Ancient Hawaiian songs speak of “the striped sea.” “The cloud banks of Kona / They are incomparable, unsurpassed / The cloud banks of Kona / The striped sea / The peaceful sea of ​​Kona”, reads the lyrics of a traditional mele that tells of a love story between the king of Hawaii Kamehameha II and a noblewoman. But beyond the romantic story, it records that the natives had noticed a kind of band that marked their seas. And they, like scientists, have long suspected the importance of these warmer water ‘patches’ of the sea, known to be created naturally by the convergence of ocean currents, tides, and variations. on the seabed. However, although these areas are also known to be rich in plankton, taking an X-ray of the fauna that inhabits these specks has been a challenge for years.

Now, an international group has revealed the secret of combining marine experiments with satellite view, there is a whole hidden marine world, a network of of fish, just below the oceanic surface that it is home to hundreds of thousands of animals of a hundred different species. The results have just been published in “Scientific Reports”.

‘In a previous study, our surface mapping suggested that there was a very strong connection between ocean habitats along the coast of Hawaii. But now, thanks to satellite technology, we have finally been able to observe billions of animals living in these patches, as well as organic debris and microplastics that make up this ecosystem, “says Greg Asner, director of the Arizona State University Center. for Global Discovery and Conservation Science (GDCS) and co-author of the study along with researchers from NOAA’s Pacific Islands Center for Fisheries Sciences and the University of Hawaii, Manoa.

The team collected more than 130 plankton samples within the surface patches and surrounding waters along the leeward coast of the island of Hawaii. The objective was, in addition to observing the volume of microorganisms that float in the surface layer of the ocean, called the pelagic zone (up to 200 meters deep), to find fish larvae and marine fauna to be able to catalog it. These data were then combined with a new satellite-mapping technique of the spots. More than a hundred shoebox-sized satellites were used to peer inside these patches and see their marine life.

This is how the researchers realized that these surface patches create a network of larval ‘nurseries’ containing more than 100 species of fish and other types of animals. And there are not only larvae: entire families live in these warm waters, making it a key ecosystem in the ocean. For example, coral reef fish were found, such as horse mackerel, triggerfish, or goatfish; Predators were also found, such as the mahi-mahi (or dorado); even deep-sea fish, such as lanternfish, and various invertebrates, such as snails, crabs, and shrimp.

The diversity is so great that an estimated 10% of all Hawaiian marine species are represented here. And that its surface only covers 8% of the 600 square kilometers analyzed in the study. “These spots contained 39% of the fish larvae found, more than 25% zooplankton and 75% floating organic debris, such as leaves and feathers,” the researchers explain. Also, these hot spots had a density of larvae seven times greater than the surrounding waters. That is, a whole life hidden in just 200 meters of depth and within these small spots.

We were surprised to find larvae of so many species and even entire families of fish unique to surface patches, “says Jonathan Whitney, NOAA research marine ecologist and another of the study’s authors. “The fact that they harbor such a large proportion of larvae, in addition to the resources they need to survive, tells us that they are essential for the replenishment of adult fish populations.”

But these spots don’t just serve as ‘marine nurseries’, they also help keep coral reefs healthy and resilient, creating hotspots for larvae, bridging reefs, and pelagic ecosystems. ‘Our findings are part of an important story that is being formed around the role of biological stains on the surface and maintenance of coral reefs. The great biodiversity and biomass of the patches, combined with their ocean movement along the coast, form a superhighway for species that effectively connects and generates an interconnected regional reef ecosystem, ”the researchers say. But while the spots may seem like safe places for hatchlings within the fearsome ocean, dangers await there too. And these are not part of the food chain, not at least naturally: within the study area, 75% of the floating plastic garbage and 95% of the total plastic debris accumulated in the spots.

Our work illustrates how these oceanic features (and the behavioral attraction of animals to them) impact the entire surface community, with implications for the replenishment of adults that are important to humans for fishing, recreation, and other services. of ecosystems, ”says Margaret McManus, co-author of the study and professor and chair of the Department of Oceanography at the University of Hawaii at Mānoa. “These findings will have a broad impact, changing the way we think about ocean features such as pelagic hatcheries for fish and ocean invertebrates.”