Was it beneficial or harmful for the Chthamalus barnacle to add the Balanus barnacle? Explain.

meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.