Pacific goose barnacle

Pollicipes elegans is a goose barnacle, a stalked cirripede crustacean of the family Pollicipedidae, described by Lesson in 1831 ^[1]. In Peru it is known as "percebe" ^[2]. It lives attached to rocks in the intertidal zone on shores pounded by waves ^[3]. Its range in the eastern Pacific is broken into several separate stretches, from Baja California, in Mexico, to northern Peru ^[4]. In Peru it supported an export fishery to the Iberian Peninsula that ended with the collapse of the populations on the Lobos islands ^[4].

Like other goose barnacles, its body is divided into a muscular stalk, or peduncle, which houses the adhesive gland and the ovary, and a capitulum of plates that encloses the body and the filter-feeding legs, or cirri ^[4]. Below the lower lateral plates of the capitulum it has a single row of plates, its caudal appendages are made of several segments, and the stalk scales, oval and taller than wide, point up towards the capitulum ^[4].

Compared with the Atlantic Pollicipes pollicipes, its capitular plates are a more reddish orange, it has a single plate on each side between the median lateral and the rostrolateral, where that species has two, and its rostrolateral and carinolateral plates sit closer to the median lateral ^[4]. In some specimens a few plates, such as the tergum, are a brighter orange than the rest ^[4].

On the Peruvian coast in 1985, the animals measured were between 11 and 141 mm in total length, 60.3 mm on average, and weighed between 0.10 and 12.80 g ^[3]. At Callao, those living in brighter spots were smaller and paler, with a more compact stalk ^[3].

Similar species

• Pollicipes polymerus: It lives further north and may overlap with this species only in Baja California ^[4]. It is told apart by more than one row of plates below the lateral plates, caudal appendages of a single segment and spine-like stalk scales pointing outwards ^[4].

Its northern limit is at Punta Santa Domingo, on the Pacific coast of Baja California, where it may overlap with Pollicipes polymerus ^[4]. Unlike the other species in the genus, its range is fragmented: there are populations in northern and central Mexico, in El Salvador and Costa Rica, on mainland Ecuador and in northern Peru, with stretches in between where it has not been found, and it does not live in the Galapagos Islands ^[4].

In Peru its usual southern limit is at Punta Aguja, Piura, at 5° 47′ S, and on the Lobos de Tierra and Lobos de Afuera islands; during El Niño or warm conditions it can spread as far as Chilca, at 12° 29′ S, and persist there for a few years ^[4]. In April and May 1985, after the 1982-1983 El Niño, it was found at many localities between Yasila, Paita, and Chilca, Lima ^[3].

It lives in the middle of the intertidal zone on rocky shores heavily exposed to the swell, on sharp-edged and steep rock, above all in crevices, cracks and the vertical faces of large boulders, where it forms patches of between 0.8 and 15 m² ^[3]. A genetic study links its absence from long stretches of the tropical coast to sea temperature and to a lack of suitable habitat, since sandy beaches and estuaries abound there and rocky shores are few ^[5].

It is a hermaphrodite but in practice breeds with its neighbours: in Baja California, 79% of the broods analysed had more than one father, with up to 5 fathers per brood, and the number of fathers rose with the density of the cluster ^[6]. In the same study, none of the 4 solitary animals carried embryos, and in the 3 broods with a single father the young carried alleles absent from the mother, which makes self-fertilisation unlikely ^[6].

Pollicipes species have a short penis, shorter than the cirri, and in this species fertilisation is carried out mainly by the closest neighbours; if it also fertilises by releasing sperm into the water, that would only work over short distances or within the cluster ^[4]. The only data on its breeding calendar come from Yacila, in Paita, where the share of animals carrying eggs was highest in November ^[4].

In the laboratory, second-stage nauplius larvae from Mexico, El Salvador and Peru showed different ranges of temperature tolerance, with those from El Salvador the most tolerant ^[4]. Mexican larvae tolerated more heat when collected in the northern summer than in winter, a seasonal adjustment not seen in larvae from Peru ^[4].

