Japanese Sardines Discovered in Californian Waters: What Does This Mean for Oceanic Biodiversity?

Research scientist Dr. Gary C. Longo, from the National Oceanic and Atmospheric Administration (NOAA) Fisheries, and his team were shocked to discover the unlikely presence of Japanese sardines in their genetic analyses of sardines collected from the west coast of the US.

The samples collected during NOAA’s 2021–2022 surveys revealed that, while all samples in 2021 were Pacific sardines, samples from 2022 included a mix of both Pacific and Japanese species – never before documented in this region. Published in Molecular Ecology, the researchers linked their arrival to warming ocean conditions, likely opening up a “migration corridor.”

Climate-driven migration

Ocean warming, driven by climate change, is reshaping marine ecosystems worldwide. Prolonged periods of abnormally high sea surface temperatures, known as marine heatwaves, are becoming more frequent and intense, fundamentally altering ocean habitats. These heatwaves can create "corridors" of suitable conditions allowing organisms, like sardines, to expand their ranges into previously inaccessible regions.

“These warm conditions were implicated in several biological phenomena including a shift in distributions of marine organisms and may have provided favorable conditions for the dispersal of the Japanese sardine across the North Pacific,” said Longo, speaking to Technology Networks.

The North Pacific has experienced significant warming over the past decade, including well-documented marine heatwaves like the "Blob" in 2013–2015. These temperature anomalies have disrupted established patterns in the California Current, a major ocean current that drives nutrient cycling and species distribution along the West Coast.

The warming North Pacific may have provided a hospitable migration pathway for the Japanese sardines, away from their native range near Asia to the California Current.

Temporary visitors or permanent residents?

The potential for Japanese sardines to establish a permanent population on the West Coast hinges on several ecological and environmental factors. One key consideration is their adaptability to the California Current ecosystem, including their ability to find suitable spawning grounds and sufficient food resources.

Another critical factor is the persistence of favorable ocean conditions. If marine heatwaves continue and warming trends persist, the corridor that facilitated their migration may remain open, increasing the likelihood of long-term establishment.

“Whether Japanese Sardines are here to stay or are ephemeral visitors is an important question that we don’t know the answer to. The annual California Current Ecosystem Survey (CCES) conducted by NOAA’s Southwest Fishery Science Center (SWFSC) is really how we detected their presence and will be how we monitor their presence into the future.”
Dr. Gary C. Longo

Ecological impacts of Japanese sardines in the California Current

If Japanese sardines decide to establish a permanent residence in North American waters, their presence could disrupt the delicate balance of the California Current ecosystem. The introduction of Japanese sardines could alter the marine food web, either by increasing overall prey availability or by competing with Pacific sardines.

“A big question is whether or not Pacific and Japanese sardine can hybridize and produce viable offspring. They are relatively young sibling species that share a common ancestor ~200,000 to 300,000 years ago but we did see evidence for structural variation between their genomes, which can hinder gene flow between closely related species. We are currently developing a DNA panel to be able to detect hybrids moving forward,” Longo explained.

What could this mean for oceanic biodiversity?

The newly emerging corridor for sardines could also facilitate the dispersal of other temperate species in the eastern and western North Pacific, which were previously confined to specific regions.

“Sardine can be thought of as indicator species for changing ocean temperatures; a canary in the coal mine, of sorts. The potentially emergent habitat corridor for sardine may also enable dispersal in other temperate species across the North Pacific that were previously restricted, but we don’t know what species may follow. This is another reason why long-term monitoring programs are so important – they establish a baseline and allow for detection of novel dispersal events such as this,” said Longo.

“In my opinion, the most important take away from this finding is the importance of long-term monitoring programs, such as the Southwest Fishery Science Center’s (SWFSC’s) California Current Ecosystem Survey, for detecting shifts in baselines and novel events such as this,” Longo added.

Reference: Longo GC, Minich JJ, Allsing N, et al. Crossing the Pacific: Genomics reveals the presence of Japanese sardine (Sardinops melanosticta) in the California current large marine ecosystem. Mol Ecol. 2024:e17561. doi: 10.1111/mec.17561

About the interviewee:

Dr. Gary C. Longo is a research scientist at Ocean Associates Inc. contracted to the NOAA’s SWFSC. Longo earned his PhD in ecology and evolution from the University of California, Santa Cruz, where he studies molecular evolution in embiotocid surfperches.