bars on their sides), and several spotted puffers. Puffers aren’t the most hydrodynamic fish in the sea, having roughly the dimensions of a shoe box. But look at an “o’opu” against a background of peppered sand and you’ll appreciate one reason why they persist.
A school of small triggerfish glided toward me as I reached the first cauliflower coral heads and algae-covered boulders of the shallow reef zone. They were jet black, with iridescent white trim running down the co-joined dorsal and anal fins on the top and bottom of their bodies. They use these long fins to propel themselves with seemingly awkward yet remarkably effective “ballistiform” propulsion rather than thrusting with the tail. When in danger, these feisty fish deploy a small, powerful spine on top of their head (the “trigger”) to powerfully anchor themselves into crevices of the reef.
A ridiculously skinny, cigar-shaped, yellow trumpet fish (called a “nünü”) cruised past me without seeming to move a fin. I almost didn’t notice it an inch below the surface, hugging the wavering mirrored ceiling. From the side it looked like a drifting two-foot stick – from the front it was nearly invisible. These are one of those species, like flying squirrels, aye-ayes, or komodo dragons that seem more like cartoons than real animals. But nature finds unique, sometimes extreme solutions to the varied challenges of a harsh and changing world.
It was a little murky, so I headed down the reef. A loosely organized group of gray unicorn tangs scooted away. Their namesake forehead nubs seemed almost as humorous as their wide-eyed frowns and puffed-out lower lips as they flicked their tiny pectoral fins. A straggler grabbed a last bite of leafy brown algae before grumpily crossing my path, flashing a blue bar on the narrow caudal peduncle connecting his tail and body.
Moving from just five to ten feet of water, the character of the reef changed dramatically. Green and yellow cauliflower corals became broader, forming hemispherical colonies with symmetrical folded branches. Beige and green lobe corals anchored to the spine of the ridge grew in expansive plates and mounded lobes. This “reef bench” zone was where the highest densities of corals grew, though slowly even in this optimal regime. Chaotic interactions of biologic, geologic, and hydrodynamic forces transformed transient arches, crevices, and walls into ecosystems for countless fish, invertebrates, and plants.
Red slate pencil urchins with broad, rounded spines poked out conspicuously like flat sidewalk chalk. Related but distinct, black and purple spiny boring urchins were tucked into holes they had scoured from the reef. At first glance, they seemed static armored vestibules. But on closer inspection their many appendages moved freely, with a complex purpose remarkable for such seemingly simple animals.
A long-nosed butterflyfish cautiously poked its needled snout between two fat coral lobes. I hovered, finger tips on exposed rock to avoid damaging the reef, or my own flesh. The fish soon ignored me and resumed probing the living reef for tiny worms and fish eggs. It’s long, slender mouth, perfectly engineered by eons of natural selection, fit neatly into nooks and crannies among the tangle of reef and porous lava rock. Its vivid yellow coloration notwithstanding, the hand-sized fish seemed quite docile, rocking with the gently surging water. I imagined that for tiny polychaete worms and shrimp, the predator didn’t seem so docile. To prey, the pinpoint black mouth must have seemed to flash thunderously out of nowhere, suddenly filling their whole world.
I dropped over a ledge and stood in fifteen feet of water. The entire length of the reef out to seventy feet was bordered by rippled bands of peppered sand. I went pretty negatively buoyant there because once on this sloping sand bar, it was possible to simply walk along and inspect the reef from below. It was like strolling around wide-eyed through a huge, brilliant aquarium in surround-sound.
In twenty feet of water, I took off my fins and dug them deeply into the sand, placing a loose rock on the exposed ends to hold them against the subtle heartbeat swell. My bubbles rose like jellyfish domes gurgling to the surface. I kneeled on the sand and watched them rise above me and rupture against the pink-bright mirror. A decorated collector urchin inched along. Once I saw one of these prickly pincushions decorated with a lighter and a tampon for camouflage; this one had a more natural disguise of algae, shell bits, and crumbled coral.
Snapping shrimp were audible between my predominant breathing. Different animals made very different sounds and various parts of the reef were consequently identifiably distinct. I felt the lightly rippled sand with my toes as I headed down the gently sloping reef.
Christmas tree worms and gray feather dusters flowed from lobe corals, rocks, and rubble. They fanned the water, filtering out suspended particles, cycling life-blood matter. Even at this shallow depth, greens and reds of the corals dimmed; blue light travels deepest, whereas other colors are quickly absorbed. Many deep water fish and invertebrates are thus red because they appear black to visual predators. Colorful fish like Achilles tangs with vivid orange patches around the base of their tails look blander on the reef shelf than in two feet of water.
Down the changing slope, I peered under a familiar ledge at forty-two feet. The rock was peppered with invertebrates. Barnacles lined the underside, grasping for invisible particles in that common mode of filter-feeding. Tunicates, sponges, and snails filled in the remaining gaps in the shoulder-to-shoulder life. Orange-band surgeon fish, ornate butterflyfish, and yellow tangs darted in and out of the darkness. One night, a six-foot moray eel slithered out of this opening and slipped along my bare leg; I tended not to crawl in it too much thereafter or poke my hands in dark crevices. But I lingered for several minutes, gazing at the diversity and abundance of life tucked in the small alcove. There was little reason to suspect the dive was about to become exhilarating, and a little frightening.
The spine of the reef ended in about seventy feet of water. It wasn’t a definite conclusion, but a gradual transition from a coherent point to a dense assemblage of car-sized boulder to widely scattered smaller rocks and coral rubble. The smooth-groomed bar of deep sand between the two reefs faded similarly away. Rope-thin garden eels poked out from the furthest reaches of the sand, swaying with the current like grain in a gentle plains breeze. Patient and cryptic, they waited to ambush stray wrasses or other small fish that happened off the reef. Any disturbance sent them zipping back into burrows.
Outside the reef, a loose-rubble shelf sloped quickly away. On some edges, Hawaiian coral ecosystems seem broad, but they are in fact quite tight to shore compared with the massive expanses of many shallow South Pacific and Caribbean reefs. A bathymetric side view of the vertical rise to the Hawaiian Islands correctly scaled with the vast surrounding water depth shows these islands as igneous columns shooting almost straight up. Reefs hug the edges, bolstering the islands for future generations as these pillars crumble back to the sea.
We turned back from bluer depths and walked (literally walked despite being six stories under water!) back up the sandy stretch, entering the amphitheater of breaking waves, crunching parrotfish, snapping shrimp, and the occasional distant vessel. At thirty feet we paused for a brief dive stop.
I was adjusting my weights when my buddy tapped me on the shoulder and placed his flat hand vertically on his forehead. I froze for an instant in a mixture of excitement and concern, recognizing the symbol for shark. A good-sized “manō” had followed us up the slope.
The twelve-foot tiger swam slowly toward us. We moved together in a defensive posture and I scooped a jagged rock from the bottom and bit my regulator like a football mouthpiece. When the brute was perhaps thirty feet away, it turned slightly and began to slowly circle us. The sun dappled the rippled sand and highlighted vertical bars on the sharks’ side. The great fish investigated us, swimming deliberately. Its eyes were piercing black diamonds locked on mine, its jagged teeth tangled thorns. The reflection of the overhead sun off the sand illuminated its white belly, spotlighting the predator. The omniscient sounds of the reef faded away and the ocean seemed motionless.
Its tall, dark tail sliced the water with a threatening, understated ease. My breathing quickened in a
