An interdisciplinary work revealed the ability of the alga Macrocystis pyrifera to remain in the same places that the first expeditions to the southern channels were mapped.

Dr. Alejandra Mora-Soto achieving the first global high-resolution map of these marine bastions.

Daniela Jofré, IDEAL Center. Between 1832 and 1834, the renowned English biologist Charles Darwin toured much of Chilean and Argentine Patagonia aboard the HMS Beagle. On this ship he would write down his observations on the terrestrial and marine species of the place. One of the annotations that he mentions in his diary is about the biodiversity of the underwater forests of huiro along the southern channels, comparing them with the tropical terrestrial forests.

Almost two hundred years after that expedition, Dr. Alejandra Mora-Soto, from the University of Oxford, developed her doctoral research on the forests of Macrocystis pyrifera (commonly called huiro or giant sargassum), using diving, drone flights and satellite images, achieving the first global high-resolution map of these marine bastions.

However, after this work, the following question remained: What was the long-term trend of this ecosystem? Ancient records were needed to be able to compare the state of the huiro forests and verify whether they had increased or decreased in recent decades, assuming the current scenario of global warming and climate crisis.

This is how Dr. Mora-Soto went to the United Kingdom Navy Hydrographic Office (UKHO) to present her work and became the unprecedented opportunity to have in her hands the first nautical charts of the HMS Beagle. “I was lucky enough to be in contact with these letters completed in 1834, scan them, georeference them and find records of huiro forests, which I was able to compare with the current satellite map,” says the researcher.

The observational and historical record, compared with the current characterization of 309 kelp forests located in mainland Patagonia, Falkland Islands and South Georgia Island, revealed a striking situation: The huiro forests that were registered almost 200 years ago were still mostly in the same places and to the same extent nowadays.

“We are talking about a marine ecosystem that has remained in the same places despite all the changes that have occurred during the Anthropocene,” explains Dra. Mora-Soto.

Huiro forests also have the ability to adapt to the diverse geomorphology of the southern hemisphere.

Not only was there confirmation in the islands of the eastern subantarctic area such as Falkland or South Georgia, since it was also possible to verify the distribution of these Patagonian marine forests already investigated in the 1970s and 1980s by researchers Paul Dayton and Brigitta Van Tussenbroek, who carried out the first field samplings of this time, participating in this study as co-authors and referents of the marine ecology of this type of giant macroalgae worldwide.

A “super alga”

How did these marine forests remain almost intact all this time? The investigation determined a few points. “The huiro forests hold on to rocks, which move at very short speeds for geological times, where 200 years is like a blink of an eye. Unless there had been a direct removal of the algae, the changes were going to be imperceptible,” says the geographer.

Temperature is another factor to consider, since the multidisciplinary team determined that the thermal range of the southern waters did not exceed 17°C, which has allowed M. pyrifera not to be affected (for now) by the increase in sea temperature, being considered an algae of temperate and cold waters.

Huiro forests also have the ability to adapt to the diverse geomorphology of the southern hemisphere. “In the case of the Falkland Islands, the forests are long and extensive because the intertidal zone has little slope and is exposed to the ocean. In Patagonian channels and fjords, as well as in South Georgia Island, algae develop on steep coasts formed by glacial action, additionally, they receive a greater presence of fresh water due to the melting of nearby glaciers,” comments the researcher.

The permanence of the huiro forests in southern Patagonia contrasts with the bleak outlook in other areas of the planet. “In places like Tasmania these macroalgae are disappearing, on the Australian coast the cover of M. pyrifera has decreased by at least 95%. New Zealand has also reported problems and lately the Pacific Rim of the Northern Hemisphere,” explains Dr (c). Mauricio Palacios, researcher at the Center for Dynamic Research on High Latitude Marine Ecosystems (IDEAL) and coordinator of the Marine Program for Marine Conservation for Chile of the Wildlife Conservation Society (WCS) Chile.

The work published in the scientific journal “Journal of Biogeography” can be viewed through an online map, generated by the work team.

Palacios, who is the study’s co-author, also mentions the adaptive capacity of this brown macroalga, previously monitored in a work of his authorship. “In places with adverse environmental conditions, such as in Yendegaia Bay, Tierra del Fuego, where there is a constant contribution of meltwater from the Stoppani glacier and which constantly incorporates cold, fresh water, with a lot of sedimentary material, which prevents the entry of light to the system, this giant species still persists without major complications. This environmental condition in this type of Patagonian fjords and channel systems could be super stressful and even so, M. pyrifera continues to carry out its physiological activity without major problems”.

The researcher highlights that this work brought together the research of leading world-class macroalgal ecology researchers and remote sensing specialists from the United Kingdom, the United States, Mexico and Chile. “This is, perhaps, the most complete study that exists and that includes much of the subantarctic distribution of the species, and not to mention the time scale that it considers almost 200 years”, he says.

Ramifications of the study

The work published in the scientific journal “Journal of Biogeography” can be viewed through an online map, generated by the work team.

“It is not just a comparison of algae samples. The nautical charts also give us indications of the first contacts between the Beagle’s crew, captained by Fitz Roy, and the Yagán people. The writings of the trip can now be contrasted with the cartographies generated in that expedition”, comments Dra. Mora-Soto.

“I hope that this research has other types of ramifications, perhaps taken to the field of social sciences. With this work we are also talking about new narratives, these forests exist and persist, and it is essential to know them and protect them. Chile could position itself as a world leader in the protection of macroalgae forests”, reflects the geographer.