Why are scientists particularly concerned about the impact of rising carbon dioxide levels on marine diversity?

Scientists are particularly concerned about the impact of rising carbon dioxide (CO2) levels on marine diversity due to several interrelated reasons:

1. Ocean Acidification: When CO2 is absorbed by seawater, it reacts with water to form carbonic acid, which lowers the pH of the ocean. This process, known as ocean acidification, can have detrimental effects on marine organisms, particularly those with calcium carbonate shells or skeletons, such as corals, mollusks, and some plankton species. Acidification reduces the availability of carbonate ions, which are essential for these organisms to build and maintain their structures. This can lead to weaker shells and skeletons, making them more vulnerable to predation and environmental stresses.

2. Coral Bleaching: Rising sea temperatures, which are linked to increased levels of greenhouse gases like CO2, can lead to coral bleaching. This occurs when corals, stressed by high temperatures, expel the symbiotic algae (zooxanthellae) that live in their tissues and provide them with food through photosynthesis. Without these algae, corals lose their color and their main source of nutrients, which can lead to widespread coral death. Since coral reefs are biodiversity hotspots, their decline has cascading effects on the entire marine ecosystem.

3. Disruption of Food Webs: Changes in ocean chemistry and temperature can affect the distribution and abundance of plankton, which form the base of the marine food web. This can have ripple effects up the food chain, impacting fish populations, marine mammals, and birds. For example, changes in the timing of plankton blooms can misalign with the breeding cycles of fish and birds that rely on them for food, leading to reduced survival rates.

4. Habitat Loss: Rising CO2 levels contribute to global warming, which can lead to the melting of polar ice caps and the loss of important marine habitats. Species that depend on these habitats, such as polar bears, seals, and penguins, may face significant challenges as their hunting and breeding grounds disappear.

5. Ocean Deoxygenation: Increased CO2 levels and higher temperatures can reduce the solubility of oxygen in seawater and disrupt ocean circulation patterns, leading to areas of low oxygen known as hypoxic zones. These zones can be deadly for marine life, causing die-offs and altering species composition and ecosystem function.

6. Extreme Weather Events: Climate change, driven by rising CO2 levels, is associated with more frequent and severe weather events such as hurricanes and typhoons. These events can cause physical damage to marine ecosystems, such as coral reefs and mangroves, and lead to increased sedimentation, which can smother marine life.

The cumulative impact of these factors on marine diversity is a major concern for scientists, as it can lead to the loss of species, reduced ecosystem services, and altered marine food supplies, which are critical for the livelihoods and food security of billions of people worldwide.