Burrowers and Shellfish

Life in Mud and Sand

Most of the bottom of West Meadow Creek and for that matter, all of Smithtown Bay, is soft sediment, from coarse sands to soft gooey muds, A broad shallow area between Long Beach and the Nissequoge river,, less than 10 m depth consists of hard bottom alternating with sandy bottoms. From the air, one can see a series of sand waves near shore. As one approaches West Meadow Beach from the north, the bottom becomes very shallow, less than 5 m at low tide, and a narrow pass separates West Meadow Beach from a sand spit across in the village of Nissequogue. We then approach the entrance to West Meadow. West Meadow Creek is usually lined with marsh grass, but the intertidal zone is generally muddy sand, and the bottom is sand, which is maintained by deposition and erosion by the continual strong tidal currents. So in summary, soft sediment is a major part of the sea bottom environment. This is where we find clams and worms and an amazing array of species that live within the soft sediments. You may see nothing but burrow openings when snorkelling, but the sediment below is teeming with burrowing organisms. Here is an imagined subbottomscape.

Typical burrowing organisms found in soft sediments of this region. Note the permanent burrows maintained by both clams and worms, and also worm-like creatures that free-burrow through the sediment.

Burrowing animals are extremely important for the ecology of sediments. Their movements help aerate the pore waters of the sediment. Without burrowers, sediment pore water oxygen will soon by consumed by microbes and the sediment pore water will be anoxic and smell of hydrogen sulfide, which gives that rotten egg smell so characteristic of mudflats.

Let’s consider one worm, used a great deal for bait in fishing. You will find them in intertidal sand and gravel flats, and fishermen dig up these flats with pitchforks to separate the large worms from the sand.

Nereis virens worm on surface of sediment.

This is the burrowing sandworm Nereis virens, a common resident of sands and gravelly sands. It burrows freely through the sand or sometimes occupies semipermanent burrows and lives a few cm to as much as 25 cm below the surface. It is a predator, feeding on other small soft invertebrates, but is also a scavenger and can even digest cellulose. It is also prized as bait for fishing, so many dig it up, hopefully using a pitchfork, since shovels tend to cut up many of the soft-bodied invertebrates. I have heard diggers think that this resource is infinite, since larvae colonize from the water. But this is not true and the bottom of Sand Street beach looks like it has been bombed, it is so overdug.

Sand worm bait diggers at Sand Street Beach, Stony Brook NY 10/1602024. See the pitted surface of the sand, due to continuous digging. This cannot be good for the worm population.

Bloodworm, Glyceria dibranchiata

Another common burrowing worm is the bloodworm Glycera dibranchiata. This worm is also a carnivore and has four rather sharp fangs that are embedded in an eversible proboscis. It feeds on burrowing species like amphipods and polychaete annelids. If you dig them, they may “bite” you and draw blood.

Proboscis of Glycera dibranchiata with copper-rich hard teeth

The health of the soft sediment is strongly coupled to burrowing and pollution. As we add more and more nutrients, the sediment is overburdened with organic matter and the pore water has less and less oxygen. Over time in Long Island Sound, sediments are no longer dominated by deep burrowing worms and clams, and the pore water becomes devoid of oxygen = anoxic. The policies of recent decades is to reduce nitrogen pollution into Long Island Sound and help forestall the disappearance of deep burrowing creatures and dominance by shallow burrowing species and anoxic sediments and bottom waters.

Healthy sediments to right where deep burrowers burrow and oxygenate sediment. As pollution and warm waters develop, sediments are more like the left, where shallow burrowers dominate and sediments are devoid of oxygen in porewaters (from Levinton 2022).

Some Common Burrowers in West Meadow Sediments

Molluscs – Molluscs usually have an external shell of calcium carbonate. Often this shell helps in burrowing through the sediment. Most bivalves are suspension feeders, and use cilia on their gills to generate a current, which draws in water into the clam’s feeding chamber within the shell. Food particles, like algal cells, are trapped by cilia on the gills and transported by ciliary currents eventually to the gut, where digestion occurs.

