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R&D on Threatened Species: FGCSIC Proyectos Cero

JOSé TEMPLADO

Museo Nacional de Ciencias Naturales, CSIC

JAVIER GUALLART

Universidad Católica de Valencia

The Patella ferruginea limpet: an endangered marine invertebrate

The Patella ferruginea is possibly the most threatened species in the Mediterranean, making it emblematic of efforts to conserve the marine environment.

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The species of the Patellidae family are commonly known as limpets. This family includes five genera: Helcion, with four species on the South African coast; Cymbula, with eight species also living on the coast of South Africa, some of which extend to the north on both sides of the African continent and one of them reaching the Alboran Sea (C. nigra); HIGHLIGHTSProfile: Javier Guallart and José TempladoGlossary
Scutellastra, with about 20 species in the Pacific and Indian Oceans, mainly in the southern hemisphere; Patella, with ten species in the Northeast Atlantic and Mediterranean, and Ansata (= Patina) with a single species in the European Atlantic (A. pellucidus). However, differentiating the species from one another is complicated and the family’s taxonomy is undergoing continual revisions.

Limpets are associated with temperate or relatively cold seas, which is where they are most diverse and where they are the dominant shellfish in the rocky intertidal strip. The variety of species decreases towards the subtropics, and only a few species have successfully adapted to tropical seas. The greatest variety of limpets is found concentrated along the coasts of South Africa, while in the Americas there is only one species of this family, the Scutellastra mexicana, which is also the largest in size. This gastropod lives distributed along the American Pacific coast from Mexico to Peru.




Adult specimen of Patella ferruginea (approx. 70 mm in diameter). / Photo: Javier Guallart.



Limpets have a highly uniform shell which is typically a somewhat depressed conical or sub-conical shape, with no spiral winding and an oval or nearly circular outline. The shell is usually thick with prominent radial ribs. Patellidae anatomy reveals some very archaic structures showing them to be among the most primitive gastropods still in existence today.    

The Patellidae are one of the most successful families of all gastropods at conquering rocky surfaces in the intertidal zone, a marine habitats subject to some of the harshest and most changeable conditions. Many of their morphological and biological peculiarities can be interpreted in terms of their adaptation to this environment. They adhere strongly to the rock and are able to withstand dry conditions. They feed by grazing on various types of algae, mainly small-sized varieties. Very few species have broken away from these coastal rocky substrates and those that have live on large infra-littoral algae.

Most species are protandrous hermaphrodites (such that the males are the smaller individuals), although some species have separate sexes. Fertilisation is external and synchronous in both sexes. Larval development consists of a short trocophore swimming phase.

In some places limpets are harvested for human consumption, which has severely reduced some populations. This is a particular cause for concern in species with small ranges, such as those endemic to certain islands, such as Patella gomesi in the Azores, Patella piperata in Madeira, Patella candei in the Canary Islands and Patella lugubris on the Cape Verde islands.

Some limpets on the mainland are included on various lists of threatened species, such as Scutellastra mexicana on the Pacific coast of Central America or Patella ferruginea in the southwestern Mediterranean. It is precisely this latter species which is the focus of this article.


Patella ferruginea 
The Patella ferruginea limpet is one of the most emblematic species for marine environment conservation in the Mediterranean given that it is perhaps the species most at risk of extinction. The shells of Patella ferruginea are one of the most characteristic elements of shell mounds from the Paleolithic to the Neolithic period throughout the western Mediterranean basin, indicating that it has been It is easily distinguished from other Mediterranean limpets by its large and sturdy shell with pronounced broad ribsconsumed by man since prehistoric times. Perhaps due to human pressure, the species has been disappearing from large areas, especially from the northern Mediterranean shores. Today, as detailed below, it has been relegated to the western sector of the North African coast, isolated points in southern Spain, Corsica and Sardinia, and a few small islands in the central Mediterranean. The decline of the species, which may have been further accelerated by the progressive deterioration of the coastline, continues at an alarming rate and many of their stocks are on the verge of disappearing. This has led to limpets being included on various lists of endangered species (Annex IV of the Habitats Directive, and Annex II of the Berne and Barcelona Conventions). It is also included in the Spanish Catalogue of Endangered Species in the “endangered” category (BOE, 22 June 1999, no. 148: 23921-23922). As a result, it is the first invertebrate and, indeed, the first marine species, for which a national conservation strategy has been developed in Spain (published in 2009).




