Marine Organisms

Marine organisms are found in every maritime ecosystem across the globe. They form a diverse group of species, each with unique physical traits that enable them to survive in the challenging conditions of the ocean, such as extreme depths, pressure, and darkness. Examples of common marine organisms include phytoplankton, zooplankton, seaweeds, and seagrasses. This article provides an overview of marine organisms, which will be useful for preparing the Environment section of the UPSC Civil Services exam.

Common Marine Organisms

Plankton

Plankton refers to organisms that drift on the surface of water bodies like rivers, lakes, and oceans. Phytoplankton and zooplankton, microscopic plants and animals, inhabit nearly all aquatic ecosystems, except some fast-moving waters. Water currents mostly carry plankton, as they have limited movement. Tropical seas, especially near mangroves, show high productivity and diversity in plankton populations.

Phytoplankton

Phytoplankton are microscopic plant organisms that live in both freshwater and marine environments. The name “phytoplankton” comes from the Greek words phyto (plant) and plankton (drifting). These include protists, bacteria, and single-celled plants, such as cyanobacteria, diatoms, dinoflagellates, and green algae. Phytoplankton are responsible for producing over 60% of the Earth’s oxygen. They use chlorophyll to capture sunlight and convert it into chemical energy, similar to land plants. Phytoplankton play a vital role in the food web and are the primary producers in marine ecosystems, forming the basis of the aquatic food chain.

Zooplankton

Zooplankton are heterotrophic plankton that feed on phytoplankton and other organic matter. These organisms cannot produce their own food, so they consume other plants or animals for sustenance. Zooplankton are critical in the food web and contribute to nutrient cycling and the transfer of organic matter to secondary consumers like fish. They are more abundant in mangrove areas than in surrounding coastal waters. Zooplankton communities are essential for assessing the productivity and health of ecosystems. Key examples include copepods, protozoa, and larvae of fish, crabs, and lobsters. Zooplankton can be divided into holoplankton (permanent plankton, such as copepods) and meroplankton (temporary plankton, such as juvenile starfish and clams).

Sea-Grass

Sea grasses are flowering plants found on the ocean floor. These marine angiosperms spend most of their lives submerged in water. They typically have narrow, strap-like or oval leaves and rely on sunlight for photosynthesis. Sea grasses grow best in sandy or muddy substrates, though they can also thrive in rocky areas. Important species include Sea Cow Grass (Cymodocea serrulata), Needle Seagrass (Syringodium isoetifolium), and Ribbon Grass (Enhalus acoroides). Despite once thriving in regions like the Gulf of Mannar, seagrasses are now endangered in many parts of the world.

Seaweeds

Seaweeds refer to various marine plants and algae found in the ocean and other water bodies. Seaweeds belong to different groups of macroalgae, including red algae (Rhodophyta), brown algae (Phaeophyta), and green algae (Chlorophyta). These organisms play a vital role in carbon sequestration and produce at least 50% of the Earth’s oxygen. Seaweeds, such as kelps, also provide critical habitats for marine life, supporting fisheries and other organisms in marine ecosystems.

Conclusion

Marine organisms face significant challenges in saltwater habitats due to the high salt concentrations. In saline environments, ions are distributed evenly, leading to excessive salt levels in the bodies of marine organisms. To maintain internal balance, these organisms excrete concentrated urine to remove excess salt, helping them survive in the salty waters of the ocean.