral reefs are distributed around the world.

Also visit ReefBase homepage for a lot of the latest information and status reports concerning the coral reefs.

Learn more about the largest coral reef system in the world in Australia and the Australian Institute of Marine Science.

Waters Around the Continental Shelf

Coastal Oceans are waters that lie above the continental shelf. This is where most of fish come from, where coral reefs grow, and were we swim and play. In fact, while the oceans cover 71 percent of Earth, only 7 percent of that is coastal oceans. This small strip of land is affected adversely by humans in many ways including over-fishing, industrial pollution, and agricultural runoff. These practices may in turn effect us as fish availability varies, algal blooms occasionally occur, and water quality fluctuates through time. Overall, coastal oceans can be generalized more easily by dividing them up into temperate and tropical coastal areas.

For our video, we chose to examine the temperate Coastal Oceans around the west coast of Sweden, and looked at three animals in this habitat: lobsters, sea pens and jellyfish.

Temperate Coastal Oceans

Tropical Coastal Oceans:

Coastal oceans in tropical areas have similar characteristics to their temperate counterparts. However, there are certain habitats in the tropics that are not found in the temperate regions of Earth. A great example of this is the coral reef.

Coral reefs are biologically diverse and rich habitats that occur in relatively nutrient-poor environments along coastlines. Areas that have too many nutrients often harbor too much algal growth to sustain coral growth.  To learn more about the coral reef we have set up an entire page dedicated entirely to this tropical coastal biome.

The Pelagic Zone

The word pelagic is derived from the Greek work pélagos, meaning open ocean. It is the name for oceanic water not in direct contact with a shore or the bottom.

It is by far the largest aquatic biome terms of volume, but in comparison to many of the other biomes, it is a desert.

Pelagic sub-zones

The pelagic zone is further divided up into vertical sub-zones as seen in the image below. This biome vertically joins with the Deep Sea biome once the illuminated surface layers are passed. For more information on the deeper pelagic waters, please also visit our deep sea biome page.

Our large Oceans

Seen from space, Earth is truly a water planet. About 71 percent of Earth’s surface is water, and the average depth of the oceans is just under 4,000 meters (about 13,000ft.) Life on the planet has a few basic requirements to survive. We need energy of some kind, and to most animals that mean that they will have to eat. To get food, an animal has to be where there is food, or be able to go where there is food. The same goes with reproduction. Many marine organisms reproduce sexually and need to find a mate to reproduce.

Most other biomes are in close proximity to land of some kind which usually helps in both these cases, but the pelagic zone is simply defined as waters that are not directly connected to land in any direction, neither horizontally nor vertically. So organisms living in the pelagic zone  must go where there is food and locate a partner to reproduce.

In the aquatic world, the clear blue pelagic waters are somewhat of a water-desert. The biomass out here is much lower than many coastal waters per unit volume, but there is still a lot of organisms that live here.

A lot of the marine fish we eat come from pelagic fisheries. Some commercially important species of fish are Pacific mackerel, jack mackerel, Pacific sardine and Blue-fin tuna. Unfortunately today, many fish stocks have been over-exploited and some species, such as many shark species, even face extinction due to overfishing. On top of this, many pelagic animals that are not targeted by the fishing boats, such as dolphins and turtles, sometimes also get affected by negative fishing methods.

The different pelagic sub-zones

Epipelagic – The Illuminated Surface zone

[Origin of the word: Gr. Epi – ‘near to, upon’]

The epipelagic zone stretches from the surface down to the depth where photosynthesis can no longer occur because of the limited light, generally about 200 meters. Since light is absorbed quickly with depth, only a small percentage of the sunlight ever reaches this far down.

Since sunlight is needed for photosynthesis, nearly all primary production of the ocean occurs here. In fact, a great percentage of the oxygen in the atmosphere comes from the primary production out in the open oceans! As a result of this, the epipelagic zone is also where most pelagic animals are found, and they are often big. Tunas, sharks and large marine mammals such as whales and dolphins travel in these waters. We also find planktonic jellyfish and comb jellies.

The photosynthetic organisms here are dominated by phytolankton, diatoms and dinoflagellates that have evolved specialized features to stay in the surface waters and not sink such as air bubbles or small droplets of special oils. Some also have spines that increase their surface area and slows down sink rate.

Clear, well-lit open water is also a dangerous place to be in for many organisms when such large predators are around. For this reason many small animals only come up to the epipelagic zone at night and spend the sunlit hours deeper.

A camouflage coloration found on many animals that live in the open ocean is counter-coloration: light-colored undersides and darker backs. Seen from above, a dark back blends in better with the darkness of the depth, but a light colored belly will blend in better with the bright surface when seen from below.

