The hidden crevices Slattery and his team were looking for are just one of countless ocean ecosystems. In fact, the world’s oceans are a wonderland of diversity. They cover about 70% of Earth’s surface and house a greater variety of flora and fauna than all land masses combined. In shallow, temperate regions, forests of tall brown seaweed known as kelp provide both food and habitat to a wide variety of organisms. Meanwhile, algae that cling to the underbelly of sea ice in the Arctic and Antarctic Oceans form the base of a food chain that ultimately supports whales and polar bears.

29-9

29-10

29-11

Lots of ecosystems means lots of ecosystem services, including temperature moderation (ocean water absorbs a lot of heat and releases it slowly), nutrient cycling, and support for large populations of commercially valuable fish. In particular, coral reefs are especially valuable for their services: protection of coastal areas from storms, purification of the water (many reef occupants are filter feeders), provision of recreational opportunities, and support of important commercial fisheries. They even serve as a source of current and potential medicines such as antibiotics and anticancer drugs. And oceans have absorbed a good bit of the CO₂ we have released due to fossil fuel burning, reducing the atmospheric warming that CO₂ would have caused if all of it had remained in the air.

Marine ecosystems, much like terrestrial ones, vary by location. In the ocean, depth is a key determinant of environmental conditions. About 80% of all sunlight is absorbed in the first 10 meters of the water column, and even more is absorbed in murky waters. Because sunlight supplies both heat and the essential energy for photosynthesis, upper layers of the ocean are much warmer and more productive than lower layers. In fact, most life-forms are found in shallow waters where light can penetrate; both heat and productivity dwindle further down the water column into deeper depths.

Scientists have divided the oceans into zones, based on depth. Each region differs in the amount of available sunlight, which in turn affects rates of photosynthesis and thus strongly impacts the diversity and abundance of ocean life at that level. Ocean regions are also identified by their proximity to land; the closer to land and to rivers that empty into the ocean, the more nutrient rich the area, and thus productive, the ocean community. In fact, estuaries, regions where rivers empty into the ocean, are known as the nurseries of the sea because many species come to these areas to spawn. INFOGRAPHIC 29.3

29-12

Coral reefs like the one that Slattery was studying are found in shallow tropical waters between latitudes 30˚ north and south of the equator. These reefs make up the most biodiverse communities in the oceans, some with more than 1,000 species of fish alone. But they are under attack from many forces: overfishing, coastal development, and pollution coming from land and sea. NOAA estimates that 75% of all tropical reefs are negatively impacted by human activity and environmental changes. Other species of coral live deep below the surface in icy, dark waters of temperate and tropical seas. These deep-sea coral form the basis of ocean communities as deep as 6,000 meters (20,000 feet) and are found in every ocean of the world. They too are threatened by overfishing and acidification as well as deep sea oil and gas exploration. INFOGRAPHIC 29.4