Adult specimen (approx. 80 mm diameter) covered with barnacles and carrying a juvenile (approx. 18 mm in diameter) on its shell. It is not uncommon for juveniles to be attached to the shells of adults, which does not necessarily mean that was where they started life. / Photo: Javier Guallart.


It is a conspicuous gastropod on account of its size, the pronounced ribs visible on its shell, and because it lives above sea level. This has made the species easy and tempting prey for man. Specimens can exceed 10 cm in diameter, but usually they are no bigger than 80 to 90 mm. The larger specimens can weigh over 180 g, or 65 g of flesh without the shell. It is easily distinguished from other Mediterranean limpets by its large and sturdy shell with pronounced broad ribs (between 30 and 50), making the edge very sinuous. The ribs are often nodular and somewhat irregular, and the shell is often eroded and colonised by epibiont organisms such as barnacles and algae. The external colour of the shell in the case of clean specimens is rusty to cream coloured, and marble white on the inside, with a darker central zone (muscle scar) and dark brown inner edge. The foot of the adult is yellowish orange at the base and dark grey on the sides. The cephalic region is also dark in colour, with the blackish tentacles standing out. The shell of juveniles measuring less than 20 mm is highly characteristic in that it is very flat and has a small number of thick ribs that extend over the edge, giving it a star-shaped outline. The background colour is an off-white, with thick dark concentric bands rising over the ribs.

Patella ferruginea is currently limited to the northern coast of Africa between the Straits of Gibraltar (Ceuta) and Cape Bon and the island of Zembra (Tunisia), some parts of southern Spain, the Isla de Alboran, the west coast of Corsica and Northern Sardinia and the island of Pantelleria, in the Strait of Sicily. The species appears to be extinct today on the coast of the French and Italian mainland, although there have been some relatively recent sitings on the Tuscan coast. The populations of Corsica and Sardinia also seem to be in decline. On the coast of the Spanish mainland its range extended from near the Strait of Gibraltar to Cabo de Gata (Almería) until very recently, although populations have progressively fragmented, declined and disappeared. At present, it is estimated that only about a thousand specimens remain, distributed along the coast of Andalusia, but the population might not be dense enough to reproduce.

It is on the North African coast where there are still thriving populations of Patella ferruginea. In Melilla and Ceuta there are large contingents, and the Chafarinas Islands have the healthiest populations. Another enclave of the species is on the Habibas islands in Algeria.

This limpet lives in the upper mediolittoral level, where algae cover is very light and an imperceptible microbial biofilm of diatoms, cyanobacteria and other algae propagules predominates, on which it seems to feed. It is almost always above sea level in the lower area occupied by the Chthamalus stellatus barnacle and above the belt of red algae and the sea snail Dendropoma petraeum. It shows a slight preference for areas exposed to the waves.




Picture of individuals of 3 limpet species coexisting: Left, Patella caerulea, in the middle Patella ferruginea and right, Patella rustica. The specimen of Patella ferruginea is a small adult, measuring about 40 mm in diameter. / Photo: Javier Guallart.


Adults are sedentary and move only to feed, travelling short distances, which they tend to do when they are washed by the waves, preferably at high tide, and at night. When individuals finish feeding they return to the same resting place (i.e. they exhibit homing behaviour). Each individual therefore leaves a mark or print on the rock as a halo of calcareous algae grows in the space between the sole of the foot and the edge of the shell.

The robustness of its shell and the adhesive force of its foot protects the mollusc from many predators, especially during adulthood. Its main predators are Eriphia verrucosa and Pachygrapsus marmoratus crabs, and the gastropod Stramonita haemastoma, which is able to pierce the shell even of adults measuring up to about 60 mm. Patella ferruginea is considered a long-lived and slow growing species. It does not reach sexual maturity until the end of the second year of life and there is good evidence that it can live for more than ten years. Some authors have suggested that it can even reach 35 years, although there is as yet insufficient evidence to verify this. 

There has been some controversy about the species’ mode of reproduction. There is a marked gender segregation by size: between 25 and 40 mm specimens are all males, but at larger sizes the proportion of females gradually increases, coming to predominate among groups of larger specimens.

