Particle Motion Revolution: Sounds Move Ocean Life in Mysterious Ways

Image: Clownfish larvae video release

In the beginning there was nothing...then there was sound...

...It is nighttime in the wide, open and vast ocean...miles and miles of the most absolute deep blue surrounds a damselfish larvae. With only a few millimeters in length it navigates inspiringly the open dark waters...it drifts and maneuvers the water column and currents...then something hits it...

It is the a gentle movement of particles in the water which hits the diminute larvae. The water particle movement was originated by a sound...but not just any kind of sound...it is the sound of its same specie living in the closest reef at hand. The small damselfish larvae corrects it position and steers in wide dark ocean waters. It sets heading and destination...soon the movement of particles become sounds. It has reached the reef where it will live all its life, a pristine reef off the Hawaiian Island of Maui. There -in just one square meter of reef it will perpetuate its specie.

The journey of this amazing small larvae which faced all odds of destruction in the open ocean started out with the movement of particles movement caused by sound. Today -grown in full the Damselfish once a small larvae relishes in making its own sounds from that Hawaiian Reef it calls home...

Environmental Research reported on September 5 on a new acoustic study developed by the Woods Hole Oceanographic Institution WHOI which assures to have “clues to coral health and reef conservation”.

When we think about ocean sounds we usually think of big giants of the oceans but sound and the deep acoustic channel of the ocean -which everyday is more altered by human noise pollution is key for the survival of millions of ocean species and ocean life as we know it.

Ocean acoustics is a field that is just being born and WHOI has developed a method to study not only ocean sounds but the movement of particles which sounds generate in the ocean. They assure that it is this movement that can be measured which is key for fish larvae.

The new study of WHOI was conducted solely in Hawaiian Reef off Maui. They call for similar studies to be conducted throughout the World to expand the knowledge.

“This study will help researchers understand the ways that marine animal larvae use sound as a cue to settle on coral reefs,” WHOI says. The report was published in Nature and Scientific Reports.

WHOI concluded that sounds which adult fish and invertebrates create in reefs may not travel far enough for larvae -which hatch in the open ocean -to hear them. This finding itself speaks of the importance of noise pollution and how altering sounds in a rich life environment can have devastating consequences for many species.

“To keep a reef healthy, you need a constant supply of new larvae to repopulate animals that die off,” Max Kaplan lead author of the paper and a graduate student in the MIT-WHOI Joint Program in Oceanography explained.

“How larvae find reefs has been a big question, though. We think sound may play a role in attracting them, but exactly how far away they can sense those sounds has not yet been accurately measured,” Kaplan added.

Conservation today is much like the ancient traditional art of weaving. In the past decades humanity has chosen the main threads and cut the main cloths of conservation actions but today scientists, decision makers and every other one involved faces the challenges of "fine weaving". Fine weaving conservation actions challenges force us to focus on the smallest aspects of life because they are among the most predominant.

While the global tendency of creating and establishing new Marine Protected Areas MPAs continues to grow -led by the recent creation of the largest protected area on Earth in Hawaii the question on how to effectively protect them comes into play.

Conservation International on September 2 discussed whether Protected Areas are just “Paper Parks”.

“Ocean protection means more than lines on a map,” Conservation International said.

“Last week President Obama expanded the Papahanaumokuakea Marine National Monument in northwestern Hawaii, making it the largest marine protected area MPA in the world. But how do lines on a map translate into actual conservation outcomes for the world’s oceans?” Conservation International asked.

Noise pollution has often been underestimated and is usually left out in the policy of MPAs. Laws against noise pollution are rare and scarce.

Conservation International Expert Laure Katz explained the importance of managing MPAs to avoid them from becoming “Paper Parks”. Katz added that despite advances today only 4% of the World's Oceans are protected. “Most Marine Scientists agree that we need 20% to 30% of the ocean to be protected,” Katz stated.

If we draw the line for plastic contamination and overfishing why are we still so hung on to not protecting the ocean from noise pollution? Isn't it all connected?

Science Daily reported on September 6 on a new Study of the University of Adelaide which linked Nutrient pollution to ocean acoustic alterations.