In Peru it usually shares the rock with other crustaceans, echinoderms, anemones and polychaetes, and above all with the small mussels Semimytilus algosus and Perumytilus purpuratus; in 1985 molluscs made up 65% of the organisms in the communities studied, crustaceans 33% and polychaetes 1% ^[3]. Its stomach contents held digested organic matter, remains of copepod nauplii and diatoms ^[3].

The predatory snail Concholepas concholepas, the anemone Phymactis clematis and the brittle star Ophiactis kroeyeri have also been recorded with it, and the sea stars Stichaster striatus and Heliaster helianthus live near its lower limit on the shore ^[4].

Its Peruvian populations respond strongly to El Niño: during the 1982-1983 event its abundance rose sharply on the mid-shore at several sites, and when it ended it fell while the mussels and the giant barnacle Austromegabalanus psittacus increased ^[4]. During the 1997-1998 El Niño, by contrast, warm water and guano washed off by the rains caused mass die-offs on Lobos de Afuera island ^[5].

Mitochondrial DNA shows the Mexican populations to be strongly differentiated from those of El Salvador and Peru, the 3 regions exchange no appreciable numbers of individuals, and the data favour the populations at the ends of the range having split off from a tropical stock rather than arising from a step-by-step colonisation across the tropics ^[5]. In Peru genetic diversity is lower than in El Salvador and the effective population size smaller than in Mexico and El Salvador, perhaps also because of the bottlenecks caused by strong El Niño events ^[5].

On the Lobos de Tierra and Lobos de Afuera islands, IMARPE monitoring estimated 39.5 million individuals in 1995, a figure that fell to 2.5 million in 2002 and to 0.4 million in 2010 and 2015; in 2015 the biomass was only 3 t ^[4]. A lack of rules and enforcement led to the collapse of the population on both islands by the mid-2000s, fishing there was closed in 2007, and no recovery has been seen since ^[4].

In 2002 the Ministry of Production set a harvest season for the whole Peruvian coast from 1 February to 30 November, banning collection in December and January to protect the summer, its main season of breeding and recruitment ^[7]. That same year, faced with a possible 2002-2003 El Niño, harvesting was exceptionally allowed in December 2002 and January 2003, and collectors were told to leave part of the animals attached to the rocks as a surface for larvae to settle on ^[8].

On the mainland, the individual quota allowed in Piura fell from 100 kg per month per fisher in 2017 to 3 kg in 2019, which suggests that those populations are overexploited too ^[4].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

A 1985 chemical analysis by IMARPE, made on the stalk of animals from Yasila, Paita, gave 14.00% protein, 2.80% mineral salts, 5.00% fat and 77.80% water ^[3].

Paita had a traditional small-scale commercial harvest, and after the 1982-1983 El Niño the beds that had formed between Yasila and Chilca were exploited from 1984 to early 1985 ^[3]. Harvesting centred on Chimbote and Paita, and the catch went mainly to Spain, with a maximum volume of 3000 kg ^[3]. Gathering it is hard and dangerous, because it means climbing down slippery crevices where the waves can throw the collector against the rocks, and it is only possible at low tide with a calm sea ^[3].

The main Peruvian fishery was on the Lobos de Tierra and Lobos de Afuera islands, in Lambayeque, and exported fresh and frozen goose barnacles to Spain and Portugal; it had 2 strong periods, from 1992 to 1995, with annual landings of 14 to 34 t, and from 2001 to 2002, with 19 to 28 t ^[4]. Exports to the Iberian Peninsula stopped after that fishery closed, and some commercial harvesting continues today on the coast of Piura ^[4].

In Peru it lives mainly on the rocky coast of the north, down to Punta Aguja, in Piura, and on the Lobos de Tierra and Lobos de Afuera islands ^[4]. In 1985 it was most abundant on a large cliff at Yasila, Paita, with 234 animals per 0.0625 m² in patches of 15 m² ^[3]. The 2026 Master Plan of the Mar Tropical de Grau National Reserve lists it among the key or threatened species present in the Isla Foca sector, a sector where taking species considered key, threatened or endemic is not allowed ^[2].