Tolerance and response of Zostera marina seedlings to hydrogen sulfide

Populations of Zostera marina L., the common seagrass of Pacific Northwest shallow marine environments, has undergone local extinction in coastal embayment's where it has traditionally existed. Because the habitat created by these plants is important for near-shore productivity and biodiversity, declining populations and local extinctions can have serious ecosystem consequences. One possibility for the failures of population increase and re-colonization of embayment's with complete loss is an increase in sediment H2S. We designed experiments to test the influence of various H2S concentrations on Z. marina seedlings. To do this we immersed seedlings in five different concentrations of H2S (68 μM, 204 μM, 680 μM, 2.04 mM and 6.8 mM) in 2010, and three additional concentrations (400 μM, 500 μM and 800 μM) in 2011. Treated seedlings were consistently killed above 680 μM. In addition, high doses (680 μM, 800 μM, 2.04 mM and 6.8 mM) of H2S caused depression of photosynthetic output, as well as causing Photosystem II to become inactive whereas Photosystem I remained active. At low doses of H2S (68 μM) it appears that photosynthesis increases. Our observations also suggest that this plant may adapt to lethal H2S concentrations if subjected to multiple, but gradually increasing sub-lethal H2S concentrations. These results suggest that Z. marina seedlings are consistently killed at concentrations of hydrogen sulfide found in localities that have experienced declines and local extinctions, and ultimately can be used to explain the lack of re-colonization in these sites.

► Zostera marina seedling health is reduced when exposed to H2S.
► LD50 for Z. marina seedlings is 488 μM at 48 h and 333 μM after 7 days.
► Photosynthetic rates (Qmax) decrease with high levels of H2S.
► PSII becomes inactive whereas PSI remained active at high levels of H2S.
► Levels of H2S found in the field suggest H2S may be limiting seedling recruitment.