At a mile long, La Jolla Shores makes for a fun beach stroll, particularly during very low tides when I can walk on hard-packed sand. During these times, I head to the pilings that support Scripps Pier, as well as to the rock pile at the far north end of the Shores. These two substrates do not disappoint when it comes to seeing colorful ocher sea stars (Pisaster ochraceus). Though the species name, ochraeus, hints at the animals’ ocher pigmentation — ocher typically defined as a yellowish earth tone — these sea stars may also be brown, orange, red, or purple. It’s curious that individual ocher stars link arm-in-arm or pile one atop another, each sporting a different color. What is the color variation about? For the longest time, no one had a clue. Relatively recently, a research group chose to tackle the question. Its results, though not definitive, have at least spilled some of the ocher stars’ colorful secrets. While complete answers to the color puzzle aren’t available, I think the progress made so far is worth sharing. Ocher sea stars range from along our coast throughout the California Current, so the survey included sites from Southern California to Alaska, including British Columbia. It turns out that, across the board, north to south, most ocher stars are brown-reddish, with orange animals a relative minority. The purple stars are most limited on the open coast but at sites in isolated areas, such as inlets off Washington and British Columbia, purple ocher stars comprise almost the entire population. Because color shifts in an isolated population suggest a species is or is in the process of diverging from the original population, purple stars were subjected to genetic studies. Results showed that not only isn’t the purple population distinct, no ocher star, no matter the color or location, showed enough of a genetic difference to even be close to becoming a separate species. Of course, with so many possible color variations, even in individuals sharing a tide pool, the likelihood of a single underlying genetic component cannot be disregarded. So while not back to square one, because the researchers knew for certain they were dealing with one genetic population, the link between color and animal continued to evade. They next considered other parameters, such as diet, to provide an explanation. Interestingly, individuals living along the open coast from California to Washington dine on the ubiquitous California mussel Mytilus californianus, whereas purple ocher stars found in protected coastal areas feed on acorn barnacles (Balanus spp.). Prey consumed is less about choice because no mussels were found in those isolated areas. Yet, food is a clue because mussels harbor carotenoid pigments, not unlike those responsible for turning carrots orange. Can it be that the orange pigment in mussels is responsible for the ocher sea stars’ yellowish, orange and red pigments? Likely so, at least in part. If stars aren’t pigging out on mussels, does it mean that purple is their true underlying color? Unfortunately, the answer here isn’t cut and dried. Along other protected shoreline of Washington and Canada, communities of purple stars do have access to mussels and yet they remain purple. True, these are bay mussels (Mytilus sp.) not the California species but they harbor the same carotinoids. And what of the purple ocher stars I see locally in tide pools and on pier pilings in La Jolla? They live along the open coast surrounded by California mussels. So what’s the impetus here? Adding to the confusion are results from in-house laboratory studies, which correlate color to maturity. Some ocher sea stars were observed flip-flopping on color, such as when some orange adults turned purple over time and when juveniles didn’t stick to one color. After this study, it looks like age, water turbulence, food source and genetics may individually or collective determine where in the color spectrum an ocher sea will land, at least for a time. As is the hallmark of research, once begun, more questions arise than answers realized. While researchers continue exposing the shady secrets of ocher sea stars, my interest extends beyond the hows of color variation to the whys of color variation. That the natural world is anything but frivolous, I wonder what benefits the different colors impart. — Judith Lea Garfield, biologist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to [email protected].