The research, led by Inbar Dahan of Tel Aviv University together with colleagues including Tom Shlesinger and Jonathan Belmaker, surveyed coral reef communities along the steep slopes of the Gulf of Aqaba, one of the northernmost coral reef systems on Earth. The team focused on four groups spanning radically different biologies: fishes, hard corals (Scleractinia), soft corals (Octocorallia), and sponges (Porifera). Fishes were followed down to approximately 150 meters, into the lower mesophotic twilight zone, while the benthic groups were sampled to depths of roughly 45 to 70 meters. All four groups overlapped across the shared range down to about 55 meters, allowing a rare like-for-like comparison within a single location.

The technical apparatus behind the study was considerable. Fishes were counted using baited remote underwater stereo-video systems, known as stereo-BRUVs, deployed at 123 geo-referenced stations between 8 and 149 meters. Each unit consisted of paired cameras mounted on a steel frame baited with roughly 800 grams of mashed anchovies, recording hour-long videos from which abundance was estimated using the maximum number of individuals of each species observed in a single frame—a standard technique that prevents double counting of the same individuals. In total, 3,632 fish from 173 species were recorded. Hard corals were surveyed across 60 permanently marked 3-square-meter plots at depths of 2 to 55 meters, with more than 8,300 individual colonies photographed and identified, 93 percent to species level, with voucher specimens deposited at the Steinhardt Museum of Natural History. Octocorals were censused along 80 photographic belt transects between 1 and 45 meters, yielding 3,886 colonies from 30 taxonomic units. Sponges were documented through 337 photo-quadrats at depths from 5 to 70 meters, with deep samples captured by a remotely operated vehicle fitted with laser scaling beams, producing records of 992 individuals across 64 taxonomic units.

The analytical centerpiece was the Measurement of Biodiversity framework, or MoB, a statistical approach developed to decompose species richness into its underlying “proximate” drivers. The framework recognizes that any change in richness along an environmental gradient can arise from three distinct mechanisms operating alone or in concert: changes in the total number of individuals (abundance), changes in how evenly those individuals are distributed among species (evenness), and changes in the degree to which individuals of the same species cluster spatially (intraspecific aggregation). MoB works by constructing three rarefaction curves for each depth bin—an individual-based curve that depends only on the species abundance distribution, a non-spatial sample-based curve that adds the effect of abundance, and a spatial sample-based curve that further incorporates aggregation. Subtracting these curves isolates the individual contribution of each driver, and comparing the slopes against depth, with randomization-based null models, tests whether those contributions are statistically meaningful.

The headline finding is striking divergence. Only fishes followed the classic pattern, with richness declining steeply from shallow waters down to about 60 meters before reaching a plateau. Sponges did the opposite: their richness increased monotonically from the surface to 60 meters, with sponges becoming progressively more numerous in deeper waters. Hard corals peaked in richness at around 10 meters and then declined modestly, while soft corals showed little consistent change, though a sampling gap between 4 and 34 meters means fine-scale peaks at intermediate depths may have been missed. When the team repeated the analysis restricted to the shared 0-to-55-meter range, these contrasts persisted, confirming that they reflect genuine biological differences rather than artifacts of unequal sampling extents.

Even more revealing was what the MoB analysis uncovered about mechanisms. Across all four taxa, abundance emerged as the most consistent driver of richness change with depth—but the direction of that abundance shift, and therefore its effect on richness, differed dramatically among groups. In fishes, the abundance effect was strongly negative with depth, meaning that thinning numbers of individuals directly reduced species counts, a pattern that intensified with increasing sampling scale. In sponges and hard corals, the abundance effect was positive: greater numbers of individuals in deeper zones promoted higher richness there. Soft corals showed a weak, statistically insignificant abundance trend. Meanwhile, evenness played a contrasting role: for fishes, declining evenness at depth suppressed richness, whereas for soft corals, greater evenness at depth boosted it. Spatial aggregation, measurable only for fishes and hard corals where geo-referenced data existed, proved a secondary player, with evidence that aggregation reduced fish richness mainly at intermediate depths around a breakpoint at roughly 37 meters.

The authors argue that these results demand a rethink of how marine biodiversity gradients are quantified. For many benthic organisms, ecologists conventionally record percent cover rather than individual counts. But cover and abundance can move in opposite directions: hundreds of tiny sponge recruits may contribute almost nothing to cover while dramatically enriching the count data, whereas a few massive colonies can dominate cover while registering as only a handful of individuals. Because the MoB framework explicitly requires count data, this study’s use of individual-level records was essential for revealing the strong abundance–richness linkage—information that cover-based surveys would have obscured. The authors call for the routine integration of standardized counts alongside cover estimates to build a fuller picture of community change along depth gradients.

