Introduction to Aquatic Biomes - Online Tutor, Practice Problems & Exam Prep

Aquatic biomes are primarily defined by their physical and chemical environments, categorized into freshwater (e.g., lakes, rivers) and marine biomes (e.g., oceans). Zonation in these biomes includes distinct areas like the intertidal zone, littoral zone, and pelagic zone, each supporting specific organisms. Seasonal turnover in lakes and ocean upwelling are vital processes that replenish nutrients and oxygen, enhancing ecosystem productivity. Understanding these dynamics is crucial for grasping aquatic ecology and the interactions within these environments.

Introduction to Aquatic Biomes

This video, we're going to begin our introduction to aquatic biomes. Now aquatic biomes are those that are covered by a significant amount of water. And unlike terrestrial biomes, which are primarily characterized by their climate and vegetation, aquatic biomes are primarily characterized by their physical and chemical environments, such as their salt concentrations, for example. And we'll be able to talk more about this idea in our next video. Now aquatic biomes can be divided into 2 major categories, which are freshwater and marine biomes.

Now freshwater biomes have relatively low salt concentrations, usually less than 0.1% salt, and include things such as lakes, rivers, and streams. Now marine biomes, on the other hand, have relatively high salt concentrations, usually about 3% salt and include the world's oceans. On the left-hand side in our image, we have an example of a freshwater biome, this lake in Slovenia called Lake Bled, and on the right, we have an example of a marine biome, an ocean. It's important to note that, collectively, all of the freshwater biomes on Earth only account for just 3% of all of Earth's water, which is very little. And the rest of the water on Earth is accounted for by the marine biomes, which means that the marine biomes account for 97% of all of Earth's water.

So moving forward in our course, we're first going to cover the freshwater biomes, such as lakes, rivers, and streams, and then we'll shift our attention over to the marine biomes. So this here concludes our introduction, and I'll see you all in our next video.

Introduction to Aquatic Biomes Example 1

So here we have an example problem that wants us to indicate if the following environmental factors of aquatic biomes are physical or chemical. Notice that we've got these five different environmental factors of aquatic biomes listed below. We need to label each of them as either physical or chemical. A chemical aspect of the environment, as its name implies, refers to the presence, absence, amount, or composition of some chemical that's dissolved in the water. Whereas, the physical aspects refer to essentially everything else. You can think of it as the non-chemical characteristics of the environment that do not refer to the amounts or the compositions of chemicals.

Notice the first one here says salinity, and salinity refers to the amount of salt dissolved in the water. So, that is going to be a chemical aspect. The next one here says water depth, and the depth of the water literally is just referring to how deep we're looking into the water—how many meters below the surface of the water, if you will. This isn't referring to any specific presence, absence, or composition of a chemical. So the water depth is going to be a physical aspect of the environment.

Next, we have nutrient and oxygen concentration, and, of course, this refers to specific chemicals dissolved in the water. So this is going to be a chemical aspect. Light intensity refers to the amount or intensity of light, and light is not going to be dissolved in the water. Thus, light intensity is more so considered a physical aspect of the environment. The temperature refers to the average amount of energy and speed, the kinetic motion that the molecules have. It is not referring to the presence, absence, or composition per se. For that reason, this is also going to be a physical aspect of the environment.

That here concludes this example problem, and I'll see you all in our next video.

Photosynthetic organisms in aquatic biomes tend to live near the surface, as there is more light availability. Is this constraint of light availability a physical or chemical factor?

• A. Physical.
• B. Chemical.
• C. Both.
• D. Neither.

Zonation in Marine Biomes & Lakes

In this video, we're going to talk about the zonation in marine biomes and lakes. Marine biomes and lakes are both physically and chemically divided into several different zones or areas. These zones allow us to easily define and better understand aquatic habitats as different organisms are found living only in specific zones. Notice down below, we're showing you a diagram only for the zonation in marine biomes, and we're not actually showing you a diagram for the zonation of lakes. That's because those two diagrams are very similar to each other, so we've decided to highlight some of the most important differences in the zonation of lakes over here in this box on the right.

Now the first zone we're going to look at is the intertidal zone, which, as its name implies, is just the zone or area between the tides. It's between the high tide and low tide marks. The intertidal zone only applies to marine biomes. It does not apply to lakes because lakes do not experience tides the same way oceans do. On that same train of thought, the continental shelf is also only going to apply to marine biomes and does not apply to lakes.

The continental shelf is really just this shelf that you can see right here just before this major drop-off. Notice that we're labeling the edge of the continental shelf right here because that's going to help us define the next zone, which is the neritic zone, which we also have defined over here on the right. We can use the unique first letter 'n' in neritic zone to remind us that the neritic zone is the nearshore shallow area between the low tide and the edge of the continental shelf. Again, because the continental shelf only applies to marine biomes, the neritic zone only applies to marine biomes. However, lakes still have a nearshore shallow area, and so the analogous zone in lakes is the littoral zone.

