Science News - February 17, 2007

RED FISH, BLUE FISH With a wide variety of techniques, scientists are working to take a good look into the sea. Nicholas Makris and his fish-tracking research group at the Massachusetts Institute of Technology recently unveiled a sensor that can observe 10,000 square kilometers at a time over the continental shelf.

Older tracking systems for fish could cover just 100 square meters at a time. Those systems gave only rough ideas of the size of huge fish clusters that moved, spun off satellites, split, fused, and swerved this way and that. In a test off the coast of New Jersey, the new tool detected what may be the largest fish school ever recorded in one image, the researchers report in the Feb. 3, 2006 Science. It covered an area the size of Manhattan and included some 20 million fish.

On a very different scale, fish biologist Tracey Sutton has been considering the rare fish that he has pulled out of collecting nets lowered to the deepest waters of the

Mid-Atlantic Ridge. Based at Harbor Branch Oceanographic Institution in Fort Pierce, Fla., Sutton has cruised on census expeditions along almost the entire length of the ridge.

“It’s a beautiful place,” he says.

There he found tubeshoulders that when prodded squirt blue, luminescent clouds out of tubes on their shoulders. Sutton speculates that a fish living in velvet-black darkness might use a sudden blue glow to illuminate prey or to startle a predator.

On the ridge, Sutton found 10 or 20 tubeshoulders at a time instead of the one or two tubeshoulders that have shown up in samples from deep water elsewhere. He suggested at the Ocean Sciences conference in Honolulu last year that these supposedly nomadic loners gather at seamounts, which may be spawning grounds.

Sutton also collected hundreds of normally hard-to-find stoplight loosejaws (Malacosteus niger). These fish emit red light from a comma-shaped patch beside each eye, one of the few animals known to glow red. Despite having big fangs and a jutting jaw, the stoplight loosejaw feeds mostly on little crustaceans about as difficult to subdue as alphabet soup.

“I couldn’t for the life of me figure out why it would do that,” Sutton says. In the past 2 years, though, he and several other biologists have concluded that the wimpy diet of these loosejaws supplies them with the materials for the eye pigments that let them see red.

Seamounts and ridges may attract other deep-sea species that otherwise would be widely dispersed, Sutton speculates. If so, as state-of-the-art fishing fleets push into deep frontiers, fisheries managers need to watch out for damage to such exotic creatures.

The census is finding where fish aren’t as well as where they are. Sharks don’t seem to frequent the ocean’s abyss, below 3,000 m, say Imants G. Priede of the University of Aberdeen in Scotland and his colleagues. They looked at world-wide fish-sighting records and their own sampling data from five cruises in the northeastern Atlantic. Shark species ply the waters down to 2,000 m, they report. In the depths though, sharks rarely appear, although bony fish live there. Sharks are “apparently confined to about 30 percent of the total ocean,” the researchers reported in the June 7, 2006 Proceedings of the Royal Society B. That puts all of them within the reach of fishing fleets, so “sharks may be more vulnerable to over-exploita-tion than previously thought,” the researchers concluded.

LITTLE GUYS Gauging the diversity of smaller creatures isn’t necessarily straightforward under water. The tropics have long been hailed as rich in species, yet sea spiders may be most diverse in, of

all places, Antarctica. “Some of the most amazing species live there, like those with one or two extra body segments,” says Claudia Arango of the Queensland Museum in South Bank, Australia.

The sea spiders, or pycnogonids, arise from an ancient lineage of arthropods and look like their sister group of terrestrial spiders. The sea spiders have some social skills, such as male parenting, Arango notes. She says that she’s looking forward to using samples collected from census expeditions to clarify sea spiders’ evolutionary history.

The census also stumbled upon a new species of the so-called Jurassic shrimp. To the trained eye, like that of the creature’s discoverer Bertrand Richer de Forges, that shrimp looks impossibly ancient, as if a small, pinkish dinosaur had come to life.

Crustaceans such as this may have given rise to modern decapod crustaceans, including lobsters and crabs as well as shrimp.

Scientists had assumed that the lineage went extinct some 50 million years ago. But in 1908, a U.S. research vessel in the Philippines caught a single shrimp that belonged to this group. This living fossil sat generally unnoticed in a museum of the Smithsonian Institution for 67 years before two French scientists recognized what it was. Biologists have since collected only about two dozen more specimens.

In October 2005, Richer de Forges of the Institute of Research for Development in New Caledonia led a cruise to the Coral Sea as part of the Census of Marine Life. A collecting net slowly trawling a rocky,

uncharted surface at a depth of 400 to 500 m brought up another shrimp with the ancient characteristics. “We immediately recognized the very special shape,” Richer de Forges says.

He described it as a new species in the March 31, 2006 Zoosys-tema. Since then, another systematist has given it a genus of its own, and it’s now called Laurentaeglyphea neocaledonica.

Even smaller animals are providing surprises for the census, says Russell Hopcroft of the University of Alaska, Fairbanks. He studies zooplankton, animals that are weak swimmers and so are swept along with ocean currents. In this category, there’s “incredible diversity,” Hopcroft says.

The group includes members from at least 15 or so animal phyla, the big categories just below kingdoms. “It’s much easier to find new species than it is to find time to work up the descriptions,” says Hopcroft.

For example, one cruise in the Arctic doubled the known diversity of comb jellies there, from 5 species to 10. Comb jellies have the same diaphanous look as jellyfish but aren’t closely related to them. Ranging in size from a few millimeters to perhaps a third of a meter for rare oceanic species, they move by beating rows of tiny paddles and prey on other jellylike animals.

When Hopcroft goes on a cruise, he makes special efforts to collect frail plankton with filmy tissues. Jellyfish may be the most widely known examples, but plenty of other kinds of sea animals, such as salps, have jellylike bodies. To find them, Hopcroft drags an extrafine mesh, extra gently, through the water.

His photographs of a typical catch show translucent shapes shimmering under artificial lights. The creatures range from a few millimeters to a few centimeters in length and may be shaped like barrels, bells, or bananas with wings. Few people have seen even preserved specimens, Hopcroft says, and even fewer have seen them moving naturally.