Submerged Aquatic Vegetation (SAV)

Submerged aquatic vegetation (SAV), including eelgrass, provide vital coastal habitat. SAV may benefit from increasing CO₂ and even locally elevate pH, but SAV species still face other climate and human-caused threats.

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Species Role

The extensive system of bays, barrier islands, and shallow coastal lagoons of the Mid-Atlantic region provide important habitat for both fresh and saltwater vascular plants, collectively known as submerged aquatic vegetation (SAV).

SAV are shallow-water ecosystem engineers that modify their physical and chemical environment as they grow. In doing so, they provide many ecosystem services:

Act as essential nursery habitat and feeding grounds for marine species
Stabilize and accrue sediments
Reduce wave action and shoreline erosion
Absorb excess nutrients and CO2
Oxygenate the surrounding water

Challenges Facing Mid-Atlantic SAV

Despite historic abundance, SAV populations in the Mid-Atlantic have been adversely affected by deteriorating water quality associated with human activity. Declining water quality, combined with disease outbreaks and damage from hurricanes in the early 20th century, have left SAV area at a fraction of their historic range in the Mid-Atlantic. Beyond the Mid-Atlantic, SAV are in decline globally, facing ongoing threats from coastal development, dredging, pollution, and climate change.

Restoring SAV in the Chesapeake Bay

While SAV losses have been severe, many Mid-Atlantic states are committed to protecting and expanding current SAV habitat. Efforts to control nutrient and sediment loading from the land have led to improved water quality conditions in many areas, aiding in the recovery of SAV beds.

On the seaside of Virginia’s Eastern Shore, restoration efforts have resulted in the growth of over 7,000 acres of eelgrass (seagrass species). While progress has been made,, concerns remain for the future of SAV in the Mid-Atlantic as CO2 induced climate warming may be particularly stressful for heat-intolerant species such as eelgrass.

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CO2 Effects on SAV Photosynthesis

Because aquatic plants require CO2 to perform photosynthesis, future increases in pCO2 could improve growth among SAV species. In fact, present day CO2 partial pressure (pCO2) limits photosynthetic rates of most SAV species, including wild celery, widgeon grass, and eelgrass.

Consequently, the negative effects of climate warming induced by elevated CO2 may be at least partially offset in these species by increased photosynthetic rates in an acidified coastal environment, as demonstrated by recent theoretical and experimental efforts.

References

Batiuk, R. A., Bergstrom, P., Karrh, L., Naylor, M., Wilcox, D., Moore, K. A., Kemp, M., Koch, E., Murray, L., Stevenson, J. C., Bartleson, R., Ailstock, S., Teichberg, M., Carter, V., Rybicki, N. B., Landwehr, J. M., & Gallegos, C. (2000). Chesapeake Bay Submerged Aquatic Vegetation Water Quality and Habitat-Based Requirements and Restoration Targets: A Second Synthesis. https://d38c6ppuviqmfp.cloudfront.net/content/publications/cbp_13051_13053.pdf

Invers, O., Zimmerman, R. C., Alberte, R. S., Pérez, M., & Romero, J. (2001). Inorganic carbon sources for seagrass photosynthesis: An experimental evaluation of bicarbonate use in species inhabiting temperate waters. Journal of Experimental Marine Biology and Ecology, 265(2), 203–217. https://doi.org/10.1016/S0022-0981(01)00332-X

Lloyd, N. D. H., Canvin, D. T., & Bristow, J. M. (1977). Photosynthesis and photorespiration in submerged aquatic vascular plants. Canadian Journal of Botany, 55(24), 3001–3005. https://doi.org/10.1139/b77-337

Moore, K. A., & Jarvis, J. C. (2008). Environmental Factors Affecting Recent Summertime Eelgrass Diebacks in the Lower Chesapeake Bay: Implications for Long-term Persistence. Journal of Coastal Research, 10055, 135–147. https://doi.org/10.2112/SI55-014

Orth, R. J., Luckenbach, M. L., Marion, S. R., Moore, K. A., & Wilcox, D. J. (2006). Seagrass recovery in the Delmarva Coastal Bays, USA. Aquatic Botany, 84(1), 26–36. https://doi.org/10.1016/j.aquabot.2005.07.007

Zimmerman, R. C., Hill, V. J., & Gallegos, C. L. (2015). Predicting effects of ocean warming, acidification, and water quality on Chesapeake region eelgrass. Limnology and Oceanography, 60(5), 1781–1804. https://doi.org/10.1002/lno.10139

Zimmerman, R. C., Kohrs, D. G., Steller, D. L., & Alberte, R. S. (1997). Impacts of CO2 Enrichment on Productivity and Light Requirements of Eelgrass. Plant Physiology, 115(2), 599–607. https://doi.org/10.1104/pp.115.2.599

Zimmerman, R., Hill, V., Jinuntuya, M., Celebi, B., Ruble, D., Smith, M., Cedeno, T., & Swingle, W. (2017). Experimental impacts of climate warming and ocean carbonation on eelgrass Zostera marina. Marine Ecology Progress Series, 566, 1–15. https://doi.org/10.3354/meps12051

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