This landmark discovery, detailed in their article published in the international journal Animals in May 2025, highlights how rising ocean temperatures are progressively remapping the habitable ranges of marine life. Prior to this study, Turbo sazae, a common marine snail species, predominantly occupied the temperate waters along Korea’s southern shores. However, comprehensive field surveys and genetic testing reveal a significant expansion nearing 37 degrees north latitude adjacent to Uljin on the eastern coast, suggesting real-time ecological changes underway in response to warming seas.

At the heart of this research lies a collaborative effort between KIOST’s Tropical and Subtropical Research Center and the Tidal Flat Research Institute at the National Institute of Fisheries Science. Led by Dr. Hyun-sung Yang and Dr. Young-Ghan Cho, these teams integrated ecological, physiological, and genetic datasets to understand how Turbo sazae populations exhibit remarkable connectivity between distant regions. The genetic analyses demonstrated strikingly similar haplotypes among snails from Jeju Island and those newly established along the eastern coast, signifying that larval dispersal via key ocean currents—such as the Tsushima Current—facilitates the northward colonization of new habitats.

From an ecological standpoint, this northward range expansion underscores the dynamic response of benthic ecosystems to climate-driven stressors. Of particular concern is the effect of ‘barren ground’ formation, a process characterized by the replacement of coastal kelp forests by white calcareous algae, which effectively transforms productive rocky habitats into near-deserts. Such habitat shifts have profound implications for benthic organisms, including Turbo sazae, whose populations and physiological states appear intricately linked to these environmental changes.

Further studies conducted by KIOST’s Jeju Bio Research Center reveal a nuanced understanding of the species’ population dynamics. Contrary to previous assumptions attributing population declines around Jeju Island to altered feeding behaviors driven by the proliferation of urchin barrens, the new research elucidates that reduced immune function—most likely due to elevated water temperatures—is the primary factor undermining Turbo sazae survival and reproduction. This insight is pivotal as it shifts the focus from trophic interactions to physiological resilience when considering the species’ response to climate stress.

The metabolisms and immune systems of marine invertebrates such as Turbo sazae are highly temperature-dependent. Prolonged exposure to warmer waters can suppress key immune pathways, rendering these organisms more vulnerable to pathogens and environmental stressors, which this comprehensive study confirms with robust experimental data published in Marine Environmental Research in February 2025. These findings signal broader implications for marine biodiversity under ongoing climate change scenarios: species that cannot adjust physiologically may face local extinctions or be forced to migrate in search of more hospitable environments.

Genetic connectivity analyses provided by the KIOST-led research highlight that the dispersal of Turbo sazae larvae is closely aligned with prevailing oceanic currents. The Tsushima Current, a warm-water current flowing northeastward along the Korean Peninsula’s southeastern shores, plays an instrumental role in ferrying larvae from southern populations toward more northerly coastal zones. This current-driven migration supports the species’ capacity to colonize novel habitats, effectively enabling range expansions consistent with shifting thermal niches.

Beyond its ecological significance, this research serves as an exceptional model for understanding the mechanisms underlying marine species’ responses to climatic perturbations. By integrating morphological assessments with genetic data and physiological experimentation, the study paints a comprehensive picture of how environmental pressures drive evolutionary and distributional changes in marine taxa. Such integrated approaches are vital in forecasting the future impacts of climate change on marine ecosystems and crafting adaptive management strategies.

The clear link established between rising sea temperatures and habitat shifts signifies a need for continued monitoring and scientific investigation. KIOST President Hyi Seung Lee emphasizes that temperature increases in marine environments represent a core driver of ecosystem change. He highlights KIOST’s commitment to advancing knowledge through science to anticipate and mitigate the consequences of climate-driven shifts in marine biodiversity, ensuring more resilient ecosystems and informed conservation policies.

Moreover, this research sheds light on broader patterns of marine biodiversity redistribution across the globe. Many marine species are exhibiting poleward shifts in their geographic ranges, underscoring the pervasive effects of climate change on oceanic life. The new findings about Turbo sazae exemplify this global phenomenon, offering concrete, genetically corroborated evidence of climate-induced biogeographical alterations in marine species assemblages.

