A global scientific team has mapped the migratory history of eelgrass, a marine plant essential for oceanic carbon storage and biodiversity, using nuclear and chloroplast genomes from samples in 16 different locations. The research suggests that eelgrass spread across the Pacific in two waves before reaching the Atlantic around 243,000 years ago.
Coordinated by GEOMAR, the research team reconstructed the global colonization timeline of eelgrass, the most prevalent marine plant species worldwide.
Descended from freshwater plants, seagrasses leverage sunlight and carbon dioxide (CO2) for photosynthesis and can thrive at depths of up to 50 meters (165 feet). Unlike algae, seagrasses possess roots and rhizomes, allowing them to grow in various marine sediments. The plants reproduce entirely underwater, producing flowers and seeds that, although not buoyant, can be carried long distances by oceanic currents thanks to seed-bearing shoots.
Eelgrass, as a keystone species, fosters diverse marine habitats in shallow waters and provides a range of ecosystem services, including carbon sequestration. Recent studies have highlighted seagrasses, including eelgrass, as vital players in oceanic carbon storage, with seagrass meadows able to bury annually between 30 to 50 times more carbon than terrestrial forest roots. However, the continual loss of seagrass beds worldwide is a rising concern.
Eelgrass Evolution Decoded
The research team, led by Professor Thorsten Reusch of the GEOMAR Helmholtz Centre for Ocean Research Kiel, used the complete genomes of 200 eelgrass individuals from 16 locations to trace and date the plant’s migratory history. The scientists’ findings, published in the scientific journal Nature Plants, prompt the question: “Can eelgrass adapt effectively to our rapidly shifting climate?”
By utilizing a phylogenomic approach, researchers determined that eelgrass plants crossed the Pacific from west to east in at least two separate migrations, likely aided by the North Pacific Current. They further used two DNA-based “molecular clocks” to determine when eelgrass populations split into new groups. The DNA mutation rate was established by comparing it to an ancient, genome-wide duplication event that occurred in eelgrass.
Eelgrass Migration Mapped
Analyses of both nuclear and chloroplast genomes revealed eelgrass reached the Atlantic via the Canadian Arctic around 243,000 years ago. This is much later than anticipated, compared to the millions of years typically associated with Atlantic immigrant species during the Great Arctic Exchange approximately 3.5 million years ago.
Reusch notes that the recent arrival suggests no eelgrass-based ecosystems – hubs of biodiversity and carbon storage – existed in the Atlantic before that time. Additionally, the Atlantic’s eelgrass meadows harbor fewer specialized animal species than the Pacific’s, suggesting that there was less time for plant-animal co-evolution to occur.
Eelgrass populations in the Mediterranean were established from the Atlantic around 44,000 years ago and survived the Last Glacial Maximum. In contrast, current populations along the western and eastern Atlantic shores only began to expand from refuges after the Last Glacial Maximum, roughly 19,000 years ago – primarily from the American east coast, facilitated by the Gulf Stream.
Genomic Diversity and Concerns for the Future
The team found significant genetic diversity differences between Pacific and Atlantic eelgrass populations, including a decline in genetic diversity in northern populations.
Dr. Lei Yu, the study’s first author, summarized, “Atlantic populations, and northern ones compared to southern ones, are genetically less diverse than their ancestors by a factor of 35 among the most and least diverse.” This is due to genetic bottlenecks during past ice ages, which raises concerns about how well Atlantic eelgrass can adapt to climate change and other environmental stressors based on its genetic makeup.
The southern range limits have already seen seagrass meadows disappear due to warming oceans, particularly in North Carolina and southern Portugal. Additionally, heatwaves have caused losses in some shallow waters in the northern distribution areas. As Reusch points out, this is concerning because no other species can replace eelgrass if the meadows fail to survive future conditions.
