Aquatic Life and Eutrophication: Understanding the Impacts
Eutrophication
Eutrophication occurs when a lake or river becomes overly enriched with nutrients. This excess of nutrients causes excessive plant and organism growth. When these organisms die and decay, they deplete the water’s dissolved oxygen, creating foul odors and an unpleasant appearance. This drastically reduces water quality and can destroy the ecosystem.
Oligotrophic vs. Eutrophic Waters
Oligotrophic waters are nutrient-poor, characterized by clear water, light penetration, minimal algal growth, and the presence of oxygen-loving species like trout. As a lake accumulates nutrients, it becomes eutrophic. Algae proliferate, making the water turbid. The decomposition of dead algae and other organisms consumes oxygen, harming fish and other aquatic life that require oxygen-rich environments. This can lead to anaerobic decomposition, further degrading water quality.
Harmful Algal Blooms (HABs)
Harmful algal blooms (HABs) result from the rapid multiplication of a single species of microalgae. These blooms, sometimes called “red tides” due to their pigmentation, can reach millions of cells per liter. The Intergovernmental Oceanographic Commission of UNESCO (IOC) coined the term HABs to describe blooms that produce potent toxins. These toxins can contaminate shellfish, leading to human poisoning. Dinoflagellates and diatoms are the primary microalgae responsible for toxin production.
Factors Enhancing HAB Formation
Most dinoflagellates, including toxic species, reproduce through simple division, allowing rapid population growth. Two main mechanisms contribute to this:
- Biological growth: Stimulated by appropriate salinity and nutrient levels.
- Physical concentration: Light winds and high sunlight can concentrate cells in specific areas.
High concentrations of toxic organisms are often observed in low salinity and relatively high temperatures. Calm winds and intense sunlight further contribute to HAB development.
Aquatic Life
Definition: Aquatic life encompasses the complex adaptations and behaviors of a species within its natural aquatic environment, contributing to its survival.
Relationships and Lifestyles
Aquatic life exhibits various relationships with its environment, including:
- Relationship with the substrate:
- Epibiosis: Living on the substrate surface (e.g., algae, barnacles).
- Endobiosis: Living within the substrate (e.g., burrowing clams, worms).
- Food gathering:
- Autotrophs: Produce their own food (e.g., algae).
- Heterotrophs: Consume other organisms (e.g., carnivores, herbivores, parasites).
- Locomotion:
- Swimming, gliding, floating, burrowing, etc.
- Reproduction: Various reproductive strategies exist.
Molluscs
Molluscs are a diverse group of aquatic animals characterized by a soft body, often protected by a calcareous shell. They are classified into seven groups:
- Aplacophora: Worm-like, without a shell (e.g., Neomenia).
- Monoplacophora: Single, conical shell (e.g., Neopilina).
- Polyplacophora: Shell with eight overlapping plates (chitons).
- Bivalvia: Two-part shell (e.g., clams, mussels).
- Gastropoda: Single, often coiled shell (e.g., snails, slugs).
- Scaphopoda: Tubular shell open at both ends (e.g., tusk shells).
- Cephalopoda: Tentacles or arms, reduced or absent shell (e.g., squid, octopus).