In the declining early evening light forty-five feet beneath the surface on a remote Indonesian coral reef, a tiny seahorse strangles another with its tail. Just three-quarters of an inch long, the diameter of a one-cent coin, and perfectly camouflaged against the windshield-sized fan-like gorgonian coral they inhabit, these creatures have a penchant for the dramatic. For my PhD research I spent six months watching and recording the antics of these mysterious and diminutive fish, collecting data on their biology and conservation--the first recorded observations of their social and reproductive behaviors. Denise's pygmy seahorses had only been recognized by science four years previously, in 2003. Like other behaviors that occur on coral reefs every day, these skirmishes have presumably been happening for millennia. We just didn't know to look for them. Most of us hear about coral reefs and see them on nature documentaries, but unless we're lucky enough to experience such awe-inspiring ecosystems firsthand, it can be hard to appreciate their intricacies. Exploring a tropical rain forest, you drip with sweat in a supersaturated and oppressive atmosphere waiting to spot an animal.

A bird might call in the distance, the insect at your feet might unleash its high-pitched whine, and, perhaps, if you're very lucky, and extremely patient, something larger might barrel toward you from the undergrowth. On a healthy coral reef, you can glimpse activity and life wherever you happen to look. Dozens of fish busy themselves with their daily commutes and travails. In one hour on an Indonesian reef you will likely see over one hundred multihued and multiform species of fishes, if not double that--scrupulous cleaners, eccentric lovers, steadfast parents. The nervous comet fish pokes its marionette of a tail out of a hole, attempting to convince you it's a menacing moray eel. Inches from your mask, a small but assertive damselfish warns you not to swim any closer to its precious algal farm. You may not know the names of all of them, but you are mesmerized: immersed in the hustle and bustle of their daily rituals. Coral reefs continue to surprise and delight.

My work has taken me all over the globe and introduced me to coral reefs in twenty-three countries. I have seen fish that wouldn't even stretch across a dime and others that are longer than two London buses. I have seen vibrant and bustling coral gardens that stretch as far as the eye can see and I have captured the first photograph of creatures that have never before been pictured alive. Elsewhere in the ocean, I have come face to face with a warty file snake deep among the roots of a mangrove forest in Indonesia, photographed animals and behaviors in Japan that were still unknown to science, and spent hours scouring an algal-covered rock face to find an unnamed relative of the seahorse in New Zealand. My aim in this book is to share some of my passion and wonder for coral reefs and the astounding variety of creatures that call them home, while allowing those who aren't lucky enough to experience this wonderful ecosystem firsthand a window under the waves.