Marine Biology Notes

Some of them can swim weekly or swim vertically so they can get to higher surface water closer to the sunlight, but when a current comes through, they can't fight the current. They have to go with the current. There are two main types of plankton, those are phytoplankton, which are algae that undergo photosynthesis, like diatoms, most of these organisms are microscopic. So here's a picture of diatoms seen under a microscope. So a plankton or animal plankton, they are not photosynthetic, they include copepods, and the larval stages of many marine organisms, like fish, sea stars, lobsters, and crabs. Again, when they're too small to swim against the current, their classified as zooplankton. Many of these organisms grow up and are able to swim against the current. 

They are then classified as nectin, which are any organisms that can move independently of ocean currents by swimming or other means of propulsion. They include things like adult fish, squid, marine mammals, and marine reptiles. Some nectin complete long migrations, and nectin are more abundant along continents and islands and in colder water, this is because the algae that they, that the base of their food chain depends upon, is also stays closer to the continents. Those necked in that complete long migrations are organisms like salmon, who swim upstream in freshwater rivers when it's time for them to spawn or reproduce. Eel do the same or do the opposite of the salmon. They grow to maturity and fresh water and then swim to the ocean when it's time for them to breed. Bentos are organisms that live on the bottom of the ocean floor. Most of these are found in the shallow coastal areas, and include things like seaweed, sea stars, and crabs. This diagram shows life zones in the ocean. The zones are divided according to the available sunlight, the distance from the shore, and the depth of the water. Let's start with zones dependent on sunlight. 

The photo zone refers to the part of the ocean where sunlight can penetrate. So in this diagram, you see the cursor is moving through the photo zone. In the top part of that photo zone, there is enough sunlight for organisms to undergo photosynthesis. So the U photo zone is that zone usually not below a hundred meters depth where organisms have enough light for photosynthesis. And the low part of the photo zone, marine animals have enough light to see predators look for food or find mates, but again, they don't have enough light for photosynthesis below that photo zone is the a photo zone where there is no sunlight. The next set of zones is based on the distance from the shore. This starts from the coastline with the inner tidal zone, which is the area where land and water are overlapping in between the high and low tides. Organisms that live in the inner tidal zone have a lot of challenges to overcome. Their constantly moved around by waves. When the tide is low, the organisms can become dried out very quickly. And with the influx of water and the receding of water throughout the day, organisms have to undergo changes in temperature, salinity, and oxygen. Past the inner tidal zone is the neuritic zone. 

This is the part of the water above the continental shelf. If you'll remember from the ocean floor notes, the continental shelf is the gently sloping part of the ocean floor where the water is shallow and sunlight can penetrate. The narrated zone only makes up 5% of the total ocean area, but is rich in biomass. There are lots of organisms and lots of different species of organisms in the neritic zone. Although it only constitutes 5% of the ocean area, it supports over 90% of the world's commercial fisheries. The pelagic zone refers to open ocean at any depth, the part of this plague zone where sunlight can penetrate has plankton and nectin. The a photo part has organisms in this picture like the giant squid, which has been pulled up in this picture by a fisherman. The deeper part of the water is known as the benthic zone, and this includes any bottom dwelling organisms like kelp, sponges, crabs, sea and enemies, sea stars. And worms. The abyssal zone reversed to that part of the benthic zone that is the deepest part of the ocean floor, organisms here have to undergo extremely high pressures, low temperatures, a lack of sunlight, so few organisms can survive in the deepest parts of the ocean. Those that do rely mostly on scavenging for food. For instance, this brittle star you see in the picture feeds on tiny decaying particles that are falling from the surface in that brutal star is filter feeding, brewing worms do the same thing. Other larger organisms feed on larger pieces of food that are falling from the surface. 

These scavenger organisms include the grenadier, the tripod fish, and the hagfish. Again, here are layers, different zones in the water, light, vertically, we start with the U photo zone where photosynthesis occurs. The photo zone where sunlight can penetrate and the a foot of zone where there is no sunlight and that makes up the majority of the ocean area. Or the ocean volume, and then moving horizontally from the shore, we start with the inner tidal zone between high and low tide. The neuritic zone, which covers the rest of the continental shelf, and then the open ocean known as the pelagic zone. And there are special areas of the ocean floor that contain hydrothermal vents. These are areas where sea water seeps into the cracks of the crust, the earth's interior heat heats the water. It becomes superheated and saturated with minerals. When those vents extrude the water into the open ocean, the water cools and can't hold all the minerals, this causes the minerals to precipitate back into the water. So their nicknamed black smokers because you're seeing tiny drops of minerals precipitating into the open ocean. These are interesting to marine biologists because they have discovered hundreds of species living around the vents, and unlike other ecosystems on earth that depend on sunlight, these hydrothermal vents depend on a certain type of bacteria that can change chemicals released from the vents into energy. Which brings us to this discussion of primary productivity. 

