Amazon reef

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The mouth of the Amazon (top right), in front of which lies the most densely populated section of the reef

The Amazonasriff ( Portuguese Recife Amazonas , english Amazon Reef or Amazonian Reef ) is a large-scale calcareous algae - and Schwammriff system off the coast of North Brazil and French Guiana . It is one of the largest reef systems in the world with a length of 970 km and an area of ​​about 9500 km². The announcement of its discovery in April 2016, following an oceanographic study of the region from the year 2012, but to a few clear signs on hard floors and reef structures in front of the river delta of the Amazon moved. Signs of this had been known since the 1950s.

Geography and ecology

Location of the Amazon reef

The reef has been identified as a calcareous algae and sponge reef system. It extends over a length of about 1000 km, is about 50 km wide and covers an area of ​​about 9500 km². It lies on the edge of the shelf at depths of 30 to 120 m.

Since the Amazon Current is one of the most muddy bodies of water in the world, it is surprising that reef-forming organisms grow in front of its delta, which elsewhere prefer clear, salty and sun-drenched waters. Reefs are usually not located in the estuary of large rivers, because these often have a lower salinity and higher acidity than the open sea and carry a lot of sedimenting suspended matter with them. It was therefore previously assumed that the sediment-rich Amazon current led to a gap in the reef distribution of the Atlantic Ocean . It seems as if there is a saltwater habitat suitable for reef-building organisms below the freshwater stream that originates from the Amazon .

The large sponge Xestospongia muta is common in the northern sector, but there is unusually light in color
Montastraea cavernosa , one of the few hard coral species in the Amazon reef

There are three different reef areas:

  • The southern section, into which the muddy Amazon water flows for only three months each year. It provides a habitat for the zooxanthelate stony corals known from other reefs , as there are opportunities for photosynthesis for the zooxanthellae living in symbiosis with them .
  • Mainly red algae grow in the central section .
  • In the northern section there are many sponges and other azooxanthelate reef builders, as the muddy Amazon water there ensures poor light conditions for more than six months a year.

In the reef, the red algae (Rhodophyceae) are the dominant group of algae with 25 species; there are also six types of green algae (Chlorophyta) and four types of brown algae (Ochrophyta). Calcareous algae are ubiquitous and particularly common in the northern zones of the reef. In the southern and central sections of the reef there are 34 species of seaweed , mostly species that are widespread and found elsewhere in deeper zones. 61 species are represented by sponges. Large, massive, jug-shaped shapes dominate. Sponges that grow in an encrusting manner are rare and are limited to the growth of other sponges. The sponges reach their greatest biodiversity in the central sector. In the southern section there are two species of drilling sponges ( Cliona ) associated with hard corals.

The octocorals are the most numerous of the cnidarians with 26 species. There are also many types of hydrozoan , two types of black corals (Antipatharia) and the fire coral Millepora cf. alcicornis . Zooxanthelate hard corals are only found in the central and southern sectors. Overall, the hard coral fauna is impoverished with only twelve species and their populations are only of low density. Individual coral species that were discovered in 1999 resemble those in the Caribbean , which suggests that they migrated from there to the Amazon reef.

Most (86%) of the 73 species of fish identified so far feed on other fish and larger invertebrates, some feed on plankton and two are herbivorous and detrivorous, respectively . There are also four species of angelfish that mainly feed on sponges. 80% of the fish species are widespread and spawn pelagically . Snapper (including Lutjanus purpureus the "Southern red snapper"), various groupers and lobsters are important for fishing .

The reef flora and fauna are likely to be more threatened by oil exploration than by climate change. In the 21st century, the Brazilian government licensed more than 80 blocks for oil extraction, 20 of which are already in production.

discovery

The first signs of a reef became known as early as the late 1950s when an American research vessel picked up sponges from the ocean floor. Further signs came in 1977 when the first coral reef fish were spotted in the area and in 1999 when Caribbean coral species were found in remote regions of the Amazon Delta. Even so, there was no major study until 2012. Then an international research team led by Rodrigo Moura of Federal University in Rio de Janeiro and partners from the University of Georgia carried out a survey of the area on the research vessel RV Atlantis . This research referred to the findings from the 1970s, including a map that marked potential locations on the Amazon coast.

literature

Individual evidence

  1. ↑ a b John Vidal: Huge coral reef discovered at Amazon river mouth . The Guardian . April 22, 2016. Retrieved April 23, 2016.
  2. ↑ Maddie Stone: There's a Gigantic Reef Surrounding the Amazon River and Nobody Noticed . Gawker Media . April 22, 2016. Retrieved April 23, 2016.
  3. ↑ a b c d e f Rodrigo L. Moura et al. (2016)
  4. ^ A b Robinson Meyer: Scientists Have Discovered a 600-Mile Coral Reef . Atlantic Media . April 21, 2016. Retrieved April 23, 2016.
  5. ↑ a b Alan Flurry: Scientists discover new reef system at mouth of Amazon River . Omicron Technology Limited. April 22, 2016. Retrieved April 23, 2016.
  6. ↑ Rachel Nuwer: Shining Light on Brazil's Secret Coral Reef . Smithsonian Institution . April 22, 2016. Retrieved April 23, 2016.
  7. ↑ a b c Craig Welch: Surprising, Vibrant Reef Discovered in the Muddy Amazon . National Geographic Society . April 22, 2016. Retrieved April 22, 2016.
  8. ↑ Collette Bruce, Ruetzler Klaus: Reef Fishes Over Sponge Bottoms Off the Mouth of the Amazon River . United Nations . 1977. Retrieved April 23, 2016.

Web links

Commons : Amazon Reef  - collection of images, videos and audio files

Coordinates: 1 ° 0 ′ 0 ″  N , 49 ° 0 ′ 0 ″  W.