The Tide Is Out

Sunburst Anemones— Producers and Consumers

Sunburst anemones are one of the easiest to find and most fascinating animals in the tide pools. Unlike anything that lives on land, these creatures provide endless enjoyment for beginner tide poolers, especially children that can feel the pull of the anemone’s tentacles on their fingers. 

Despite being so common, sunburst anemones are incredibly beautiful and play a pivotal role in intertidal ecosystems. See below for everything you need to know about these unique creatures.

1. Quick Facts
2. Appearance 
3. Diet
4. Habitat and Range 
5. Behavior
6. Interesting Facts

Quick Facts

• Common names for Anthopleura sola include sunburst anemone and starburst anemone.
• Function as both producers and consumers.
• Once considered the same species as the aggregating anemone, but recently classified separately.
• Like all anemones, sunburst anemones are in phylum Cnidaria, related to corals and sea jellies.
• Their stinging tentacles are not powerful enough to harm humans.
• Can be found in the intertidal zone as well as the sub-tidal zones to depths of up to 65 ft.
• Often confused with aggregating anemones and giant green anemones.

Appearance 

The sunburst anemone is pretty easy to identify: if you see an anemone growing by itself at the tide pools, it’s probably a sunburst. As you can see from the images above, the sunburst anemone is round, ranging from a single inch to 6 inches across. It has radial lines that spread to the tentacles on the center disc, called the oral disc because the anemone’s mouth is located in the center. Sunburst anemones have five rows of tentacles that can be tipped with purple, bright green, or brown. 

The column which attaches the anemone to the rock has sticky ridges which collect shells, small rocks, and other debris. When the tide is low, the anemone can close up its tentacles inside this column. The debris stuck to the column acts as a layer of protection and camouflage for the creature’s soft body

Sunburst anemones grow alone instead of right next to other anemones. They are sessile, meaning that they do not move once attached to the rock. There is wide color variation in sunburst anemones from bright green, to pale white, to yellowish brown. This is due to the anemone’s symbiotic relationships with microscopic organisms (both plankton and algae) that live inside its digestive tract. You can read more about these in the section below about what the anemone eats, but the organisms living inside the anemone give each one its distinct color. Don’t be fooled, however. The green coloring on sunburst anemones often leads to misidentification as giant green anemones, but these are less abundant. 

Diet

Anemones are best known as being predators, snagging crustaceans, copepods, isopods, plankton, small fish, and anything else that comes close to its waving tentacles. In this fashion, sunburst anemones function as consumers, eating other animals. Their tentacles house cells called nematocysts that deliver a powerful sting that will paralyze a small animal. But all a human will feel of the nematocysts is a gentle tug toward the anemone’s mouth. 

In addition to predation, these creatures have another way of obtaining food. In the section above, we talked about the microscopic plankton and algae that give sunburst anemones their various colors. These organisms are often photosynthetic, meaning that they can produce energy from sunlight— like plants. Dinoflagellates (zooxanthellae) and green unicellular algae (zoochlorellae) are some of the animals that can live inside sunburst anemones. The anemone gets the energy that these organisms make and the organisms get protection living inside their host. Thus all parties benefit. 

Anemones that produce their own food through these symbiotic relationships prefer to be in the sun while those that rely strictly on predation don’t mind being completely under a rock and out of the sunlight. 

Because of their unique hunter and gatherer life style, sunburst anemones function as both consumers and producers in the tide pools. Some studies claim that anemones put as many nutrients into the ecosystem as some algae through their symbiotic relationships. 

Habitat and Range 

Sunburst anemones are very common in the intertidal zone as they can live for short periods of time out of the water. They often attach themselves to partially hidden rocky surfaces as shelter from drying out in the sun and from predators. While they are solitary, they often grow close to one another, but will fight if they another anemones tries to live too close. 

The range of sunburst anemones is from northern/central California to Baja. They are very common is these cool waters, but have also been seen in warmer pacific waters along southern Mexico. 

Behavior

Despite being sessile and lacking eyes and ears, sunburst anemones display some very distinct behaviors. They have been known to be incredibly aggressive toward genetically dissimilar anemones. If a sunburst anemones detects another anemone that’s trying to live too close for comfort, it can attack with tentacles called acrorhagi that have concentrated amounts of nematocysts to sting and possibly kill the other anemone. This behavior is a result of competition for food and other resources. 

Sunburst anemones have a few predators such as shag-rug nudibranchs (Aeolidia papillosa), and certain species of sea stars and snails. If one sunburst anemone is being attacked by a predator, it can release a chemical into the water to alert other anemones in the area to close up and defend themselves. 

If you happen to see or hear a squirt of water come up from around your feet at the tide pools, you may have stepped on or near a sunburst anemone. They have the ability to shoot water a good distance compared to their size as a defense mechanism, most likely as distraction. Check to make sure you haven’t stepped on a camouflaged anemone if this happens to you. 

Interesting Facts

• The life span of sunburst anemones is not known, but some think that they could live over 100 years! One study housed a sunburst anemone in captivity for 80 years and claimed that it only died due to a laboratory mistake.