Soft-Shell Clam Mya arenaria

 

Soft-shell clam Mya arenaria in life position. Shell length is 10 cm

Soft-shell clams are found in the muddy lower intertidal. They live with the siphon pointing upward and draw water in through their siphons, filtering phytoplankton across the gills. The small ones are quite active, but the large ones live in a more or less permanent burrow. They exist in about one tenth of their natural density, owing to overdigging and harvesting. They are good for all of us, because they graze planktonic algae and help reduce dense phytoplankton blooms.

Hard Clam, or Northern Quahog, Mercenaria mercenaria

If you walk in the middle of West Meadow Creek on the sandy bottom, barefoot, you will feel the nice fine sand on the bottom. But you may feel a hard surface, just beneath the sediment surface. This feeling about with your toes will reveal hard clams, Mercenaria mercenaria, who live just beneath the sediment-water interface. They have fairly short siphons, so even the big ones are near the surface, unlike soft-shell clams that can live much deeper, owing to their relatively longer siphons. But the siphons of both function in the same way. An incurrent siphon brings in water from the outside across the gills, which trap food particles. The outcurrent siphon returns water to the water column above.

 

Living position of northern Quahog, Mercenaria mercenaria

Juvenile northern quahog, with characteristic ridges

Adult northern quahog, ca 12 cm long

Hard clams are treasured seafood, especially because they can be easily dug from the surface sediments with a clam rake. They were once a major fishery on Long Island, but were severely overfished, especially in the 1970s, when they essentially disappeared from Great South Bay, but also from the quiet intertidal sands of West Meadow Beach. They are still abundant within Stony Brook Harbor and more spottily along the shores of West Meadow area. Owing to high bacteria counts, clamming is permanently prohibited within West Meadow Creek, but there are hard clams in this area, which hopefully act as a spawning sanctuary area. Hard clams start out life as immatures, then become spawning males, and then with further increased size, switch to making eggs, which are also spawned into the water column. Sperm fertilize eggs in the water column, which develop into swimming larvae, which feed on algae in the water, and then move to the bottom and settle to the sediment suirface after a few weeks. They go through a process known as metamorphosis to develop into young clams.

 

Razor Clam Ensis directus

Razor clam on sand surface (Massachusetts Div. of Marine Fisheries)

Razor clams are found with the long shells vertically positioned in deep burrows usually in clean sand just at the bottom of the tidal zone. Those who find them tend to keep them a secret, but they are actually rather common, especially at lower interidal sand bars on West Meadow Beach. They live in deep burrows, which are pre-dug to allow escape from predators. As you dig in summer they will escape downward by digging rapidly. Those who can find these delicious clams will not tell you where they are!

Some folks I met dug up a bucket of these creatures!

Bucket of razor clams dug up by restaurant collectors.

Surf clam Spisula solidissima similis

On the south shore of Long Island, the surf clam Spisula solidissima can be found in great abundance, and has been a major bottom fishery, especially off the coast of New Jersey in subtidal sandy bottoms. But surf clams can also be abundant in Long Island Sound. They were once very abundant in lower and mid-intertidal medium sand off West Meadow Beach, but they were overharvested and, like the northern Quahog, are now very hard to find there. A study of their genetics shows that they are genetically distinct from the surf clams in deeper waters off our Atlantic coast, but are instead likely closely related to a southern subspecies, Spisula solidissima similis. These clams are vigorous burrowers and dig below the surface, connecting to the water column with fairly short siphons. They depend upon phytoplankton for food, much like northern quahogs and oysters. For more information see: The “Southern” Surfclam (Spisula Solidissima Similis) Found North of Its Reported Range: A Commercially Harvested Population in Long Island Sound, New York.  Matthew P. Hare, James Weinberg, Olga Peterfalvy, Maureen Davidson, Journal of Shellfish Research Vol. 29, Issue 4, (Dec 2010) , pgs 799-807

The local subspecies of surfclam, Spisula solidissima similis.