Significantly, the study contributes to the conceptual framework of climate adaptation among marine organisms, underscoring the interplay between physiological tolerance, genetic connectivity, and environmental change. Understanding these complex dynamics is crucial in predicting which species can persist, adapt, or migrate as climate change accelerates. Also, the research underscores the importance of accounting for indirect effects, such as compromised immune function, rather than focusing solely on direct habitat alterations.

In conclusion, the comprehensive work conducted by KIOST and its partners provides a scientific breakthrough in marine biology, offering critical insights into how climate change is reshaping marine life along Korea’s coasts. The northward expansion of Turbo sazae delineated through genetic markers, physiological analyses, and oceanographic context represents a telling case of climate-induced ecological change. This research not only advances academic understanding but also provides actionable information essential for coastal ecosystem conservation and sustainable management in an era of rapidly changing ocean climates.

Subject of Research: Not applicable

Article Title: Climate Change Alters Distribution of Sea Life

News Publication Date: 26-Jun-2025

Web References: http://dx.doi.org/10.3390/ani15091321

References:

• Yang, H.-s., Kwon, K.-m., Roh, H.-s., Cho, Y.-G., et al. (2025). Insights into the Genetic Connectivity and Climate-Driven Northward Range Expansion of Turbo sazae (Gastropoda: Turbinidae) Along the Eastern Coast of Korea. Animals, May 2, 2025.
• Ryu, Y.-k., Oh, C., Yang, H.-s. (2025). Effect of Diet Changes in Benthic Ecosystems Owing to Climate Change on the Physiological Responses of Turbo sazae in Waters Around Jeju Island, Korea. Marine Environmental Research, Feb. 6, 2025.

Keywords: Climate Change, Marine Biodiversity, Turbo sazae, Genetic Connectivity, Sea Temperature Rise, Range Expansion, Ocean Currents, Tsushima Current, Marine Ecosystems, Immune Function, Benthic Systems, Marine Gastropods

The study’s central discovery highlights how the secretions of extracellular polymeric substances (EPS) by Heterosigma akashiwo adhere to buoyant microplastics such as polyethylene (PE) and polypropylene (PP). These EPS coatings increase the effective density of plastic particles, leading to the formation of dense aggregates heavier than seawater. Such aggregates overcome flotation forces, resulting in sinking from the surface ocean to the seabed. This process fundamentally shifts long-held assumptions about the environmental behavior of floating microplastics, which are often considered persistent migrants predominantly at or near the surface.

To quantify sinking dynamics, the research team conducted an extensive experimental investigation using two of the most prevalent plastic polymers worldwide: polyethylene, known for its relative density near 1.0 g/cm³, and polypropylene, with a lighter density of approximately 0.91 g/cm³. More than 5,000 PE microplastic aggregates ranging between 10 and 20 micrometers were analyzed, yielding an astonishing 28% settlement rate within 20 days. In contrast, roughly 1,250 larger but lighter PP aggregates (45-75 micrometers) exhibited only 1.8% sinking over the same duration. These comparative results underscore the decisive role played by polymer density and particle size in modulating the influence of microalgal EPS, highlighting that denser plastics are more susceptible to bio-induced sedimentation.

Intriguingly, despite size and density differences, the average vertical sinking velocity of MP aggregates hovered around 63 meters per day for both PE and PP aggregates. This uniformity in settling rates suggests that the EPS-mediated aggregates adopt sedimentation dynamics largely governed by biofilm characteristics and aggregate morphology rather than polymer intrinsic properties alone. Such findings illuminate the complex interplay between biological secretions and abiotic factors, revealing how microbial colonization transforms microplastic behaviors from passive drifters to active components of benthic sediment pools.

