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Unlock This CourseMarine organisms need a variety of chemical elements to survive, grow and reproduce. Unlike land animals that get nutrients from food and fresh water, marine creatures must extract what they need from salty seawater. This creates unique challenges and amazing adaptations that have evolved over millions of years.
The ocean contains dissolved minerals and nutrients, but they're not always in the right amounts or easily available. Some areas of the ocean are like underwater deserts - they look blue and clear but are actually quite poor in nutrients. Other areas are like underwater gardens, rich in the elements that support abundant marine life.
Key Definitions:
Marine organisms need six major elements in large quantities: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P) and Sulphur (S). These make up the building blocks of proteins, DNA and other vital molecules. Without any one of these, life simply cannot exist.
Different elements serve specific purposes in marine organisms. Understanding these roles helps explain why certain areas of the ocean teem with life while others remain relatively barren.
Carbon forms the backbone of all organic molecules. In the ocean, carbon exists mainly as dissolved carbon dioxide and bicarbonate ions. Marine plants and algae use photosynthesis to convert this carbon into sugars and other organic compounds that fuel the entire marine food web.
Tiny floating plants that capture carbon dioxide and convert it into organic matter through photosynthesis, forming the base of most marine food chains.
Large marine algae that absorb carbon dioxide from seawater and can grow incredibly fast when conditions are right.
Animals that partner with algae to capture carbon and build calcium carbonate skeletons, creating entire reef ecosystems.
The Sargasso Sea in the North Atlantic appears crystal clear but is actually a marine desert. Despite having plenty of carbon dioxide, it lacks other essential nutrients like nitrogen and phosphorus. This creates a beautiful but relatively lifeless environment, except for the floating Sargassum seaweed that gives the sea its name.
Nitrogen is crucial for making proteins and DNA, but it's often the scarcest nutrient in seawater. This makes nitrogen the limiting factor for growth in many marine ecosystems. When nitrogen becomes available, marine life explodes in abundance.
Nitrogen exists in several forms in the ocean. Nitrate and nitrite can be used directly by plants and algae, while ammonia is toxic in high concentrations but useful in small amounts. Some specialised bacteria can even convert nitrogen gas from the atmosphere into forms that other organisms can use.
Special bacteria convert nitrogen gas into ammonia that other organisms can use. This process requires lots of energy but is essential for adding new nitrogen to marine ecosystems. Some of these bacteria live freely in the water, while others form partnerships with marine plants.
Phosphorus is essential for making ATP (the energy currency of cells) and DNA. Unlike nitrogen, phosphorus doesn't exist as a gas, so it can only enter the ocean through weathering of rocks on land or from deep ocean currents that bring up phosphorus-rich water from the depths.
Areas like the coast of Peru and California experience upwelling, where deep, nutrient-rich water rises to the surface. These zones are incredibly productive because they bring phosphorus and other nutrients from the deep ocean to surface waters where photosynthesis can occur. This creates some of the world's richest fishing grounds.
Marine organisms also need tiny amounts of various trace elements. Iron is particularly important because it's needed for photosynthesis and oxygen transport, but it's often scarce in open ocean waters.
Large areas of the ocean have plenty of major nutrients but lack iron. This creates high-nutrient, low-chlorophyll zones where phytoplankton can't grow despite having access to nitrogen and phosphorus. Scientists have experimented with adding iron to these areas and seen dramatic increases in marine plant growth.
Saharan dust blown across the Atlantic provides iron to marine ecosystems, supporting phytoplankton growth thousands of miles from land.
Underwater volcanic vents release iron and other trace elements, creating oases of life in the deep ocean.
Ship ballast water and pollution can introduce both beneficial and harmful trace elements to marine ecosystems.
Marine organisms have evolved remarkable strategies to survive in nutrient-poor environments. These adaptations show the incredible ingenuity of life in finding ways to thrive even when resources are scarce.
Many marine organisms have become incredibly efficient at capturing and using nutrients. Some can absorb nutrients at concentrations so low they're barely detectable, while others have developed ways to store nutrients for times when they're not available.
Many marine organisms form partnerships to share nutrients. Coral polyps house algae that provide them with food, while the algae get a safe place to live and access to the coral's waste products, which contain essential nutrients.
Human activities significantly affect nutrient availability in marine ecosystems. Understanding these impacts is crucial for protecting ocean health and the organisms that depend on balanced nutrient cycles.
Runoff from farms and cities can add excess nutrients to coastal waters, leading to algal blooms that use up oxygen and create dead zones. While nutrients are essential for life, too much of a good thing can be devastating for marine ecosystems.
Each summer, excess nutrients from the Mississippi River create a massive dead zone in the Gulf of Mexico. The nutrients fuel algal blooms that consume oxygen when they decompose, creating an area where most marine life cannot survive. This demonstrates how human activities can disrupt natural nutrient cycles with serious consequences for marine ecosystems.