SMART Lab Publishes Global Synthesis on Ocean's Sound Scattering Layer and Marine Ecosystem Dynamics
On April 14, 2026, the SMART Lab team from Shanghai Ocean University published a comprehensive global synthesis in Acta Oceanologica Sinica, systematically mapping the composition and behavior of the Sound Scattering Layer (SSL)—the ocean’s “biological mirror”—and its implications for future fisheries and climate change.
The Ocean’s “Greatest Migration”
The SSL is a ubiquitous acoustic phenomenon caused by dense aggregations of zooplankton and small pelagic fish that reflect sound from echosounders. A primary feature of these layers is Diel Vertical Migration (DVM)—often called the largest daily migration of animals on Earth. These organisms typically ascend to the surface at night to feed and descend to deeper waters during the day to avoid predators.
“The SSL plays a crucial role in vertical energy transfer and carbon flux,” the researchers note. Recent estimates suggest that the Deep Scattering Layer (DSL), a subset of the SSL, may contain up to 90% of the global fish biomass—nearly 100 times the current annual marine capture.
Regional Findings and Variations
The review meticulously examines SSL characteristics across the Pacific, Atlantic, Indian, and Polar oceans, as well as the coastal waters of China:
- Pacific Ocean: In the Northwest Pacific, researchers identified over 600 zooplankton species, with distribution patterns heavily influenced by the Kuroshio and Oyashio currents
- Atlantic Ocean: The study notes that predation pressure and water temperature shape migration; larger-bodied species dominate colder waters with stronger migration amplitudes
- Polar Regions: In the Arctic and Antarctic, illumination is the dominant driver. Remarkably, SSL organisms remain active even during the “polar night,” perceiving subtle changes in light that trigger migration
- Coastal China: In the Yellow Sea, the Yellow Sea Cold Water Mass (YSCWM) acts as a critical habitat for Pacific krill, which form dense layers near the seabed during the day
The Future of Deep-Sea Fisheries
As the global community looks toward the “twilight zone” for new sources of animal protein, this research warns that large-scale exploitation must be guided by accurate scientific surveys. The authors emphasize that gaps in long-term monitoring—particularly in the Northwest Pacific—must be closed using autonomous platforms like unmanned surface vehicles and underwater gliders.
“This review not only reveals the ecological responses of mesopelagic organisms but also provides essential guidance for stock assessment and sustainable harvesting,” says the research team.