These data strongly suggested the species to be protrandrous hermaphrodite. However, very recent studies have shown that individuals can change sex in both directions, and not just from male to female. It is therefore necessary to investigate the factors that determine this change of sex and its role in population dynamics, as well as many other as yet unknown aspects of its reproductive biology.

The annual reproductive cycle is concentrated in just a short space of time (August to November), while the rest of the year they are totally sexually inactive. Spawning takes place in late November, which appears to be timed to coincide with the first storms, once specimens are mature. After a short swimming larval stage the juveniles settle in the same habitat as the adults. However, many aspects of larval life in the natural environment are as yet unknown, such as the larvae’s ability to disperse, their location in the water column or factors that induce them to initiate metamorphosis.

In its first round of Proyectos Cero on Endangered Species, the Fundación General CSIC recently awarded funding for a project focusing on this species entitled “Plan de acción para las propuestas de viabilidad de la lapa en peligro de extinción, Patella ferruginea” (Plan of Action for proposals for the viability of the endangered limpet, Patella ferruginea). This project is due to last three years and aims to study in depth the reproduction of the species, both in the wild and in captivity. The goal is to use aquaculture techniques to obtain juveniles and thereby enable populations to be restored if they are affected by a natural disaster.

The field work will take place mostly in the Chafarinas Islands (a protected enclave where the best stocks of the species are to be found) and will take into account the genetic structure of populations, both globally and locally in the archipelago, when considering any future reintroduction of specimens. 

Profile: Javier Guallart and José Templado

Javier Guallart
Has a PhD in Biological Sciences from the University of Valencia, where he taught aquaculture. In the last few years he has worked on various projects related to two lines of research: studies on species of commercial interest, and research on endangered marine species, particularly invertebrates. Much of his recent work has been carried out for the Chafarinas Islands National Park Authority, where he has been investigating aspects of the biology and population dynamics of Patella ferruginea for over 10 years. Much of the knowledge acquired has substantially changed some received ideas about the biology of this iconic species and helped lay the foundations for the development of the National Strategy for the Conservation of the Patella ferruginea. He is a regular collaborator of José Templado and Annie Machordom’s team at the Museo Nacional de Ciencias Naturales (National Museum of Natural Sciences).

José Templado
Is a CSIC assistant professor at the Museo Nacional de Ciencias Naturales (National Museum of Natural Sciences) in Madrid. His research has focused on various aspects of the study of marine biodiversity including: taxonomic, systematic, evolutionary, biogeographic and genetic aspects and issues relating to reproductive biology and invasive species. He has participated in oceanographic surveys in various parts of the world. His work has helped clarify the evolution of the mitochondrial genome of gastropod molluscs and described 25 new species to science. He is an adviser to the Ministry of Environment, Rural and Maritime Affairs on issues relating to marine reserves and endangered marine species and has published several books on these subjects. He has participated as an expert in the preparation of the Annexes to the Barcelona Convention for the Protection of the Mediterranean, in the drafting of the Spanish Strategy for the Conservation and Sustainable Use of Biological Diversity and the development of the National Strategy for Conservation of the Patella ferruginea limpet.

Glossary

Rhodophyta
Red algae.

Cyanobacteria
Also known as “blue-green algae,” cyanobacteria are a very primitive group of bacteria that are capable of photosynthesis.

Diatoms
Group of unicellular algae common in aquatic environments and characterised by their having a silica-impregnated rigid or semi-rigid membrane.

Proterandrous hermaphroditic species
Species in which individuals are initially male and at some point in their lives change sex to become female.

Intertidal rocky zone
This is the coastal strip which lies between the minimum and maximum levels reached by the tides.

Epibiont organisms
Organisms living on the surface of other organisms.

Grazers
Animals that feed by scraping off small algae that grow on the substrate.

Trocophore
Type of swimming larva characteristic of some groups of marine invertebrates such as molluscs.

Vermetidae
Group of tubular shell gastropod molluscs (not spiral shelled) that live cemented on to the underlying rock.

Published in No. 03


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  • Lychnos. ISSN: 2171-6463 (Spanish print edition),
    2172-0207 (English print edition), 2174-5102 (online edition)
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