The ecosystem will be destabilized as abiotic resources like available space are reduced.
Key species found on the barrier island will move to a new habitat.
Explanation:
Due to living of humans on the barrier Island with adversely affected the organisms present on that Island because the loss of habitat occur due to living of humans and the important species migrated to other habitats where no humans are present. So this action greatly change the environment of barrier Island and the ecosystem will be destabilized.
They get runoff into water sources which can be injested by fish which can be injested by birds or any animal who eats the fish or drinks the water including us!