Ecosystems on the Edge: Underwater Light and Seagrass

Summary

The Chesapeake Bay is facing a serious environmental crisis as pollution from land runoff and the atmosphere is choking off the light that seagrasses need to survive. These underwater plants are crucial to marine life, providing habitat for juvenile fish and food for many species. The increasing presence of phytoplankton, fueled by excess nutrients, blocks light and consumes oxygen, harming the ecosystem. Scientists are working to understand the causes behind the decline in seagrasses and are focused on reducing nutrient runoff to restore the bay's health, aiming for clearer waters and a thriving aquatic environment.

Takeaways

• 😀 Light is essential for marine life, especially for the growth of seagrasses, which provide habitat for small and juvenile marine animals.
• 🌱 Seagrasses are vital for maintaining marine ecosystems and supporting food sources for millions of people worldwide.
• 💡 Pollution from land runoff and atmospheric pollution is blocking the light seagrasses need to grow, which threatens marine ecosystems.
• 🛑 Excess nutrients from sources like farms, municipalities, and suburban lawns contribute to harmful algae blooms, further blocking light in the water.
• 🌊 The clouding of water from algae blooms deprives submerged aquatic vegetation (SAV) of the light necessary for growth, leading to ecosystem degradation.
• 🔬 Scientists, like Chuck Gagos from the Smithsonian Environmental Research Center, are researching the factors causing the loss of seagrass light supply.
• 📉 In the 1960s, scientists noticed a decline in seagrass beds in the Chesapeake Bay, which were once abundant at depths of 2 meters but now only grow to about 1 meter.
• ⚡ The scattering and absorption of light by small particles like clay, decaying organic matter, and phytoplankton block light from reaching the seagrasses.
• 🍃 Phytoplankton, fertilized by excess nitrogen and phosphorus from human activity, have grown in numbers, exacerbating the problem by blocking light and consuming oxygen.
• 🌍 The entire marine food chain is affected when seagrass habitats disappear, leading to a loss of food sources for fish and other organisms.
• 🔍 The team measures light penetration in water using tools like a Secchi disk and light meters to determine how far light can reach and what's blocking it.
• 📊 The lab findings show that about 40% of the particles in the water are organic, which is detrimental to seagrasses, as organic matter blocks more light and consumes oxygen.
• 🌾 Reducing nutrient runoff into the Chesapeake Bay is key to restoring seagrass growth and preserving the health of the marine ecosystem.

Q & A

Why is light important for marine life, especially seagrasses?

Light is crucial for marine life because it enables the growth of vegetation like seagrasses, which are foundational for marine ecosystems. Without adequate light, seagrasses cannot thrive, affecting the entire food chain.

What is the main environmental issue causing a decrease in seagrass populations in the Chesapeake Bay?

Excess pollution, especially from land runoff, is choking off the light supply necessary for seagrasses to grow. Nutrients from farms, municipal sources, and suburban lawns contribute to water clouding, blocking sunlight.

How does pollution impact the light that reaches the seagrasses?

Pollution introduces small particles into the water, including clay, organic matter, and phytoplankton. These particles scatter and absorb light, reducing the amount that reaches the seagrasses, hindering their growth.

What role do phytoplankton play in the pollution of the Chesapeake Bay?

Phytoplankton populations increase due to excess nitrogen and phosphorus from human activities. These blooms block light and contribute to oxygen depletion when they decay, both of which negatively impact seagrasses.

Why are seagrasses considered indicators of water quality?

Seagrasses require abundant light to grow. When they begin to disappear, it signals that water quality has deteriorated, indicating a decrease in the available light at the bottom of the water body.

What historical changes have occurred in the seagrass beds in the Chesapeake Bay?

In the 1960s, scientists observed a decline in seagrass beds in the Chesapeake Bay. Historically, seagrasses grew down to a depth of 2 meters, but now they only grow to about half a meter, showing a significant reduction in their habitat.

What are the two primary tools used to measure light penetration in the Chesapeake Bay?

The two tools used are the Secchi disk, a simple device to measure water clarity, and a light meter, which measures the absorption of light at various depths in the water.

What is the difference between organic and inorganic particles in the water, and why does it matter?

Organic particles, like phytoplankton, are more harmful because they block more light and consume oxygen when they decay. Inorganic particles, like clay, are less detrimental to seagrasses, as they don’t affect oxygen levels as much.

What has been the recent trend in the amount of organic matter in the water, and what is the ideal percentage?

Currently, about 40% of the suspended particles in the water are organic, which is twice as high as it should be. Ideally, organic matter should constitute around 15% to 25% of the total suspended solids.

What actions can help restore seagrass populations in the Chesapeake Bay?

Reducing nutrient runoff into the bay can protect existing seagrasses and support their growth. With less pollution, more light will reach the seagrasses, helping restore their populations and the marine ecosystem.