Summarize how the over harvesting of a single species such as baleen whales can affect an entire ecosystem

Over harvesting can affect an entire species, because it can change relationships in the food web, for example with too many whales many organisms could lose their food source and homes, or even worse, could go extinct!

The over-harvesting of a single species of whale such as baleen whales can negatively affect an entire ecosystem because whale fecal matter contains many essential nutrients like phosphorus, nitrogen, iron that help the microalgae(phytoplankton) to grow.

These microalgae support the population of zooplankton and zooplanktons support the population of small invertebrates like krills and small fishes.  

Studies showed that a decrease in the population of baleen whale decreases the primary production i.e., the production of phytoplankton in oceans which in turn decrease the population of krills and fishes. So the overharvesting of one species can affect the whole ecosystem of the ocean.

answer; i believe the correct answer is (a)0