Brandyn Lucca – blucca@uw.edu
Bluesky: @brandynlucca.bsky.social
Instagram: @brandynmark
Applied Physics Laboratory, University of Washington, Henderson Hall (HND), 1013 NE 40th St, Seattle, Washington, 98105, United States
Joseph Warren
Instagram: @warren.bioacoustics.lab
Bluesky: @warren-lab.bsky.social
Affiliation: School of Marine and Atmospheric Sciences, Stony Brook University
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Imagine standing on the beach in New York City, looking beyond the harbor over the horizon where rolling waves meet an armada of ships lined up to unload their cargo. What remains hidden from view are the vast underwater plains, valleys, and canyons teeming with marine life beneath the surface. From a bird’s-eye view, this area forms the New York Bight, a stretch of ocean off the coast of New York City situated between southern New Jersey and eastern Long Island. This seascape offers prime real estate for animals ranging from copepods to whales.
Some animals often gather along the shelfbreak, where the relatively flat, shallow seafloor of the continental shelf dramatically changes to the deep sea. Others prefer life in a well-known ecological hotspot and one of the largest marine canyons in the world: the Hudson Canyon. Like many people, marine animals choose habitats based on the amenities they offer, but their preferences can evolve as they age or in response to environmental shifts. Some may leave the New York Bight entirely, while others may settle in undiscovered hotspots elsewhere. But how can scientists find these hotspots in the first place?
How do scientists “see” beneath the waves?
Researchers use a technique called “active acoustics” to get snapshots of where animals are in the water column across large areas that can complement other sampling methods like nets. With this approach, they send out short pulses of sound from a moving ship and measure the echoes that bounce back from the seafloor or are created from animals that live in the water column. The equipment scientists use to measure these echoes is similar to bottom-finders and fish-finding systems used by fishers and boaters. The results can reveal dense fish schools clustered along the steep walls of a canyon or zooplankton aggregations in the near-surface waters along the shelfbreak. These patterns help scientists better understand how seascapes shape habitat preferences among marine organisms (Figure 1).
Echograms are one way to visualize acoustic backscatter, with color scale units corresponding to the total energy in echoes measured from marine organisms. This echogram reveals how animals are distributed vertically in the water column along a ship transect that crossed the Hudson Canyon. The dark gray region corresponds to the seafloor.
To carry out this research, scientists measure echoes from animals in the water column, collect fish and zooplankton using nets and trawls, and measure how temperature and salinity (and other environmental factors like oxygen) vary in the ocean as you go down in depth. Researchers collected the data for this study during seasonal surveys aboard a research vessel that covered the waters south of Long Island, New York, out to the shelfbreak, approximately 140 miles away (Figure 2).
Acoustic surveys were conducted along seven transect lines (black lines) with biological and seawater sampling stations at each square point. The white lines represent isobaths, or lines of constant depth, at 25, 50, 100, 500, 100, and 2000 m. The orange and red stars indicate where the Hudson Shelf Valley and Hudson Canyon begin.
Location, location, location: Hotspots change with the seasons
The New York Bight regions with the most fish and zooplankton (as measured by our echosounders) change with the seasons. In winter and early spring, most organisms concentrated farther offshore, often along the canyon edges or beyond the shelfbreak. As summer arrives, these biological hotspots grow along the shelfbreak, especially in and around the canyons, and move closer to shore. By fall, acoustic measurements showed that fish and zooplankton spread more evenly across the continental shelf.
For fish living near the seafloor, a seasonal feature called the Mid-Atlantic Cold Pool plays a major role in their movements. This layer of cold water forms on and above the seafloor over part of the continental shelf each spring and slowly decreases in volume throughout the summer. When the Cold Pool forms, many near-bottom fish shift away from their spatial extent due to the fish having temperature preferences and gather in the Hudson Canyon, other shelfbreak canyons, inshore areas, and the Hudson Shelf Valley. As the Cold Pool shrinks in late summer, their distribution becomes more like the broader patterns observed for overall biological backscatter (Figure 3).
An example echogram of biological backscatter near the shelfbreak. The 9º (gray) and 10º (black) isotherms, or lines of constant temperature, approximate the lateral and vertical extent of the Mid-Atlantic Cold Pool that, in this case, nearly walled this aggregation off from the inshore waters on the continental shelf entirely.
From underwater sound to action: Guiding management decisions
The New York Bight is a dynamic and productive ecosystem that experiences significant fishing pressure, shipping activity, and offshore energy development. By combining acoustic surveys with biological net sampling and oceanographic measurements, scientists can identify areas that fish and zooplankton may prefer (or avoid) throughout the year. Surveys such as this one help guide management decisions that balance the economic and commercial health of the New York Bight.
Brendan Smith – brendan.smith@dal.ca
Twitter: @bsmithacoustics
Instagram: @brendanthehuman
Dalhousie University, Department of Oceanography, Halifax, Nova Scotia, B3H 4R2, Canada
Additional author:
Dr. David Barclay
Popular version of 1aAO4 – Passive acoustic monitoring of a major seismic event at the Main Endeavour Hydrothermal Vent Field
Presented at the 187th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0034918
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
The Main Endeavour Hydrothermal Vent Field (MEF) is located on the Juan de Fuca Ridge in the Northeast Pacific Ocean. This ridge is a seafloor spreading center, where tectonic plates pull apart and new oceanic crust is formed as magma upwells from beneath the earth’s surface. This movement of the earth’s crust causes cracks to form, allowing seawater to penetrate downwards towards the magma below, where it circulates and eventually resurfaces into the ocean at temperatures over 300 degrees Celsius. Uniquely adapted organisms thrive at these sites, surviving from energy provided not by the sun, but by the heat and chemical composition of the vent fluid.
