Lesser known than coral reefs, marine seagrass ecosystems are rich in biodiversity and are powerhouses when it comes to sequestering carbon dioxide. Yet, much remains unknown about the ecology of seagrass beds, including detailed information on how seagrass spread their seeds and colonize new area. Now a recent study in Marine Ecology Progress Series documents that several species of marine animal are key to dispersing seagrass, overturning the assumption that seagrass was largely dispersed by abiotic methods (such as wind and waves).
“Traditional thinking is that eelgrass disperses by abiotic mechanisms such as floating seeds, floating reproductive shoots, or currents pushing seeds along the seafloor,” explains lead author Sarah Sumoski with the Virginia Institute of Marine Science. “Our study shows that eelgrass seeds can also be dispersed through consumption and excretion by fish, terrapins, and birds—providing a means to bring seeds to isolated areas.”
The researchers studied eelgrass (Zostera marina), a type of seagrass, in the Chesapeake Bay in the eastern U.S. Feeding nearly two thousand eelgrass seeds to five species—including three fish, one turtle, and one seabird—the researchers found that the seeds survived the passage through the animal’s guts and germinated successfully. But survival isn’t the only important thing to a plant: distance also matters. If a plant species is to colonize new areas it will need to ensure its seeds can go far.
 Mangroves and seagrass, two hugely important marine ecosystems, in Indonesia. Photo by: Rhett A. Butler. |
“We estimate that the fishes could disperse eelgrass seeds 10s to 100s of meters, while the maximum dispersal distance for terrapins is around 1,500 meters, or about a mile. The scaup [seabird] was the champ, with a maximum dispersal distance of more than 10 miles,” explains Sumoski.
While dispersal by winds and currents are also likely important, Sumoksi says that seagrass seeds dispersed by animals may have a better chance for survival.
“[Animals] prefer to live under the conditions that favor seagrass growth and thus will tend to carry seeds to areas where they’ll germinate. Wind and currents can easily disperse seeds into areas unsuitable for seagrass growth.”
A study last year found that the world’s seagrass beds stored around 20 million metric tons of carbon, even though the ecosystems covered just 0.2 percent of the Earth. Compared to forests, seagrass ecosystems were capable of storing more than twice as much carbon per square kilometer. Yet these ecosystems are hugely imperiled by dredging, coastal development, and poor water quality. Already nearly a third of the world’s seagrass ecosystems have been lost, though restoration is possible in many cases.
CITATION: James W. Fourqurean, Carlos M. Duarte, Hilary Kennedy, Núria Marbà, Marianne Holmer, Miguel Angel Mateo, Eugenia T. Apostolaki, Gary A. Kendrick, Dorte Krause-Jensen, Karen J. McGlathery & Oscar Serrano. Seagrass ecosystems as a globally significant carbon stock. Nature Geoscience. 2012. doi:10.1038/ngeo1477.
Sarah E. Sumoski, Robert J. Orth. Biotic dispersal in eelgrass Zostera marina. Marine Ecology Progress. Vol. 471: 1–10, 2012. doi: 10.3354/meps10145.
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