Spawning bivalves receive a helping hand

The Martha’s Vineyard Shellfish Group assists Mother Nature in providing a bountiful population of clams in Island waters.

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Emma Green-Beach moves fertilized eggs to buckets. Phytoplankton is contained in the colored containers. – Adrianne Ryan

As the weather and waters begin to warm, Islanders raking for clams in coastal waters will become a familiar sight. Heartier souls harvest clams year-round. This rich natural resource does not come entirely naturally. The Martha’s Vineyard Shellfish Group (MVSG), a nonprofit that works closely with the shellfish departments in the six Island towns, does much to lend a helping hand.

The towns annually support the MVSG with tax dollars. In return,

the Shellfish Group works to preserve and enhance a variety of shellfish across the Island. Their activities include active monitoring of water quality, and raising juvenile shellfish that are later “seeded” in Island waters.

In early April, shellfish biologist Rick Karney, longtime MVSG director, called to let me know that the quahogs were spawning. But what is spawning? Since it has been quite a while since high school biology, I had to look it up. According to Merriam-Webster, the full definition of “spawn” is (v.intr.) 1
: to deposit or fertilize spawn
; 2
: to produce young especially in large numbers
; (v.tr.) 1
a: to produce or deposit (eggs) — used of an aquatic animal.

How do quahogs spawn?

The term quahog refers to a large hard-shell clam, as opposed to the smaller cherrystone and the even smaller littleneck — all are clams, Mercenaria mercenaria, to be exact. In the wild, quahogs spawn through a process of external fertilization, and the sperm and egg are brought together through the actions of winds and tide.

Each male clam produces hundreds of millions of sperm, which increases the likelihood that eggs will be fertilized. Life in the wild is not always kind to ambitious sperm, however, which is where the Shellfish Group steps in. The germination process began in early spring, when shellfish constables from across the Island (except for West Tisbury, where the water is not sufficiently salty for quahogs; they raise oysters instead) collected and delivered quahogs. The clams were then “ripened” at the hatchery for a month, living in warm water and fed a diet of phytoplankton, microscopic algae, until it was time to spawn.

Located in a small gray building overlooking Lagoon Pond, the hatchery consists of two levels of small workspaces crowded with a variety of tubes, sinks, tables, hissing fans, gurgling tanks, and four-foot-tall translucent containers filled with colorful liquids. These huge tanks contain the phytoplankton which are fed to the shellfish.

As I climbed the steep stairs to the upper level, I saw Rick peering over a table. Spread out in front of him were dozens of glass Pyrex containers filled with quahogs. Marked with their town of origin, some of the more frisky ones were already starting to become active. In one container, the water was quite milky from the high concentration of sperm.

Rick explained that in nature, the quahogs would not be spawning this early in the season, as the water is still too cold. In the hatchery, however, this was the best time to induce spawning so there would be sufficient time for the hatchery to grow them into mature, healthy animals.

The day before their expected time to spawn, the clams receive a beauty treatment: an iodine bath, followed by a scrub and a long rest overnight out of water. When they are placed in their Pyrex homes the next day, they are then primed, ready to open up and release eggs or sperm, depending on the sex. According to Rick, if they were simply scrubbed and placed directly in water, they would be “freaked” and nonreceptive. Leaving them out overnight to recover renders them more relaxed. The next day, siphons out, they are ready to go.

A prime stimulus for the clams is water temperature. They are fooled by the warm water, which mimics the conditions in which the quahogs would normally spawn. In the laboratory, hot water is flushed under and around their Pyrex containers, to make them think it is their time.

Initially, only a few of the males were producing. Rick took advantage of this by gathering sperm from this more active group. Like Johnny Appleseed, he took his pipette and spread the sperm to both the males and females in the other Pyrex containers. By manually depositing sperm near their siphons, he mimicked the random effects of nature.

It was not long after that that the other males, stimulated by the presence of foreign sperm, were spurred to take action. Each active male released hundreds of millions of sperm as it joined the biological race to reproduce. An hour later, the females followed suit, releasing millions of their eggs.

As the eggs and sperm arrived, the shellfish staff were kept busy collecting them into their sex-segregated buckets. By this time, many of the eggs had already been fertilized in their Pyrex incubators.

Once the activity slowed down, Rick went downstairs to carefully mix the cache of fertilized eggs. This ensures genetic diversity. He also took a small sample for a count. From 30 individuals, an equal number of males and females, he estimated that 30.5 million eggs were produced, from which 8 to 10 million would survive.

These offspring started producing shells within 24 hours. They will continue to develop in warm water until they reach one to two millimeters in size, at which point they will be too big to remain at the hatchery. At this point the shellfish constables will bring them to cooler waters around the Island. In the cooler water, their development slows. They will spend a few months living in floating sandboxes or nursery wraps, stored safely above the crabs which would otherwise eat them.

In September and October the constables will plant them in Island waters, where they will burrow until harvested by Islanders, who will enjoy the sweet, salty flavor of freshly harvested clams.

Adrianne Ryan is a freelance photojournalist who is interested in the life and culture of Martha’s Vineyard.