Which Of The Following Changes In Eastern Pacific Ocean Food Webs Is Typically Associated With La Niña Events?
Which Of The Following Changes In Eastern Pacific Ocean Food Webs Is Typically Associated With La Niña Events?
Answer: La Niña events are climatic conditions characterized by cooler-than-average sea surface temperatures in the central and eastern Pacific Ocean near the equator. These events are part of the El Niño-Southern Oscillation (ENSO) cycle and typically lead to significant changes in oceanic and atmospheric conditions, which in turn affect marine ecosystems and food webs.
1. Increased Nutrient Upwelling
During La Niña events, the trade winds strengthen, which enhances the upwelling of cold, nutrient-rich water along the eastern Pacific coast. Upwelling is a process where deep, cold, and nutrient-laden waters are brought to the surface. These nutrients, primarily nitrate and phosphate, support phytoplankton growth. Phytoplankton forms the base of the aquatic food web, and increased primary production supports larger populations of zooplankton, fish, and higher trophic levels, including marine birds and mammals.
Example: The Peruvian Anchoveta fishery often flourishes during La Niña events due to the increased availability of phytoplankton, which serves as a foundational food source for anchovies.
2. Enhanced Fishery Productivity
With increased phytoplankton production due to nutrient upwelling, there is typically a boost in the overall productivity of the marine ecosystems in the eastern Pacific. This increase in productivity supports larger populations of small pelagic fish, such as sardines and anchovies, which are crucial components of the food web. These small fishes are prey for larger predators, including larger fish species, seabirds, and marine mammals.
Real-World Impact: Fishermen usually experience better catches during La Niña due to the greater abundance of commercially important fish species, which can positively affect local and regional economies dependent on fisheries.
3. Changes in Predator and Prey Dynamics
As primary and secondary production increases, there can be shifts in predator-prey relationships within the food web. Species that rely on smaller fish and zooplankton may experience population increases due to the abundant food supply. However, this can also lead to increased competition among predators if the supply of prey does not keep pace with the growing predator populations.
Example: During La Niña, an increase in larger predatory fish populations may be observed, but if prey populations do not increase sufficiently to support the larger predator numbers, it can lead to changes in species distribution as predators migrate in search of more abundant resources.
4. Impact on Marine Birds and Mammals
Marine birds and mammals typically benefit from La Niña conditions due to the increased availability of fish. Seabirds like gulls, pelicans, and albatrosses may experience better breeding success and higher chick survival rates because of the increased food supply. Similarly, marine mammals, including seals and sea lions, may thrive due to the abundance of fish.
Observation: The breeding colonies of species such as the Peruvian pelican may see higher success rates during La Niña events, reflecting the overall health of the marine food web.
5. Changes in Species Composition and Distribution
La Niña events can lead to temporary changes in the composition and distribution of species in the eastern Pacific. Warmer water species might retreat to other regions, while cold-adapted species could thrive in the cooler waters typical of a La Niña. Such changes can alter the biodiversity and balance within the ecosystem temporarily.
Long-term Implications: Over an extended period, frequent or severe La Niña events might lead to shifts in species’ geographic ranges, potentially affecting local biodiversity and the structure of marine ecosystems.
6. Variability and Resilience of Ecosystems
The variability introduced by La Niña events highlights the resilience of ocean ecosystems. These ecosystems have evolved with the natural oscillations of ENSO, and while individual species might experience stress or benefit differently, the overall ecosystem tends to oscillate back toward a state of balance over time. However, increased frequency or intensity of such events, compounded by human-induced stresses like overfishing and climate change, could impact the resilience and recovery of these ecosystems.
In conclusion, La Niña events typically result in increased nutrient upwelling in the eastern Pacific, boosting the productivity of marine food webs and positively affecting fisheries and higher trophic levels. These changes underscore the complex interactions within ocean ecosystems and the influence of climatic patterns on marine biodiversity and food web dynamics. Understanding these interactions helps in managing and conserving marine resources effectively, particularly in the face of evolving climatic conditions.