Blue, mysterious and arriving by the millions: the alien-like creatures blanketing US beaches

[eppur_se_muova]

8. ''It is modified to be blue" ... that's quite a trick, since the carotenoids are yellow to red -- named after carrots.

Turns out to be something I had already encountered in another context -- the pigment is complexed with proteins which cause (somehow!) the absorbance spectrum to shift. Wikipedia doesn't have much of an article on carotenoproteins, but fortunately one can find other citations:

Carotenoproteins and Carotenolipoproteins

In combination with proteins and lipids, carotenoids also give rise to the wide range of blue, green, purple, and brownish colors of marine life. Complexes of carotenoids and proteins, known as carotenoproteins and carotenolipoproteins, dominate in the exoskeleton of crustaceans, coelenterata, and many other marine species. Although astaxanthin itself appears as a red pigment, when it is complexed with various proteins the light absorbance shifts, which results in green, yellow, blue, and brown colors. This is demonstrated by the appearance of the red color when crustaceans are cooked, which is the result of the denaturation of the proteins and release of the astaxanthin chromophore. The American lobster, Homarus americanus, displays an abundance of green colors but also with shades of black, red and blue, which is almost entirely astaxanthin complexed with protein and chitin. Astaxanthin at over 90% purity has been identified from the blue goose-barnacle within the inner and outer body tissues as well as the ripe eggs. The green astaxanthin protein of lobsters, ovoverdin, persists unchanged until shortly before the eggs hatch, whereby the protein moiety is then released, liberating astaxanthin.

https://www.brineshrimpdirect.com/about-us/articles/natural-astaxanthin/

This may very well be the first citation of brineshrimpdirect.com on DU.

So, that "other context": I knew that the reason lobster shells turn bright red, and shrimp turn pink, when cooked is due to the breakdown of a protein-pigment complex, of a type similar to that in Velella. Apparently, it's even the same pigment, astaxanthin ("xanthin" comes from the Greek word for 'yellow', btw). Since Velella isn't a crustacean I didn't make the connection, but apparently the pigments originate in algae which are eaten by all manner of marine animals, who incorporate the pigments into their own coloration. In fact, shrimp eat algae and use the pigment to color their exoskeletons red ( which is good as black in very deep water, protecting them from predation), but are consumed by salmon in turn, turning their flesh the iconic pink color we all know as "salmon pink".

So, if you were to cook, V. velella, it should turn red or pink!