What ultimate environmental forces lie behind the proximate abundance patterns remains an open question, and the data suggest it is not simply the familiar monotonic gradients of light and temperature. Sponge and hard coral abundance actually increased toward depth, the opposite of what declining light availability alone would predict for photosynthetic reef-builders. The authors propose several candidate explanations, including disturbance regimes: storms and marine heat waves strike shallow waters disproportionately, potentially suppressing the abundance—and thus richness—of sessile organisms like sponges and hard corals near the surface, while mobile fishes largely evade these events and recover quickly. Recent work at the same study area documented exactly this asymmetry following an extreme storm in the region, with fish communities rebounding rapidly while coral recovery lagged. Hydrodynamics, larval transport, resource availability, and species interactions may further shape abundance patterns in ways that differ among taxa.

Habitat type also left a clear fingerprint on fish diversity. When the team separated their fish dataset into consolidated coral-reef habitat along the western coast and unconsolidated soft-sediment habitat to the north, they found that both richness and abundance started high in shallow consolidated habitat and declined sharply, converging with the more gradual unconsolidated-habitat curves at around 75 meters. This pattern points to the structural complexity of coral reefs as a powerful amplifier of shallow-water diversity, one whose influence weakens with depth where common constraints likely dominate in both habitat types.

A further insight concerns scale. Biodiversity metrics are notoriously scale-dependent, and the MoB framework allowed the researchers to test how the direction of each driver’s effect changed as sampling effort increased. Encouragingly, they found broadly consistent patterns when combining sampling units, though the magnitude of effects generally grew with scale—particularly for sponges, where the positive abundance effect strengthened markedly. Site-level sensitivity analyses and alternative depth-binning schemes (10, 15, and 30 meters) reproduced the main findings, reinforcing the robustness of the taxon-specific signatures. For fishes, a clear community breakpoint emerged near 60 meters, consistent with previous global studies identifying a major transition on mesophotic reefs at that depth, while a second transition near 37 meters likely reflects the loss of shallow-water schooling planktivores.

The study carries practical implications for conservation planning. Biodiversity hotspots are meant to anchor the placement of marine protected areas, and the Yam Ha-almogim Marine Protected Area in the Israeli Gulf of Aqaba hosted two of the study’s main sites. If different taxonomic groups peak in richness at different depths—fishes in the shallows, sponges in the upper mesophotic—then protecting a single depth band cannot safeguard the full spectrum of reef biodiversity. The finding that sponges and soft corals maintain or increase diversity well below the depths where fish diversity wanes also strengthens the case, made by earlier studies, that mesophotic ecosystems are not merely degraded extensions of shallow reefs but ecologically distinct communities deserving protection in their own right.

The broader message, the authors conclude, is one of challenging convention while revealing hidden commonality. The conventional expectation of universally declining richness with depth fails, yet beneath that surface disagreement lies a coherent mechanism: abundance gradients govern richness gradients across the board, even when the gradients themselves run in opposite directions for different organisms. Future work, they suggest, should now connect environmental conditions—the light, temperature, hydrodynamic, and disturbance regimes of the reef—to the proximate drivers of abundance, evenness, and aggregation, to explain why a sponge and a fish living on the same slope answer the question of depth in such utterly different ways.

At the core of this research is the investigation of complex sound scattering layers that interact with the various biological and physical components of the mesophotic coral ecosystem. These layers play a pivotal role in shaping not just the acoustic environment but also the ecological interactions within this underwater realm. Through the analysis of sound propagation, the study sheds light on how marine organisms utilize sound for navigation, communication, and foraging. The interplay between sound and the physical features of the coral habitat creates a unique acoustic tapestry that has significant implications for the survival and adaptability of marine species.

The research utilized state-of-the-art acoustic monitoring techniques to gather data on sound scattering and the associated water column dynamics within the mesophotic zone. These depths, typically ranging from 30 to 150 meters below the surface, represent a vital habitat where sunlight penetrates, facilitating photosynthesis and supporting diverse forms of marine life. By monitoring the acoustic signals across various frequencies, researchers were able to document how sound behaves differently in this complex environment compared to shallow reef areas.

As the study reveals, the interaction between sound and the water column is influenced by multiple factors, including water temperature, salinity, and the presence of suspended particles. These variables can markedly affect the sound speed and attenuation, leading to variations in how sound travels through this submerged landscape. The findings underscore the importance of understanding not only the biological aspects of coral ecosystems but also the physical characteristics that influence resident species and their behaviors.