Primary productivity refers to the production of organic compounds from inorganic substances. In other words, this is the base of our food chain where certain organisms can take in or inorganic substances like carbon dioxide and other chemicals, and change them to organic compounds that other organisms can feed from and get energy from. One type of primary productivity is photosynthesis. This is using light energy to convert water and carbon dioxide into glucose. Photosynthetic organisms are the green plants that we see every day and are the base of most food chains on earth. In the water, remember the base of most of those food chains are these photosynthetic algae. But another type of primary productivity is chemosynthesis, where small organisms are using hydrogen sulfide in hydrothermal vents as an energy source and converting that into organic compounds that other organisms feed from. Remember, the chemosynthetic organisms are found around hydrothermal vents and only make up a small amount of the primary productivity in the oceans. Most of the productivity as in as on land comes from photosynthetic organisms. And the amount of photosynthetic productivity depends on the available sunlight and the nutrients available to the photosynthetic organisms. 

Nutrients that are necessary for photosynthesis are elements like nitrogen, phosphorus, and iron. So productivity is going to change depending on what part of the ocean the organisms are in. In the polar oceans, it stays cold year round. So the top of the water is cold, the middle of the water is cold, the bottom of the water is cold. This is a good thing for nutrient transfer, most of the nutrients in the ocean sink down to the ocean floor. So if the density and the temperature throughout the vertical layers stays the same, nutrients can rise up to the surface and reach the photosynthetic organisms near the surface of the water. So high latitude areas in polar oceans have higher nutrient concentrations, so they're not limited by the nutrients, but they have smaller amount of solar energy than other oceans. This is because they undergo long periods of darkness where they can't photosynthesize at all. In the tropical oceans, sunlight is not a problem. The sunlight is more direct and penetrates deeper into the water and they have sunlight year round. The problem in tropical oceans for these primary producers is that the thermal pine creates a barrier. 

When the water at the surface is very warm and the deep water is cold, that cold deep water is more dense and therefore can't rise up and bring nutrients to the surface. So all the nutrients accumulate at the bottom of the ocean, the sunlight is at the top, so photosynthetic organisms have a lack of nutrients. And productivity and temperate oceans depends on the seasons, the seasons affect the thermal line. As well as the availability of sunlight, so the productivity changes throughout the years are throughout the year as seasons change. Upwelling are important sites for our marine organisms. Upwelling are sites where cold water warm surface water is pushed away from the shore out further to sea. And when you push the top part of the water out to sea, it allows the water below it to rise up to take its place. So as this cold water rises, it brings nutrients to the surface and microscopic plankton feed on these nutrients and grow and reproduce like crazy. So this is good for the fishing industry because then the fish will feed on those plankton. This map shows the world's oceans and just the red areas here highlighted show upwelling sites.

So let's look at this area around Peru, for instance, Peru is a great place for the fishing industry. And in Peru, these strong trade winds blow across the continent and push the warm surface water here out further in the Pacific Ocean. So that allows the cold deep waters to rise up along the coast right here and bring nutrients with it. So now you've got this concentration of nutrients and you're in a warm tropical area. So the fishing industry does very well in upwelling regions. So on this map, only 1% of the total ocean, these areas highlighted in red, are places where upwelling can happen. However, even though this is only making up 1% of the ocean area over 50% of all the fish caught in the world happen at these upwelling sites. So they're extremely good for marine organisms because they're allowing nutrients to rise to the parts of the water. Where their sunlight, so those photosynthetic organisms aren't limited in either nutrients or availability of sunlight. A tropic level refers to a feeding stage and the transfer of energy throughout the food chains and oceans is very inefficient. For instance, let's look at this diagram. It's showing sunlight hitting the surface of the water, so if we start out with 50,000 units of radiant energy coming from the sun, when plankton, feed, or use that solar energy and photosynthesis, they only are allowed to save 2% of that energy. 90% of the total solar energy that has reached the surface is lost. 

So when they're holding on that to that 2% of total energy that came from the sun, that's 10,000 units. When the next zooplankton feed on the phytoplankton, only 10% of that energy is conserved and 90% of the energy is lost. The next stage, when the nectin start to feed on these zooplankton, again, we have another 10% efficiency, 90% of the energy we had at the second stage is lost. Continues through larger nectin and then to humans who eat the largest fish like bluefin tuna and at this 5th tropic level, you're only actually consuming 1% or one unit of energy for every 500,000 units of sunlight that came in. So the most important thing to gain from this diagram is that the energy transfer through trophic levels is very inefficient.