Why do some kinds of tidepool animals come in multiple colors?

Nature Talk
1

This is something I have been trying to figure out for years and it has me stumped. From my experience most mammals, birds, reptiles, amphibians, insects, and so on come in one color pattern and while other color patterns may occur, they are often rare.
So why is it that a wide variety of tide-pool species are frequently found in more than one color pattern. (If this occurs in other habitats or species let me know.)

For example, I’ve seen both orange and purple variations of the ochre sea star.
https://www.inaturalist.org/observations/238621094
https://www.inaturalist.org/observations/223670060

Mottled stars come in a very large range of colors.
https://www.inaturalist.org/observations/224063999

I’ve seen members of the genus of isopods Gnorimosphaeroma (which are usually dark grey) in orange. Are they a completely different species, maybe?
https://www.inaturalist.org/observations/225178282

Individuals of different snailfish species (such as the tidepool snailfish) can have many different color patterns and markings
https://www.inaturalist.org/observations/225342471
https://www.inaturalist.org/observations/242951138

Stout coastal shrimp.
https://www.inaturalist.org/observations/242952198
https://www.inaturalist.org/observations/242952192

Crescent gunnels.
https://www.inaturalist.org/observations/236793694
https://www.inaturalist.org/observations/224505141

And I’ve seen this in many other species. I’m guessing they are all caused by different things. A lot of these species aren’t even from the same phylum. A few of my theories are that they change color as they age, it’s because of what they eat, or what habitat they live in.
So, does anyone know why any of these are caused?

(All the observation links I put down lead to my own observations but other people’s show the same thing.)

1 Like
2

I don’t know about any of your examples, but mollusks often have very different coloration within the same species. Sometimes this is diet, sometimes habitat, sometimes age, sometimes genetic. We don’t always know why, though. But people are trying to find out!
https://forum.inaturalist.org/t/winklewatch-a-community-science-project-on-snail-colour/54080

2 Likes
3

Interesting! Thanks.

4

In plants - why this one species comes in so many different colours
https://www.inaturalist.org/taxa/119370-Drosera-cistiflora

1 Like
5

When variations like this are common, I suspect that color isn’t important. Orange starfish aren’t more likely to be eaten than purple ones or more likely to find mussels to eat so natural selection doesn’t favor one color over the other. The only thing we can really say is that the different colors exist because they can.

In many other cases, one color morph is standard and the others are rare, such as the white and pink morphs of normally blue chicory (Cichorium intybus). In this case there probably is strong selection against the odd colors because pollinators use the color to find the flowers. If bees learn that blue chicory flowers are good, they go from blue flower to blue flower and tend to ignore the white and pink flowers, which therefore don’t set as much seed.

It’s also possible that the chemical differences that cause the colors we see also cause some other difference that is important to survival and reproduction and color itself is just a side effect.

5 Likes