Burrowing Predatory Snails in Sediment

Two moon snails are found in West Meadow. Neverita duplicata (formerly Polinices duplicata) and Euspira heros have spherical shells and are found commonly in interidal and shallow subtidal sands. Let’s just focus on N. duplicata, which has a lovely brownish shell, up to 5 cm or so in diameter. The shell is almost spherical, and females make a very characteristic egg case, where the eggs are embedded in a layer of sand. These snails are voracious predators and use a drilling apparatus called a radula to drill holes in the shells of other molluscs, like clams. They have large “feet” which can wrap around the clam. After drilling the hole, the clam opens and the snail inserts its muscular proboscis to get soft tissue. Amazingly enough, this snail is a major predator of razor clams! You can tell a moon snail drill hole because it has a countersink in the hole (look it up! If you took wood shop in school you would know what this is!). Sometimes you will see a razor clam shell sticking out of the sediment. This is the result of the killing by a moon snail!

The burrowing snail Neverita duplicata. Left – shell, Middle – snail upside down, Right – female with sand egg case.

 

Restoring Shellfish Populations

Shellfish have suffered major declines in abundance over the past decades. Oyster reefs once abounded in New York waters, and were widespread on soft bottoms in Long Island Sound. Major fisheries existed, most notably the one in Oyster Bay, New York. But oysters, hard clams and other species were abundant and widespread in West Meadow until the end of the 1970, when rich clam beds off West Meadow Beach, and abundant clams within West Meadow Creek were over exploited and are now decimated. The northern quahog Mercenaria mercenaria has some spotty abundant populations still, especially in the inner parts of Stony Brook Harbor. Replenish programs are underway in SB Harbor and also by a mariculture group in the Stony Brook Yacht Club. But the soft shell clam Mya arenaria has been decimated by commercial clammers and nearly gone. We have a lot to do to restore these populations. They are not only good to eat, they are suspension feeders and can keep our shallow waters clean of harmful algae. To do this we must take a balanced approach of reducing nutrient input (from septic tanks, lawns etc.) to reduce the algae, and to restore the clams that can eat the algae. I focus here on restoring the shellfish.

There are two main approaches to restoring shellfish:

1. Shellfish Farms: Hatchery to Planting

2. Spawner Sanctuaries Leading to Natural Colonization

 

Shellfish Farms: Hatchery to Planting

This approach involves a number of technical steps. An important detail: oysters are sequential hermaphrodites, after a juvenile stage, smaller oysters have male function and produce sperm only, which are shed into the water during a restricted spawning season (usually June-July). As the oysters grow in size, they switch to production of eggs, which are also shed into the water column in time with sperm release. At a shellfish farm, oysters with male and female function must be induced to spawn in a tank. So….. First, broodstock spawning occurs by placing males and females in a large aquarium. A hatchery aqauarium is used, where Bivalves are induced to produce gametes, which swim in the water. Fertilization occurs and the zygotes become swimming larvae. Larval culture follows, where larvae are fed with cultured algae (usually single-celled species that are cultured in nutrient broth). The larvae are stirred in a tank until they are ready to settle. If they are oysters, the larvae are usually placed in a tank with shell, known as culch, and the larvae settle and cement to the shells, which are transplanted to the natural environment on the bottom, sometimes directly on a shell reef, otherwise in cages, usually kept above the bottom. The cages have mesh, with openings of about 5 mm, which allows water with oxygen to circulate but also gives access to algae from the circulating water column to feed the oysters.

Oyster hatchery approach. From Element Seafood.

