Skip to main content
Not yet registered?
Slide Show: Life on the Reef at Palmyra Atoll
What does life on an unspoiled reef look like?
Slide Show: Life on the Reef at Palmyra Atoll
FISH EGGS Several groups of small reef fish, such as gobies (Gobiidae), damselfish (Pomacentridae), and dottybacks (Pseudochromidae), include species that lay clutches of eggs in protected crevices. An unidentified fish laid its eggs, which have developed into embryos about 0.02 inch (0.55 millimeter) in diameter, on the underside of a settlement tile. Using the energy stored in golden drops of oil, these embryos grow well-developed eyes and elongated bodies that stay tightly wrapped within their capsules until hatching.
COCONUT CRAB The coconut crab (
) is the largest land invertebrate in the world. Originally distributed on islands throughout the Indo-Pacific region, the mostly nocturnal crab has been overexploited for food and extirpated on most islands inhabited by people. Like other members of its terrestrial hermit crab family, when it is younger and smaller, the coconut crab has an asymmetrically twisted body adapted to use coiled snail shells. Eventually it outgrows available shells and molts to become a nontwisted, free-living crab.
CORAL PREDATOR An egg cowrie snail (
), its velvety black mantle contrasting with its glossy white shell, consumes a leather coral (
sp.) on a back reef at Palmyra Atoll.
TINY CRABS An unidentified small crab about 0.08 inch (two millimeters) wide, possibly
sp., found on the undersides of settlement tiles. Studying the tiles under a microscope, researchers sometimes find one bright, shiny compound eye looking back at them from a small hole in the surface where the crabs take refuge.
SEA SLUG An undescribed nudibranch sea slug (
sp.) about 0.08 inch (two millimeters) long, crawls over a bryozoan colony on an experimental settlement tile. Many nudibranchs in this group tend to eat cnidarians such as hydroids, sea anemones and corals. Rather than being sensitive to their prey's stingers, however, these slugs consume without triggering the stinging structures, and then co-opt and deploy them in their own bodies as a defensive mechanism.
LIMPETING ALONG The keyhole limpet (
sp.) subsists on algae and is a relative of the snail. This specimen, just 0.18 inch (4.5 millimeters) long, cruises across a red encrusting seaweed (
sp., aka burgundy crust alga).
HEAVY GRAZING? An experimental settlement tile, attached to the bottom of a back reef habitat at Palmyra Atoll. The pink coloration on the reef and the tile (sometimes called "pink paint" or "reef cement") is crustose coralline algae, which becomes especially common in places where seaweeds are heavily grazed by herbivores (such as this small school of convict tang,
) or limited by other extreme ecological conditions.
D. Brumbaugh & K. Holmes
OVERCROWDING Space on reefs is a tight commodity, even on the mostly dark undersides of corals and on small crevice walls. The undersides of settlement tiles simulate this microhabitat, just 0.4 inch (11 millimeters) wide, allowing for the examination of lethal competition among diverse plant and animal species. Here, pink crustose coralline algae ("pink paint") is being overgrown by a species of bryozoan (a group of colonial animals that are physically smaller though morphologically more complex than corals) that is equipped with spiny appendages, which in turn is being overgrown by a white, meshed sponge. Another orange bryozoan species appears poised to enter the fray from the lower right corner.
GROWING COLONY A young coral colony (belonging to the family Poritidae), at the three-polyp stage and 0.04 inch (0.95 millimeter) wide, grows on an experimental settlement tile amidst even smaller spiral tube worms (
NEW COLONY A small coral colony, composed of just three polyps some 0.05 inch (1.3 millimeters) wide, grows on top of some small polychaete worms and a sparse "turf" of a red alga, which in turn have colonized a surface of crustose coralline algae that has died and is becoming covered by a microscopic green alga.
NEW RECRUIT With its short tentacles extended, a new coral recruit, just 0.025 inch (0.65 millimeters) wide, grows among a fine filigree of hydroids (a distant colonial animal relative of corals) on the border of two seaweeds, a crustose coralline alga and a burgundy crust alga (
NEW POLYP After metamorphosing into a new polyp, a young coral will start to develop its skeleton. Here, through the transparent soft tissue of the polyp, which is 0.045 inch (1.16 millimeters) wide, we see the coral's skeleton, known as the corallite. Symbiotic zooxanthellae, single-celled algae inside the coral's cells, are also clearly visible as tiny dark balls throughout much of this coral.
METAMORPHOSIS A recently metamorphosed coral recruit, about 0.03 inch (0.84 millimeter) wide, grows on a settlement tile. Corals, like most marine animals, have a larval stage that disperses though the water column. When it finds suitable cues, this larva will settle to the bottom, and metamorphose into a polyp with a central mouth. Most reef-building corals also contain symbiotic, single-celled algae called zooxanthellae inside them, which allows the coral–zooxanthellae combination to function like plants, transforming light into chemical energy. Here, we see some of these zooxanthellae, appearing as tiny brown spots, within the young coral.
NEW REEF A new coral recruit, with a single polyp just 0.07 inch (1.8 millimeters) wide, has settled on the edge of an encrusting seaweed (a crustose coralline alga) overgrowing another alga (
sp.). Several colonies of tunicates, resembling fried eggs and connected by fine threadlike stolons, also grow nearby, as does a finely branching red seaweed. Two white polychaete worm tubes also emerge through one of the encrusting seaweeds.
Celebrate our 170th Anniversary with us!
Get 2 years of All Access for just $170
Save $28 now!