Answer:
The immediate effect is overpopulation of phytoplankton & zooplankton, & the sudden decrease of predators such as whales and sea birds.
Krills are secondary consumers, and the disappearance of Krill would lead to the destruction of the food web, as sooner or later, all the species would die. However, you must note that they are not the only consumers & consumed, and other species can help regulate and outsource.
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