Romance! Danger! Hope! And the wildest sex even you can imagine.

In her new book Sex in the Sea, coral reef ecologist Marah J. Hardt dishes on the swinging sex lives of sea creatures, the perils they face from pollution to overfishing, and new hope for keeping the ocean healthy and its residents randy.

For Valentine’s Day Hardt talked to National Geographic about gigantic sperm, courtly lobsters, and why sexually satisfied sea life is good for everyone.

View Images Male Osedax (a genus of worm) are so much smaller than females that researchers once mistook the males for sperm. Photograph by The Natural History Museum, Alamy

What made you decide this would be a great book to write?

I was at a party when [a woman] said, “I just wish I could be in the body of a guy and know what’s going in their heads!” I said, “Yes, if only we could be parrotfish.” The conversation stopped. I said, “They start as females and when they get to a certain stature they become male, so one fish knows what it’s like for both sexes.”

Everybody had wide eyes, so I thought, let's see how far I can take this. I said, “Imagine you’re fishing on a reef and you are catching all the biggest fish. You’re taking out all the males… this adds a totally different level of complexity to management.”

Later I overheard someone from the conversation telling another guest at the party, “Did you know fish change sex?“ I thought that’s it! The ocean has the most bizarre sex stories! If we talk about sex and make it funny we can weave in these conservation messages, because ultimately successful sex is the heart of sustainability—it drives the abundance we all depend upon in the ocean, whether it’s for food or reefs that protect our coastline or novel medicines.

If we want a healthy ocean we have to make sure it’s safe for sex (see photos of corals).

View Images Hardt says that male Ostracods "produce absolutely humongous sperm, ten times the size of the male himself." Photograph by FLPA, Alamy

For Valentine's Day, which marine creatures could give pointers in being romantic?

Lobsters! Their romance comes after some pretty kinky foreplay, including the “love potion” of mutual urine showering, followed by cohabitation. A female does this really cool thing…she lifts her big claw up and taps the male, first on one side then the other like she's knighting him. The message is “Stay with me baby, we’re about to have some action!”

She then molts, leaving her soft-bodied and very vulnerable. But the male is a tender lover. He gently picks her up in his legs, cradles her, and rolls her onto her back … and then in the missionary position they get busy.

What marine animal has it the toughest in the dating world?

Male sperm whales literally cover the entire pacific ocean looking for a mate, using sound to navigate and likely, sending out signals that help show off their size. Unfortunately they’re often competing with sonar testing, oil and gas exploration, and ship traffic. Human activities have made if more difficult for them to find each other through all that noise.

In blue whales, they have been documented as singing lower on the register in recent decades. Overfishing had wiped out the population by 95 percent. Researchers suspect that after whaling, blue whales were needing to shout “WHERE ARE YOU?” at a higher pitch, which doesn't travel as far but is louder.

Watch: How abstaining boobies get sexier.

As their numbers have slowly gone up, the whales don't have to look as far for a mate, and competition has increased. Bigger males can make deeper sounds, which females in many species find sexier. Male blue whales are well… I can’t do a good Barry White impression but that’s what I envision!

So whales have music…don’t ostrocods have mood lighting?

Yes! Ostrocods are little crustaceans, like a shrimp encased in a lima bean shell. They send out this goo that lights up and they use it to create patterns to attract females. It really does look like little fire flies in the sea.

Researchers were able to get fossils over 400,000,000 years old and create a 3D model of the animal. In one case they were able to see this absolutely gigantic phallus (about one-third the length of the animal’s body and they actually come in pairs) so they think it evolved from a paired set of limbs. Modern ostracods today are similarly well-endowed and some produce absolutely humongous sperm, ten times the size of the male himself.

View Images "Mass coral spawning," says Hardt. "It’s a life changing experience." Photograph by Nick Caloyianis, National Geographic

What wild, kinky ones totally surprised you?

Osedax, which means bone-devouring. In these worms, the female live on the bones of dead whales that have fallen to the deep sea. Researchers found females with sperm inside them but couldn't find the males. Turns out …what they thought were sperm, were actually the males. You have this female packed with microscopic dwarf males who just shoot out sperm for her all day.

You began and ended with corals. Why is that?

Mass coral spawning…it’s a life changing experience. You’re witnessing this rhythm of nature that has been around for millions of years and despite all the threat and decline, these corals, every year, right on time, are still pushing the next generation forward. There’s something hopeful in that for me.