You can think that the 'l' in littoral is for the 'l' in lakes. Also, notice that littoral is spelled with two back-to-back identical letters, two back-to-back 't's, and so is the word shallow. Hopefully, that can remind you that the littoral zone is this nearshore shallow area in lakes. The next zone that we're going to look at is the oceanic zone, which is also defined over here on the right-hand side. Again, we can use the unique first letter 'o' as a memory tool to remind us that the oceanic zone is the offshore deep water that's extending beyond the continental shelf.

Again, the oceanic zone is only going to apply to the ocean's marine biomes. However, lakes do still have an analogous zone, which is the limnetic zone. Again, you could think the 'l' in limnetic is for the 'l' in lakes. The next zone we're going to look at is the pelagic zone, and what you'll notice is that the pelagic zone is bracketing the neritic and oceanic zones, because it refers to both of them. The pelagic zone refers to all of the water in the entire open ocean, and it can be defined as the neritic zone plus the oceanic zone.

Once again, you can use the unique first letter 'p' to remind you that it is going to be a plus, and so it's going to be the addition of neritic and oceanic zones. The pelagic zone also applies to lakes, but it's going to be the addition of the littoral and limnetic zones. Now the last zone that we have defined over here on the far right is the benthic zone, and the benthic zone, again, we can use the first letter 'b' as a memory tool to remind us that it's referring to the entire ocean bottom. The benthic zone also applies to lakes as well, so it could be the entire lake bottom. Notice that over here in the image, the benthic zone is labeling the entire bottom of this floor here, regardless of how deep it is.

We also have these two additional zones labeled here in the image, which are the photic zone, right here, and the aphotic zone. The photic zone is a more superficial surface layer that, as its name implies, receives enough photons of light to power photosynthesis. The aphotic zone is deeper, and it does not receive enough photons of light to power photosynthesis. So, photosynthetic organisms would not be found there. This here concludes our lesson on the zonation in marine biomes and lakes, and I'll see you all in our next video.

Introduction to Aquatic Biomes Example 2

So here we have an example problem that wants us to indicate if the aquatic zones are found only in oceans, which will indicate with the letter o, only in lakes, which will indicate with the letter l, or in oceans and lakes, which will indicate with the letters ol. And so the first zone that we have here is the intertidal zone, which recall from our last lesson video, the root inter is a root that means between. And so the intertidal zone is a zone or an area that falls between the high tide and the low tide. And lakes do not experience tides in the same way that oceans do, and so the intertidal zone does not apply to lakes. It applies only to oceans.

So for that reason, we can put an o here. Now, next, what we have is the oceanic zone, and as its name implies with the term oceanic, this zone only applies to oceans and not lakes. So the oceanic zone refers to the offshore deeper water that falls beyond the continental shelf. And the analogous zone in lakes is referred to as the limnetic zone. And so, you can think that the l here in limnetic is for the l in lake, and so we can put an l here for that. Now, next, what we have is the benthic zone, and recall that the b in the benthic zone can remind us that this is the entire bottom of the ocean or lake.

And so the benthic zone applies to both oceans and lakes, so we will put both o and l here in this blank. Next, what we have is the photic zone, and the photic zone refers to the zone of the water that receives enough photons of light to drive photosynthesis. And so, the photic zone applies to both oceans and lakes, and it's going to be the upper part of the water. And so, we can put both o and l here for that. The aphotic zone, recall, is the opposite of the photic zone, so it's the part of the water that is deeper than the photic zone and does not receive enough photons of light to drive photosynthesis.

And again, this can be found in both oceans and lakes, so we can put both o and l here. Next, what we have is the neritic zone, and the neritic zone only applies to oceans, not lakes. The neritic zone, recall, is the nearshore shallower area, and it is going to correspond only between the areas of the low tide to the edge of the continental shelf. Now, the analogous zone in lakes is going to be the littoral zone, and so you can see that, again, the l in littoral zone can remind you of the l in lake, and so it's only going to be applying to lakes, not oceans. Then what we have is the pelagic zone, and recall that the pelagic zone is going to be the oceanic zone plus the neritic zone in oceans.

Or in lakes, it's going to be the limnetic zone plus the littoral zone. And so the pelagic zone applies to both oceans and lakes, so for that reason, we can put o and l. And then last, but not least, what we have here is the continental shelf, and the continental shelf is only going to apply to oceans since lakes don't tend to have a continental shelf, so we can just put an o here. So this here concludes our brief example problem, and I'll see you all in our next video.

In which of the following regions would you expect to find photosynthetic organisms?

• A. Abyssal zone, benthic zone, & neritic zone.
• B. Intertidal zone, benthic zone, & neritic zone.
• C. Intertidal zone, photic zone, & neritic zone.
• D. Littoral zone, aphotic zone, & intertidal zone.

Detritus is organic matter produced by the decomposition of dead organisms. Considering that detritus tends to sink in water over time, in which ocean zone does detritus make up the base of the food chain?

