Editor’s Note: “The Richest Reef” follows members of a scientific dive team as they attempt to pinpoint the center of the most biologically diverse marine ecosystem in the world. Long considered our planet’s most species-rich piece of ocean real estate, the Western Pacific’s “Coral Triangle” is a continent-sized patchwork of habitats, populations, and communities. Expedition scientists are trying to identify exactly which section of this rich mosaic is most diverse, but their effort carries with it far more meaning than a simple dot on a map would suggest. Along the way, they’ll discover dozens of new species, visit dive sites and depths no one has seen before, and gain a better understanding of the factors that promote biodiversity and the role these species-rich areas play in sustaining healthy ecosystems. See below for a list of all posts in the series.

The dive guide signals to the boat captain to push a bit farther around the point. As he does, the six of us pull on wetsuits, fins and masks, then finally the air tanks and buoyancy compensators that will keep us alive and stable underwater for the next hour or so. Before we plunge in, we take a quick GPS reading. We also toy briefly with the idea of naming the site “Guapo,” after our suave dive guide, before settling on the more geographically relevant name “La Laguna.” I’ve learned that it’s not unusual for the scientists on this expedition to want to explore previously unnamed locations. They tend to steer clear of popular dive sites, both because they’re seeking diverse habitats–not necessarily picturesque ones–and because they want to avoid having any impact at all on the relatively few and tiny marine protected areas here.

I’m here as part of the day’s “Invertebrates Team B,” which includes Kathy Ann Miller, UC Berkeley’s curator of algae, our seaweed expert; Joseph Comendador, a sponge specialist from the National Museum of the Philippines; Sarah Cohen from San Francisco State, an expert on a group of colonial invertebrates known as tunicates; Will Love, one of the expedition’s dive-safety officers and underwater photographer extraordinaire; and Elise Ong, a biology student at Macalester College.

Geared up and ready, we all tumble backward out of the boat on the count of three. With everyone settled at the surface, the guide gives the signal and we begin our descent in unison. We fall through the water as the ocean floor, which sits 40 feet below, begins to reveal itself. Apart from the darting and shifting fish shapes beneath us, the seascape is surprisingly muted, filtered by the water itself and by the less-than-perfect visibility–blue and gray, varying only in shade and form as far as the eye can see. As exciting as it may be to defy death by breathing underwater, the scene itself is surprisingly uninspiring. But as we approach the bottom, it’s like someone turning up the lights to reveal the Technicolor world that’s been there all along.

We make subtle buoyancy adjustments to arrest our descent just three or four feet above the seafloor. From here, I immediately begin to notice what I couldn’t see before: there are organisms everywhere. And practically every animal and plant I see is living on top of some other life form. The rubbly bottom is far from barren and is interspersed by car-sized coral heads parked irregularly like vehicles in a lot with no lines. The layers of biomass are so thick that it’s impossible for me to tell whether the coral heads are constructed on foundations of volcanic basalt or the calcium carbonate skeletons of countless ancient corals. It hardly matters. What’s important is the structure itself–stability and a few extra feet of elevation in this constantly shifting world.

We move slowly and systematically along the bottom–our pace far more like a group of people looking for someone’s lost contact lens than hikers on a nature walk. It’s definitely slower and more focused than a typical recreational dive. The scientists search and probe every square meter in an area the size of a large conference room. With surgical scissors, dive knives, and bare hands, they collect small pieces, and occasionally whole specimens, of species they haven’t seen before–or at least haven’t seen here. They then tuck these finds into plastic or mesh collection bags and small plastic jars before inching forward in search of more.

I’m paired on this dive with Joseph, so our focus is on sponges. However, because I’m ignorant to what distinguishes an unusual sponge from a typical one, all I can do is adjust my pace and focal length to match Joseph’s, stay out of his way, and point out things that grab my attention in the hope that they might be of interest to him. Of course my focus quickly wanders far beyond sponges.

The closer I look, the more I see. Attached to each mound is the wildest and most colorful variety of organisms imaginable. There are both hard and soft corals in every possible configuration. Anemones, tunicates, sponges and algae seem to take up any available space in between, or simply perch on top. Interestingly, very little of the algae looks like the stuff that home aquarium buffs periodically scrub from the inside of their tanks. There are seaweeds that look and feel like they’re made of gelatin; others that I see nestled in cracks shimmer like Faberg? eggs; another variety looks like the stuff model-train enthusiasts use to construct tiny forests. Sponges vary dramatically, too, from giant barrels that could hide a small diver–or an aggressive titan triggerfish–to tube sponges that look like pastel-colored, Nerf-brand musical instruments.

The vast majority of these organisms make their living by filter-feeding. That imperfect visibility I mentioned earlier is due largely to what scientists call “marine snow,” an ultra-high concentration of nutrients in the water that sometimes makes it feel like you’re in the midst of a blizzard or a sandstorm in slo-mo. What is less than ideal for divers looking for uninterrupted views is fantastic for filter-feeders. In this rich world, finding food requires little more than raising a specialized appendage and waiting for something to blunder into it.

Of course, not all animals on the reef sit still and wait for their meals to come to them. Before long, I’ve spotted my first nudibranch. Thrilled, I watch as the slug skims across the surface of a colony of tunicates en route to a tasty sponge, its flamboyant colors warning would-be predators not to take this toxic bite. Nearby, there are starfish and sea cucumbers, sand dollars and urchins tucked into crevices or scooting along just above, or just under, the surface of the various patches of sand. At some point I realize I’ve been looking down so closely at the ocean bottom, I’ve hardly noticed the fish. When I do, I see them ahead, schooling by the multi-colored hundreds and spilling out of every possible hiding place once we’ve passed by.

This is only my second dive in the Philippines and if it wasn’t clear on dive #1 a couple of hours ago, I see now why this place has proven to be more diverse than any other ocean ecosystem. Not only are there piles of living creatures directly in front of me, but also it seems that every coral head in this tiny dive site possesses a different assemblage of organisms than the one next to it.

The scramble for space and for access to light and nutrient-rich currents are largely responsible for the layers of life I see before me. But it’s not all about competition here. Cooperative relationships abound. Next, we’ll look at some of the fascinating mutualistic and commensal interactions that drive life on the reef and in the rubble.

Other posts in this series:

The Richest Reef: Exploring the Most Diverse Marine Ecosystem on Earth

The Richest Reef: No Such Thing as Packing Light

The Richest Reef: Life in Layers

The Richest Reef: A Symbiotic Society

The Richest Reef: A Bagful of New Species

The Richest Reef: Deep Diving into the Twilight Zone

The Richest Reef: Where Have All the Predators Gone?