If you spot a splash of electric blue drifting along the shoreline, it's probably not a plastic bag. That pulsing blob is likely either a Portuguese man-of-war or a blue jellyfish , one of the most striking marine invertebrates you can find floating near beaches in the Northern Hemisphere (primarily in the North Atlantic region).

Despite their vibrant appearance, blue jellyfish are not actually fish. But like other jellyfish species, they're plankton — drifting creatures at the mercy of the ocean.

These animals move with the current, unable to swim against it, and rely on the wind and waves to determine where they end up. They're part of a fragile yet ancient marine ecosystem.

Meet the Blue Jellyfish

A blue jellyfish ( Cyanea lamarckii ) is typically light blue or violet with a t

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