Moreover, the anthropogenic impacts on coral ecosystems, such as pollution and noise from marine traffic, present additional challenges. As human activities escalate, the acoustic environment is altered, potentially disrupting the delicate balance of these ecosystems. This research highlights the need for establishing marine protected areas that take into consideration both the ecological and acoustic aspects of marine habitats. Such protective measures can help enhance resilience against environmental stressors, giving coral ecosystems a fighting chance in an era of rapid change.

Investigating the soundscape of mesophotic coral ecosystems also opens new avenues for understanding species interactions and behaviors. For example, various fish species rely on specific acoustic cues for spawning rituals and territory establishment. Understanding how these interactions are influenced by sound propagation in complex undersea environments can inform conservation approaches that account for the subtle, yet critical connections within marine life.

Furthermore, this research serves as a wake-up call for the scientific community regarding the significant role that sound plays in marine ecology. The conventional focus on visual and biological aspects must be expanded to incorporate acoustic studies if we aim to fully grasp the functioning of these interconnected underwater worlds. The research thus advocates for interdisciplinary approaches, drawing from acoustics, marine biology, and environmental sciences, to create a comprehensive understanding of coral reef dynamics.

In addition to its ecological implications, the study resonates with wider environmental concerns, particularly in the context of climate change. As our oceans warm and acidify, the survival of coral reefs hangs in the balance. By exploring the intricacies of sound and water-column dynamics, scientists gain insights into the resilience of these ecosystems and their ability to adapt to changing conditions. The findings empower conservationists to develop targeted strategies for protecting marine biodiversity while fostering public awareness about the intricate connections between sound and life beneath the waves.

The research also highlights the significance of collaborative efforts among scientists, local communities, and policymakers. Engaging local communities in conservation initiatives can establish a greater sense of stewardship over marine resources. By fostering a connection between people and their underwater environments, there is potential for developing innovative solutions that align conservation efforts with local cultures and economies.

In summary, the exploration of complex sound scattering layers and water-column dynamics

over mesophotic coral ecosystems unveils a fascinating dimension of underwater ecology that has far-reaching implications for conservation strategies. As we continue to face the challenges posed by climate change and habitat degradation, understanding the interplay between sound and marine life emerges as a critical avenue for safeguarding coral reefs and their diverse inhabitants. This groundbreaking research offers both a glimpse into the hidden acoustic world of our oceans and a vital call to action for the protection of these invaluable ecosystems.

By recognizing the significance of sound in these vibrant underwater landscapes, we not only enhance our scientific understanding but also strengthen our commitment to preserving the natural world for future generations. The findings pave the way for further studies that will continue to unravel the complexities of marine environments, shaping our approach to conservation and stewardship in the years to come. Acknowledging and acting upon the insights from this research will be vital in cultivating a sustainable future for the stunning coral reefs that so many marine species depend on for survival.

The beauty of the mesophotic coral ecosystem, intertwined with its intricate acoustic properties, continues to captivate researchers and conservationists alike. By equipping ourselves with knowledge and understanding, we arm ourselves against the threats faced by these vital habitats, fostering a collective responsibility to protect and cherish our marine heritage. In this brave new era of marine exploration and ecological awareness, the deep sounds of the ocean tell stories of life, resilience, and hope.

As we embrace the age of interdisciplinary research, it becomes increasingly clear that the future of coral reefs hinges on our ability to listen—to the sounds of the sea, to the messages of marine life, and to the calls for urgent action to protect these precious ecosystems. Our oceans are alive with sound, and through our continued investigations, we will unravel the secrets of their depths, striving to ensure that these complex marine environments endure for generations to come.

Subject of Research: The dynamics of sound scattering and water column interactions over mesophotic coral ecosystems in southwest Puerto Rico.

Article Title: Complex sound scattering layer and water-column dynamics over a mesophotic coral ecosystem: Southwest Puerto Rico, U.S.A.

Article References:

Cheriton, O.M., Storlazzi, C.D., Sherman, C.E. et al. Complex sound scattering layer and water-column dynamics over a mesophotic coral ecosystem: Southwest Puerto Rico, U.S.A.
Coral Reefs (2025). https://doi.org/10.1007/s00338-025-02747-1

Image Credits: AI Generated

DOI:

Keywords: Coral reefs, sound dynamics, marine ecosystems, conservation, Puerto Rico, acoustic monitoring.