Seamounts in the largest Marine Park in the Americas

The Desventuradas Islands, in the eastern Pacific Ocean, seem like gigantic, arid volcanic rocks. Since last year, they are surrounded by the largest marine park in the Americas. The government of Chile created the Nazca-Desventuradas Marine Park (PMND) to set aside and protect from all exploitation an area of 300,000 square kilometers (nearly 116,000 square miles) around the islands of San Felix and San Ambrosio and the islets of González and Catedral. A still wild area in pristine state, it is remote and relatively unexplored with an incomparable marine biodiversity. It is now a marine park even more impressive than the Motu Motiro Hiva (Sala y Gómez) Park, created in 2010. In the recent CIMAR 22 cruise, organized by CONA (National Oceanographic Committee) in 2016, several scientists from Ecology and Sustainable Management of Oceanic Islands (ESMOI) participated to explore the seamounts in the area of these islands located 850 km (530 miles) to the north of the Juan Fernández archipelago, with the objective of generating up-to-date scientific information for the PMND and the zone of economic exclusion of Juan Fernández.
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The seamounts of the region of the Desventuradas Islands were formed several million years ago in an area that is very close to where the island of Rapa Nui (Easter Island) is found today. Due to the slow, but constant, movement of the Nazca Plate, these mountains have traveled toward the east over the last 10 million years and are now 2800 km (1740 miles) distant from Rapa Nui. In spite of having moved so far, the majority of them have kept their original shape – some are pointed spires, others have a flat summit and yet other have enormous rock walls. Just as the mountains that we see on dry land, some are small while others are immense. As a result, their summits can be found a few meters (yards) under the water or up to several hundred meters deep. Those that are high enough to rise above the sea are what we know as islands.
A scientific expedition, led by the Pristine Seas Project of the National Geographic Society and by Oceana made the first documentation of the marine ecosystems of the Desventuradas in February of 2013. In addition to the South American sea lion and the giant spiny lobster, 28 species of fish were registered, of which five are also found around Rapa Nui. 70% of the fauna is shared with Juan Fernández. However, more than 95% of the fish is endemic, which is the highest amount known among marine ecosystems on the planet.
So, what other species of animals live on the seamounts surrounding the Desventuradas? In spite of distancing themselves from Rapa Nui, they could possibly show traces of their past. Might we encounter similar species on these seamounts as on those around Rapa Nui? Or, after being separated for such a long time, might they have developed a distinct and unique fauna? The seamounts around the Desventuradas are among the least explored in the South Pacific. Just to get to them requires 2 days of navigation from the continent and the first challenge is to find one in the open ocean. Fortunately, there are registries of some of them with exact coordinates, but in other cases the coordinates are not so exact and finding them is more a matter of luck. During the CIMAR 22 expedition, we found and explored 7 seamounts in the Desventuradas eco-region.
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Exploring the depths of the ocean is not an easy task. Scuba diving gives access only to the first few tens of meters. In some areas that are too deep or considered too dangerous, we use ROVs (Remotely Operated Vehicle), which are mini-submarines directed by remote control through a connecting, umbilical cable. On the CIMAR 22 cruise on board the “Cabo de Hornos”, the same ROV that was used to study the Apolo and Pukao seamounts in the waters off of Rapa Nui was used again. This ROV, belonging to Oceana, can reach depths of up to 500 m (1645 feet). During the cruise, we also used a seafloor rake which let us collect biological samples, since the video from the ROVs isn’t always sufficient to classify the animals, especially the smaller ones like starfish, corals and mollusks. The ROV is useful for those animals that move slowly or are immobile. The faster ones, like fish and small crabs, can make a quick escape.
We were able to study 7 seamounts in the Desventuradas, ranging from 50 to 350 m (165 to 1150 feet) deep. Each one was different from the previous one. Some were rocky with enormous crabs and lobsters. Others had sandy floors with small rocks where fish and corals live. Still others held so many sea urchins that we couldn’t see the sea floor. Each seamount was a world in itself. Throughout, we also saw sharks, moray eels, many species of coral, starfish and shrimp. We were able to collect many samples of the animals, the majority of which we are still trying to classify. Most of them are not well known and are not found in other places. It’s very possible that we are dealing with some entirely new species. We also found similarities between some species of the Desventuradas and Rapa Nui, such as some algae, fish and worms. However, very few species of sea urchins and starfish are the same on both islands and several fish, sponges and corals have not been found at all on Rapa Nui. From this, we can theorize that the Desventuradas could be considered an intermediate point between the species of the continent and those of Rapa Nui. When we are able to analyze the data, we will determine the fauna which lives on these seamounts and thus understand its fragility and the importance of protecting the PMND.
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