In the extreme northeast of the island of Lanzarote (Canary Islands) we find a unique natural space, a product of the island’s volcanic activity, called the La Corona lava tube, in honor of the volcano that formed it. It is a cavernous structure with access to the sea, almost 8 kilometers in total length, and of which at least one and a half is below sea level. That part is called the Atlantis Tunnel . In its emerged part, in the more or less central area, three openings stand out in the ground, caused by the collapse of the tunnel roof, called jameos : the Jameo Chico , from where you can access the cave system, the Jameo Grand e , and the so-called Jameo de la Cazuela ; in addition to an underground lagoon. These structures form the so-called Jameos del Agua .
The formation of jameos
Lava tubes form when the surface of a lava flow cools and solidifies while lava below continues to flow and eventually drains away. As a result, all that remains inside is waste rock. During its formation, no life forms reside within it or survive the passage of the lava, so once it is formed, it remains a bare, lifeless tube of volcanic rock . Radiometric dating methods estimate that the Los Jameos del Agua volcanic cave system formed between 27,000 and 15,000 years ago.
This is not a hermetically sealed cave. Its exit to the sea and, also, the subsidence of the land that form the jameos are entrance ways through which certain living beings access the cave system. These animals can settle inside it, and even, if enough time passes, adapt and form communities of that system. And so it happened.
Colonization and speciation
After the last glaciation, and with the tunnel already formed, the sea level rose, and with it water entered the tunnels , flooding some depressions inside, forming lagoons. With the water came animals ; different species of crustaceans, polychaetes and even sea cucumbers. Currently, the only exchange of water between the interior lagoons and the sea is through cracks and pores in the rocks, but it no longer allows animals to enter or exit.
Thus, the animals that entered these jameos lost contact with the outside populations. Isolated, they suffered a very different selection pressure from their oceanic counterparts, and the evolutionary process did its job. New, unique species , non-existent anywhere else, are formed in the underground lagoons of the lava tube. They are maintained thanks to the organic matter that falls from the jameos, which provides them with a source of food. They specialize in a completely dark environment, with constant and practically invariable temperatures.
A blind white crab
Among those endemic species of the Jameos del Agua, non-existent in the rest of the planet, a crustacean stands out. A small crab, no more than three centimeters. In honor of the place where he lives, he receives the name of jameíto . Its scientific name: Munidopsis polymorpha .
The species of the genus Munidopsis normally inhabit bathyal and abyssal zones, but the jameíto is an exception. Its isolation in the Jameos del Agua has led to certain particular adaptations , which make it extraordinarily specialized. Among them, being completely white or blind, two very common forms of regressive adaptation among troglobitic animals —those that live in caves—. These animals take advantage of the night, when predation is less, to migrate out of the lagoon, taking advantage of the resources that arrive through the large openings in the ceiling of the cavern, and submerge again at dawn.
The curse of vile metal
Until the 70s of the last century, the jameitos enjoyed a high population density, limited only by the number of nooks and crannies in which to shelter. However, since the construction of the art, culture and tourism center created by César Manrique in 1968, and due to the massive influx of tourists, the population of jameítos began to be decimated . The animal that today is a symbol of Lanzarote was on the verge of extinction, especially for a gesture that for tourists was as innocent as throwing coins into the water .
Contrary to the superstitious belief that it would bring good luck, throwing coins into the lagoon where the small crabs reside generated, on the one hand, a serious alteration of the ecosystem’s microbiota ; a coin passes through many hands and rests on many surfaces, and can carry many microorganisms that, entering a new ecosystem, can destabilize it. He highlighted the large number of fecal bacteria that proliferated in the environment, and which are usually very present on coins.
On the other hand, quite corrosive salt water can slowly break down coins. This caused contamination of the water by metals such as iron, copper, zinc or nickel, and the consequent impact on fauna.
The removal of coins was complex and today a large number of posters expressly prohibit throwing money or any other material into the waters of the Jameos. All in order to protect an endemism, a symbol of the island, which is listed in Spain as an endangered species .
References:
Iliffe, T. M. et al. 1984. Marine Lava Cave Fauna: Composition, Biogeography, and Origins. Science, 225(4659), 309-311. DOI: 10.1126/science.225.4659.309
Martinez, A. et al. 2018. Volcanic Anchorage Habitats of Lanzarote. In OT Moldovan et al. (Eds.), Cave Ecology (pp. 399-414). Springer International Publishing. DOI: 10.1007/978-3-319-98852-8_19
Martínez, A. et al. 2020. Tossed ‘good luck’ coins as vectors for anthropogenic pollution into aquatic environment. Environmental Pollution, 259, 113800. DOI: 10.1016/j.envpol.2019.113800
Royal Decree 139/2011, of February 4, for the development of the List of Wild Species under Special Protection Regime and the Spanish Catalog of Endangered Species, Pub. L. No. Royal Decree 139/2011, BOE-A-2011- 3582 20912 (2011)
Signorelli, S. et al. 2007. The Jameos del Agua cave (Lanzarote, Canary Islands): some morphological and geological features of a spectacular lava tube adapted to auditorium. En A. M. Malheiro et al., Volcanic Rocks (pp. 45-51). Proceedings of the International Workshop on volcanic rocks.
Wilkens, H. et al. 1986. Origin and age of the marine stygofauna of Lanzarote, Canary Islands. Communications from the Hamburg Zoological Museum and Institute, 83, 223-230.