Nature
California Marine Creatures That Change Sex, Cross-Dress, and Defy Gender Norms
Sea creatures that defy gender expectations — and their not-so-natural chemical threats
Sex in the sea doesn’t always go as planned. Much like terrestrial intercourse, there are a lot of hormones involved. And as with terrestrial romping, many sea creatures’ sex defies gender norms.
Fish change sex from male to female, or disguise themselves as the opposite gender to gain the upper hand. Some male fish carry their young or are so tiny that after intercourse they fuse into their larger female partners.
Ah, sex in the ocean. Weird and wonderful.
Let’s dive in, shall we?
Sea life and changing sex
Protandrous and protogynous fishes
You’ve probably heard that when an anemone-dwelling colony falls under stress, clownfish change from male to female — a factoid that Disney delicately omits in Pixar’s Finding Nemo. Such fish are sequential hermaphrodites, which means that changes in their environmental conditions may lead to changes in hormonal expression and sex. This type of sex change, where the largest fish with the highest chance of reproductive success becomes female, is called protandry.¹
Lots of California sea life also make this change. Oysters do it. Shrimp do it. Blue-banded gobies, much like anemone-dwelling clownfish in tropical climates, live amidst tiny rocks covered with dazzling strawberry anemones. These gobies don’t stray too far from their hiding places, and so they often change from male to female because… well, they aren’t likely to find another opportunity to breed for quite some time!
It is more common to find examples of protogynous fish, or fish that change from female to male along the Californian coast. California Sheephead juveniles all start their lives as rosy-colored females, but the single strongest fish in a group later becomes male to breed with the remaining femmes of the group.²
Nudibranchs, bryozoans, and barnacles — Oh my!
Nudibranchs, barnacles, and bryozoans are hermaphrodites, aka nonbinary icons. Because they contain both sets of sexual organs, nudibranchs can fertilize each other at the same time by stabbing each other with their gametes. This is how they do it if you want to see it for yourself.
Bryozoans or moss animals are tiny colonies of animals that often live on kelp. They are much easier to see under the microscope than with the naked eye. While these animals can produce both eggs and sperm to create new bryo-babies, these sexual pathways may not be at the same stage of maturity at the same time.
Barnacles are often hermaphrodites or sequential hermaphrodites, much like the sex-changing fish described above. But unlike these fish, barnacles do something special. Every year, barnacles must grow a new penis. A penis, might we add, that can reach up to eight times the length of a barnacle’s body and that holds the record for the longest proportional member across all animal kingdoms. Some penises unfold like accordions to reach far-away mates while other barnacles simply release their sperm and hope for the best.
While most land snails are hermaphrodites as well, many sea snails of subclass prosobranchia are either male or female.
Spawning, asexual reproduction, and dismemberment
During spawning, male and female sea creatures (for example, corals and sea urchins) send their gametes into the briny sea, hoping for the best.
But many species that reproduce via spawning also engage in some form of asexual reproduction.³ Cnidarians, the group that makes up corals, anemones, and jellyfish, are capable of sexual reproduction during their adult stage, or asexual reproduction at the polyp stage. Some echinoderms like sea stars and California Warty Sea Cucumbers spawn but can also reproduce asexually when cut in half.
Imagine you lost your arm. If you were a starfish, not only could your arm regrow, but that lost arm could potentially form another individual. A clone. Alas, human limb regeneration remains a subject for sci-fi fans and stem cell researchers.
As long as we are talking about alternative and asexual reproduction, let’s talk about sharks. Did you know that female sharks can store sperm, and even give birth via cloning or parthenogenesis?
Parthenogenesis, a type of asexual reproduction that happens when some female animals produce offspring without fertilization, has been reported in zebra sharks, leopard sharks, and some species of hammerheads.
Cross-Dressing Cephalopods
Cephalopods, specifically octopuses and squids, often employ a variety of gender-bending techniques when mating. Many octopuses are fairly solitary animals, coming in contact with one another only to breed. The male has a modified arm called a hectocotylus that doubles as a penis. He initiates intercourse carefully — after all, many females of his species are cannibals.
The cross-dressing bit comes a bit later. In some species, large octopus males guard the entrances of females’ dens. The only way another male can get past the much larger and stronger bouncer is to hide his hectocotylus and trick everyone involved into believing he too, is a lovely lady octopus. By the time he meets the female, the ‘sneaker’ octopus drops his cross-dressing act.
Deep-sea squid on the other hand might not care what sex they take for their partners. A 2011 study published in the Royal Society journal Biology Letters found that both male and female squid had stored sperm from different mates in their bodies.
