Taxonomy

Rarity

Abundance rates how many are in suitable habitat. Find difficulty rates how hard it is to locate one on a daylight snorkel or freedive through 50 ft. A higher find score means a harder search. The rarity category also reflects the kind of encounter; it is not an average of the 2 scores.

Seasonality

Location

Hopkins' rose lives in tide pools and on rock in the low intertidal zone, and it lives only where its food lives. That food is a single species of pink bryozoan, a colonial animal that grows as a thin crust over rock. A tide pooler who finds that pink crust is in the right place to look.

The animal is only about 1 inch long, 2 to 3 centimeters, and covered completely in long, rose-pink projections that sway in the water. The color makes it hard to miss once the eye is close enough to the rock.

Deep Dive

The pink is borrowed from the food. Hopkins' rose feeds on one pink encrusting bryozoan and nothing else, extracting the soft tissue of the colony with specialized teeth, and it takes its color from that prey. The pigment is a carotenoid called hopkinsiaxanthin. A chemist described it in 1949 as a new compound and named it after the slug, and the bryozoan's own tissues carry it too.

The species also has boom years. In the weeks before January 2015, researchers from UC Santa Barbara, UC Santa Cruz, the Bodega Marine Laboratory and the California Academy of Sciences found Hopkins' rose in tide pools from San Luis Obispo County to Humboldt County at densities of up to dozens per square meter. Those were the highest numbers and the northernmost records since the El Nino years of 1983 and 1998, and a similar bloom had hit the Central Coast in 1977. A model published in 2011 had predicted strong arrivals of young slugs whenever the water ran warm, currents flowed north and upwelling was weak, which is what was happening. By 2017 it had even been seen spawning in southern Oregon, a shift researchers tie to the warm water anomaly of 2014 in the North Pacific.

Every Hopkins' rose is male and female at once, and mated slugs lay pink, ribbon-like egg masses on rock. The ribbon is laid from the outside working inward in a counterclockwise motion, which leaves a clockwise spiral. The eggs hatch into tiny larvae that drift as plankton before settling to grow into adults.

The name honors a patron. Frank Mace MacFarland described the species in 1905 and named it for his friend Timothy Hopkins, the patron of the marine laboratory. The scientific name has changed twice since, most recently in 2024, but the common name has kept his.

Where to Find Them

Researched habitat and range candidates

These locations have suitable habitat within the species range. An assignment is a possible encounter, not a confirmed sighting at every beach. Season, depth, and local conditions still matter. Historical habitat without present-day evidence is excluded.