During the summer months, north-easterly winds often herald the arrival of blowflies on beaches along Australia’s east coast. But while blowflies – or to give them their more formal name, the Pacific man-of-war – are common on Australian shores, they are not native to coastal waters. Instead, they spend most of their lives on the open ocean, drifting with the wind and current.
Blowflies are just one of the many organisms that have made their home on the ocean’s surface. Some of these animals are hydrozoans, such as the bluebottle.
There is the sailor who sails with the wind, Velella veellawhich has a stiff, transparent, oval sail about two inches long, attached to its bright blue float, and Porpita porpitasometimes called the blue button, which is shaped like a disc about three centimeters in diameter, surrounded by stinging polyps. But there is also the strikingly beautiful sea dragon; crustaceans such as shrimp, buoy barnacles and small swimming copepods; and even mollusks such as the violet snail and Relusia.
Collectively known as theneuton, these creatures are not tied to one place. Instead, they move with the wind and water. Sometimes they gather in huge drifts, living islands of veella and blue flies such as those that occasionally wash up on beaches in Australia or the west coasts of Canada and the United States. At other times, they clump around floating debris or spread sparsely over hundreds or even thousands of square miles.
Despite its ubiquity, theneuton remains relatively poorly understood and critically understudied. Only a handful of articles about the ecosystem are published each year, and only three of the 400 proposals received earlier this year for the International Zooplankton Production Symposium concerned theneuton.
Marine ecologist Professor Kerrie Swadling, from the University of Tasmania, puts it bluntly. “We know more about deep-sea vents than we do about the Neuston.”
The reasons for this ignorance are partly historical. Although several important studies on theneuton were published in the 20th century, they were written in Russian by scientists from the Soviet Union and were largely ignored outside the Eastern Bloc. But for the most part, the lack of research on theneuton is a result of the practical challenges associated with observing organisms unevenly distributed across the vastness of the open ocean.
Professor Kylie Pitt from Griffith University specialises in jellyfish ecology. She says: “The ephemeral nature of neuston makes it difficult to study. You see large numbers of jellyfish or blue bottles and then you can’t find them.”
In recent years, however, there has been an increase in interest in the Neuston. New research not only highlights the importance of seawater to the health of diverse ocean ecosystems, including coral reefs and the deep ocean, but also highlights important gaps in our knowledge about how changes in the marine environment affect them.
The person most responsible for the neuston’s increased visibility is Dr. Rebecca Helm. Now an assistant professor at Georgetown University in the United States, Helm was scrolling through Twitter in 2018 when she came across a tweet about The Ocean Cleanup’s plans to remove plastic from the oceans by sweeping a floating net across the surface.
Helm says she immediately wondered what the potential impact of this technology would be on neuston, so she began investigating it.
“At first I just did some digging in my spare time. But once I did, I realized how little information was available and how little had actually been done about this group of animals.”
Helm could have left it at that if the pandemic hadn’t meant she was locked out of her lab for months. “I suddenly had all this vague time to delve deeper into this, and I became really fascinated.”
‘An inverted seabed’
Helm’s reaction is easy to understand. The ocean surface is an extremely challenging environment: food is often scarce and survival requires the ability to withstand not only waves and storms, but also the heat of the sun and high levels of ultraviolet radiation. This last part may help explain why so many Neuston species are blue: the color not only acts as camouflage, but also acts as a built-in sunscreen that reflects UV rays.
However, to survive in neuston, animals must also find a way to stay at the surface. For free-swimming species such as copepods and zooplankton, this is easy. But for other organisms, special adaptations are needed.
Hydrozoans such as the blowfly and velella use gas-filled floats, while the buoy barnacle extrudes air into the cement it would otherwise use to attach itself to ships and rocks, creating a substance somewhat like pumice that it uses as a float. Similarly, violet snails suspend themselves beneath rafts built from hardened mucus bubbles. There is even a form of free-floating sea anemone that hangs upside down at the surface using a float in its pedal disk.
Intriguingly, this need for a float helps explain one of the most surprising discoveries of Helm’s research: that many of the animals that live in the neuston are not particularly closely related to other free-swimming species. Instead, they are descended from species that are normally attached to the sea floor and have migrated upward, meaning that the neuston is, in a very real sense, what Helm calls “an inverted seafloor,” clinging to the ocean’s surface.
