Seahorses are among the most rare and romantic creatures in the Chesapeake Bay. But their continued existence in bays and oceans around the world is threatened by destructive fishing techniques and pollution, according to Dr. Amanda Vincent, a zoologist and expert on seahorses with the International Union for the Conservation of Nature (IUCN).
“Seahorses live in the world’s most important most threatened marine habitats, like seagrasses, mangroves, coral reefs, and estuaries. Those are all in trouble, and seahorses with them,” said Dr. Vincent, who also serves as Director of Project Seahorse at the University of British Columbia.
The reproductive cycle of seahorses is remarkable. Males and females pair off and dance, often wrapping their tails around each other. They circle, as they change colors and make clicking sounds at each other with their skulls until they click in unison.
When they mate, the male gets pregnant. The female extends a tube from her ovary to inject eggs into the male. The male fertilizes the eggs in his pouch, nourishes and carries the embryos, and gives birth to hundreds of seahorse fry.
In many species of seahorses, the couples repeat their ritualistic dances every morning to reinforce their marriage-like bonds.
“There is a real commitment to the partner in these pair bonded animals, probably partly because these animals live at such low densities and move so little that looking for a new partner would be jolly hard work and possibly quite risky,” Dr. Vincent said.
Seahorses have only tiny fins, and so they are easily buffeted by currents. To survive, they cling to underwater grasses with their tails, and hide, using chameleon-like skin. They ambush small shrimp and other prey, vacuuming them up with their long snouts.
The only species of seahorse that lives in the Chesapeake Bay is the lined seahorse, which gets its name from its zebra-like stripes. They grow to about eight inches, and are classified as threatened by conservation biologists.
On a recent morning at the National Aquarium in Baltimore, Morgan Denney, an aquarist, fed a lined seahorse, pouring a cup of brine shrimp into its tank.
“You expect a fish to be a really expert swimmer. And that is not seahorses,” Denney said. “They rely completely on their prehensile tail to grip onto the sea grasses. The grasses are very important to their survival.”
Unfortunately, more than half of the habitat for lined seahorses in the Chesapeake Bay -– eelgrass -– has disappeared since the 1970s. Pollution from fertilizers, sewage plants, and other sources cause algal blooms that block the light that eelgrass needs to survive.
Climate change also could be playing a role in the eelgrass decline, by creating spikes in summer water temperatures that cook the fragile plant, which is sensitive to heat and at the northern edge of its range in the Chesapeake, according to research by Dr. Robert Orth, Professor of Marine Science at VIMS.
Because they prefer saltier waters, lined seahorses tend to remain in the southern half of the Bay, and even there, they are relatively rare. The Virginia Institute of Marine Science (VIMS) surveys the Bay every year by dragging a net to sample for fish. In 1,224 trawls last year, researchers only found 48 lined seahorses, according to VIMS.
Dr. John Musick, Emeritus Professor at VIMS, said not enough data have been collected over time to conclusively determine whether lined seahorses are in decline in the Bay. But he said it is logical to assume that seahorse numbers have probably fallen over the decades as the amount of eelgrass covering the Bay’s bottom has shrunk.
“As the grasses decline, those animals that depend on the grasses for their cover and their habitat have to decline too,” Dr. Musick said. “If there is no cover, there is no place for the seahorses to live.”
Globally, many species of seahorses are in decline. About 48 species of seahorses –- from sea dragons to pot bellied sea horses -- inhabit the world’s oceans and bays, and 20 percent of these species have been identified by IUCN as endangered or vulnerable. Not enough information is available about the rest to determine their status, according to Dr. Vincent.
Many seahorses are caught to be ground up and sold in Chinese traditional medicines, or are shipped to pet stores in America. But the biggest threat is bottom trawling by shrimp boats around the world, Dr. Vincent said.
“The first thing we need to do is basically end bottom trawling,” Dr. Vincent said. “Bottom trawling is like clear-cutting the ocean. It’s utterly ridiculous in what it extracts. It kills everything in its path or takes it out of the ocean. It mows down the bottom habitats and leaves death and destruction in its wake.”
One way to help seahorses, Dr. Vincent suggests, is for consumers to stop eating shrimp.
“Seahorses are primarily caught in shrimp trawls,” Dr. Vincent said. “And if we want to deal with the conservation pressures on seahorses and on so much other marine life, we’ll address this really serious waste, this bottom trawling.”
She said it would be a tragedy if our lack of attention to the underwater world resulted in Earth losing its most marvelous of innovations: the male pregnancy.
By Tom Pelton
Chesapeake Bay Foundation
(Photo at top of lined seahorse thanks to National Aquarium in Baltimore)