by Robin Agarwal
Originally published in the October 2019 Edition of Between the Tides
Looking like a fanciful Pokémon creature made out of pink, blue and yellow-striped candy corn, Babakina festiva (Roller, 1973) is one of California’s more infrequently-seen nudibranchs and an even more infrequent visitor to the northern half of our state. It was therefore with great delight that nudibranch researcher Maria Schaefer spotted one of these rarities at Fitzgerald Marine Reserve’s Seal Cove on August 30, during one of the last early morning minus-tide cycles of the summer.
The common name for B. festiva, Single-stalk Aeolid, comes from their unusual rhinophores, chemical sensory organs on their head that resemble ears. Unlike most nudibranchs’ rhinophores, which appear distinctly separate from each other, B. festiva rhinophores appear to be fused at their base. Its genus name honors the esteemed Japanese sea slug researcher Dr. Kikutaro Baba.
Babakina festiva rhinophores (contrast enhanced)
B. festiva are not seen every year at Fitzgerald, but Schaefer and I were hoping to spot one of these beautiful animals, since many of the same favorable weather conditions were developing as in the years they were last seen at the reserve: 2015 and 2016. According to iNaturalist.org observation data, no B. festiva had been seen north of Los Angeles County since those years, with the exception of one 2018 sighting at 40′ depth off Anacapa Island by scuba instructor Douglas Klug, and my own observation of a single specimen in Monterey Harbor earlier this year, in April 2019. The Monterey B. festiva was our inspiration for further investigations at Fitzgerald this summer.
“Colorful rare animals such as B. festiva can bring people together in their quest to see unusual beauty in nature,” says Schaefer. In fact, Shaefer and I first met in 2016 at Seal Cove, the day after my first discovery of a B. festiva at Fitzgerald; we were both hunting for more. She continues: “It was great fun after those intervening years for us to get back on the same reef again in late August, and lo and behold, we saw another B. festiva.”
Nudibranchs are picky carnivores,
feeding on very specific hydroids,
sponges, anemones and other
invertebrates according to species
While the published range of B. festiva extends from Nayarit, Mexico to Duxbury Reef in Marin County, California, these beauties are far more likely to be encountered in the warm-water tidepools of San Diego County and points south. However, it appears that when anomalously warm El Niño conditions bring warmer-than-normal water temperatures north, as in 2015-17 and perhaps to a certain extent this summer, settlement (the transition of a planktonic nudibranch larva, called a veliger, to its more familiar adult, slug-like form) appears to increase for some southern nudibranch species such as B.festiva. For those interested in further reading on this topic, northern range extensions for 37 species of nudibranchs, with an average shift of 270 km during this period, were extensively researched by Dr. Jeffrey Goddard of UC Santa Barbara and published in September 2018.
The settlement of these beautiful nudibranchs may also coincide with increased availability of food, but we cannot be certain: nudibranch research scientists do not have enough data yet to identify the preferred prey of B.festiva. Nudibranchs are picky carnivores, feeding on very specific hydroids, sponges, anemones and other invertebrates according to species; this is the primary reason that most species of nudibranchs are nearly impossible to keep in captivity for any length of time.
Based on their morphology, educated guesses have been made regarding B. festiva’s preferred habitat and prey, and more research is undoubtedly called for in the future. “With that big, broad snowplow foot, they look like
they hang out in sand,” says evolutionary biologist Brenna Green, comparing them to the even bigger-footed Cerberilla sp. nudibranchs of the tropical Indo-Pacific. “So if they do live in sand, that probably rules out hydroids; they might feed on anemones.” Indeed, our recent B. festiva at Seal Cove was found crawling on red algae near sand, as was the Monterey Harbor specimen earlier this year.