71% of the Earth’s surface corresponds to the oceans and only 5% of the total is completely studied. These are figures that help to understand how a large part of the planet is still a great unknown and among the least analyzed parts are deep waters. His PhD thesis focused on David Barros (Sedimentary Basin Analysis Group, CIM-UVigo), which highlights the great difference between surface waters, up to 500 meters, where they carry out most of human activities such as fishing exploitation , transportation or recreational activities, and the vast ocean depths. It is because of this “knowledge gap” and the huge amount of unknown space on the planet that the researcher chose to study the biodiversity of organisms in deep-water ecosystems. He explains that between 100 and 150 new marine species are described per year, so it would take 50 years to get a real idea of the biodiversity of marine fish in the oceans. But in a context of climate change, overexploitation of resources and mass extinction of species, Barros considers “more necessary than ever” to expand the knowledge of the species that inhabit the oceans and their biological characteristics.
His thesis focused on verifying the effectiveness of techniques based on the use of DNA as a “barcode” (DNA Barcoding) to identify and distinguish species based on the degree of similarity between them. He explains that it is a tool widely used in species of commercial importance for the delimitation of fish stocks, but it is hardly used for deep-sea species. A second focus of analysis was the use of molecular techniques with morphological data to resolve uncertainties in already known species of deep-sea fish and, thirdly, he also studied the evolutionary processes that take place in some of these species.
Three groups of species studied
In his thesis, David Barros focused on three groups of species to apply both barcode and molecular techniques. The first of these is the Lepidion lepidion, of which two species were considered to exist, one endemic to the Mediterranean (Lepidion lepidion) and the other in the Atlantic (Lepidion eques). With the use of DNA, he confirmed that it is a single species but he was also able to study the genetic connectivity in its distribution area and the results show “the existence of different processes of contraction and expansion of their populations over thousands of years”. This represents an example of how deep sea species are also affected by variations that take place over time.
Another species studied was the genus Gaidropsarus, a group with eight recognized species in the North Atlantic and the Mediterranean. The researcher explains that “the use of morphological data combined with DNA showed three possible synonyms (that is, when two species are actually one)” and, therefore, the number of known species of this genus would be reduced by five. Barros considers the case between G. mediterraneus and G. guttatus “especially interesting”, since the latter is considered an endemism of Macaronesia”, that is, the archipelagos of Cape Verde, Wild Islands, Azores, Madeira and the Canary Islands. According to the results obtained in his research, “it would be a population perhaps in the process of speciation in this area, so it could be subject to special protection.” Four individuals of the genus Gaidropsarus from deep-sea oceanographic expeditions were also analyzed and the results obtained showed that “they didn’t belong to any of the known species”, so they could be new species for science. In fact, the analyses continue, but at least one new species has already been described by Portuguese researchers and named Gaidropsarus mauli.
Finally, the third group studied in David Barros’s thesis is the Notacanthiformes order, a group of primitive fish related to the eels that inhabit the seabed of continental slopes throughout the world. The researcher carried out the first complete evolutionary analysis at the genus level for the notacanthiformes using DNA, external morphology and internal morphology (bones) and the results confirmed the previous hypothesis raised by Japanese researchers “that the Lipogenys gilli species belongs to the Lipogenyinae subfamily within of the Notacanthidae family ”. The study also allowed estimating the origin of the Notacanthiformes order during the Cretaceous (145-65 million years) and the diversification of the group after the fifth mass extinction, “the one that ended with the dinosaurs”, That coincides approximately “with a general fish diversification event that took place after this extinction. ”
Results that evidence the great ignorance of the ocean depths
For Barros, the set of data obtained shows “the degree of ignorance that exists about the fish species that inhabit the ocean depths.” But his thesis also served to solve various problems regarding the existence or not of some species and to raise new questions “that will need future research.” The scientist points out that “evolutionary and population studies show that deep-water ecosystems and the species that inhabit them are subject to the same forces and pressures as those that inhabit the surface” and this evidences their sensitivity to change “, According to Barros, this is of great importance in the face of challenges such as that of global warming.
The Sedimentary Basin Analysis Group, CIM-UVigo research are cofunded by the European Union through the ERDF Operational Program Galicia 2014-2020.
Source: DUVI