Environmental Biology (Part -2)

Marine Ecosystems

Marine ecosystems are the largest ecosystems on Earth, covering about 71% of the planet's surface and containing 97% of its water. They host a vast diversity of organisms, including brown algae, corals, cephalopods, echinoderms, dinoflagellates, sharks, and many more.

Zones in the Ocean

Scientists have divided the ocean into five main layers or zones, which extend from the surface to the most extreme depths. Each zone has unique characteristics and supports different forms of life.

1. Epipelagic Zone (Sunlight Zone)

Depth: Surface (0) to 200 meters (0 to 656 feet)

Characteristics: This is the uppermost layer of the ocean where most visible light exists, allowing photosynthesis. It supports a wide range of marine life, including phytoplankton, fish, whales, and sharks.

2. Mesopelagic Zone (Twilight Zone)

Depth: 200 to 1,000 meters (656 to 3,281 feet)

Characteristics: Receives very limited sunlight, not enough for photosynthesis. Bioluminescent creatures start appearing in this zone. Life includes squids, jellyfish, and various fish species.

3. Bathypelagic Zone (Midnight Zone)

Depth: 1,000 to 4,000 meters (3,281 to 13,124 feet)

Characteristics: Completely dark, with no sunlight penetration. The temperature is near freezing, and the pressure is very high. Inhabitants include deep-sea fish and giant squids.

4. Abyssopelagic Zone (Abyssal Zone)

Depth: 4,000 to 6,000 meters (13,124 to 19,686 feet)

Characteristics: Pitch dark, near-freezing temperatures, and immense pressure. Sparse life includes invertebrates like deep-sea cucumbers and certain types of shrimp.

5. Hadalpelagic Zone (Hadal Zone)

Depth: 6,000 meters to the ocean floor, including the deepest ocean trenches

Characteristics: Extreme pressure and cold temperatures. Life is scarce, with organisms like amphipods and specially adapted worms. The deepest point is in the Mariana Trench at 10,911 meters (35,797 feet), where the temperature is just above freezing, and the pressure is 800 times that on the surface.

Additional Zones

Littoral Zone (Intertidal Zone): The area between high and low tide marks, where the ocean meets the land.

Neritic Zone: Extends from the low tide mark to the edge of the continental shelf, rich in nutrients and marine life due to sunlight penetration and proximity to land.

Oceanic Zone: Beyond the continental shelf, encompassing the majority of the ocean's volume and divided into the zones mentioned above.

Each of these zones supports different types of marine ecosystems and organisms, contributing to the ocean's overall biodiversity and ecological complexity.

Freshwater Ecosystem

Contrary to marine ecosystems, the freshwater ecosystem covers only 0.8% of Earth's surface and contains 0.009% of the total water. Despite its relatively small size, it supports a diverse range of organisms and plays a crucial role in the Earth's ecological balance.

Freshwater Zones

Lentic Systems (Standing Water): These include lakes and ponds, which have relatively still water.

1. Littoral Zone

Location: Near the shore of a lake or pond

Characteristics: This is the warmest zone because it is shallow, well-lit, and can absorb more of the sun’s heat. It sustains a diverse community, including several species of algae, rooted and floating aquatic plants, grazing snails, clams, insects, crustaceans, fishes, and amphibians.

2. Limnetic Zone

Location: Near-surface open water surrounded by the littoral zone

Characteristics: Well-lit and extends to the depth penetrated by light. It is occupied by phytoplankton, zooplankton, and higher animals. This zone produces food and oxygen that supports most of the lake’s consumers.

3. Profundal Zone

Location: The deepest part of the lake

Characteristics: Much colder and denser than the littoral and limnetic zones. Little light penetrates this zone, making it aphotic (without light) and lacking in oxygen. It is inhabited by fish adapted to cool, dark waters.

4. Benthic Zone

Location: The bottom of the lake or pond

Characteristics: Inhabited by organisms that can tolerate cool temperatures and low oxygen levels. Mostly decomposers, detritus feeders, and fish that move between zones inhabit this area. It is nourished mainly by dead matter that falls from the littoral and limnetic zones and by sediments washing into the lake.

Lotic Systems (Flowing Water): These include rivers, streams, and creeks, where the water is in constant motion.

1. Riffles

Location: Shallow areas with swift water flow over rocky or gravelly substrates

Characteristics: High oxygen levels due to turbulent water, supporting algae, certain insects, and fish species adapted to fast currents.

2. Pools

Location: Deeper, slower-moving sections of a stream or river

Characteristics: Lower oxygen levels compared to riffles, providing habitat for aquatic plants, fish, and invertebrates that prefer calmer water.

3. Runs (Glides)

Location: Areas of smooth, unbroken flow between riffles and pools

Characteristics: Moderate flow and depth, serving as transition zones with a mix of species from both riffles and pools.

Wetland Zones and Pond zones:

Wetlands are transitional areas between terrestrial and aquatic ecosystems and can include marshes, swamps, and bogs.

1. Emergent Zone

Location: Edges of the wetland

Characteristics: Plants rooted in the soil but emerging above the water surface, such as cattails and reeds. This zone provides habitat for birds, insects, and amphibians.

2. Floating-Leaved Zone

Location: Deeper parts of the wetland

Characteristics: Plants with leaves floating on the water surface and roots anchored in the soil, such as water lilies. This zone offers habitat and food for various fish and invertebrates.

3. Submerged Zone

Location: Deepest parts of the wetland

Characteristics: Plants entirely underwater, like pondweeds, crucial for oxygenating the water and providing habitat for fish and invertebrates.

These zones in freshwater ecosystems support a rich diversity of life and play vital roles in maintaining ecological balance, water quality, and providing resources for numerous species, including humans.