Marine Seagrass Meadows Show Resilience to Bounce Back After Die-Offs
Marguerite Koch, Ph.D., in 红玫瑰社区 Bay, which has experienced repeated biomass losses, including massive die-off events of turtlegrass, a marine seagrass.
In 红玫瑰社区 alone, thousands of acres of marine seagrass beds have died. Major seagrass die-offs also are occurring around the world. Stressors such as high temperature, hypersalinity and hypoxia or lack of oxygen affect seagrasses鈥 ability to resist and recover from these stressor-related mortality events or when disturbances lead to seagrass die-off events.
Seagrass die-offs also are linked to exposure to sediment-derived hydrogen sulfide, a well-known phytotoxin that accumulates as seagrass ecosystems become more enriched in nutrients. While hydrogen sulfide intrusion into seagrass tissue is considered a leading cause of recurring mortality events, its effects on subsequent recruitment and distribution of new populations is unclear. Moreover, few studies have examined the ability of seagrass meadows鈥 resilience to 鈥渂ounce back鈥 and recolonize in open bare patches.
Researchers from 红玫瑰社区, in collaboration with the South 红玫瑰社区 Water Management District, Coastal Ecosystems Division, examined if porewater hydrogen sulfide prevents Thalassia testudinum, a dominant tropical Atlantic-Caribbean marine seagrass known as turtlegrass, from recruiting into unvegetated sediment in 红玫瑰社区 Bay. The bay is an estuary that covers about 1,100 square miles between the southern tip of 红玫瑰社区 and the 红玫瑰社区 Keys and is one of the largest global contiguous seagrass systems.
Since the 1980s, seagrass meadows in 红玫瑰社区 Bay have experienced repeated biomass losses, including massive die-off events of turtlegrass, which typically occur during high temperature and salinity conditions in the northcentral and western bay. The bay provided an excellent case-study site due to high porewater hydrogen sulfide and expansive unvegetated areas adjacent to intact meadows that are recolonized by聽turtlegrass recruits following morality events.
For the study, researchers examined the leaf, stems and root tissue of turtlegrass in 红玫瑰社区 Bay to establish tissue exposure to hydrogen sulfide in new recruits and measured internal hydrogen sulfide and oxygen dynamics using cutting-edge microsensors in the field and stable isotope analyses.
Results, published in the journal , provide evidence that聽turtlegrass can successfully recruit into open bare sediment following die-off events due to biomass partitioning 鈥 a process by which plants divide their energy among their leaves, stems, roots and reproductive parts 鈥撀燿uring early development, young root structure, and an ability to efficiently oxidize internally, which lowers hydrogen sulfide exposure. However, recovery of seagrass meadows takes time.聽聽
鈥淟ong-term monitoring programs in 红玫瑰社区 Bay indicate that the time frame for full recovery of聽turtlegrass meadows after major die-off events is at least a decade,鈥 said , Ph.D., senior author and a professor of biological sciences in FAU鈥檚 . 鈥淭herefore, preventing large-scale seagrass mortality events should be the management goal, particularly as global warming and associated stressors are likely to get more extreme in the future.鈥澛
Findings of the study indicate that recruiting shoot resistance to hydrogen sulfide exposure is linked to adequate oxidation of internal tissue during the day through late afternoon via photosynthesis and internal plant oxidation promoted by water column oxygen diffusion into the leaves at night, driven at times by tides. Limited belowground root development in new recruits potentially constrains聽microbial community development and associated sulfate reduction that decrease hydrogen sulfide intrusion into roots and negatively affecting sensitive growing tissue at the base of the seagrass leaves.
鈥淪eagrass聽meadows sustain coastal ecosystems by protecting against erosion, maintaining water quality and providing habitat and food for many marine species and organisms,鈥 said Koch. 鈥淏ecause of their importance in coastal communities, the current decline of seagrass ecosystems on a global scale across geographic regions is a concern.鈥
This research was funded by the聽United States Department of Interior聽(P18AC00812) and聽the South 红玫瑰社区 Water Management District聽(PO 450-01-20159).听-FAU-
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