Nutrients, Blooms, & Dead Zones: Abiotic Factors Page 73

Abiotic Factors in Ocean Ecosystems Depth (pressure, light availability, oxygen availability) Movement of water (currents, upwelling, downwelling, waves, and tides) Salinity, density, and temperature Nutrient availability

Depth and Pressure At sea level, there is 1 atmosphere (atm) of pressure. Each 10 meters of depth, you gain another 1 atm of pressure. Human bodies can only withstand around 3 to 4 atm of pressure. Deep diving animals such as sperm whales and leatherback sea turtles have adaptations that allow them to handle the pressure such as collapsible lungs, redirected blood flow, and soft shells. Other deep sea creatures have gelatinous body structures due to pressure.

Light Availability In the ocean, the amount of light that penetrates through depends on the depth and the color of the light. Blue light penetrates the farthest, which is why the ocean appears blue. Red light penetrates the least. The ocean is divided into three light zones: Euphotic zone: 0-200 meters – the distance to which sunlight penetrates Twilight or dysphotic zone: 200-1000 meters – sunlight decreases with depth, making photosynthesis impossible Midnight or aphotic zone: 1000+ meters – no light at all

Nutrient Availability In order for photosynthesis to take place in the ocean, certain nutrients must be available to the phytoplankton (plant plankton), algae, and seagrasses. The most important nutrients in the ocean are nitrates (NO3-) and phosphates (PO43- ) as they are both needed by plants and algae.

Nitrates Nitrates occur from the “fixation” or joining of nitrogen and oxygen through lightning, cosmic radiation, or nitrogen fixing bacteria. Nitrates can also be added to the environment un-naturally (this is bad) through: Discharge from water treatment plants and septic tanks Run-off from farms, fertilizers, and agricultural lands

Phosphates Phosphates are found naturally in rocks and are released into the environment as those rocks break down. Phosphates can also be added to the environment un-naturally (this is bad) through: Run-off from farms, fertilizers, and agricultural lands Florida uses “phosphate-free” fertilizers because of how much phosphate is already present in our soil

Eutrophication Eutrophication - excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land Causes algal blooms (such as red tide) All the floating algae cuts off sunlight to other plants, halting photosynthesis and depleting the oxygen Anoxic zones (also known as dead zones) form, causing massive die-offs of fish

Red Tide Red Tide is an algal bloom caused by excess nutrients in the water. It is caused by a microscopic algae called a dinoflagellate. The specific dinoflagellate responsible is known Karenia brevis Can cause respiratory illness in all mammals (including humans) and can be ingested as a toxin by fish and other marine species.

Anoxic or Dead Zones In the Gulf of Mexico, the constant dumping of excess nutrients from the Mississippi River. Last summer, the dead zone was about the size of New Jersey (8,776 square miles) It fluctuates seasonally, shrinking during each winter and growing during each summer.