The Motion of the Ocean: Sex in the Sea and the Fascinating Life of Ocean Babies

Why do ocean sex and babies matter?          

Marine animals getting it on may sound like the plot for a comical romance novel, but the “motion of the ocean, in the ocean” is key to human welfare. Sex in the sea influences food security, coastal protection, tourism and recreation, and global climate change. Baby fish, crabs, lobster, and oysters grow up to be important food sources. Coral babies lay the foundation for new coral reefs, which buffer our homes from storms and provide habitat for many sea creatures we love to snorkel with. Baby marine animals grow up to be beautiful and fascinating creatures that fuel our curiosity and inspire awe for the natural world.

Ocean sex: Strange and wonderful

Sex in the sea is as varied and unusual as the animals and colors that exist there. There are numerous reproductive strategies that marine animals engage in, which include animals changing sex, having many mates or no mates at all, along with other bizarre strategies unique to ocean creatures.

A prime example of sex-changers in the ocean are clownfish. Clownfish live within sea anemones in groups of two large fish and many small fish. The two large fish are the only sexually mature fish, a male and female breeding pair, and all of the smaller fish are male. If the female is removed, her male mate rapidly changes sex to female and the next largest fish in the group increases in size and takes over the role as the sexually mature male.

Some animals, like seahorses, have only one mate throughout a breeding season. Elephant seals on the other hand, are promiscuous and mate with many different individuals. The largest and most dominant male elephant seal often reproduces with many females, thereby producing the most young. Other organisms, like corals, don’t even require a mate. Corals clone themselves by dividing their bodies in half, with each half developing into a full individual.

One of the most bizarre reproductive strategies is found in the deep sea in anglerfishes. The male anglerfish is tiny and poorly developed. His only goal in life is to find a female in the vast darkness of the deep sea, a feat which he accomplishes by smell. Upon finding a potential mate, he bites into her skin, releasing a chemical that digests the skin of his mouth and her body, fusing them together. The male becomes a parasite, dependent on the female for survival, and exchanging sperm for nutrients.

The alien world of ocean babies

After getting it on, many marine animals, such as crabs and fish, release their babies, known as larvae, out into the water. These microscopic young, often around the size of a pinhead, look very different from the adult parents. For example, the adults may look like typical crabs but their babies look like tiny translucent unicorns. Their transparent bodies help these sea babies to blend into the clear water of the open ocean and avoid being spotted by predators.

During the weeks or months in which marine larvae are adrift at sea, the motion of ocean currents carries the babies away from where they were born. Similar to children going off to college, the babies are on their own in the open ocean feeding, fleeing, and surviving. Dispersal in the ocean is thought to be beneficial for several reasons. One may be that free floating babies may have the potential to disperse long distances and colonize new habitats. In addition, since the babies feed out in the open ocean, the young and the adults are not competing for the same meals. As a further benefit, babies that are released out into the ocean may be able to avoid the hungry mouths of bottom dwelling fish and other predators.

Bringing it home

Once the marine babies are done feeding, growing, and developing in the open ocean they need to find their way home. Larvae use a complex and fascinating suite of senses, such as smell, hearing, and sight, to find their way to join the adult habitat. For example, many marine young, such as oysters and clams, follow their nose to the smell of adults, which indicates a suitable place to settle down. Other animals, such as some reef fish and crabs, follow their ears to favorable habitat by cuing in on the clicking made by shrimp living on the reef. Although we often think of coral reefs as serene and peaceful places, in reality they are a cacophonous band of animals creating a soundtrack that sounds similar to frying bacon in the rain. Baby reef crabs and fish can orient toward the sounds of the reef to locate the right spot to begin life as an adult. Once they have a destination in mind, larvae are able to exert a small amount of control over their movement in the ocean by swimming up and down in the water, riding currents moving in different directions, similar to a multi-level highway.

The strange and wonderful sex that goes on in the sea and the alien babies that are born, grow into the adults that we rely on for seafood, tourism and recreation, and coastal protection. The next time you visit the coast, sit down for a nice seafood dinner, or snorkel over a coral reef, contemplate how essential the motion of the ocean is to sustain life in the sea and for human and environmental welfare.