Why in the news?

A 2024 study in Ecology and Evolution reports that insects such as ladybirds and dragonflies in temperate regions are turning lighter due to frequent heatwaves. Over half of the world’s oceans have become greener in the last two decades. Forests are turning browner. Coral reefs, including those in Gulf of Mannar and Lakshadweep, are facing repeated bleaching. These visible colour changes reflect large-scale climate stress on ecosystems.

What is Ecological discolouration?

Ecological discolouration refers to measurable changes in the natural colour patterns of ecosystems caused by environmental stress. It can be caused by:

1. Pigment Alteration: Changes in the concentration or type of biological pigments like chlorophyll (green in plants/algae), melanin (darker tones in animals), and carotenoids (yellow/orange) often due to UV exposure or nutrient shifts.
2. Symbiotic Loss: The most prominent example is coral bleaching, where corals expel their colorful symbiotic algae (zooxanthellae) due to thermal stress, leaving behind a white skeleton.
3. Species Composition Shifts: The replacement of native species with others such as invasive toxic dinoflagellates or algae blooms can physically change the color of water bodies or forests.
4. Biogeochemical Disruptions: Alterations in cycles (like nitrogen or carbon) can lead to soil or water changes, such as the formation of dark terra preta soils or anaerobic “black spots” in marine sediments.

Functions in Ecology

1. Early-Warning Indicator: Visible fading or darkening provides an immediate signal of ecosystem instability.
2. Stress Proxy: It serves as a measurable metric for temperature stress, chemical pollution, and habitat degradation.
3. Biodiversity Marker: Mapping color variations across a landscape helps scientists track the loss or gain of biodiversity in real-time

How is climate change altering ocean colour?

1. Ocean Greening: Over 50% of global oceans have become greener in the last two decades.
2. Algal Proliferation: Greener waters indicate increased algal presence.
3. Sunlight Blockage: Algae reduce water clarity and limit sunlight penetration.
4. Oxygen Depletion: Decomposition of algal blooms lowers oxygen levels, harming marine organisms.

What is Coral bleaching?

It is when corals expel the colorful, nutrient-providing algae (zooxanthellae) living in their tissues due to stress, turning them white, but they aren’t dead yet. Prolonged stress from rising ocean temperatures (climate change) or other factors like pollution causes them to starve and potentially die, leading to reef ecosystem collapse.

What happens during bleaching?

1. Stress triggers expulsion: Corals are stressed by changes in water temperature (usually warming), light, salinity, or nutrients.
2. Algae leave: Stressed corals expel the symbiotic algae (zooxanthellae) that live within them and provide food and color.
3. Coral turns white: Without the algae, the coral’s transparent tissue reveals its white skeleton, making it appear “bleached”.

How does coral bleaching reflect marine ecosystem stress?

1. Indian Reef Impact: Bleaching reported in Gulf of Mannar, Palk Bay, Lakshadweep, Andaman & Nicobar Islands.
2. Thermal Stress Mechanism: Corals expel symbiotic algae under heat stress, turning white.
3. Mortality Risk: Repeated bleaching increases coral death probability.
4. Ecosystem Disruption: Coral reefs support marine biodiversity and fisheries.

What does forest browning indicate?

1. Vegetation Stress: Forests are turning browner due to climate stress and habitat degradation.
2. Pigment Reduction: Chlorophyll loss reflects reduced photosynthetic efficiency.
3. Habitat Instability: Browning signals declining ecosystem resilience.

How are insects adapting through pigmentation change?

1. 2024 Study Finding: Ladybirds and dragonflies in temperate northern regions are becoming lighter.
2. Heatwave Response: Lighter pigmentation reflects sunlight and prevents overheating.
3. Melanin Composition:
   1. Eumelanin: Produces brown/black shades; absorbs more heat.
   2. Pheomelanin: Produces yellow/red tones.
4. Reproductive Impact: Pigmentation shifts may affect mating patterns and reproductive timing.

What historical example shows climate-driven colour adaptation?

Climate-driven colour adaptation refers to the process where, in response to changing environmental conditions (temperature, humidity, UV radiation) caused by climate change, species evolve or plastically alter their body or flower pigmentation to improve survival, thermoregulation, or reproduction.

1. Industrial Revolution Case: Soot darkened tree bark.
2. Peppered Moth Shift: Dark variants survived due to improved camouflage; light variants declined.
3. Adaptive Principle: Species become darker in colder climates and lighter in warmer conditions. 
4. Butterflies (Colias meadii): A long-term study (1953-2012) showed that wing melanization in these butterflies decreased with increasing temperature, but this pattern varied by region, showing higher melanism in the hotter southern USA.

How does deforestation affect species colour diversity?

1. Amazon Study (Biodiversity and Conservation): Deforestation reduces bright colour displays in butterflies.
2. Habitat Disturbance Effect: Disturbed forests show less diverse butterfly palettes.
3. Regeneration Signal: Naturally regenerated Amazon forests show improvement in colour diversity.

What are the ecological implications?

1. Camouflage Disruption: Alters predator-prey balance.
2. Thermoregulation Shift: Pigmentation change modifies heat absorption.
3. Biodiversity Indicator: Colour variation reflects ecosystem health.
4. Systemic Climate Signal: Large-scale discolouration indicates long-term environmental stress.

Conclusion

Ecological discolouration represents a visible manifestation of climate-induced ecosystem stress. Ocean greening, forest browning, coral bleaching, and pigmentation shifts in species indicate disruption in biological processes and habitat stability. These changes signal declining ecosystem resilience and rising vulnerability to extreme climatic events. Monitoring such colour shifts can function as an early warning tool for biodiversity loss and guide targeted climate adaptation and conservation strategies.

PYQ Relevance

[UPSC 2017] ‘Climate Change’ is a global problem. How India will be affected by climate change? How Himalayan and coastal states of India will be affected by climate change?

Linkage: Climate change impact is a recurring GS-3 theme linking environment, disaster vulnerability, and sustainable development. Coral bleaching, ocean warming, and marine ecosystem stress are important for coastal impact analysis, while Himalayan glacier melt, altered monsoons, and extreme events are crucial dimensions when examining climate change effects in India.

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