New Species of Portuguese Man-of-War Discovered Off Japan

A team of researchers from Tohoku University has identified a new species of the Portuguese man-of-war, named Physalia mikazuki, off the coast of Japan. This discovery marks a significant addition to marine biodiversity, as it is the first time a Physalia species has been formally described in Japan. The new jellyfish was found at Gamo Beach, located in the Tohoku region, nearly 2,000 km (1,243 miles) north of its typical habitat around Okinawa.

The Portuguese man-of-war is known for its unique gas-filled balloon that allows it to float on the ocean’s surface. Unlike most jellyfish that reside deeper in the water, Physalia uses its balloon as a sail, gliding with the wind and currents. While large groups can occasionally be swept ashore due to changing weather patterns, this particular species was not previously recognized in northern waters.

Chanikarn Yongstar, the first author of the study, expressed the challenges of documenting the distinct body structures that differentiate Physalia mikazuki from its relatives. “It was a very involved process recording all the unique body structures that distinguish it from the other four species of Physalia,” Yongstar stated. The research involved thorough comparisons with historical drawings of jellyfish anatomy, highlighting the complexity of this species.

For years, scientists believed that Physalia utriculus was the only Portuguese man-of-war found in the area. However, a recent study combining anatomical observations, DNA analysis, and oceanographic modeling revealed that Physalia mikazuki had coexisted in the same waters, largely unnoticed. The sighting at Gamo Beach prompted further investigation, uncovering that the two species had been sharing the habitat.

Kei Chloe Tan, who conducted the DNA analysis, confirmed the species’ distinctiveness: “Our morphological and DNA analyses confirmed that these specimens represent a new species, distinct from its tropical relatives.” Despite this exciting revelation, researchers are left with questions about how this jellyfish arrived in the cooler northern waters.

To investigate this, scientists analyzed historical ocean temperatures and currents. Their findings indicated that the Kuroshio Current is shifting northward, with coastal waters warming by 2 to 4 °C (3.6 to 7.2 °F). Such changes have permitted Physalia mikazuki, typically a tropical species, to venture into these cooler environments. The study highlights the broader implications of climate change on marine ecosystems and biodiversity.

Using particle simulations, researchers demonstrated the potential migration path of Physalia mikazuki. The simulations indicated it could have drifted north along the Kuroshio Current, blending in with its tropical counterpart. The journey to Sendai Bay took approximately 30 days, reaching as far as Aomori in about 45 days. Muhammad Izzat Nugraha, a co-author of the study, described the simulation process: “I ran a particle simulation – which is like dropping bright red beach balls in the water, then making data-based estimations to track where they will end up.”

The discovery of Physalia mikazuki serves as both a scientific milestone and a warning. Its painful sting, along with tentacles that can grow several meters long, necessitates close monitoring along the coast to ensure beachgoer safety. This finding underscores the ongoing need for research into marine life as climate change continues to shift ecosystems.

Published in Frontiers in Marine Science, this study exemplifies the importance of integrating taxonomy, DNA analysis, and ocean modeling to uncover hidden species. As environmental changes reshape marine habitats, the findings from this research provide a crucial glimpse into the future of ocean biodiversity.