Potential Solutions and Future Research Directions
“One potential restoration strategy might involve borrowing genetic diversity from Pacific eelgrass to enhance diversity in the Atlantic. Our next plan is to analyze the eelgrass pangenome. A new reference genome from Pacific eelgrass is currently being developed and should provide further insights into the adaptive capacity across its global habitats,” stated Prof. Jeanine Olsen, emeritus professor from the University of Groningen, who initiated the study and coordinated the collaboration between the Joint Genome Institute (JGI) and the research team. So, while the verdict on rapid adaptation is yet to be determined, there is reason for hope.
Reference: “Ocean current patterns drive the worldwide colonization of eelgrass (Zostera marina)” by Lei Yu, Marina Khachaturyan, Michael Matschiner, Adam Healey, Diane Bauer, Brenda Cameron, Mathieu Cusson, J. Emmett Duffy, F. Joel Fodrie, Diana Gill, Jane Grimwood, Masakazu Hori, Kevin Hovel, A. Randall Hughes, Marlene Jahnke, Jerry Jenkins, Keykhosrow Keymanesh, Claudia Kruschel, Sujan Mamidi, Damian M. Menning, Per-Olav Moksnes, Masahiro Nakaoka, Christa Pennacchio, Katrin Reiss, Francesca Rossi, Jennifer L. Ruesink, Stewart T. Schultz, Sandra Talbot, Richard Unsworth, David H. Ward, Tal Dagan, Jeremy Schmutz, Jonathan A. Eisen, John J. Stachowicz, Yves Van De Peer, Jeanine L. Olsen and Thorsten B. H. Reusch, 20 July 2023, Nature Plants.
DOI: 10.1038/s41477-023-01464-3
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Frequently Asked Questions (FAQs) about Eelgrass Global Dispersal
What is the main focus of the research mentioned in the text?
The main focus of the research mentioned in the text is to trace and understand the global colonization history of eelgrass (Zostera marina), a foundational marine plant species, using nuclear and chloroplast genomes from samples across multiple locations.
Why is eelgrass considered important in marine ecosystems?
Eelgrass is considered important in marine ecosystems because it serves as a foundational species that provides critical habitats for diverse marine life and contributes to various ecosystem services, including carbon uptake and storage. Seagrass meadows, like those formed by eelgrass, have been recognized as crucial nature-based contributors to oceanic carbon storage.
How did eelgrass spread across different oceans?
The research findings suggest that eelgrass spread across different oceans through a series of colonization events. It first crossed the Pacific from west to east, likely supported by the North Pacific Current. It then reached the Atlantic through the Canadian Arctic about 243,000 years ago.
Why is the recent arrival of eelgrass in the Atlantic significant?
The recent arrival of eelgrass in the Atlantic is significant because it indicates that there were no eelgrass-based ecosystems in the Atlantic before that time. This has implications for the biodiversity and carbon storage potential in the region, as the Atlantic’s eelgrass meadows exhibit fewer specialized animal species compared to those in the Pacific.
What are the concerns related to the genetic diversity of eelgrass populations?
The research highlights significant genetic diversity differences between Pacific and Atlantic eelgrass populations. Northern populations are found to be less genetically diverse than their ancestors due to past ice age-related bottlenecks. This raises concerns about how well Atlantic eelgrass can adapt to climate change and other environmental stressors based on its genetic capacity.
What potential solutions are proposed to address the loss of eelgrass meadows?
One potential restoration strategy suggested by the researchers is to borrow genetic diversity from Pacific eelgrass to enhance diversity in the Atlantic populations. However, more research is needed, and ongoing efforts to develop a new reference genome from Pacific eelgrass aim to provide further insights into the adaptive capacity of eelgrass across its global range of habitats.
Why is the loss of seagrass meadows, including eelgrass, a concern?
The loss of seagrass meadows, including eelgrass, is a concern because these ecosystems are vital for marine biodiversity and contribute significantly to carbon storage. The ongoing loss of these meadows, attributed to factors like warming oceans and heatwaves, may have profound ecological consequences and negatively impact various marine species and ecosystem functions.
More about Eelgrass Global Dispersal
- Nature Plants: “Ocean current patterns drive the worldwide colonization of eelgrass (Zostera marina)”