General depth range of the Epipelagic Zone: 0 – 200 meters

Mesopelagic – The Twilight Zone

[Origin of the word: Gr. Meso – ‘middle’]

In the mesopelagic zone there is no longer enough light for photosynthesis. The light that does penetrate can provides enough light for hunting if you have good eyes. Many animals do vertical migrations down to the mesopelagic to hide during the day.  With the darkness of night, it is safer again to migrate closer to the surface where there is generally more available food.

Many creatures that live in this zone are also transparent, a good camouflage in this zone where there is barely enough light to see. Some animals here have also developed larger eyes to make best use of the limited light.

In addition to decreased light, oxygen concentrations are also very limited. So organisms that live down here have to be able to survive low oxygen levels as well.

Squids, nautilus shells and swordfish are a few species that can be found down here.

General depth range of the Mesopelagic Zone: 200 – 1000 meters

Bathypelagic – The dark zone

[Origin of the word: Gr. Bathus – ‘deep’]

Below the mesopelagic, no light will ever reach (unless it comes from bioluminescence: organisms that can create their own light).

The bathypelagic zone is defined as the zone that goes down and past the continental slope. The pressure down here is great; only organisms with special adaptations to survive such pressures can live this deep. For example, the swimbladder that we see in many fish at the surface is missing in fish down here. The food source here is limited to the debris of dead material that sinks like snow from the above zones. Staying still to conserve energy is common. Some fish attract prey by going fishing. For example, anglerfish have a small glowing bioluminiscent rod attached to their head. Other fish get attracted to the light and becomes a meal for the anglerfish.

The water temperature stays fairly constant down here between about 2-4 degrees C, (about 35-39 degrees F).

General depth range of the bathypelagic Zone: 1000 – 4000 meters

Abyssopelagic – The “bottomless” zone

[Origin of the word: Gr. abussos – “bottomless” – ‘a’ = without + ‘bussos’ = depth]

This zone is usually where the continental slope levels off. More than 30 percent of the bottom of the ocean is said to be situated here.

General depth range of the Abyssopelagic Zone: 4000 – 6000 meters

Hadopelagic – The “Underworld”

[Origin of the word: Gr. Hades – was the name of the Greek God of the Underworld. Hades is also the word for the Underworld itself. In Greek the word also means ‘unseen’]

Some parts of the ocean floor have deep trenches that can reach several kilometers deeper than the surrounding ocean floor. These zones, which cover less than 2 percent of the ocean bottom,  are referred to as the hadopelagic zones.

A lot of these trenches are still unexplored, and so far only a few species have been observed here. Not many organisms down here would ever survive being brought up to the surface because of the incredible pressure and temperature difference on the way. Very little detritus falls this far down so food is thought to be very limited to these organisms.

General depth of the trenches in the Hadopelagic Zone: 6000 – 11000m The deepest part of the ocean is The Challenger Deep in the Mariana Trench at approximately 11,021 meters (36,160 feet). (Ref. NODC Frequently Asked Questions )

For more information on the deep zones, including video, go to our deep sea biome page.

Useful Links

Find out more about pelagic fisheries by the Pelagic Fisheries Research Programme.

Do you want to make sure the fish you are eating isn’t over-fished? Check out FishWatch to find a list of good choices.

The intertidal zone is defined as the area between the high tide and low tide mark.

Organisms that live in this zone have to deal with difficult environmental conditions, being both submerged in sea water and exposed to the air. They have to bear the great physical impact of waves, desiccation, and sunlight. Occasionally there are rains which saturate them in fresh water. There are lots of moving rocks and sediment in the water which can damage small critters. Plus, there is a risk of predation, not only from ocean-based animals but terrestrial animals as well.

We’ve created this video on the intertidal biome to give you a quick introduction to life in this habitat.

Tidal background

The tides are formed as a result of the gravitational forces between Earth, the sun and the moon. Twice a month the three will be aligned as a result of Earth’s movement around the sun and the moon’s orbit around Earth. When this happens, the gravitational pulls will be strongest ,and we will experience the greatest differences between high (flow) and low (ebb) tides. We call these tides Spring tides. On the contrary, the time half way between two spring tides, which occurs when we see the moon as half, the tidal difference will be the smallest, called Neap tides.

With this background it could sound like the size of the tide would only depend on the gravitational pulls between Earth, the moon and the sun, but this is not the case. The topography of the ocean bottom plays a great roll in how large the tide will be.

Different types and distribution

Intertidal habitats are found all over the world although the tidal range various extremely depending on location.

Some areas experience hardly any tidal difference at all. The west coast of Sweden in fact has greater ocean surface level differences depending on changes in atmospheric high- or low air pressures, which has nothing to do with tides. On the opposite side of the Atlantic Ocean, in South Eastern Canada, we find the greatest tidal differences in world in the Bay of Fundy. Spring tides here create a 20 meter difference between high and low tides.

Adaptations by organisms in the Intertidal zone

The type of organisms occupying the tidal habitat varies greatly depending on where we are on the planet. For example, temperate rocky intertidal areas will have totally different species than a tropical mangrove habitat. Coral reefs are also often affected by tidal differences, which may even totally expose the corals out of the water during low tides.

