In this article, the discussion focuses on the lake food chain. The food chain explains how food energy transfers from one organism to another within a system. The primary producers, such as phytoplankton and bacteria, synthesize their own food, which becomes available to consumers.
Key Differences Between Aquatic and Terrestrial Organisms
The chemical and physical characteristics of water and air expose aquatic and terrestrial organisms to different environmental conditions:
1. Supporting structures: Aquatic organisms do not need body structures as strong as terrestrial organisms.
2. Density: Water has a density close to that of organisms living in it. Its viscosity is about 50 times higher than air, making movement costlier in terms of energy for aquatic organisms than for terrestrial ones.
3. Oxygen concentration: Water holds less oxygen compared to air, meaning aquatic organisms need to perform more work to access the same amount of oxygen as terrestrial organisms.
4. Carbon dioxide levels: The concentration of free carbon dioxide is higher in water than in the atmosphere, allowing aquatic plants to have more inorganic carbon available than terrestrial ones.
5. Nutrient absorption: Aquatic autotrophs access dissolved nutrients in water without needing specialized transporting structures.
Both aquatic and terrestrial ecosystems follow a similar process where matter and energy flow through organisms, forming a food chain. The energy eventually degrades into heat, while matter is recycled through various stages of complexity.
Read Also: Powdery Mildew: Description, Damages Caused, Control and Preventive Measures
Classification of Aquatic Organisms Based on Their Roles in the Ecosystem
1. Primary Producers: These autotrophic organisms synthesize organic matter using energy from the sun and inorganic substances. They include unicellular algae, free-floating phytoplankton, periphyton attached to substrates, and aquatic plants in the littoral zone. Photosynthetic and chemosynthetic bacteria are also part of this group.
2. Consumers: Consumers rely on primary producers for food. They are categorized as primary (feeding on autotrophs), secondary (feeding on plant-eating animals), and tertiary consumers (feeding on secondary consumers). Carnivorous fish, birds, and fish-eating mammals represent the final link in the aquatic consumer chain.
3. Detritivores: Detritivores consume dead organisms and waste products, breaking them down into simpler chemical structures.
4. Decomposers: These are primarily heterotrophic bacteria that decompose organic molecules into inorganic constituents (mineralization), which are then reused by autotrophs, contributing to nutrient recycling.
Classification of Aquatic Organisms Based on Their Habitats
1. Plankton: This group includes animals (zooplankton), plants (phytoplankton), bacteria (bacterioplankton), and viruses (virioplankton). They inhabit both the littoral and pelagic zones. Autotrophic phytoplankton and bacterioplankton perform photosynthesis in the euphotic zone. Some planktonic organisms move but cannot resist water currents, thus floating with the water masses.
2. Virioplankton: Viruses are small organisms made of nucleic acids (RNA or DNA) within a protein capsule. They reproduce within living cells, existing in both extracellular and intracellular phases. In the intracellular phase, viruses replicate within host cells, often causing them to lyse and release new viral particles into the environment.
3. Bacterioplankton: These prokaryotes, including autotrophic and heterotrophic bacteria, range from 0.2 to 2 µm. Autotrophs like cyanobacteria and chemosynthetic bacteria derive energy from light or mineral oxidation, while heterotrophs rely on organic matter. Archaea, genetically distinct from bacteria, also belong to bacterioplankton and thrive in extreme environments.
Roles of Bacteria in the Food Chain
Bacteria contribute to organic matter breakdown by hydrolyzing complex substances and recycling dissolved organic matter into new bacterial cells, which are consumed by larger organisms.
A. The Phytoplankton’s Role in the Food Chain
Phytoplankton, primarily algae, form the foundation of the food chain, synthesizing organic matter through photosynthesis. The carbon and oxygen used in this process come from atmospheric CO2, and glucose (C6H12O6) is the end product. Photosynthesis consists of two phases:
i. Light-dependent phase: Solar energy is captured by chlorophyll and converted into NADP and ATP, energy-rich molecules that are unstable.
ii. Dark phase (Calvin cycle): ATP and NADP help produce energy-rich carbohydrates, which are stored and used to create new organic matter, leading to cell division.
