Throughout this month swimmers along the north shore of the Vineyard have found krill-like creatures washed up on the beach by the millions. Large quantities of the tiny creatures have been observed as far west as Menemsha. The wrack line at Lambert's Cove Beach is covered with them.
"I have seen them in Menemsha harbor so thick you can walk on them," said Mike Syslo, director of the Massachusetts Lobster Hatchery in Oak Bluffs. Mr. Syslo works for the state Division of Marine Fisheries and in the last several years he has been out sampling the water for the state's shellfish monitoring program.
Called Hyperiid amphipod, the scientific name is Hyperia galba. They are about a centimeter in length and look like tiny shrimp. Seagulls feed on them.
There was some speculation earlier in the month that the creatures were dying from red tide, but Mr. Syslo said this is not so. The reason is more likely a population collapse, a dramatic change in water temperature or a change in salinity due to rainwater, the biologist said.
The appearance of amphipods in these waters is not that unusual. They were found in large numbers along the shoreline in 2001 and again in 2002. The creatures were first identified through the help of Rick Karney, who is executive director of the Martha's Vineyard Shellfish Group. Mr. Karney's staff collected samples and sent them off to George R. Hampson, an oceanographer at the Woods Hole Oceanographic Institution. Mr. Hampson named the creatures.
Striped bass are known to feed on amphipods. Greg Skomal, a shark expert for the commonwealth, said he suspects the high number of basking sharks seen early in July were attracted to the creatures. Plankton eaters love amphipods.
They are also likely whale food.
Bill Walton, a fisheries and aquaculture specialist with the Cape Cod Cooperative Extension and Woods Hole Sea Grant program, said he had not heard about the amphipod bloom on the Vineyard, but he is familiar with amphipods. Mr. Walton works at the Southeastern Massachusetts Aquaculture Center in Barnstable.
Amphipods populations can explode because of environmental changes, Mr. Walton said. "Basically most people don't see them because they are so small. But at times you get population explosions. We don't always know why. Maybe the food is good for them. I get calls from around Cape Cod and the Islands about these massive blooms of little amphipods. Everyone is looking for a cause."
"Plants and animals go through population explosions," Mr. Walton said. "Blooms also have a tendency to have a bust. Maybe what ever they are eating ends, runs out. Then they crash," he added. He speculated that this is what happened on the Vineyard.