by Christoph Weigel
Note in advance: this is, once again, a longread. So if you're more into looking at the small side of life consider skipping the first section and proceed directly to '...and Venus's hair'. Unlike most STC posts, the first section, 'Island Stories...', contains a heap of links – most direct to pictures/photos from the island in question with the purpose to lead you virtually closer to its story than swaths of words possibly could (some come with their Spanish flavor). Call it, if you like, STC's first steps towards 'augmented reality'.
El Hierro is the last in a row of islands in the Canary archipelago, Atlantic Ocean: the farthest west and farthest south, the smallest, and youngest. Its geographic coordinates 27°45'N 18°00'W translate to a longitude of ~450 km west of the Moroccan coast, and to the latitude of Tampa, Florida. All the Islas Canarias are of volcanic origin, and El Hierro rose from the sea approximately 1.1 million years ago (see here for the complicated geological history of the 'Canary Island Seamount Province' (CISP) ). Successive eruptions and landslides shaped the island until major volcanic activities ceased around 10,000 BC. Aa and pahoehoe lavas, volcanic tubes, cones, craters, dykes, bombs and jable ‒ all witness these comparatively recent activities.
Today, El Hierro has a diameter of ~25 km and an area of 280 km2. Its highest elevation, el Malpaso, reaches 1,500 mamsl (= meters above mean sea level; being more familiar with the micrometer/nanometer range I wasn't even aware of this unit! ). Due to this high elevation El Hierro has, despite its small size, several distinct climate and vegetation zones. The northeast and all terrain >700 m profit from the steady trade winds that come with clouds from which the vegetation 'harvests' water, especially during the hot and dry summer months. Due to its lush greenness during winter and spring, the central plateau, la Meseta de Nisdafe, could be easily mistaken for some rural Irish idyll. The greater part of the upper zone, however, is covered with forests, rain forest-like laurisilva (Fayal-Brezal ) with many endemic trees and plants (Macaronesia ), a great variety of lichens such as Ramalina canariensis (lichen aficionados: explore this blog! ), and extended pine forests (Pinus canariensis, with impressive, up to 30 cm long needles, and a largely fire-resistant bark ).
In the island's 'comfort zone' (~200 m to ~900 m in the north-eastern part ) one finds the endemic Monanthes muralis, Echium hierrense, and Aeonium canariense, and, where the terrain allows it, rare dragos (Dracaena sp.) among other trees such as palmeras (Phoenix canariensis ), higueras (Ficus carica ), almenderos (Prunus amygdalus ), damascos (Prunus armeniaca ), duraznos (Prunus persica ), and, of course, grapevine (mostly the Malvasia variety, which yields wines that are... well no, not really ). More recently, pineapple, banana, and mango were planted in the 'sub-tropical' climate of the el Golfo region. El Hierro's entire costal zone, with steep rocky slopes, is inhabited mostly by lichens, including orchilla (Roccella tuberculata ), and salt-tolerant plants like Artemisia. The southern part of the island is dry, desert-like. The sparse vegetation there is a mix of Sabina trees (Juniperus turbinata subsp. canariensis ), Tabaiba bushes and tuneras (Euphorbiaceae and Opuntia littoralis, an invasive/human-imported succulent, was used in the 19th century to cultivate cochinilla lice (Dactylopius coccus) for the production of carmine dye ).
El Hierro lacks a natural harbor and was therefore always exempt from transatlantic shipping routes to and from the Americas. This might explain why neither of the two great voyaging naturalists made a stopover in El Hierro. Both really missed something – and, alas, I have only mentioned the island's geology and flora, and not mentioned its fauna at all ! In 1799, Alexander von Humboldt explored El Hierro's much larger sister island Tenerife for a week, en route to South America and while on that island, he climbed the 3,718 m Teide volcano. In Humboldt's time the description of the Canary Islands, including El Hierro, came from 'Noticias de la historia general de las Islas de Canaria' written by the priest, naturalist, and native Tinerfeño José de Viera y Clavijo (1731 – 1813). While Humboldt cites this work in his famed opus 'Le voyage aux régions equinoxiales du Nouveau Continent,...', the two apparently never met. Thirty years later, in January 1832, Charles Darwin, who dearly wanted to follow Humboldt in climbing the Teide, landed in Santa Cruz de Tenerife, on board of the HMS Beagle. But just as they were about to set anchor, a boat from the Health Office came out and an officer informed the captain, FitzRoy, that they were not allowed to go ashore due to a cholera outbreak in England. So they sailed on... Finally in 1836, Darwin spent a few days on Terceira (one of the Aҫores islands further north in the Atlantic Ocean, also of volcanic origin), the last stop before the return of HMS Beagle to Britain.