“Nutrient pollution emptying into seas from cities, towns and agricultural land is changing the sounds made by marine life -and potentially upsetting navigational cues for fish and other sea creatures,” researchers from the University of Adelaide concluded.

Run off pollution environments studied by researchers turned out to be more silent than healthier comparable ecosystems studied. Scientists registered sounds which they identified as snapping shrimps, sea urchins and fish vocalisations. In Australia researchers studied kelp forests affected by runoff pollution and found that their sounds are similar to “dead-zones” environments.

"We know that sound is very important for some species of fish and invertebrates to find sheltering habitats in reefs and seagrass beds. The demise of biological sounds is likely to have negative impacts on the replenishment of fish populations," the experts from the University of Adelaide concluded.

They added that suitable management and approach of acoustic policies could be effective in reversing the impacts.

Terramar Project still today is trying to explain the importance of ocean acoustic to the general population.

“We’re all familiar with noise around us, and we know it can become a problem - especially if you live near an airport, train station, highway, construction site, or DIY-enthusiast neighbour.But most people don’t think that noise is a problem under water, “ they explain. “But when we put a hydrophone into the water, no matter where in the world’s oceans, it’s never quiet!”

To expect ocean life impacted by noise pollution to grow up healthy or for fish larvae to find their way home in midst of noise contamination is the same as expecting a young baby to grow healthy in a stressed environment or a 2 year old to find his way home alone in the middle of noisy downtown.

WHOI explained that sound works differently underwater. They believe that measuring particle motion of sound is a breakthrough in Ocean Acoustics.

“There had been no field measurements of reef particle motion,” WHOI explains.

They described the work necessary to breath through the acoustic field as “painstaking acoustic measurements of a healthy reef system”.

Their main focus was to effectively measure two different components of sounds underwater -pressure waves and particle motion. Pressure waves are those which human ears can hear while particle motion are “physical vibrations of the water column as a sound wave rips through it”.

Because particle motion travels farther than pressure waves it is believed to be of importance in the understanding of how most fish and marine species detect sound.

Until now no study had focused on recording it.

Species like squid, octopus, and shrimp, for example, can detect vibrations through nerves embedded in their flesh. Similarly, adult fish sense them through the motion of tiny bone-like structures called otoliths inside their skulls.

To register particle motion MIT-WHOI Joint Program Student Max Kaplan had to think outside the hydrophone box. Kaplan used a sensitive accelerometer which he attached alongside a hydrophone to get both measurements -pressure and particle.

Marine life does not only hear sounds it actually feels it. “The data the accelerometer provides is directly relevant to how marine organisms sense sound,” PhD adviser -WHOI Associate Scientist Aran Mooney explained.

“Particle motion is really the relevant cue for marine animals,” Mooney adds. “When we’re measuring pressure, we’re measuring the wrong thing -it only gives a ballpark sense of what marine species here. We think studying particle motion is a big step to figuring out how larvae find their way to a reef.”

Why hasn't particle motion been used before? Measuring it is a challenge for engineers and technology developers.

David Mann President of Loggerhead Instruments -company which actually designs small accelerometers for marine research spoke about these challenges.

“To sense particle motion an accelerometer has to be able to move along with the water as the sound passes by. It can’t be mounted rigidly on frame or on the bottom but it also can’t be allowed to drift loosely with the currents. It’s a lot harder to use than a hydrophone,” Mann said.

“In general, average sound levels were low and perhaps too faint to be used as an orientation cue except very close to the reef. However, individual transient sounds that exceeded the mean values, sometimes by up to an order of magnitude, might be detectable far from the reef, depending on the hearing abilities of the larva. If sound is not being used as a long-range cue, it might still be useful for habitat selection or other biological activities within a reef,” WHOI concluded.

“Many species living on reef systems are extremely localized,” Kaplan explains. “For example, some Damselfish species live their entire adult lives within one square meter so finding the best possible location is key to their survival.”

“In cases like that, sensing sound on order of meters would make a big difference,” Kaplan said. “If you hear sounds of your species instead of predators, you might be more inclined to settle in a specific spot.”

In the US, the National Oceanic and Atmospheric Administration NOAA takes ocean noise and ocean acoustic very seriously.