Further experimentation simulated the cold, dark conditions characteristic of benthic ocean floors where these microplastic aggregates eventually come to rest. The team sought to determine whether microbial degradation processes, particularly bacterial colonization, might disaggregate or otherwise remobilize settled plastics back into the water column. Notably, while copious bacterial populations were observed on aggregate surfaces, no measurable resuspension of buoyant MPs was detected. This lack of upward flux indicates a predominantly one-way transport mechanism, suggesting that microalgal aggregation facilitates long-term sequestration of microplastics within seabed sediments rather than promoting their recycling to surface waters.

The ecological significance of these findings cannot be overstated. Given the ubiquity of Heterosigma akashiwo blooms coinciding with peak plastic pollution inputs in temperate coastal regions, this biological pathway provides critical insight into natural remediation processes. By mediating microplastic sinking, this microalga influences spatial distribution and potential exposure risks for benthic organisms, altering contaminant transport and ecosystem dynamics. These processes likely affect carbon cycling as well, since sinking plastics coupled with biofilms can become vectors for organic carbon export into the deep ocean.

This research marks an important leap in marine ecology and pollution science, offering a carefully quantified, mechanistic understanding of how microbial interactions shape the environmental fate of marine microplastics. The experimental design, focusing on realistic polymer types and particle sizes, strengthens the ecological relevance of the results, bridging laboratory observations to in situ oceanic phenomena. The study sets a new standard for incorporating biological factors into predictive models of microplastic behavior, a critical advancement toward comprehensive marine pollution management.

Looking ahead, KIOST plans to deepen its investigations by developing advanced detection technologies and predictive analytical tools aimed at monitoring the influx, formation, and ecological impacts of microplastics throughout marine ecosystems. These innovations are expected to refine risk assessments of plastic pollution and inform sustainable mitigation strategies, particularly in regions prone to both elevated plastic loadings and frequent harmful algal blooms.

From a methodological standpoint, the study’s experimental approach stands out for its rigorous simulation of natural parameters, including temperature gradients, light availability, and microbial community interactions. Such realism ensures that findings accurately reflect the multifaceted conditions governing microplastic fate in coastal marine systems. The integration of microbiological assays with polymer science effectively captures the interdisciplinary essence required to tackle oceanic pollution challenges.

This study also expands the scientific discourse on microplastic sedimentation by emphasizing the role of microalgal secretions rather than relying solely on physical aggregation or abiotic settling processes. This nuance recalibrates previous models that underestimated the biological complexity underpinning microplastic transport, paving the way for subsequent research into other microorganism-plastic interactions throughout diverse marine habitats.

Ultimately, the KIOST findings signify a promising natural attenuation mechanism wherein marine microalgae, notorious for their harmful red tides, inadvertently facilitate the downward migration and sequestration of plastic pollutants. This dual role highlights the need to consider ecological trade-offs when evaluating algal bloom impacts on ocean health. By elucidating this novel bio-physical interaction, the study contributes both to theoretical frameworks and practical policy development addressing one of the ocean’s most pressing environmental crises.

This research was generously supported by the Korea Institute of Marine Science & Technology Promotion (KIMST) under the project “Land/Sea-based input and fate of microplastics in the marine environment,” funded by the Ministry of Oceans and Fisheries of the Republic of Korea (RS-2022-KS221604). The collaborative efforts of marine biologists, polymer chemists, and oceanographers at KIOST epitomize the integrative research necessary to decode and manage the complex patterns of marine plastic pollution in the 21st century.

Subject of Research:
Not applicable

Article Title:
KIOST Reveals Process by which Marine Microalga Heterosigma akashiwo Causes Buoyant Microplastics to Sink

News Publication Date:
10-Apr-2025

Web References:
http://dx.doi.org/10.1016/j.jhazmat.2025.137242

References:
Baek, S. H., Lim, Y. K., et al. (2025). Impact of Heterosigma akashiwo on the environmental behavior of microplastics: Aggregation, sinking, and resuspension dynamics. Journal of Hazardous Materials.

Keywords:
Marine ecosystems, Microplastics, Heterosigma akashiwo, Extracellular polymeric substances, Microalgae, Plastic sinking dynamics, Red tide, Marine pollution, Polyethylene, Polypropylene, Sedimentation, Oceanography