The first human settlers arrived on El Hierro around 500 BC. They probably came from the Atlas mountains in northern Africa and brought along goats and crops, maybe also fig and almond trees. Among the scarce archaeological remains of their culture are the Tagoror, thought to have been a ceremonial meeting place, and Los Letreros, a series of petroglyphs displaying numbers and alphabetic signs that resemble those used by the ⵉⵎⴰⵣⵉⵖ, oops!, the Berber people in North Africa (Figure 2). Linguists believe that these first settlers called themselves Bimbapes, later vulgarized to 'Bimbaches' by the Castillian (=Spanish ) conquerors, 1405 ff. (The first settlers of the Canaries are summarily referred to as Guanches and were, according to Wikipedia, "ethnically and culturally absorbed by Spanish settlers" during the 15th century. You can imagine what it means to be "absorbed"... a story of blood, sweat and tears ). Fast forward to the 21st century. In 2000, El Hierro was included in the UNESCO list of 'Biosphere Reserves' but the efforts of the Cabildo, the island's political authority, to achieve sustainability for the island and its ~10,000 inhabitants in medium-term did not end here: since 2014 the island's electricity (most of it, to be more precise ) is produced by a new hydroelectric plant, with the aim to soon run the island on "100% renewables". So, the residents have a beautiful island as their cherished home (no platitude! ), and a reasonably stable political and economical situation despite the precarious job situation particularly for the young Herreñas y Herreños. All this led many people in El Hierro to be cautiously optimistic about their perspectives (my observation ). The dormant, maybe even extinct volcanism below them – the last eruption occurred in 1793, in the island's remote south-west – had largely slipped from their awareness.
However, in July 2011 volcanic activities became again noticeable (since 1990, volcanic activities on the Canaries are continuously monitored by the national IGN ). So the islanders have set out to prepare for a possible eruption in the not-too-distant future. Up until the end of October of that year, a constant series of earth tremors with magnitudes of ~2 was recorded, with epicenters mostly at depths of ~15 km and running in a pretty straight north-south line (Figure 3). Geologists soon assumed that a lava chamber deep down was successively (re)filled. Which was obviously the case since from late October patches of pale-colored water began appearing off the island's southern coast, 1.8 km south of La Restinga village (Figure 4). Dead fish floated on the ocean's surface, and locals noted a strong smell of sulfur in the air (paraphrasing here Ana Sotomayor's internship report for the IEO ). The eruption continued until March 2012, leaving the 'tip' of the volcano's cone just 88 metres below the surface. During the eruption, the inhabitants of La Restinga were briefly evacuated but, fortunately, there were no casualties or reports of major damages on the island. As of today, the submarine volcano (officially baptized 'Tagoro' in 2016, as a reference to the Tagoror site mentioned above, yet hotly disputed by the Herreños ) is still active in a degasification phase, releasing heat, gases and metals that produce significant physico-chemical changes in the surrounding waters.
...and Venus's Hair
An international team of researchers onboard RV Ángeles Alvariño investigated the eventual recovery of the benthic ecosystem after the Tagoro eruption in 2012 during the MIDAS El Hierro 2014 expedition (their cruise took place in the first half of November 2014, that is, 2.7 y after the eruption ). Operating IEO's Liropus 2000 ROV ('remotely operated vehicle') equipped with a hi-res camera system and sampling capabilities, they discovered and sampled in numerous dives extensive filamentous microbial mats. The white filaments making up the mats were several centimeters long and attached to the lava substrate; they named them 'Venus’s hair', because of their macroscopic characteristics (that is, after their in situ appearance under water, which became glibbery and less appealing onboard. According to ancient myths, Venus, the Roman goddess of love, was born of sea foam and wed to Vulcanus, the god of fire and volcanos ). Detailed microscopic analyses of the Venus’s hair filaments revealed that they are formed by long trichomes of contiguous bacterial cells (diameter ranging from 3 to 6 μm) within a 36 – 90 μm-wide sheath colonized by bacteria (Figures 5 + 6). These filaments are similar to those formed by members of the genus Thioploca (Gammaproteobacteria, Thiotrichaceae ), but Venus's hair is firmly attached to the substrate, whereas the latter are not and thus can move through the sediment and in the water column. (Elio had already mentioned earlier in this blog the giant Thioploca mats on the seafloor off the coast of Chile, Pacific Ocean ). Roberto Danovaro and his collaborators measured a high Sulfur content of up to 0.008 pmol/µm3 in the filaments, comparable to what was found for other Thiotrichaceae as Beggiatoa and Thioploca, whose metabolisms are fuelled by inorganic sulfur compounds released by geothermal fluids and/or by sulfate reduction processes. But unlike in the former, the elementary sulfur is not confined to vacuoles in the filamentous bacteria that make up Venus's hair.
