The word used most often for any drifting creature in the sea is plankton. Plankton literally means “drifter” or “wanderer”. Most plankton, including planktonic fish, can swim. Some can adjust their position in the water column – rising near the surface at night, sinking deeper during the day.
With miles and miles of open blue water, the swimming fish must keep swimming. To do this requires lots of energy, so open water fish must consume a lot of high energy food. Drifters just drift. Hang with the currents, enjoying the moment, eating what they can. As you can imagine, there are not many fish living this lifestyle. Many fish live like this after they hatch in their larval stage – but as adults, most live on the bottom, others in the open blue.
Sunfish are weird looking fish with large bulbous head, long angular dorsal and ventral fins, and no tail – it’s a swimming/drifting head. These large open water drifters can reach seven feet long, seven feet high, and weigh over a ton. Sunfish can hold their position and undulating their dorsal and ventral fins, move slowly through the water. Often, they will turn on their sides and just hang there looking somewhat like a floating board. Small creatures are attracted to them and may be consumed. Their diet is primarily jellyfish, though they have been known to take small fish, crustaceans, and even algae.
Though rarely seen near shore, they have been, and one was actually spotted inside Pensacola Bay. They occasionally wash ashore dead. any know this fish by its scientific name – Mola mola – or simply the mola.
Sargassum Fish are members of a frogfish family named for the common seaweed that it typically drifts with. Sargassum is a type of brown algae that produces air bladders called pneumatocyst. These bladders allow the seaweed to drift in large mats at the surface where they get sunlight. Some sargassum mats are huge in size and form an ecosystem that shelters hundreds of small fish and invertebrates, even baby sea turtles. The coloration of the Sargassum fish matches the Sargassum weed perfectly.
Like other frogfish, the first dorsal spine is modified into an appendage resembling a fishing rod complete with a lure. When prey are in view, the Sargassum fish will extend the illicium (as the lure is called) and actually move it back and forth to make it look like live bait. They are “fishing” for small creatures in the Sargassum mat.
Most members of the Sargassum community flee the seaweed when the currents bring it too close to the shore. If you are at the beach when the Sargassum is drifting just off the shore, wade out with a small dip net and snag a patch. Place in a bucket of water and see who comes out. You might get lucky and catch one of these camouflaged drifters.