Stories in Washington

Nature's Non-Binary Fluidity in Our Global Oceans

A clownfish pokes its head out from an anemone.
Clownfish Clownfish can change their sex under certain circumstances. © Michael L. Thomas

Growing awareness of the complexities of sex and gender is one of the many reasons we join in celebrating the diversity represented by the Seattle Pride festivities. But did you know that sex is not so distinctly defined among many animals? It often shifts in the most fluid of environments: the ocean.

A bright orange clownfish floats within the tentacles of an anemone.
Clownfish An orange clownfish within its home anemone in Kimbe Bay off the coast of New Britain, Papua New Guinea. © Vanessa Messmer

Warning: Our first example contains major spoilers. As in, spoiling the magic of one of your favorite animated adventures. Outside the imaginary world, Nemo’s dad may never have set out on his oceanic odyssey. In fact, Nemo’s dad would have become Nemo’s mom upon her untimely death by barracuda. Clownfish live in groups dominated by a single breeding pair made up of a dominant female and slightly less dominant male. The rest of the hangers-on are subordinate males. When the dominant female dies, the dominant male assumes her role—and her sex—and a subordinate male levels up to take his place.

Several small fish swim around a large coral.
Blue-headed Wrasses Wrasses circle a colony of fire coral on the reef of Del Este National Park, along the SE coast of the Dominican Republic. © 2009 Jeff Yonover

The blue-headed wrasse takes a different tack. Each day, a single dominant male awaits passing females and spawns with the whole group. A pretty good life, right? And the other wrasse know it, so he has to be big and aggressive to defend his position. But some smaller guys have figured out a weakness in the system. Disguised as females, so sporting a yellow rather than blue head, they “sneak” into the spawning spree and release sperm on the down-low to try and fertilize some of the eggs the females release.

The females have their own strategy to spurn the system as well. When the dominant blue-headed wrasse dies, the largest female ascends to his place in the hierarchy—assuming his position along with his sexual characteristics. Her behavior becomes more aggressive, she exhibits male courtship behavior and her head transitions to the tell-tale blue. Her ovaries become testes and begin to produce sperm. Within a week, this new dominant wrasse is fertilizing the eggs of the harem.

Above and below the surface of the ocean, throughout the natural world, sex and gender are more complicated than most people realize. We are proud to share some of the science—and proud to support the human nature of Seattle’s community.