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, West Meadow Creek is usually line 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.

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.

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 2023).

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.

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.

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.

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.