There are (at least) two objects known as a "sea bean."
One is a hard seed washed ashore by the ocean. These can include coconuts, This kind of sea bean uses the ocean's currents to spread far and wide, much as other plants might spread their seeds on the wind or on a dog's fur. It is also known as a "drift seed." Because they have so far to travel and doubtless undergo many adventures on their way, these sea beans are covered by a hard shell which must be heavily scored - scarified - if it is to germinate. Other drift seeds and drift fruits include the mango, seaside hibiscus, hog plum, tropical almond, and nothing nut.
The second type of sea bean is a small green strand, a little like miniature asparagus. The James Beard Foundation explains that these sea beans are like "Nautical haricots verts. Popeye may have had spinach, but a seafaring vegetarian's delight is the sea bean. The American sea bean is a type of samphire (SAM-fy-uhr) known as salicornia. Its other aliases are glasswort (it was used to make glass at one time), marsh samphire, and sea pickle. Sea beans proliferate on both the Pacific and Atlantic coasts. Some have spiky green leaves that make the plant look like a skinny miniature cactus without the needles. Others look surprisingly similar to Chinese long beans. The crisp leaves and stems smell and taste like sea salt." Personally, I'm eating some right now and I would say that they taste exactly like salt water, although that's a rather fine distinction. When held in the mouth to warm up, they begin to taste a little like olives, probably because the salty flavor is reminiscent of their brine.
These bright green sea beans are often found pickled in jars at farmer's markets or gourmet food establishments; however, "foodies" also heartily recommend their use as a garnish. They are often described as tasting salty or fishy if cooked; however, it is rarely indicated whether this is supposed to be good or bad.The few examples of hard-shelled sea beans that can be eaten are found in a wide variety of places depending on the local culture, as their inner meat (such as that of the coconut or acorn) generally has many uses.