Metagenomic analyses of shotgun sequenced DNA from dissected filaments allowed the researchers to assemble 21 partial genomes (with a completeness of >80% ), 16 of which affiliated with Proteobacteria and the remaining 5 with Bacteroidetes. Quantitatively prevailing in all reads were those of 'bin 11', which showed for multiple markers that this ~82% complete genome affiliates with the family Thiotrichaceae (Gammaproteobacteria ). The highest similarity (~78% of average nucleotide identity (ANI); for comparison: the ANI between E. coli and Salmonella spp. genomes is ≈80% ) was observed with the draft genome of Thioploca araucae, (yes, the bug from Chile, 'araucae' pointing to this origin ) sharing 1,105 of 3,191 predicted proteins (equivalent to 34% ) with an average amino acid identity of 51%. Although not yet cultivated and with its genome only to ~82% complete, Danovaro et al. propose their filamentous bacterium as a candidate for a new genus and species: Thiolava veneris, formally correct: Candidatus Thiolava veneris.
The filamentous structure of Venus's hair, characterized by long trichomes of contiguous cells, is apparently a successful strategy for the colonization of pristine volcanic substrates. The sessile strategy keeps the microbes in close proximity to the volcanic seepage, providing continuous access to essential elements required for their metabolism. The sheathed structure, the strong mechanical resistance, and the chemical properties of the filaments might, in addition, offer protection from protist or metazoan grazers. Together, these features provide advantages for the colonization (see below ) of the new habitat created by the submarine eruption.
The numerous 'excursions' of the ROV allowed Danovaro et al. to obtain a more complete picture of the spatial extension and biological complexity of the 'Tagoro assemblage'. The microbial mat covered an area of ~2,000 m2 around the summit of Tagoro's cone, at depths of 129 – 132 m. They employed high-throughput 16S and 18S rRNA amplicon sequencing to access the species composition of the entire 'assemblage' (rather than DNA shotgun‑ sequencing of isolated filaments as above ). To their surprise, Thiotrichaceae sequences did not contribute significantly to their data set while Epsilonproteobacteria accounted for 55% of all bacterial sequences (Sulfurimonas 39%, and Sulfurovum 14% ), followed by Gammaproteobacteria (~10% ) and Alphaproteobacteria (~10% ). With 0.03%, archaea provided a negligible contribution. However, this seeming 'imbalance' is comparable to the situation found, for example, in the 'hedgehog' structures of dental plaque: Streptococcus and Actinomyces, the 'basement species' that allow the formation of the complex community through their adherence to the substrate, contribute only a minor quantitative part to 'hedgehog community'. Besides prokaryotic rRNA sequences, the coiffeurs of Venus's hair found sequences of metazoan taxa belonging to the meiofauna (arthropods, annelids, and nematodes ). The mats also contained larvae and juveniles of benthic fauna, indicating that Venus's hair can sustain the entire life cycle of the smallest benthic metazoan organisms, for which microbes are an important food source. So roughly 2.5 years after the Tagoro eruption life had again firmly established a complete local food web.
It was actually not a big surprise for Roberto Danovaro and his team to find Epsilonproteobacteria dominating the 'Tagoro assemblage' as Campbell et al. had already concluded in their review from 2006: "Members of this proteobacterial class are not commonly found in marine planktonic communities but typically dominate deep-sea hydrothermal environments and are known to play significant roles in carbon and sulfur cycling in such ecosystems." What still puzzles microbiologists, though, is the how & when some intrepid Epsilonproteobacteria made it all the way from hydrothermal vents into the gastro-intestinal tract of vertebrates, including reptiles, birds, and mammals. Helicobacter pylori, for example, has been around in our ancestors for so long that it is possible to trace human migration across Earth by the specific H. pylori strains their descendants carry. Not puzzling any longer is the question of how helicobacters spread among mammals, in one case at least. When Mark Achtman and co-workers asked "Who ate whom?" they found convincing evidence that the large felines acquired Helicobacter their way, that is, by controlling population sizes of early African hominids roughly 200,000 years ago.
It is very likely that the Bimbapes, the first settlers, arrived on El Hierro already equipped with "their" helicobacters, which now have, as it turns out, distant cousins thriving close-by at the Tagoro volcano. Much like the Dutch botanist & microbiologist Lourens Baas Becking had coined it: " ...but the environment selects" by extending the quote by his colleague Martinus Beijerinck: "Everything is everywhere,..." (I suspect that this first part of the quote was initially a microbiologist's curse – ending with a heartfelt 'godverdomme!' – while fighting with contaminations of lab cultures rather than having this close‑to‑philosophical flavor to which we refer when we cite it today ). By the way, it was Beijerinck who first studied sulfate reduction by Desulfovibrio desulfuricans, a Deltaproteobacterium. Deltaproteobacteria are also members of the 'Tagoro community' albeit at a low percentage.
Disclosure: I have no contract with El Hierro's tourist authority. Yet over the last two decades I spent most of my vacations there, twice participating at la bajada. Frontpage picture: adapted from Panel 11.16 in: Hernández Pérez MS. 2002. El Julan, ISBN 84-7947-307-X.
Christoph Weigel is lecturer at the Life Science Engineering faculty of HTW, Berlin’s University for Applied Sciences and an Associate Blogger for STC