As a small hatchling, almost everything. Anything that can fit a small hatchling into its mouth, will do so. Most common predators of eggs and hatchlings on land are racoons, herons, ghost crabs and sea gulls. Most common predators in the water are any large fish and sharks. Once a turtle gets to adult size, several feet in length, then it has very few predators.
Humans are a major predator of sea turtles at all life stages.
Yes it could, but only during the warmer summer months. It is common for turtles to be seen off the coast of New England, especially Rhode Island. Sea turtles feed offshore of these areas, but do not nest. Loggerheads eat crabs, clams and other shellfish. Anything that can fit a small hatchling into its mouth, will do so.