Composition of Freshwater Phytoplankton Communities
Phytoplankton communities are diverse, including prokaryotes like cyanobacteria and eukaryotes from taxonomic groups such as Diatoms, Chrysophytes, Cryptophytes, Dynophytes, Euglenophytes, and Chlorophytes.
1. Prokaryotic cells: Photosynthesis occurs within invaginations of the cell membrane, and chromosomes are dispersed in the protoplasm.
2. Eukaryotic cells: These cells have specific organelles like chloroplasts for photosynthesis, and chromosomes are present in the nucleus.
3. Cyanobacteria: Blue-green algae with prokaryotic cell structures and chlorophyll a, which they share with eukaryotic algae. Some cyanobacteria, such as Anabaena and Microcystis, produce toxins and reduce water quality.
4. Diatoms: These algae have siliceous cell walls and chlorophyll for photosynthesis.
5. Chrysophytes: Single-celled algae typical of freshwater environments low in calcium, often with flagella and scales of cellulose.
6. Cryptophytes: Algae with two long flagella and chlorophyll, found in freshwater environments.
7. Dynophytes: Algae with intermediate chromosomes, containing chlorophyll.
8. Euglenophytes: Flagellate algae in eutrophic freshwater environments.
9. Chlorophytes: Green algae with chlorophylls a and b, similar to higher plants.
B. The Zooplankton Community in Freshwater Ecosystems
1. Protozoa: Unicellular organisms, moving by cilia, feed on bacteria or detritus and transform organic matter into forms usable by higher organisms.
2. Cnidarians: A diverse group including jellyfish and corals, many of which live in marine environments but also found in freshwater.
3. Rotifera: Microscopic animals related to worms that feed on algae, protozoa, bacteria, and detritus, some of which are carnivorous.
4. Cladocerans and Copepods: Planktonic crustaceans that feed on filtered food particles and reproduce through parthenogenesis (Cladocerans) or sexual reproduction (Copepods).
The transformation of organic matter by heterotrophs is called secondary production. Annual net secondary production sums the total biomass produced, accounting for losses due to mortality, predation, and emigration.
Read Also: 15 Medicinal Health Benefits Of Lysimachia clethroides (Gooseneck Loosestrife)
The Benthic Zone and Its Role in Aquatic Ecosystems
The benthic community lives in and on the sediment at the bottom of water bodies. It includes both mobile and sessile organisms like fungi, bacteria, plants, and animals. Aquatic macroalgae and macrophytes, which grow in close association with the benthos, account for a significant portion of primary production in water.
A. Phytobenthos or Periphyton (or “Aufwuchs”)
Phytobenthos refers to microscopic autotrophs attached to submerged surfaces. These organisms grow in areas where light can penetrate and include filamentous algae, cyanobacteria, and chlorophytes.
B. Macrophytes or Hydrophytes
These plants grow in aquatic environments and may be emergent, floating, or submerged. Examples include reeds (Phragmites spp.), water chestnut (Trapa natans), and free-floating plants like water hyacinth (Eichhornia crassipes).
C. Nekton, Neuston, and Psammon
1. Nekton: Aquatic animals like fish and mollusks that move independently of water currents.
2. Neuston: Microscopic organisms living at the water-air interface, including protozoa, bacteria, and larger organisms like insects.
3. Psammon: The animal community living in interstitial water of sandy beaches, including protozoa, rotifers, and crustaceans.
The lake food chain highlights the energy transfers among organisms in freshwater environments. The producers, mainly phytoplankton and bacteria, form the foundation, supporting various groups of consumers and sustaining aquatic ecosystems.
Do you have any questions, suggestions, or contributions? If so, please feel free to use the comment box below to share your thoughts. We also encourage you to kindly share this information with others who might benefit from it. Since we can’t reach everyone at once, we truly appreciate your help in spreading the word. Thank you so much for your support and for sharing!
Read Also: Top 20 Proven Benefits of Ginger Plant
Frequently Asked Questions
We will update this section soon.