Ocean acidification affects zooplankton by causing reduced calcification rates in species that form shells and by disturbing their acid-base (metabolic) physiology, which can impact other bodily functions.
Ocean acidification is a significant environmental challenge driven by the absorption of excess carbon dioxide (CO2) from the atmosphere into the ocean. This process leads to a decrease in seawater pH, an increase in hydrogen ions, and changes in the availability of carbonate ions. These chemical shifts have various impacts on marine organisms, including zooplankton.
Zooplankton, a diverse group of small animals drifting in the water column, play a crucial role in marine food webs. Their responses to ocean acidification are varied depending on the specific species and their life stage. However, direct effects on their biology have been observed.
Direct Impacts on Zooplankton
Based on research, direct responses of zooplankton to increasing ocean acidity can include:
- Reduced Calcification Rates: Many zooplankton species, such as pteropods (often called "sea butterflies") and foraminifera, build shells or skeletons made of calcium carbonate. As the ocean becomes more acidic, the availability of carbonate ions decreases, making it harder for these organisms to build and maintain their shells. This can lead to weaker or thinner shells, or a reduced ability to grow them, making them more vulnerable to predation or environmental stress.
- Disturbance to Acid-Base (Metabolic) Physiology: Organisms need to maintain a stable internal pH to ensure their metabolic processes function correctly. Ocean acidification can disrupt the acid-base balance within zooplankton's bodies. This metabolic disturbance can affect various physiological functions necessary for survival, growth, and reproduction.
These direct effects can have cascading consequences for zooplankton populations and the wider marine ecosystem. Reduced calcification or physiological stress can impact growth rates, reproductive success, and survival, potentially leading to declines in certain zooplankton populations. Given their position at the base of many marine food chains, changes in zooplankton abundance and health can have significant repercussions for organisms that feed on them, including fish, seabirds, and marine mammals.
While the zooplankton response to acidification is variable across different species, the fundamental impacts involving reduced calcification rates and disturbance to acid-base (metabolic) physiology represent key challenges posed by ocean acidification.