The authors speculate that these cephalopods have poorer visibility than their open ocean counterparts and a greater chance of passing off their genetic information if they just go for it without even clarifying the sex of their partners. And by skedaddling before these partners decide to make a quick lunch of their attacker.
Gender-nonconforming creatures
Seahorses
It’s equally important to point out at least two more gender-nonconforming species browsing California waters. After completing an elaborate courtship dance, seahorses mate. The female transfers mature eggs to the male’s brood pouch, where eggs are fertilized. The babies continue to grow in the pouch until contractions toss the entire litter, which may have up to 1000 individuals, into the briny shallows.
(Sea horse dads get a gold star for sharing half the burden of birthing, even if these fish do little to care for their young after this process is complete.)
Pacific football fish, and many other angler fish
While sexual dimorphism typically dictates that females of a species grow smaller than their male counterparts, this trend doesn’t hold up for Pacific football fish and other anglers. The male is much smaller than the female, and his freedom ends the day the duo mates.
Much like the deep-sea squids described above, Pacific football fish and other anglers aren’t picky about who they choose for mates. If males come across a fertile female, he will bite onto the body of the damsel, deliver his sperm and essentially melt into the body of his mate, becoming a parasite that will continue to draw nutrients and oxygen from the larger mobile female.
That’s sure *one way* to make sure the pair is bonded for life!
Chemicals and climate leading to sexual tension
I wish I could end this article here, closing with a few lines celebrating the weird and wonderful adaptations sea creatures have evolved to make the most of their turbulent lives and spread their genetic information to their offspring.
But our environment is in crisis. And the ocean is under threat.
Not all sex change happening in the shallows is natural. One chemical used in antifouling paint, tributyl tin (TBT), helps prevent mollusk overgrowth on ship hulls. It’s an important tool for sailors who want to avoid boat damage. It’s also illegal in California because this chemical is toxic to local wildlife and even causes sex changes in gastropods around the world.
Fertilizers from agricultural runoff and ethinyl estradiol, the hormone present in the birth control pill, are wreaking havoc on freshwater and marine ecosystems. Even at low concentrations, these chemicals force permanent, one-way sex changes in fish that could make it impossible for local populations to breed (for lack of partners of the opposite sex.)
These aren’t small local problems affecting small populations of fish and wildlife. According to BBC Earth,
“Scientists have already demonstrated that temperature can have a profound effect on the sex ratio of populations… A 2008 study published in the journal PLoS ONE, surveying 59 species, found that an increase in water temperature of just one to two degrees Celsius can alter the sex ratio from 1:1 to 3:1 (three males for every female) in both oceanic and aquatic species.”
Green Sea turtle eggs rely on temperatures that trigger the embryos to develop into exclusively male or female broods. Warmer temperatures (above 88.8° Fahrenheit or 31° Celsius) produce female hatchlings. Cooler temperatures produce males.
Researchers at the University of Swansea suggest that sex ratios in turtles at the Cape Verde Islands in the Atlantic could all be 90% female if warming trends continue. Others suggest that temperatures here and in many other locales may become too unbearable for the turtles to survive at all.
This problem is larger than chemical pollution or antifouling agent bans. It’s about climate change. It’s about rising global temperatures driving biodiversity loss and the warning signs entwined with marine animals’ hormonal pathways.
Earth’s sea creatures are migrating, coexisting, and switching gender.
That’s our ocean communicating in the only way it knows how.
Sexual solutions
But these California marine creatures that naturally change sex, cross-dress, and defy gender norms? They inspire me. They show us that our perceptions about gender norms — and societal norms in general — aren’t fixed in stone.
And so if these animals can change their sex, maybe we can change our routines and keep the world from burning. That in turn can help preserve biodiversity and keep our ocean weird and wonderful.
Let me know about the species I missed in the comments!
[1] In clownfish populations, the largest fish with the highest chance of reproductive success becomes female. She mates with one breeding male and the rest of the group doesn’t breed at all.
[2] What does this uncertainty surrounding sex mean for aquarists taking care of fish that might switch gender at any moment? Or when the gender of said fish remains unknown? One aquarium I’ve worked with named their resident Giant Sea Bass Princess because he — she — or they — would not eat their food unless it was placed right in front of them. And yes. Princess is a gender-neutral name. I will die on this hill.
[3] For more examples of sea creatures that use both a spawning sexual phase and asexual reproduction phase, see Everything You Have Always Wanted to Know About Sex in the Sea.
