Sea Star and Anemone

Ochre Sea Star and Anemone

When I first saw this maroon ochre starfish circling its legs around two sea anemones, the first question that came into my mind was, "does the starfish eat anemone?" Since I did not know the answer, I tried to look deeper at the sea star and anemones. The anemone in the right side looked like to be devoured by the sea star, but the anemone on top looked like the dominating specie. I reversed my question, "does anemone eat starfish?" Is there a symbiotic relationship between star fish and anemone? Or is there a predator-prey relationship between them? If so, who is the prey? Who is the predator?  These questions drove me to search for information in google, which lead me to so many sites. There are some sites which say that some species of starfish prey on anemone, then, there are other sites which say anemone prey on star fish. Anyway, here are some tidbits of information I have learned from my readings on both sea star and anemone.

A. Sea Star Feeding Behavior ( sea stars are more popularly known as starfish, but marine scientists prefer to call them sea star since star fish are not really fish) 

The ochre sea stars are the keystone species in CA rocky intertidal zone. Without them, the mussels would dominate and anemones would be crowded out. Without sea stars (or starfish), everything in the rocky intertidal zone would be mussels.

Starfish With Opened Shell on Its Mouth

 The star fish are adapted to hold onto solid shell with their hundreds of sucker-tipped tube feet that are found under each leg. The star fish don't get tired of pulling open a shell fish because they have hundreds of tube feet that don't work together, while some of the tube feet work hard to open a shell, the others rest. When the star fish succeeds in opening the shell, the stomach emerges, oozing into the crack to digest its prey. 

The Underside of a Sea Star with some of the sucker-tipped tubes exposed

Star fish are patient creatures. It takes them about 6 hours to consume a mussel, and each star fish consume about 80 mussels in a year. Now, I understand why there are so many mussels in our tidepool. In wikipedia's discussion of keystone species, it says that "sea stars are prey for sharks, rays, and sea anemones." - http://en.wikipedia.org/wiki/Keystone_species

So, anemone preys on sea stars? Ahhh, can you imagine this anemone devouring the sea star? I can't. 

Very Green Sea Anemone

It's very hard for me to imagine that the delicate looking and plant like anemone could devour a tough sea star. 

B. Sea Anemone Feeding Behavior

Sea anemones look like plants and are considered to be the flower of the sea. However, they are actually meat-eating animals. They come in different colors and sizes. 

Light Greenish/Bluish Anemone

In the center of the anemone is their mouth. Anemones stay put in one place most of their lives despite their capability to. move. They can only travel 3-4 inches an hour, or they get a free ride from hermit crab. Because they mostly stay in one place, anemones wait for their food to come close to them. When a small fish or any bearer of meat passes by, anemone sting it with their tentacles, and then push it into their mouth. 

Is This Shell Close Enough To be Devoured by Anemone?

Examples of typical anemone prey are crabs,small fish, plankton, sea urchins, sea stars, or any sea-life that comes its way. The only creature that's safe from anemone is the clownfish, which is immune to the anemone's sting, and actually use anemone's tentacles to hide from its predators. All shots of anemone above were taken with anemones underwater. When anemones are not submerged in water, they actually do not look like a sea flower at all. They are folded and look like lumps on the rock (photo below).

Folded Anemone Aggregates When Not submerged in Water

Opened Up Anemone Aggregates Underwater

Now, going back to the sea star- anemone prey predator question: Who is the predator and who is the prey? I asked my hubby, and simply basing from his observation and logical analysis, he quickly replied: " Anemone is most likely the predator and preys on starfish. Anemones don't move, they just simply stay in place, thus, they just simply wait for whoever will crawl or swim into their way. Ahhh, somehow, his very logical thinking agrees with most of the materials I read. But up to now, imagine me like this seal scratching my head because I am more emotional in my thinking, thus, it is hard for me to see the plant like anemone preying on sea stars but easier for me to imagine sea stars crashing anemones with their sucker-tipped tubes.

I can't still imagine anemone eating sea stars and crabs, maybe small shells and shrimps, eh?

It is at times like this where I wish there is a marine consultant I can ask to explain to me more about the relationship of marine lives. Someone very knowledgeable of the different relationships in the sea. I actually typed in google also for a marine science tutor, I was just curious if we also have easy access to online tutoring other than the more sought subjects such as Math, Physics, Chemistry and English. In my search, I was lead to online tutoring UK where they do not only have UK based tutors for Math, English and Science, but they also have tutors for more advanced topics like engineering, anthropology, marine biology, etc. I am tempted to contact them and ask for a support to tackle the questions I have above, though I kind of get it why the anemone is the predator and the sea star is the prey. However, it is just hard for me to imagine how as tough as sea star can be swallowed by a mushy and soft anemone. 

Anemone vs Ochre Sea Star

From what I have read, between the two, anemones are more likely to eat sea stars since since sea stars prefer to eat shells, while anemone will eat anything except it can't eat the clownfish since clownfish is immune to the anemone's venom.Though it is hard to imagine a tough covered sea star can be eaten by jelly-like anemone, but then, anemone has venomous tentacles and the other side of sea star is made of soft tubes. Maybe, when I find more answers, then, I can make high five signs like these harbor seals? :)

Now, I really understand clearly why parents would always bring us out of the doors to explore, because nature drives our curiosity, making our mind active and training us to observe and think. Let me end this post with a quote from Albert Einstein:

"Look deep into nature, and then you will understand everything better." ~Albert Einstein

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