The moving water exerts great demands on organisms in the area. If an organism lives on the substrate, it usually needs to have a way of either attaching itself to the substrate to prevent being washed away or being able to seek shelter. Barnacles settle and build a solid and permanently fixed structure on the rock. When under water, they reach out with a feathery appendage to strain the water for plankton and oxygen. When the tide goes back down, they close up the opening of the calcium structure with two plates to prevent desiccation and predation. Limpets are mollusks that stick hard to the rocky substrate by contracting the muscles in its foot and firmly grip the substrate. When times are not so rough, they use the foot to crawl on the substrate and graze tiny algae off the rock. Chitons are also mollusks with eight overlapping plates on their backs. The plates are flexible and allows the chitons to wrap around a stick to the hard surface with its muscular foot.

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Intertidal Zone Researcher Profile: Kristin Aquilino

This is a short video profile of Kristin Aquilino, a Ph.D. Candidate in the Population Biology Graduate Group at UC Davis. Kristin studies community ecology in the rocky intertidal zone at Bodega Marine Lab in Bodega Bay, CA. This video was created as a final “video blog” project for the Scientific Filmmaking workshop at Bodega Marine Lab in October 2010. The workshop was taught by Colin Bates and Jeff Morales. This video was filmed and edited by Neil Losin, Kelvin Gorospe, and Annie Schmidt (narration by Kelvin Gorospe).

Where the Tide Meets the Streams

Estuaries are bodies of water formed where freshwater from rivers or streams connect with salt ocean water. The mixed water is called brackish, and the salinity may fluctuate dramatically for example depending on freshwater input from rains and waves and tides influences from the ocean. Estuary areas include river mouths, bays, lagoons and salt marshes.

Different types of estuaries & the zones of an Estuary

Depending on the amount of influence from freshwater and marine inputs and the circulation of water, different estuaries are divided up into different categories. A salt wedge estuary is the simplest type, occurring at a river mouth where the river flows directly into the ocean. The lighter fresh river water moves over the top of the heavier seawater. The river water is flushed out and pushes back the seawater, which in turn tries to move up into the river. The location of the boundary and amount of mixing may change depending on the amount of river output, waves and tidal influences.

There are also Reverse or Inverse estuaries where the rate of evaporation is so high that salinity increases and can even be greater in the estuary than in the costal waters. When this extreme happens, the net water transport will be reversed: in at the surface (if coastal water salinity is lower) and out at the bottom (if evaporation has increased the estuary salinity so much that it is higher than coastal water and thus more dense).

The fjord-type estuaries of British Columbia, Alaska and Scandinavia are deep with a great input of freshwater from rivers and sometimes limited tidal influence. The lighter freshwater has a tendency to stay and sit on top of the deeper seawater, whereas the inward flow of seawater may be very limited.

Estuaries are not restricted to a certain climate region. They are found in temperate as well as tropical regions. The climate will have an impact on the types of species that are found.

Challenges for organisms

Two major problems for organisms living in an estuary are fluctuations in salt concentration and sedimentation.

Salt concentrations are regulated by an organism, and when the concentration in the water fluctuates, it becomes harder to adjust. Too much salt, and organisms have to be able to exclude salt uptake somehow. Not enough salt, and organisms have to be able to take up and retain salt for cellular reactions.

Organisms have various methods to control their salt intake. Osmoregulators actively regulate their salt balance (e.g. fish), whereas in osmoconformers, the organism’s internal salt balance adjusts to the external salt concentration in the water (e.g. most soft-bodied invertebrates). In both cases, dramatic or rapid changes may stress the organism and even kill it if not adapted to such fluctuations, which is why the variability in salinity of an estuary is one of the primary challenges for organisms living there.

Rains and river output often carry a lot of fine sediment that is deposited in the estuary. This often makes the water murky around river mouths. Sedimentation can also have adverse effects on many organisms. For sessile organisms (organisms that sit in one spot and can’t move) too much sedimentation can completely cover the organism and be fatal.

The fine sediment settles to the bottom and packs densely. Organic material that falls to the bottom is broken down by bacteria. The dense sediment often means that it is hard for water to aerate the bottom, which results in a poorly oxygenated bottom. The activities of these decomposing bacteria ends up using up much of the available oxygen. The end result is that many estuaries have bottoms with low concentrations of oxygen.

Still, many estuaries are areas of very high productivity and serve as homes to a great diversity of life, both in the water and above.

An Example Species: The Red Mangrove

In this short Untamed Science video, crew members Rob Nelson and Haley Chamberlain head out to the shorelines of Honduras to find the Red Mangrove, one of the most common mangrove plants. This is a great example of a plant adapted to the salty estuarine habitats. It can withstand salt water because it exudes salt from its leaves.

Links:

• US-EPA National Estuary Program