If the number of phytoplankton decrease what happen to food chain in ocean?

If the number of phytoplankton decreases, it can have significant consequences for the food chain in the ocean. Here's what would likely happen:

1. Reduced Primary Production: Phytoplankton are the primary producers in the ocean, responsible for converting sunlight into organic matter through photosynthesis. A decline in phytoplankton means less food is available for the organisms that feed on them directly, such as zooplankton.

2. Impact on Zooplankton: Zooplankton are small animals that feed on phytoplankton and other microscopic organisms. With fewer phytoplankton available, the zooplankton population would decline. This would affect a wide range of organisms that rely on zooplankton for food, including fish larvae, small fish, and seabirds.

3. Population Declines: The decline in zooplankton would have a ripple effect on the entire food chain. Fish, marine mammals, and other predators that rely on zooplankton for sustenance would face reduced food availability, leading to population declines.

4. Changes in Species Composition: The decrease in phytoplankton and zooplankton could alter the species composition of the ocean. Some species that rely heavily on these organisms for food may become less abundant, while others that can adapt to different food sources may become more prevalent.

5. Disruptions in Nutrient Cycling: Phytoplankton play a crucial role in nutrient cycling by taking up nutrients from the water and releasing them through their metabolic processes. A reduction in phytoplankton can disrupt nutrient cycling, potentially leading to changes in the chemistry and productivity of the ocean.

6. Feedback on Phytoplankton: The decline in phytoplankton can also affect the environment in ways that further impact their abundance. For example, reduced phytoplankton abundance may lead to increased water clarity, allowing more sunlight to reach the ocean's surface.

This can stimulate the growth of harmful algal blooms, further depleting nutrient resources and hindering phytoplankton recovery.

In summary, a decrease in the number of phytoplankton in the ocean would trigger a cascade of negative effects throughout the food chain, impacting zooplankton, fish, marine mammals, seabirds, and other marine life, ultimately leading to changes in the ocean's biodiversity and productivity.