What will most likely happen to this ecosystem if the herring are killed by a virus?

If the herring are killed by a virus, the ecosystem will most likely experience a trophic cascade. This means that the populations of organisms that depend on the herring for food will be affected, leading to a ripple effect throughout the ecosystem.

The first level of impact will be on the zooplankton, which are small animals that feed on phytoplankton and are an important food source for the herring and the fish that eat herring. With fewer zooplankton, the herring and other small fish that feed on them will have less food, leading to a decrease in their populations.

This decrease in the populations of small fish will then impact the larger predators that feed on them, such as cod, tuna, and other large fish. These predators will have less to eat, leading to a decrease in their populations as well, resulting in a trophic cascade.

Additionally, the loss of herring will have an impact on seabirds and marine mammals that rely on them as a food source. This will lead to changes in their behaviors, such as increased competition for food and changes in their migration patterns, which can impact other parts of the ecosystem.