Researchers Discover New Jellyfish Species Off Japan’s Coast

Researchers from Tohoku University have identified a new species of jellyfish off the coast of Japan, named Physalia mikazuki. This discovery marks the first formal identification of a Portuguese man-of-war species in Japan, expanding knowledge about marine biodiversity in the region.

The Portuguese man-of-war, known scientifically as Physalia, is distinct for its gas-filled balloon that allows it to float at the ocean’s surface. Unlike most jellyfish that reside in deeper waters, this creature inhabits the area where the ocean meets the atmosphere. Its balloon acts as a sail, enabling it to navigate with the wind and ocean currents. Researchers made the significant finding at Gamo Beach, located in the Tohoku region, nearly 2,000 km (1,243 miles) north of its typical habitat around Okinawa.

The study, published in Frontiers in Marine Science, indicates that warming seas and changing ocean currents may be driving tropical marine species further north. The name Physalia mikazuki pays homage to Date Masamune, a historical samurai known for wearing a crescent moon on his helmet.

The authors of the study, including first author Chanikarn Yongstar, undertook an exhaustive process to document the unique body structures that differentiate this species from the four known types of Physalia. “I looked at each part, comparing its appearance to old tomes where scholars drew out the jellyfish anatomy by hand,” Yongstar explained. This meticulous work was necessary to confirm the species’ distinction from its cousins.

For years, scientists believed that Physalia utriculus was the only species found in the waters between Okinawa and Sagami Bay. However, the new research combined anatomical studies, DNA analysis, and ocean modeling to uncover that Physalia mikazuki had been coexisting with its tropical relatives, unnoticed until now.

The research team’s genetic analysis confirmed the new species. Kei Chloe Tan, who conducted the DNA testing, noted, “Our morphological and DNA analyses confirmed that these specimens represent a new species, distinct from its tropical relatives.” This finding not only highlights the species’ uniqueness but also raises questions about its presence in northern waters.

Research into ocean temperatures and currents revealed a trend affecting marine life. The Kuroshio Current is shifting northward, and coastal waters are warming by between 2 °C and 4 °C (3.6 °F to 7.2 °F). These changes have allowed Physalia mikazuki, typically a tropical jellyfish, to adapt to cooler northern habitats.

Using particle simulations, scientists tracked how Physalia mikazuki likely journeyed north on the Kuroshio Current, merging with P. utriculus along the way. The simulations indicated that it took just 30 days for the jellyfish to reach Sendai Bay and 45 days to arrive at Aomori. These insights illustrate how climate change is reshaping marine ecosystems.

Co-author Muhammad Izzat Nugraha described the simulation process, likening it to dropping colored beach balls in the water to track their paths. “We were excited to find that in our simulation, all the beach balls essentially made a trail from Sagami Bay up to right where we found the crescent helmet man-o-war in the Tohoku region,” Nugraha said.

The discovery of Physalia mikazuki serves as both a scientific milestone and a cautionary note regarding the implications of climate change. The jellyfish’s venomous tentacles can grow several meters long, posing a risk to beachgoers. As researchers continue to explore marine biodiversity, this finding underscores the need for vigilance in monitoring the coastlines to ensure public safety.

This remarkable discovery not only enriches the understanding of marine life but also emphasizes how climate-driven changes are influencing ecosystems worldwide. As oceans continue to shift, tracking the movements of species like Physalia mikazuki may provide critical insights into the future of marine biodiversity.