• A. Photic zone because many organisms can photosynthesize and live here, producing organic matter.
• B. Intertidal zone because detritus is frequently washed up on shore by waves & tides.
• C. Aphotic/Benthic zones because photosynthesis cannot occur, but detritus falls to the ocean floor.
• D. All of the above.

Seasonal Turnover & Ocean Upwelling

This video, we're going to talk about seasonal turnover and ocean upwelling. There's important context to understanding these two processes: in lakes and oceans, nutrients have a tendency to continuously sink towards the bottom, leaving the surface waters nutrient-depleted. On the other hand, oxygen gas tends to become depleted at the bottom of lakes and oceans. Seasonal turnover and ocean upwelling are two processes that help to replenish nutrients in surface waters and oxygen gas in deeper waters. Seasonal turnover refers to the vertical mixing of water layers in a lake or an ocean, specifically during the spring and fall seasons.

Seasonal turnover occurs most effectively in parts of the world that experience the four classical seasons - cold winters, hot summers, and transitional spring and fall seasons. It's crucial to remember that the turnover actually happens during the spring and the fall. This mixing of water layers is driven by changes in water density, which are due to seasonal temperature fluctuations. As the water temperature changes, so does the density of the water. When the density of the water is quite similar, the water mixes very well.

However, when the temperature of the water differs, the densities also differ, causing the waters not to mix well. This fundamental concept underpins the turnover process. Let's visualize with an example focusing on lake turnover through the four classical seasons.

Starting with the winter season: unsurprisingly, we have 0 degrees Celsius and frozen ice at the top of the water. The maximum density of fresh water is around 4 degrees Celsius. As you go deeper, there's a temperature gradient, which also means there's a density gradient, preventing the water from mixing well.

When spring arrives, the turnover process can begin. The sun heats all the water to the same temperature, 4 degrees Celsius at the top and bottom, allowing the densities to match and mix well. Now, nutrients from the bottom can resurface at the top, replenishing them, and oxygen at the top can be brought down to replenish the bottom. Perfect.

During the summer, the sun creates a temperature gradient where the surface waters are hotter, creating a drastic change in temperature over a short distance, known as a thermocline. This results in a density gradient, and the waters do not mix well. However, as fall returns, the waters cool to the same temperature, 4 degrees at the top and bottom, enabling effective mixing like in the spring.

The cycle then returns to winter, completing the process. That's spring turnover for you. Now, let's discuss ocean upwelling. Ocean upwelling is the process where deep, cold, nutrient-rich water rises to replace surface waters moving along the coast. Prevailing winds push the surface waters along the coast, giving an opportunity for nutrient-rich waters to rise and replace the water being blown by the wind to the right, also allowing the surface water to bring oxygen down to deeper waters. This concludes our lesson, and I'll see you all in our next video.

Introduction to Aquatic Biomes Example 3

So here we have an example problem that wants us to choose one of the 4 potential answer options down below that best completes this statement, which says that the occurrence of turnover in lakes relies on the fact that blank. Now, of course, recall from our last lesson video that seasonal turnover or just turnover refers to the process of the vertical mixing of water layers in a lake or an ocean, specifically during the spring and fall seasons. And the vertical mixing process is actually driven by changes in water density, and those changes in water density are due to changes in the temperature of the water due to the seasons. And so, in terms of what the turnover process really truly relies on, it really is a density-driven process that's driven by the changes in water density. And so we're looking for an answer option that focuses on that aspect.

And so notice that answer option a says water is at its least dense at 4 degrees Celsius. However, recall that this is not going to be true. Instead, we said that water is at its most dense at 4 degrees Celsius, and notice that answer option b says that water is at its most dense at 4 degrees Celsius. And so this is looking like a potentially correct answer option, but let's check answer option c and d just to be sure. Now option c says nutrients sink to the bottom of a lake or ocean over time.

Now recall from our last lesson video that this is actually true. Nutrients do sink to the bottom of a lake or ocean over time. However, the turnover process does not rely on nutrients sinking to the bottom of a lake or ocean. The turnover process relies on the fact that density changes, the water's density changes as the seasons change. And so, option c, although it is a true statement in general, it's not what the turnover process relies on.

Now option d says, oxygen sinks to the bottom of a lake or ocean over time, but really this is not going to be the case. Instead, the oxygen remains towards the surface of the water and is depleted at the bottom of the water, and so, the oxygen does not sink to the bottom of the water. So this is just not going to be true. So the correct answer here is answer option b. Water is at its most dense at 4 degrees Celsius, and this is an important fact that the turnover process relies on because, once again, this turnover process is a density-driven process.

It's driven by changes in water density, so it does rely on the fact that water is at its most dense at 4 degrees Celsius and that it's at different densities at different temperatures. And so, option b is the correct answer, and I'll see you all in our next video.

How do the processes of turnover & upwelling benefit aquatic ecosystems?

• A. They allow photosynthetic organisms at the surface to receive more light.
• B. They allow photosynthetic organisms in the benthic zone to receive more light.
• C. They allow organisms at the surface to receive more nutrients.
• D. They allow organisms in the benthic zone to receive more nutrients.