Berlengas

Entry to Furado Grande

Berlenga Grande is part of the Reserva Natural das Berlengas, a protected area home to marine species of flora and fauna.

At 1.5 kilometres (0.9 mi) long and 0.8 kilometres (0.50 mi) wide, Berlenga Grande is the largest of the islands of the Berlengas Archipelago.[10] At its highest, it rises to 88 metres (289 ft) above sea level. The island has a number of notable caves, including Gruta Azul (English: "Blue Grotto") and Furado Grande (English: "Big Hole"). The Furado Grande is a natural tunnel 70 metres (230 ft) wide and 20 metres (66 ft) tall which crosses through the entire island before opening up into a dramatic bay.[9][10]

The Fort of São João Baptista (English: "Fort of St. John the Baptist") is located in the waters off the southeastern coast of Berlenga Grande, on a small islet connected to the island by a causeway/arch-bridge and anchorage to the north.[11] It has been retrofitted as a rest house for tourists to stay at while visiting the islands.[9]

The Farilhões-Forcados Islets are uninhabited islands located northwest of Berlenga Grande.

Geology of the archipelago:
  Granites of the Berlengas
  Magmatic mica schist

These islands consist of a pink granite very rare in Europe and very common in America, rich in feldspars. Erosion has created remarkable landforms, such as the "sugar loaf", or even narrow valleys with almost vertical walls (the carreiros, formed by selective erosion along subvertical fault planes), as well as numerous caves and marine tunnels[12]

The different groups of islands have different morphology, composition and origins. Berlenga Grande and Estelas are of igneous origin, composed of pink granites, and occur in outcrops with rounded morphologies, generally with flattened tops. The Farilhões Forcadas group, on the other hand, consists of metamorphic rocks, where reliefs characterized by sharp peaks and vertical cliffs stand out.[12]

Berlenga Island is a pink granite plateau with rounded shapes, marked by a very jagged coastline, where several coves, caves, arches, paths, small islets and rocks stand out. All these landforms were shaped by the continuous action of erosive processes over a long period of time. The very embedded and relatively aligned paths of Cações and Mosteiro stand out, which almost separate the island of Berlenga into two fragments, the Ilha Velha and the Berlenga itself, and give it a curious figure-eight shape.[12]

It is hypothesized that the archipelago had its origin on a horst. Its absence on the Mesozoic suggests that, during this time, the Berlengas block was essentially subjected to erosive processes. The pink granite fragments and metamorphic rocks found at Cabo Carvoeiro or Baleal, as well as in the Papoa tuff–breccia, similar to those recognized in the archipelago, confirms this hypothesis. It is also expected that this block was larger and had a different configuration than it currently has.[12]

The absence of morphological structures typical of the erosion of granitic massifs and soils on the surface of Berlenga Grande suggest that it was underwater for long periods of time. Its rounded shape and the relatively flat surface of its top propounds the presence of an ancient marine abrasion platform, confirmed by the presence of numerous erosive forms, such as potholes, which developed on top of the applanation surface when it was at the bottom of the sea.[12]

On the other hand, the existence of small cavities and caves in the cliffs above the current mean sea level, such as Furado Seco, and marine terraces that correspond to residual deposits of old beaches, located at similar altitudes, seem to indicate that sea level was once positioned on that horizon. These observations suggest significant variations in the mean sea level, possibly as a result of quaternary glaciations.[12]

Additionally, Berlenga Grande has a poorly developed drainage network, (when precipitation occurs, rainwater is taken and falls directly into the sea in cascades), which clearly evidences that the erosion rate of the granitic massif is lower than the speed of variations in the mean sea level.[12]

The older metamorphic rocks that outcrop in Farilhões and Forcadas are erosion-resistance peaks of an underwater mountain that widens considerably below sea level. These rocks are strongly deformed and contain textures and minerals characteristic of high pressure and high temperature environments, typical of the lower crust.[12]

Armeria berlengensis, an endemic of the archipelago

The flora of the Berlengas mainly consists of bushes and grasses, adapted to the strong winds, high aridity and salinity, some of them are common on the coastal mainland, others are endemic to the islands. There are two known endemic species to the islands, Armeria berlengensis and Pulicaria microcephala; and two subspecies, Echium rosulatum subsp. davaei and Herniaria lusitanica subsp. berlengiana.[17][18]

There are around 100 different plant species present on the archipelago.[18]

Human presence led to the introduction of exotic species, like the ice plant and small mammals like the European rabbit and the black rat who work to diminish the native population.[17][18]

Seagull monitoring its offspring in one of the islands

There are two species of lizard in the islands, the Carbonell's wall lizard (subs. berlengensis) and the ocellated lizard, although this last one is residual and is only seen in restricted areas of the islands such as caves and is thought to be different from the continental relatives, showing different morphological traits and demeanor.[17][19]

The Berlengas archipelago is an important breeding area for seabirds such as the lesser black-backed gull and the yellow-legged gull, whose population increased dramatically due to artificial feeding and has become a serious problem in some cases, and land birds like the black redstart and the peregrine falcon.[19] It is also in the southernmost range of the common murre (adopted as the symbol of the nature reserve)[19] and is one of the few breeding locations of the band-rumped storm petrel.

A new endemic species of snail, Oestophora barrelsi spec. nov was described in 2015.[20]

The water around the islands hosts a great variety of fish, at least 44 species are known from two study expeditions.[21] The most frequently observed fish is the common two-banded sea bream and the ballan wrasse, along with the European bass, the red porgy, the gilt-head bream and the dusky grouper, frequent on Farilhões Islets.[19]

In the 1950s the islands were an important spawning ground for school sharks.[19]

The oceanographic conditions of the archipelago commonly lead to an abundant ichthyofauna, represented by sardines and other species that feed on plankton. This attracts a lot of marine mammals, mainly cetaceans, whose species include the common dolphin, the common bottlenose dolphin, the harbour porpoise, the striped dolphin, the common minke whale and the Cuvier's beaked whale.[19]