“The NOAA Fisheries Acoustics Program is investigating all aspects of marine animal acoustic communication, hearing, and the effects of sound on behavior and hearing in protected marine species.Specifically, the program is: Developing acoustic exposure policy for NOAA,  Developing marine mammal acoustic guidance and Articulating NOAA's vision for addressing ocean noise impacts over the next 10 years via NOAA's Ocean Noise Strategy,” NOAA explains.

International Press reported on September 5 that the company Saildrone -which works with a NOAA project raised 14 million USD to fund the expansion of their fleet of sailing drones which collect crucial ocean data. The company works with acoustic instrumentation on their drones and recently completed a mission in the Arctic gathering fishery acoustic data.

"Data collected by the Saildrones will not only transform the understanding of our oceans, but will also bring insight into issues like weather, fish populations, ocean acidification and climate change -processes that will affect every person on this planet. Understanding these processes, and their rate of change, is crucial to our economies and ultimately, our survival," Richard Jenkins, founder and CEO of Saildrone spoke to the press.

The Saildrone boats have been used by scientists and engineers from the National Oceanic and Atmospheric Administration NOAA to collect valuable information about the Alaskan coast. In June two drone sail boats were deployed carrying acoustic equipment that can pick up the sounds of North Pacific right whales, one on the most endangered animals on the planet.

But as well as counting whales, the boats could be used to track shipping route noise pollution, weather prediction, oil and gas industry operations, or even to police illegal fishing.

A fleet of drones with the latest acoustic technology could help us understand better noise pollution in International Traffic Routes and coastal areas, acoustic in reefs and Gulfs and open insight on the importance of sounds for marine life. To the day Saildrone Drones are not equipped with particle motion sensors however they did travel almost 3 thousand nautical miles in 101 days and took on fishery acoustics studies under the NOAA program..

“Saildrone should provide us a much more efficient, cost effective way to at least try to identify areas and times of year where we're hearing right whales, and then we could reliably design surveys to take advantage of that information,” Doug DeMaster -Science Director at the Alaska Fisheries Science Centre assured.

Acoustics in the Arctic or in reefs is a main driver of life. “Coral reefs are hubs of marine biodiversity, and recruitment to these reefs provides the foundation of these ecosystems. Larval animals seeking the reef for settlement may use a variety of cues. A range of sounds are produced on reefs, and it is increasingly realized that these acoustic components may assist pelagic larvae in locating and orienting toward suitable juvenile and adult habitat,” the WHOI research goes technical published in full in Nature.

But still today much of how larvae find their way to reefs remains a mystery and one scientist is out to solve it. On September 2 Phys reported on the work of Steven Morgan professor of Marine Ecology at the University of California.

Leading a group of scientists Professor Morgan is deploying miniature robots designed to resemble and act as “larvae”.

Just off Bodega Bay north of San Francisco Professor Morgan is already reaping results of his study.

Professor Morgan´s robots which bio-mimic clouds of microscopic marine larvae, such as baby crabs, mussels, clams and rockfish are bringing back for the first time answers to the questions; Where do marine larvae go? How do they get there and back? And what allows them to do this?

“The research carries implications for a range of issues, including managing marine protected areas, fisheries, invasive species and the impacts of climate change,” UC Professor Morgan assures.

"How can you effectively manage something if you do not know where it goes, how it got there, and how it gets back?" Morgan asks. "The fate of larvae has been a mystery since they were discovered. If you think about yourself, you always know where your kids are and exactly how many are alive, right? It's really fundamental information."

Professor Morgan is out to shred the standing theory which assures that larvae survive on random luck and numbers. He assures that larvae have been fitted by evolution with the latest biological gifts to reach home and destination and perpetuate their specie.

The professor has already demonstrated that the anatomy of larvae which he biomimics in his drones is efficient to navigate underwater.

Furthermore his research shows that larvae stay closer to the shoreline than expected. This would put them in the area of reach of particle motion waves.

“Larvae of most species go only a mile from shore rather than far out to sea, as was once thought. They move up and down in the water column and return toward the shore using currents like a conveyor belt. Most stay below the strong surface currents to avoid getting carried out to sea,” Professor Morgan kicks it.

“People have a hard time believing that microscopic larvae control their movements in strong currents because they’re so small,” Morgan adds. “People can’t get over the fact that they are designed evolutionarily to do this.”