Reef Chemistry Question of the Day #156 Sea Urchin Color

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#156[/HASHTAG]

Why are sea urchins and their spines colored (at least, what reasons have scientists proposed)?

Pick all you think are likely.

A. It helps them find mates of the same species.
B. It warns potential predators that may associate the color with bad past experience to help drive them away.
C. It protects them from excessive UV exposure.
D. It may help prevent other organisms from growing on them.
E. It makes the spines stronger.
F. It is a poison that gets into attacking predators to deter them.
G. It protects them from superoxide radicals in the nearby water.

Good luck!

 

[surfnsalt]

,B,D,F

 

[human]

I'm going to guess C,D,F,and G, not sure about E though bc I do know the color can be effected by different chemicals absorbed from the water so I guess it's possible different colored spines could be stronger. B is also plausible bc other animals use colors to warn off predators, but I'm not sure scientists have confirmed this for urchins. OK final answer is C,D,F,G before I start second guessing myself more.

 

[metrokat]

Hi Randy - just sent you an email.

 

[Randy Holmes-Farley]

And the correct answers are:

B. It warns potential predators that may associate the color with bad past experience to help drive them away.
C. It protects them from excessive UV exposure.
D. It may help prevent other organisms from growing on them.
G. It protects them from superoxide radicals in the nearby water.

All of these have been proposed for the color molecules in sea urchins. The "true" answer may depend on the species.

These pigments are often antioxidants (G) and absorb UV (C), both of which have been suggested to be important. They also seem to discourage fouling of the urchin surfaces (D) and may be a visual clue to predators (B).

Answers that do not seem to be correct are:

A. It helps them find mates of the same species (they cannot see)
E. It makes the spines stronger (that's not been noted)
F. It is a poison that gets into attacking predators to deter them (they are not a fast acting poison)