Final answer:
A decrease in pH, or ocean acidification, negatively impacts sea urchins by hindering their shell formation due to reduced availability of calcium carbonate. This affects not only urchins but also the marine ecosystem and food web.
Step-by-step explanation:
The impact of a decrease in pH on sea urchins and other marine organisms is significant. A lower pH level, which indicates more acidic conditions, can have detrimental effects on the calcification process necessary for the development of their shells and exoskeletons. Ocean acidification results from increased atmospheric CO2 levels, leading to more CO2 dissolving in the ocean, causing acidity to increase. This acidity can disrupt the availability of calcium carbonate, a critical component that urchins and similar organisms require to build their shells. Consequently, a pH decrease in their environment can lead to weaker shells and even dissolution during their lifespan, affecting their survivability and the broader marine ecosystem.
Moreover, the impact extends to the base of the food chain, influencing organisms such as plankton that urchins might feed on, creating a cascading effect on the food web and biodiversity. This alteration in water chemistry can also affect the metabolic processes within marine organisms, leading to broader ecological consequences.