Algae or Animal? What is the Sauerkraut of the Sea?

As a fish and wildlife technician, my family and friends routinely ask me questions regarding inhabitants of the Texas coast. One that comes up time and time again is the age-old question – What is this? – usually accompanied by a photo of a seemingly alien species. While the more obscure plants and animals of the region may puzzle those less acquainted with the Texas coast, staff of the Coastal Fisheries Division of Texas Parks and Wildlife have become quite familiar with many of these species. One such species that we frequently get questions about is the sauerkraut bryozoan (Amathia verticillate). Nicknamed the “sauerkraut of the sea” for its resemblance to the delicious hotdog condiment, this plant-like organism is often seen washed ashore in clumps on the beach or tangled up in fishing gear. Its frequent summer appearances typically spark a flood of social media posts and inquiries, with people asking what it is—and more importantly, if it’s safe to touch.

With its branching network of transparent-brown stalks, sauerkraut bryozoan is often mistaken for being a type of brown algae. However, this unusual organism is neither algae nor plant, but a colony of millions of tiny invertebrate bryozoans known as “moss animals.” Though it is difficult to distinguish the individual members of the colony with the naked eye, each individual bryozoan (zooid) plays a distinct role as either a consumer, reproducer, or structural supporter. Like many invertebrates found in Texas bays and estuaries, sauerkraut bryozoans filter plankton from the water, sharing nutrients to sustain the entire colony. Their reproduction is equally intriguing: eggs develop through sexual reproduction and hatch into larval zooids, which attach to substrates like rocks, shells, seagrasses, or debris to establish new colonies. From a single ancestral zooid, these colonies can rapidly expand through budding, often growing over two meters long and 30 centimeters wide. They also reproduce asexually through fragmentation, meaning that even a torn piece can regenerate into a whole new colony, much like a sea star.

Much like the moon jellies (Aurelia aurita) that swarm our waters every summer, the sauerkraut of the sea is fond of the warm, salty waters of the Texas coast. These bryozoans not only prefer these marine environments, but they thrive in them, having adapted to withstand a wide range of water temperatures (between 50-95°F) and salinities (15-35ppt). The generalist nature of the bryozoan has equipped them with the ability to survive in temperate and tropical regions across the globe, aiding the spread of this invasive species into areas where it was not previously observed. Unlike other varieties of bryozoan, scientists have yet to discover the original origins of the sauerkraut bryozoan. Its long-term presence within the Mediterranean Sea and the existence of a co-evolved predator in the Caribbean Sea, suggests that one or both locations are likely the native home for the far-reaching species.

Encounters with sauerkraut bryozoans have become more prevalent over the years, with masses of these organisms blanketing shorelines, fouling fishing gear, and biofouling sea-going vessels up and down the Gulf coast. With the bryozoans’ continued presence, beachcombers, anglers, and mariners alike often seek advice on how to deal with these invertebrates when they cross paths with them. Luckily, these moss animals don’t sting and if you touch them, they won’t touch you back. Feel free to pick them up to clear a space on the shore for your beach towels or remove them from your fishing gear and vessel hulls. However, as appetizing as these bryozoans may seem to some, the sauerkraut of the sea is not suitable for human consumption and should not be used as a condiment for hot dogs or Reuben sandwiches!

 Lastly, don’t forget that this highly resilient invasive species can regenerate from very small fragments, so try to avoid cutting or tearing the sauerkraut colony and make sure to properly dispose of any remaining pieces in the trash when possible. It is recommended to clean, drain, and dry any beach gear and fishing equipment in the same manner as you would to stop the spread of other invasive marine species in boats. The hot water and air-dry process should prevent even the smallest individual from anchoring, surviving, and reproducing elsewhere.

Tropical expansion, inadvertent transport, and their ability to reproduce at high rates have aided the spread of the species far and wide. Whether we like it or not, it seems the sauerkraut of the sea is here to stay on the Texas Gulf coast.