The discovery of an ocean sunfish larva last year demonstrated how even some of the ocean’s giants start out life as but a speck. It gets you wondering, how on Earth do these delicate, miniature animals survive in the big blue sea? New research published in the journal Scientific Reports has revealed new insights into ocean nurseries for baby fish, finding that ocean surface slicks can act as a safe playground for more than 100 species of fish.
If you’ve ever been to the beach, you might have seen that sometimes among the textured, more splashy zones of the ocean surface there are strangely smooth areas – like someone ran over the surface with a butter knife. These areas are surface slicks, and they’re the result of water converging from ocean currents, tides, and variations in the seafloor. They’ve long been recognized as an important part of the seascape, but this is the first time scientists have identified superhighways of ocean babies occupying slicks.
The adorable discovery came about as researchers carried out over 130 plankton net tows inside the surface slicks and their surrounding waters along the sheltered coast of Hawai'i Island. They then combined their findings from the tows with satellite data on slick footprints, a novel technique for monitoring these unique ocean habitats.
Their results revealed that while slicks only cover around eight percent of the surface area studied, they contained 39 perfect of the area’s surface-dwelling larval fish. The slicks were also a valuable food source for these babies, with more than a quarter of the available zooplankton (their favorite meal) existing inside surface slicks.
The density of these wee bonny fish was seven times higher in slicks compared to the surrounding waters, which the researchers state demonstrates the value of surface slicks as a nursery habitat for marine larvae. The larva of at least 112 species of commercial and ecological importance were found inside the butter-smooth habitats. Familiar names included the larva of coral reef triggerfish; mahi-mahi, the big bright blues; lanternfish, who in later life occupy the deep ocean, and several invertebrates including snails, crabs, and shrimp.
"We were shocked to find larvae of so many species, and even entire families of fishes, that were only found in surface slicks," said lead author Dr. Jonathan Whitney, marine ecologist at NOAA, in a statement. "These 'bioslicks' form an interconnected superhighway of rich nursery habitat that accumulate and attract tons of young fishes, along with dense concentrations of food and shelter."
“The fact that surface slicks host such a large proportion of larvae, along with the resources they need to survive, tells us they are critical for the replenishment of adult fish populations."
While fascinating, the findings are cause for great concern in the light of recent well-meant innovations to rid the oceans of human-made garbage. Several prototypes that intend to clear up our seas by skimming floating trash from the water's surface are currently circulating online. Many marine scientists have been vocal across social media as to the enormous potential these machines have to wipe our entire ecosystems which exist in the uppermost layer of the water column. As well as these biodiverse nurseries, charismatic species such as the Blue dragon sea slug and Portuguese man o' war would also be greatly affected by the roll-out of such technologies.