This unexpected evolutionary link between the ocean’s surface and the seafloor reflects the growing awareness of theneuton’s role in connecting ocean ecosystems in general. Many animals from other parts of the ocean depend on it for food: numerous species of fish and fish larvae feed in theneuton, as do turtles and ocean birds such as fulmars, shearwaters, petrels and some albatrosses. Theneuton also provides essential nutrition for many species that ascend from deeper waters each night to feed as part of the diel migration.
Even though we can’t see what’s happening, that doesn’t mean it’s not important
Prof. Kylie Pitt
The neuston also plays a crucial role in the life cycles of many fish, whose larvae spend time at the surface before migrating to other parts of the ocean as they mature. “The ocean surface is an incredibly important nursery for many fish species,” Helm says. “Deep-sea viperfish can be found at the surface from a very young age. Many seahorses and pipefish, mahi mahi and sailfish also seek out the ocean surface as youngsters.”
It is likely that many fish spend time at the surface as young fish because it is safer than deeper water. Some seek shelter among the stinging tentacles of blue flies and porpita, while others hide under floating mats of sargassum. Others join the many species that gather around driftwood and other floating debris in search of food, protection or simply a scratching post to remove parasites.
Plastic and theneuton
But wood and sargassum aren’t the only types of marine debris. Although most of the more than twelve million tons of plastic that end up in the oceans each year sinks, a significant portion of the plastic that remains accumulates in the subtropical gyres, enormous current systems that circulate in the center of the Indian Ocean, the north and the South Atlantic Ocean and the North and South Pacific.
The regions at the center of the gyres are often called garbage patches, but Helm rejects that label, claiming that they are in fact Neuston environments invaded by plastic. Nevertheless, samples taken when long-distance swimmer Ben Lecomte swam through the North Pacific garbage patch in 2019 showed plastic and nasal life clumping together.
This mixing of plastic and neuston life has serious consequences for species that feed on neuston. Because they cannot distinguish between plastic fragments and food, fish, turtles and other animals consume it, resulting in malnutrition and the passing of toxins up the food chain.
The consequences of this can be catastrophic: Laysan albatrosses feed their chicks almost five tonnes of plastic each year, while on Lord Howe Island plastic appears to be linked to rising mortality among shearwater chicks.
However, the effect of plastics on theneuton itself appears to be more complex. Although animals such as fish and barnacles are likely to be adversely affected by ingesting plastic, larger pieces of floating plastic have the potential to provide shelter for some fish and fish larvae and appear to benefit sea skaters and other species that require items on which they can move. lay their eggs.
The effects of technologies designed to remove plastic from the ocean on the neuston also remain unclear. In part as a result of Helm’s advocacy, Ocean Cleanup has modified their technology to minimize the impact on neustonian life.
But Helm is not convinced. “I think it’s hard to judge whether this technology is harming neuston. We don’t understand these animals … So while they may have made efforts that may be going in the right direction, I’m skeptical that that can be said with any certainty.”
Others are less concerned, believing the neuton’s scattered distribution will likely protect it from significant damage. Although she says her views may change if the operation is scaled up in the future, Swadling points to the fact that Ocean Cleanup’s operation has only cleared a small part of the North Pacific gyre and says that “the impact so far will be negligible until then.”
Plastics aren’t the only area where our understanding of human impacts on neuston remains troublingly incomplete. Oil and chemical spills can negatively impact neuston life, as can rising air and ocean temperatures. But as a reminder of how little we know about neuston, Swadling says that not only is she unaware of a single experiment that measures the thermal tolerance of neuston organisms, but our knowledge of the ecosystem is so incomplete that we don’t even have a useful baseline for measuring change.
To bridge these gaps in our knowledge, scientists are increasingly tapping into the power of citizen science. Helm helped found Go Sea, a NASA-funded community that allows both scientists and the public to report observations of life on the surface, and has trained sailors to take samples from the Neuston in collaboration with SeaKeepers. Meanwhile, the University of NSW is developing Bluebottle Watch, a blowfly forecasting system that will use public observations, ocean surveys, laboratory experiments and computer models to monitor and anticipate blowfly swarms.
Still, there’s no doubt that this crucial ecosystem deserves more attention. “People think of the open ocean as an empty environment, but it’s absolutely not,” Pitt says. “Just because we can’t see what’s going on doesn’t mean it’s not important.”