"Then pay attention. The contract is for moving containers. The Coast Guard is still responsible for security.
Read more.
DP World to invest in port security"
Your link doesn't mention anything about US ports. DP World may well be responsible for security at ports it operates in other countries. However this deal won't affect at all the way the American ports are run.
It doesn't rule it out either and it DOES say:
is planning to invest in security issues at the ports and terminals it owns and manages around the world,