This figure shows the whole process, which requires algae for raising the larvae,and tanks where larvae can settle and metamorphose on shells. The shells are eventually transported to the open bottom site. The larvae must be grown in clean water without poisonous microorganisms. This can be a challenge and hatcheries cannot be located just anywhere. For example, a hatchy long in operation in Great South Bay was closed in recent years owing to toxicity of the local seawater.

Oyster life cycle. https://oysterheaven.org/challenges-oyster-restoration/

If you wish to do this approach with clams, the larvae will settle onto the bottom of sand, and metamorphose into tiny clams, which need to grow in protected bins of sand exposed to seawater with algae for food. When they get to ca 15 mm in length, they can be added to a sandy bottom appropriate for clam growth.

Lifecycle of the quahog Mercenaria mercenaria. https://reproductivesystem2015.weebly.com/hard-shell-quahog-clam.html

As of 2024, this approach is being taken by the Stony Brook Yacht Club Mariculture Group, directed by Anna McCarroll. She and her associates get seed from a source site of Brookhaven Town, Long Island, located on the shore of Mt. Sinai Harbor. The seed is grown for a few months and oysters reach a length of ca 10 cm and clams reach a length of ca 15 mm. The oysters are placed on hard bottom, because they have not cemented at metamorphosis to shell (so-called spat-on-shell technique) and clams are distributed into local sandy bottoms, where individuals burrow and thrive.

Spawner Sanctuaries

The idea behind spawner sanctuaries is simple and we will focus on clams burrowing in sand, where there has been some real success. Hard clams (northern quahogs, Mercenaria mercenaria), for example, reproduce by males and females releasing eggs and sperm into the water column. Fertilization occurs in the water column, and the embryos develop into swimming larvae. These larvae use tiny cilia to keep in the water column and move in currents, as they feed on algae in the water. They develop for a few weeks, change from a small ciliate larva to one with more complex morphology, and gradually grow a small larval shell and their form changes into that of a small juvenile clam appearance, but with a larval swimming structure, known as a velum. After a few weeks in the swimming stage, they lose the velum, drop to the bottom, burrow in, change morphology into a developed juvenile clam, and start using their juvenile siphons to suck water and draw algae to their gills, which collect the algae and transport it for digestion. Success! Yes, if they manage to survive!

So the clams in the spawner sanctuaries are there to reproduce and generate larvae that are swept by currents to places where they can settle and survive as adults. Where to put the sanctuaries? On Long Island, tidal creeks are often chosen, because the creeks are a bit polluted and closed to clamming. This provides an ideal place to keep populations of adult clams, assuming the creek is just polluted enough to make them unharvestable, but not too polluted to kill marine life entirely. Because we have so many septic tanks surrounding our tidal creeks, such mildly polluted sites are common. An important part of the design of spawner sanctuaries is to understand where the planktonic larvae will go. Marine scientists must develop a model of larval transport by currents, to make sure that the larvae will wind up settling where good adult habitat is present. For hard clams, that means shallow subtidal sand bottoms. On Long Island, Shinnecock Bay has been a model for understanding such interactions.

How to Measure Success of Shellfish 

Recruitment: That’s What It’s All About!

When planktonic shellfish larvae settle from the water column, they must find a proper habitat. The successful arrival of planktonic larvae, settlement, and metamorphosis into tiny juveniles is known as larval recruitment. Many larvae use chemical cues to find places to settle. These cues can be simple smells of resident individuals, like clams burrowing within the sediment, leaking chemicals such as dissolved ammonia (a waste product). Oyster larvae seek such clues but also settle on hard surfaces, especially oyster shells. But a vicious syndrome develops. As oysters and oyster reefs disappear, fewer such clues exist. Still, hard surfaces will attract oyster larvae. Here is a recent case in West Meadow Creek, where oysters settled on a flat rock in the upper intertidal. They are in danger of being eaten by a variety of predators, so their fate is uncertain. Still there is cause for hope when there is natural recruitment.

Oysters that recently settled (July 2024) on a rock on the shore of West Meadow Creek. Oyster shells are about 3 cm long.