The open ocean is surprisingly barren to the naked eye. Every now and again you will encounter a school of fish and their attendant predators, but most of the life that you find is gathered around some sort of sheltering structure like a coral reef.  In the Atlantic, the pelagic macro-algae, or sargassum seaweeds (Sargassum fluitans and Sargassum natans) serve as shelter, drawing in a tremendous variety of marine life and forming a nearly unique structural habitat in the open ocean. Without roots, a top, or a bottom, the sargassum is in constant motion until it is cast up on a beach, or sinks out of the range of light and into the depths of the ocean. The algae is buoyed in the water column by small floats called pneumatocysts, which are full of gas.

In collaboration with the Smithsonian Marine Station and Chris Meyer of the Smithsonian National Museum of Natural History, we work on the ecology, genetics, and connectivity of this community.The photos in this series illustrate the group of organisms that live in intimate association with the algae. They are camouflaged to look just like their home. Unlike the mahi-mahi and other predatory fish that come to sargassum to feed, most of these organisms are rarely found living anywhere else. In the summer and fall, when sargassum is washed ashore along Atlantic beaches, many of these creatures will still be hiding within. As with many ocean habitats, there is much more than meets the eye. Take a look and see what is hidden in the world adrift. 

For more information on these species check out the full slideshow

Editor's Note: Seabird McKeon is a postdoctoral fellow at the Smithsonian Marine Science Network and Dan Barshis is a postdoctoral scholar at the Hopkins Marine Station of Stanford University. All photos were taken by Seabird McKeon and carry a Creative Commons Attribution-NonCommercial-ShareAlike license.