Northern astarte facts for kids

Quick facts for kids Northern astarte
Scientific classification
Genus:	Astarte
Species:	borealis

Astarte borealis, also called the northern astarte, is a type of bivalve mollusc. Think of it like a clam or an oyster. It belongs to the family Astartidae. You can find these cool creatures along the Atlantic coast of North America, from Greenland all the way down to Massachusetts.

Where the Northern Astarte Lives

Astarte borealis lives in the cold, northern parts of the world. You can find them in the Arctic, Pacific, and Atlantic Oceans. Scientists have found them in places like the Baltic Sea, the White Sea in Russia, and off the coast of Northern Alaska.

They are common in the Pacific Ocean, from the Sea of Okhotsk to the Aleutian Islands. In the Arctic, they live in Russian waters from the Barents Sea to the Chukchi Sea. In the Atlantic Ocean, they are found from Newfoundland to Greenland and Iceland. They also live in Europe, in both the North and Baltic Seas.

These molluscs usually live in shallow waters, from the surface down to about 300 meters deep. They prefer water that is not too salty. If the water is less salty, they tend to live in deeper areas where the saltiness is higher. They like water with a salt level between 14 and 30 psu (parts per thousand). They can survive in water with a salt level as low as 6-8 psu.

What the Northern Astarte Looks Like

The Astarte group of molluscs can look quite different from each other. This is because they live in many different places, from southern Labrador to the high Arctic. Each place has its own unique environment.

General Features of Astarte Shells

Bivalve molluscs like Astarte have two shells that are hinged together. You can tell different species apart by looking at their shells. Things like the hinge, the patterns on the shell, the number of "teeth" inside, and the shape of the oldest part of the shell (called the umbo) are all clues. The color of the outer skin (periostracum) and the shape of the muscle scars inside also help.

The shells of Astarte molluscs are mostly triangle-shaped. But they can also be oval, egg-shaped, or almost square. Both halves of their shell are usually the same size. The shell's length is often equal to or longer than its height.

The shell surface has ribs that go around it. These ribs are usually spaced evenly and can be thin or wide. Some species, like A. esquimalti, have wavy, uneven ribs. The umbones, which are the oldest, usually pointy parts of the shell, are often wide and puffy. In older molluscs, the umbones can get worn down. This makes young and old shells look a bit different. The outer skin (periostracum) on the shell is thick or thin. It can be shiny, silky, or dull. Its color ranges from yellow to black to reddish-brown and it sticks tightly to the shell.

Special Features of Astarte borealis

The shell of Astarte borealis is usually oval, almost square, or somewhat triangle-shaped. The umbones are near the center, slightly above the middle, and are often worn down in older molluscs.

The shell has fine ribs or lines that go around it. Sometimes, there are raised ribs around the first 6–8 millimeters of the umbones. The outer skin (periostracum) is thick, fibrous, and sticks well to the shell. It can be yellow or black.

Astarte borealis has a strong hinge, like a door hinge, that connects its two shells. It also has a strong ligament that helps the shells open and close. Inside the left shell, there are three "teeth" that help the shells fit together. Two are larger, and one is very small. The right shell has two teeth; the front one is much larger than the back one.

The marks where the strong muscles that close the shell attach are deeply pressed into the shell. There is also a clear mark from a muscle that helps the foot move. Astarte borealis does not have a pallial sinus, which is a curve in the line where the mantle (a soft body part) attaches to the shell. The pallial line itself is narrow and sometimes hard to see. The inner edge of the shell is usually smooth. Very rarely, it might have tiny bumps. The lack of these bumps is usually how you can tell A. borealis apart from other Astarte species.

Astarte borealis and A. arctica are very common and look quite similar in color. Their shells are thick and heavy. The soft body parts inside only make up about 11–16% of their total weight. This thick, solid shell helps them survive on rough, gravelly bottoms. It also protects them from fishing gear like trawls and dredges.

Life Cycle and Reproduction

Like other Astarte species, A. borealis produces large, yolk-rich eggs. These eggs are sticky, which causes young molluscs to settle in groups.

The time when they release their eggs (spawn) changes depending on where they live. In Greenland and the North Atlantic Ocean, they spawn from October to December. In the Baltic Sea, they can have mature eggs almost all year round. This means they might release eggs in smaller amounts over time, rather than all at once.

Most A. borealis populations live in cold, salty, or slightly salty waters. They can handle a salt range of 8 to 35 psu. In the White Sea, they are found at many different depths. Astarte borealis can also survive without oxygen for some time. However, if they are exposed to no oxygen for too long, they will eventually die. In the Baltic Sea, their spawning season is very long, with the most mature eggs found in winter and spring.

Molluscs that live in colder, northern areas often live longer. A. borealis shows this pattern, but it can be complicated to study. Some studies using special methods have shown that A. borealis can live for an incredibly long time. In Greenland, some have lived for 150 years! In the White Sea, they can live for 48 years.

Role in the Ecosystem

Astarte borealis is a type of filter feeder. This means it gets its food by filtering tiny bits of food, like phytoplankton, from the water. They live buried about 2 millimeters under the surface of muddy sand that contains gravel.

In the White Sea, their main food, phytoplankton, starts to grow in April when the ice melts. But the biggest bloom of food happens in July and August. After the ice forms in November, there isn't much food available until spring.

Along with other species, these molluscs are very important in ocean ecosystems. They are a common part of the communities that live on the seafloor. Many predatory fish and other animals eat them. These molluscs are also important for scientists who study ancient life and how life has changed over time.