Figure 1: Black-smoker hydrothermal vent chimney at the Main Endeavour Hydrothermal Vent Field (Image courtesy of Ocean Networks Canada)
Long term measurements of hydrothermal vent activity are of scientific interest. However, the high temperatures and caustic chemical characteristics make it challenging to place probes directly in the vent flow. For this reason, passive acoustics (listening) can be a useful tool for hydrothermal vent monitoring, because the hydrophones (underwater microphones) can be located a safe distance from the vent fluid. Ocean Networks Canada have had a hydrophone at MEF continuously recording for over 5 years, and for the past year, a 4-element hydrophone array has been recording at this location.
The motion of the tectonic plates in these regions causes a lot of seismic activity, such as earthquakes. On March 6, 2024, a large ~4.1 magnitude earthquake was recorded at MEF, and earthquake rates were the highest observed since 2005. This earthquake was recorded on the hydrophone array and can be seen in the spectrogram in Figure 2.
Figure 2: Spectrogram of ~4.1 magnitude earthquake at MEF
Figure 3 shows differences in the soundscape at Endeavour before, during, and after the earthquake. The changes after the earthquake persist more than 1-week following the event. The duration and higher frequency components of the changes in the soundscape suggest sources other than seismicity.
Figure 3: Acoustic spectra before, during, and after the earthquake at MEF
The hydrophone array also provides us with the opportunity to gain further insights. For example, surface wind/wave-generated noise is a predominant source of ambient sound in the ocean, and the coherence, or spatial relationship between multiple hydrophone elements in the presence of this sound source, is well known. We can compare the measured coherence with the expected (modeled) coherence to explore any deviations, which could be attributed to hydrothermal vent activity. In Figure 4 we see differences between the measurements and model below 1 kHz (outlined by black boxes), suggesting the influence of hydrothermal vent sounds on the local soundscape.
Figure 4: Measured and modeled acoustic vertical coherence at MEF
In conclusion, passive acoustic monitoring can be used to monitor changes in hydrothermal vent fields in response to seismic activity. This earthquake provided a test case to prepare for a more major seismic event, which is expected to occur at Endeavour in the coming years. Passive acoustic monitoring will be an important tool to document vent field activity during this future event.
NUWC Division Newport, NAVSEA, Newport, RI, 02841, United States
Dr. Lauren A. Freeman, Dr. Daniel Duane, Dr. Ian Rooney from NUWC Division Newport and
Dr. Simon E. Freeman from ARPA-E
Popular version of 1aAB1 – Passive Acoustic Monitoring of Biological Soundscapes in a Changing Climate
Presented at the 184 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0018023
Climate change is impacting our oceans and marine ecosystems across the globe. Passive acoustic monitoring of marine ecosystems has been shown to provide a window into the heartbeat of an ecosystem, its relative health, and even information such as how many whales or fish are present in a given day or month. By studying marine soundscapes, we collate all of the ambient noise at an underwater location and attribute parts of the soundscape to wind and waves, to boats, and to different types of biology. Long term biological soundscape studies allow us to track changes in ecosystems with a single, small, instrument called a hydrophone. I’ve been studying coral reef soundscapes for nearly a decade now, and am starting to have time series long enough to begin to see how climate change affects soundscapes. Some of the most immediate and pronounced impacts of climate change on shallow ocean soundscapes are evident in varying levels of ambient biological sound. We found a ubiquitous trend at research sites in both the tropical Pacific (Hawaii) and sub-tropical Atlantic (Bermuda) that warmer water tends to be associated with higher ambient noise levels. Different frequency bands provide information about different ecological processes (such as fish calls, invertebrate activity, and algal photosynthesis). The response of each of these processes to temperature changes is not uniform, however each type of ambient noise increases in warmer water. At some point, ocean warming and acidification will fundamentally change the ecological structure of a shallow water environment. This would also be reflected in a fundamentally different soundscape, as described by peak frequencies and sound intensity. While I have not monitored the phase shift of an ecosystem at a single site, I have documented and shown that healthy coral reefs with high levels of parrotfish and reef fish have fundamentally different soundscapes, as reflected in their acoustic signature at different frequency bands, than coral reefs that are degraded and overgrown with fleshy macroalgae. This suggests that long term soundscape monitoring could also track these ecological phase shifts under climate stress and other impacts to marine ecosystems such as overfishing.
A healthy coral reef research site in Hawaii with vibrant corals, many reef fish, and copious nooks and crannies for marine invertebrates to make their homes.
Soundscape segmented into three frequency bands capturing fish vocalizations (blue), parrotfish scrapes (red), and invertebrate clicks along with algal photosynthesis bubbles (yellow). All features show an increase in ambient noise level (PSD, y-axis) with increasing ocean temperature at each site studied in Hawaii.