How does La Niña affect marine biodiversity?

La Niña events can significantly impact marine biodiversity by altering ocean temperatures, nutrient availability, and weather patterns.

La Niña is a climate phenomenon characterised by unusually cold ocean temperatures in the Equatorial Pacific, as opposed to El Niño, which is characterised by unusually warm ocean temperatures in the same region. These changes in ocean temperatures can have profound effects on marine biodiversity.

One of the primary ways La Niña impacts marine biodiversity is through changes in nutrient availability. Cooler waters are typically more nutrient-rich than warmer waters. During La Niña events, the upwelling of these cooler, nutrient-rich waters can lead to an increase in primary productivity, the rate at which plants and algae convert sunlight into chemical energy through photosynthesis. This increased productivity can support larger populations of herbivorous zooplankton, which in turn can support larger populations of fish and other marine animals.

However, while some species may benefit from the increased availability of food, others may suffer. Species that are adapted to warmer waters may struggle to survive in the cooler conditions brought about by La Niña. This can lead to shifts in the composition of marine communities, with some species becoming more dominant and others declining.

La Niña can also impact marine biodiversity through changes in weather patterns. The cooler ocean temperatures associated with La Niña can influence atmospheric circulation, leading to changes in rainfall patterns. This can result in increased rainfall in some areas, leading to greater runoff from land. This runoff can carry pollutants and excess nutrients into the ocean, which can lead to harmful algal blooms and other problems that can negatively impact marine life.

Furthermore, the changes in ocean temperatures and weather patterns brought about by La Niña can disrupt the timing of biological events, such as the breeding and migration of marine species. This can have knock-on effects throughout the marine food web, impacting not only the species directly affected, but also the predators and prey that rely on them.

In conclusion, while La Niña can lead to increased productivity in some areas, it can also lead to shifts in species composition, disruptions to biological timing, and increased pollution, all of which can impact marine biodiversity.