Threat to Coral Reefs: How Climate Change Is Reducing Growth and Diversity
Coral reefs face a serious future. Climate change sharply lowers their growth and threatens the biodiversity they support. A new study shows that even moderate warming can undermine reef resilience, despite corals’ natural adaptability. This finding underscores the urgent need for action to curb greenhouse gas emissions and to explore practical strategies for reducing atmospheric CO2.
Christopher Cornwall from Victoria University of Wellington highlights a sobering point. The coral’s native capacity to adapt cannot fully prevent reef erosion driven by climate shifts. The message is clear: without rapid emission reductions and new techniques to remove gases from the atmosphere, the reefs face an ongoing decline.
Coral colonies rely on a hard calcium carbonate skeleton that resembles bone in its strength, while soft polyps extend beyond the skeleton. Inside these polyps live tiny algae that provide essential nourishment for the corals, creating a symbiotic partnership critical to reef health.
Corals have a long generation time, which slows their ability to evolve in response to climatic stress. In contrast, many algae reproduce much faster, offering a route for rapid adaptation. Some algae show greater heat tolerance, and corals can gradually shift to them through uptake of more heat-tolerant strains.
The study, incorporating results from research published in Global Change Biology, examines how calcium carbonate production might change with climate change and the potential role of coral evolution in tolerance to warming seas.
Confirmed The Worst Signs
Researchers modeled three emission scenarios, projecting warming and acidification from 2050 to 2100: a temperate rise, a moderate increase, and a high-emission path. Temperature increases range from about 0.7° to 2.43°C, encapsulating a spectrum of possible futures.
Across these scenarios, average coral growth at sites worldwide remains positive only under the milder warming scenario, with nuanced regional differences. In moderate warming, growth could persist in 9% to 35% of reefs by 2050, but all reefs in the Atlantic and Indian Oceans face erosion. Under strict emission reductions, growth may narrow to 9%–13% by 2050.
The report warns that the natural adaptive capacity of corals translates into only slightly higher growth rates when emissions are kept low. In the harshest outlook, only a few hundred reefs would survive among those studied, signaling an urgent imperative to cut greenhouse gases to protect long-term reef integrity.
In the most severe scenario, a small number of reefs could persist, highlighting the immediate need for emission reductions and proactive carbon removal measures. The findings emphasize that coral resilience hinges on both slower warming and shifts in the algal partners that support coral skeletons.
Protecting coral reefs is essential for global biodiversity and coastal protection. Tropical and subtropical reefs house a substantial portion of marine life and act as natural barriers against coastal erosion by dissipating wave energy. The sustained health of these ecosystems hinges on stable sea temperatures and adequate light for photosynthesis, which underpin reef growth.
Biologists note recent coral bleaching events tied to marine heatwaves. The ongoing challenge is that continued warming will limit corals’ ability to survive and continue growing, reducing reef coverage in many areas.
Toward More Heat-Resistant Species
Many corals may not keep pace with rising temperatures, risking a loss of ecological function on a global scale. Some species with higher heat tolerance could still sustain calcium carbonate production in the most at-risk habitats, though these species typically grow more slowly.
The central challenge is the inverse relationship between heat tolerance and growth rate. The fastest-growing corals tend to be the most heat sensitive. The proposed path forward combines keeping warming below 1.5°C with aggressive carbon removal efforts and investment in resilience research.
Corals experience whitening when they lose their symbiotic algae, zooxanthellae, which provide food and color. Without these algae, corals become more susceptible to disease and eventual death, compromising reef structure and function.
Higher atmospheric CO2 drives ocean acidification, reducing the availability of calcium carbonate essential for skeleton formation. This hampers growth and development, further stressing reef systems as seas rise and light conditions change.
Global warming also contributes to rising sea levels, which reduce light access and constrain vertical reef development. More frequent and intense tropical storms and hurricanes add physical stress, causing additional damage to reef-building structures.
As a result, many coral reefs are stressed or severely damaged, with declines in biodiversity and coral cover reported across regions. A comprehensive understanding of these dynamics remains essential for informing conservation strategies and policy decisions. The study referenced here draws on the Global Change Biology findings to illustrate the potential trajectories of reef growth under different climate futures.
The overall picture stresses the need for urgent action to curb emissions and invest in methods to remove CO2 from the atmosphere. Such measures could help stabilize ocean chemistry and preserve coral-building processes for future generations.